Sensitivity degradation trend is analyzed for ASTER: Advanced Spaceborne Thermal Emission and Reflection radiometer/Visible and Near-Infrared Radiometer: VNIR onboard Terra satellite. Fault Tree Analysis is made for sensitivity degradation. Firstly, it is confirmed that the VNIR detectors are stable enough through dark current and shot noise behavior analysis. Then it is also confirmed that radiance of calibration lamp equipped VNIR is stable enough through lamp monitor of photodiode output data analysis. It is confirmed that radiance at the front of VNIR optics is, on the other hand, degraded in conjunction with sensitivity degradation of VNIR through an analysis of another photodiode output data which is equipped at the front of VNIR optics, photodiode output is scale-off at around one year after the launch though. VNIR optics transparency might not be so degraded due to the fact that VNIR output and the later photodiode output show almost same degradations. Consequently, it may say that one of possible causes of VNIR sensitivity degradation is thruster plume.
I laser scanner hanno bisogno di visibilità per funzionare, che sott'acqua è molto ridotta, a volte nulla. Quindi, come fare per rilevare in 3D velocemente e in alta definizione gli scalzi dei ponti, le banchine, i manufatti subacquei?
BlueView BV5000 è uno scanner multibeam 3D così piccolo da poter essere montato su un treppiede per rilevamenti sotto la superficie dell’acqua, come avviene normalmente con i laser scanner terrestri.
I laser scanner hanno bisogno di visibilità per funzionare, che sott'acqua è molto ridotta, a volte nulla. Quindi, come fare per rilevare in 3D velocemente e in alta definizione gli scalzi dei ponti, le banchine, i manufatti subacquei?
BlueView BV5000 è uno scanner multibeam 3D così piccolo da poter essere montato su un treppiede per rilevamenti sotto la superficie dell’acqua, come avviene normalmente con i laser scanner terrestri.
Nick - Benefits of Using Combined Bathymetry and Side Scan Sonar in Shallow W...Codevintec Italiana srl
Codevintec Days 2018 - Trieste
EDGETECH - Nick - Benefits of Using Combined Bathymetry and Side Scan Sonar in Shallow Water Surveys
Codevintec Days 2018 - Trieste
Relazione di Nick Lawrence - Edgetech
A ~25 slide presentation that explains the underlying principles and some applications of InSAR, with a particular focus on the measurement of deformation due to earthquakes. The presentation could be used in a lecture or lab setting, or provided to students for review out of class. The slides are annotated with additional background information designed to assist instructors.
AN EFFICIENT IMPLEMENTATION OF TRACKING USING KALMAN FILTER FOR UNDERWATER RO...IJCSEIT Journal
The exploration of oceans and sea beds is being made increasingly possible through the development of
Autonomous Underwater Vehicles (AUVs). This is an activity that concerns the marine community and it
must confront the existence of notable challenges. However, an automatic detecting and tracking system is
the first and foremost element for an AUV or an aqueous surveillance network. In this paper a method of
Kalman filter was presented to solve the problems of objects track in sonar images. Region of object was
extracted by threshold segment and morphology process, and the features of invariant moment and area
were analysed. Results show that the method presented has the advantages of good robustness, high
accuracy and real-time characteristic, and it is efficient in underwater target track based on sonar images
and also suited for the purpose of Obstacle avoidance for the AUV to operate in the constrained
underwater environment.
Nick - Benefits of Using Combined Bathymetry and Side Scan Sonar in Shallow W...Codevintec Italiana srl
Codevintec Days 2018 - Trieste
EDGETECH - Nick - Benefits of Using Combined Bathymetry and Side Scan Sonar in Shallow Water Surveys
Codevintec Days 2018 - Trieste
Relazione di Nick Lawrence - Edgetech
A ~25 slide presentation that explains the underlying principles and some applications of InSAR, with a particular focus on the measurement of deformation due to earthquakes. The presentation could be used in a lecture or lab setting, or provided to students for review out of class. The slides are annotated with additional background information designed to assist instructors.
AN EFFICIENT IMPLEMENTATION OF TRACKING USING KALMAN FILTER FOR UNDERWATER RO...IJCSEIT Journal
The exploration of oceans and sea beds is being made increasingly possible through the development of
Autonomous Underwater Vehicles (AUVs). This is an activity that concerns the marine community and it
must confront the existence of notable challenges. However, an automatic detecting and tracking system is
the first and foremost element for an AUV or an aqueous surveillance network. In this paper a method of
Kalman filter was presented to solve the problems of objects track in sonar images. Region of object was
extracted by threshold segment and morphology process, and the features of invariant moment and area
were analysed. Results show that the method presented has the advantages of good robustness, high
accuracy and real-time characteristic, and it is efficient in underwater target track based on sonar images
and also suited for the purpose of Obstacle avoidance for the AUV to operate in the constrained
underwater environment.
The earth�s ionosphere acts as a perturbing medium on satellite-based navigational systems like GPS. Variations in the ionosphere due to weather conditi ons caused by solar flares and coronal mass ejectio n can scatter Trans - Ionosphere radio signals producing fluctuations in both amplitude and phase and GPS cy cle slips disrupting satellite communications and navig ation. The ionosphere delay is one of the fundament al reasons for inaccuracy in GPS positioning and routi ng. The Total Electron Content (TEC) along the radi o wave path from a GPS satellite to the ground receiv er is directly proportional to the ionosphere delay . This paper proposes a method allowing to calculate the T EC with a correctness of about 2�3 TECU and to sens e Travelling Ionosphere Disturbances using GPS measur ements.
Presentation made by Prof. Adriano Camps (Universitat Politècnica de Catalunya) at ICMARS 2010 (India, 16-December-2010) on the MIRAS instrument aboard ESA's SMOS mission.
DUAL BAND GNSS ANTENNA PHASE CENTER CHARACTERIZATION FOR AUTOMOTIVE APPLICATIONSjantjournal
High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will be used in future automotive navigation systems. This system will be a composite of the United States' Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A further study of this patch antenna illustrates the absolute phase center variation measured in an indoor range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is investigated when integrated into a standard multi-band automotive antenna product. This product is evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using this evaluation file to estimate the receiver position could achieve phase motion error-free result.
DUAL BAND GNSS ANTENNA PHASE CENTER CHARACTERIZATION FOR AUTOMOTIVE APPLICATIONSjantjournal
High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will be used in future automotive navigation systems. This system will be a composite of the United States' Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A further study of this patch antenna illustrates the absolute phase center variation measured in an indoor range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is investigated when integrated into a standard multi-band automotive antenna product. This product is evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using this evaluation file to estimate the receiver position could achieve phase motion error-free result.
DUAL BAND GNSS ANTENNA PHASE CENTER CHARACTERIZATION FOR AUTOMOTIVE APPLICATIONSjantjournal
High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will be used in future automotive navigation systems. This system will be a composite of the United States' Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A further study of this patch antenna illustrates the absolute phase center variation measured in an indoor range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is investigated when integrated into a standard multi-band automotive antenna product. This product is evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using this evaluation file to estimate the receiver position could achieve phase motion error-free result.
DUAL BAND GNSS ANTENNA PHASE CENTER CHARACTERIZATION FOR AUTOMOTIVE APPLICATIONSjantjournal
High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will be used in future automotive navigation systems. This system will be a composite of the United States' Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A further study of this patch antenna illustrates the absolute phase center variation measured in an indoor range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is investigated when integrated into a standard multi-band automotive antenna product. This product is evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using this evaluation file to estimate the receiver position could achieve phase motion error-free result.
DUAL BAND GNSS ANTENNA PHASE CENTER CHARACTERIZATION FOR AUTOMOTIVE APPLICATIONSjantjournal
High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will be used in future automotive navigation systems. This system will be a composite of the United States' Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A further study of this patch antenna illustrates the absolute phase center variation measured in an indoor range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is investigated when integrated into a standard multi-band automotive antenna product. This product is evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using this evaluation file to estimate the receiver position could achieve phase motion error-free result.
DUAL BAND GNSS ANTENNA PHASE CENTER CHARACTERIZATION FOR AUTOMOTIVE APPLICATIONSjantjournal
High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will be used in future automotive navigation systems. This system will be a composite of the United States' Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A further study of this patch antenna illustrates the absolute phase center variation measured in an indoor range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is investigated when integrated into a standard multi-band automotive antenna product. This product is evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using this evaluation file to estimate the receiver position could achieve phase motion error-free result.
DUAL BAND GNSS ANTENNA PHASE CENTER CHARACTERIZATION FOR AUTOMOTIVE APPLICATIONSjantjournal
High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will
be used in future automotive navigation systems. This system will be a composite of the United States'
Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System
(GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The
major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier
phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade
antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a
low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A
further study of this patch antenna illustrates the absolute phase center variation measured in an indoor
range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is
investigated when integrated into a standard multi-band automotive antenna product. This product is
evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using
this evaluation file to estimate the receiver position could achieve phase motion error-free result.
In the modern age, High-resolution radar images can be achieved by employing SAR technique. It is well
known that SAR can provide several times better image resolution than conventional radars. The exploration for efficient
image denoising methods still remains a valid challenge for researchers. Despite the difficulty of the recently proposed
methods, mostly of the algorithms have not yet attained a pleasing level of applicability; each algorithm has its
assumptions, advantages, and limitations. This paper presents a review of synthetic aperture radar. Behind a brief
introduction in our work we are especially targeting the noise called backscattered noise in SAR terminology which
causes the appearance of speckle Potential future work in the area of air flight navigation, mapping Weather Monitoring
& during natural disaster like earth quake. The SAR having the capability, to make human visibility beyond optical
vision, is also discussed.
This content presents for basic of Synthetic Aperture Radar (SAR) including its geometry, how the image is created, essential parameters, interpretation, SAR sensor specification, and advantages and disadvantages.
APPLICATION OF SIGNAL PROCESSING IN RADIO ASTRONOMY SYSTEMSSaumya Tiwari
We discuss pulsar detection and timing pulsar profiling. We also consider image formation and radio maps cleaning using the CLEAN algorithm. Finally, we briefly discuss some future radio telescopes, which will consist of distributed phased arrays with a large number of elements.
The Use of Java Swing’s Components to Develop a WidgetWaqas Tariq
Widget is a kind of application provides a single service such as a map, news feed, simple clock, battery-life indicators, etc. This kind of interactive software object has been developed to facilitate user interface (UI) design. A user interface (UI) function may be implemented using different widgets with the same function. In this article, we present the widget as a platform that is generally used in various applications, such as in desktop, web browser, and mobile phone. We also describe a visual menu of Java Swing’s components that will be used to establish widget. It will assume that we have successfully compiled and run a program that uses Swing components.
3D Human Hand Posture Reconstruction Using a Single 2D ImageWaqas Tariq
Passive sensing of the 3D geometric posture of the human hand has been studied extensively over the past decade. However, these research efforts have been hampered by the computational complexity caused by inverse kinematics and 3D reconstruction. In this paper, our objective focuses on 3D hand posture estimation based on a single 2D image with aim of robotic applications. We introduce the human hand model with 27 degrees of freedom (DOFs) and analyze some of its constraints to reduce the DOFs without any significant degradation of performance. A novel algorithm to estimate the 3D hand posture from eight 2D projected feature points is proposed. Experimental results using real images confirm that our algorithm gives good estimates of the 3D hand pose. Keywords: 3D hand posture estimation; Model-based approach; Gesture recognition; human- computer interface; machine vision.
Camera as Mouse and Keyboard for Handicap Person with Troubleshooting Ability...Waqas Tariq
Camera mouse has been widely used for handicap person to interact with computer. The utmost important of the use of camera mouse is must be able to replace all roles of typical mouse and keyboard. It must be able to provide all mouse click events and keyboard functions (include all shortcut keys) when it is used by handicap person. Also, the use of camera mouse must allow users troubleshooting by themselves. Moreover, it must be able to eliminate neck fatigue effect when it is used during long period. In this paper, we propose camera mouse system with timer as left click event and blinking as right click event. Also, we modify original screen keyboard layout by add two additional buttons (button “drag/ drop” is used to do drag and drop of mouse events and another button is used to call task manager (for troubleshooting)) and change behavior of CTRL, ALT, SHIFT, and CAPS LOCK keys in order to provide shortcut keys of keyboard. Also, we develop recovery method which allows users go from camera and then come back again in order to eliminate neck fatigue effect. The experiments which involve several users have been done in our laboratory. The results show that the use of our camera mouse able to allow users do typing, left and right click events, drag and drop events, and troubleshooting without hand. By implement this system, handicap person can use computer more comfortable and reduce the dryness of eyes.
A Proposed Web Accessibility Framework for the Arab DisabledWaqas Tariq
The Web is providing unprecedented access to information and interaction for people with disabilities. This paper presents a Web accessibility framework which offers the ease of the Web accessing for the disabled Arab users and facilitates their lifelong learning as well. The proposed framework system provides the disabled Arab user with an easy means of access using their mother language so they don’t have to overcome the barrier of learning the target-spoken language. This framework is based on analyzing the web page meta-language, extracting its content and reformulating it in a suitable format for the disabled users. The basic objective of this framework is supporting the equal rights of the Arab disabled people for their access to the education and training with non disabled people. Key Words : Arabic Moon code, Arabic Sign Language, Deaf, Deaf-blind, E-learning Interactivity, Moon code, Web accessibility , Web framework , Web System, WWW.
Real Time Blinking Detection Based on Gabor FilterWaqas Tariq
New method of blinking detection is proposed. The utmost important of blinking detections method is robust against different users, noise, and also change of eye shape. In this paper, we propose blinking detections method by measuring of distance between two arcs of eye (upper part and lower part). We detect eye arcs by apply Gabor filter onto eye image. As we know that Gabor filter has advantage on image processing application since it able to extract spatial localized spectral features, such line, arch, and other shape are more easily detected. After two of eye arcs are detected, we measure the distance between both by using connected labeling method. The open eye is marked by the distance between two arcs is more than threshold and otherwise, the closed eye is marked by the distance less than threshold. The experiment result shows that our proposed method robust enough against different users, noise, and eye shape changes with perfectly accuracy.
Computer Input with Human Eyes-Only Using Two Purkinje Images Which Works in ...Waqas Tariq
A method for computer input with human eyes-only using two Purkinje images which works in a real time basis without calibration is proposed. Experimental results shows that cornea curvature can be estimated by using two light sources derived Purkinje images so that no calibration for reducing person-to-person difference of cornea curvature. It is found that the proposed system allows usersf movements of 30 degrees in roll direction and 15 degrees in pitch direction utilizing detected face attitude which is derived from the face plane consisting three feature points on the face, two eyes and nose or mouth. Also it is found that the proposed system does work in a real time basis.
Toward a More Robust Usability concept with Perceived Enjoyment in the contex...Waqas Tariq
Mobile multimedia service is relatively new but has quickly dominated people¡¯s lives, especially among young people. To explain this popularity, this study applies and modifies the Technology Acceptance Model (TAM) to propose a research model and conduct an empirical study. The goal of study is to examine the role of Perceived Enjoyment (PE) and what determinants can contribute to PE in the context of using mobile multimedia service. The result indicates that PE is influencing on Perceived Usefulness (PU) and Perceived Ease of Use (PEOU) and directly Behavior Intention (BI). Aesthetics and flow are key determinants to explain Perceived Enjoyment (PE) in mobile multimedia usage.
Collaborative Learning of Organisational KnolwedgeWaqas Tariq
This paper presents recent research into methods used in Australian Indigenous Knowledge sharing and looks at how these can support the creation of suitable collaborative envi- ronments for timely organisational learning. The protocols and practices as used today and in the past by Indigenous communities are presented and discussed in relation to their relevance to a personalised system of knowledge sharing in modern organisational cultures. This research focuses on user models, knowledge acquisition and integration of data for constructivist learning in a networked repository of or- ganisational knowledge. The data collected in the repository is searched to provide collections of up-to-date and relevant material for training in a work environment. The aim is to improve knowledge collection and sharing in a team envi- ronment. This knowledge can then be collated into a story or workflow that represents the present knowledge in the organisation.
Our research aims to propose a global approach for specification, design and verification of context awareness Human Computer Interface (HCI). This is a Model Based Design approach (MBD). This methodology describes the ubiquitous environment by ontologies. OWL is the standard used for this purpose. The specification and modeling of Human-Computer Interaction are based on Petri nets (PN). This raises the question of representation of Petri nets with XML. We use for this purpose, the standard of modeling PNML. In this paper, we propose an extension of this standard for specification, generation and verification of HCI. This extension is a methodological approach for the construction of PNML with Petri nets. The design principle uses the concept of composition of elementary structures of Petri nets as PNML Modular. The objective is to obtain a valid interface through verification of properties of elementary Petri nets represented with PNML.
Development of Sign Signal Translation System Based on Altera’s FPGA DE2 BoardWaqas Tariq
The main aim of this paper is to build a system that is capable of detecting and recognizing the hand gesture in an image captured by using a camera. The system is built based on Altera’s FPGA DE2 board, which contains a Nios II soft core processor. Image processing techniques and a simple but effective algorithm are implemented to achieve this purpose. Image processing techniques are used to smooth the image in order to ease the subsequent processes in translating the hand sign signal. The algorithm is built for translating the numerical hand sign signal and the result are displayed on the seven segment display. Altera’s Quartus II, SOPC Builder and Nios II EDS software are used to construct the system. By using SOPC Builder, the related components on the DE2 board can be interconnected easily and orderly compared to traditional method that requires lengthy source code and time consuming. Quartus II is used to compile and download the design to the DE2 board. Then, under Nios II EDS, C programming language is used to code the hand sign translation algorithm. Being able to recognize the hand sign signal from images can helps human in controlling a robot and other applications which require only a simple set of instructions provided a CMOS sensor is included in the system.
An overview on Advanced Research Works on Brain-Computer InterfaceWaqas Tariq
A brain–computer interface (BCI) is a proficient result in the research field of human- computer synergy, where direct articulation between brain and an external device occurs resulting in augmenting, assisting and repairing human cognitive. Advanced works like generating brain-computer interface switch technologies for intermittent (or asynchronous) control in natural environments or developing brain-computer interface by Fuzzy logic Systems or by implementing wavelet theory to drive its efficacies are still going on and some useful results has also been found out. The requirements to develop this brain machine interface is also growing day by day i.e. like neuropsychological rehabilitation, emotion control, etc. An overview on the control theory and some advanced works on the field of brain machine interface are shown in this paper.
Exploring the Relationship Between Mobile Phone and Senior Citizens: A Malays...Waqas Tariq
There is growing ageing phenomena with the rise of ageing population throughout the world. According to the World Health Organization (2002), the growing ageing population indicates 694 million, or 223% is expected for people aged 60 and over, since 1970 and 2025.The growth is especially significant in some advanced countries such as North America, Japan, Italy, Germany, United Kingdom and so forth. This growing older adult population has significantly impact the social-culture, lifestyle, healthcare system, economy, infrastructure and government policy of a nation. However, there are limited research studies on the perception and usage of a mobile phone and its service for senior citizens in a developing nation like Malaysia. This paper explores the relationship between mobile phones and senior citizens in Malaysia from the perspective of a developing country. We conducted an exploratory study using contextual interviews with 5 senior citizens of how they perceive their mobile phones. This paper reveals 4 interesting themes from this preliminary study, in addition to the findings of the desirable mobile requirements for local senior citizens with respect of health, safety and communication purposes. The findings of this study bring interesting insight to local telecommunication industries as a whole, and will also serve as groundwork for more in-depth study in the future.
Principles of Good Screen Design in WebsitesWaqas Tariq
Visual techniques for proper arrangement of the elements on the user screen have helped the designers to make the screen look good and attractive. Several visual techniques emphasize the arrangement and ordering of the screen elements based on particular criteria for best appearance of the screen. This paper investigates few significant visual techniques in various web user interfaces and showcases the results for better understanding and their presence.
Virtual teams are used more and more by companies and other organizations to receive benefits. They are a great way to enable teamwork in situations where people are not sitting in the same physical place at the same time. As companies seek to increase the use of virtual teams, a need exists to explore the context of these teams, the virtuality of a team and software that may help these teams working virtualy. Virtual teams have the same basic principles as traditional teams, but there is one big difference. This difference is the way the team members communicate. Instead of using the dynamics of in-office face-to-face exchange, they now rely on special communication channels enabled by modern technologies, such as e-mails, faxes, phone calls and teleconferences, virtual meetings etc. This is why this paper is focused on the issues regarding virtual teams, and how these teams are created and progressing in Albania.
Cognitive Approach Towards the Maintenance of Web-Sites Through Quality Evalu...Waqas Tariq
It is a well established fact that the Web-Applications require frequent maintenance because of cutting– edge business competitions. The authors have worked on quality evaluation of web-site of Indian ecommerce domain. As a result of that work they have made a quality-wise ranking of these sites. According to their work and also the survey done by various other groups Futurebazaar web-site is considered to be one of the best Indian e-shopping sites. In this research paper the authors are assessing the maintenance of the same site by incorporating the problems incurred during this evaluation. This exercise gives a real world maintainability problem of web-sites. This work will give a clear picture of all the quality metrics which are directly or indirectly related with the maintainability of the web-site.
USEFul: A Framework to Mainstream Web Site Usability through Automated Evalua...Waqas Tariq
A paradox has been observed whereby web site usability is proven to be an essential element in a web site, yet at the same time there exist an abundance of web pages with poor usability. This discrepancy is the result of limitations that are currently preventing web developers in the commercial sector from producing usable web sites. In this paper we propose a framework whose objective is to alleviate this problem by automating certain aspects of the usability evaluation process. Mainstreaming comes as a result of automation, therefore enabling a non-expert in the field of usability to conduct the evaluation. This results in reducing the costs associated with such evaluation. Additionally, the framework allows the flexibility of adding, modifying or deleting guidelines without altering the code that references them since the guidelines and the code are two separate components. A comparison of the evaluation results carried out using the framework against published evaluations of web sites carried out by web site usability professionals reveals that the framework is able to automatically identify the majority of usability violations. Due to the consistency with which it evaluates, it identified additional guideline-related violations that were not identified by the human evaluators.
Robot Arm Utilized Having Meal Support System Based on Computer Input by Huma...Waqas Tariq
A robot arm utilized having meal support system based on computer input by human eyes only is proposed. The proposed system is developed for handicap/disabled persons as well as elderly persons and tested with able persons with several shapes and size of eyes under a variety of illumination conditions. The test results with normal persons show the proposed system does work well for selection of the desired foods and for retrieve the foods as appropriate as usersf requirements. It is found that the proposed system is 21% much faster than the manually controlled robotics.
Dynamic Construction of Telugu Speech Corpus for Voice Enabled Text EditorWaqas Tariq
In recent decades speech interactive systems have gained increasing importance. Performance of an ASR system mainly depends on the availability of large corpus of speech. The conventional method of building a large vocabulary speech recognizer for any language uses a top-down approach to speech. This approach requires large speech corpus with sentence or phoneme level transcription of the speech utterances. The transcriptions must also include different speech order so that the recognizer can build models for all the sounds present. But, for Telugu language, because of its complex nature, a very large, well annotated speech database is very difficult to build. It is very difficult, if not impossible, to cover all the words of any Indian language, where each word may have thousands and millions of word forms. A significant part of grammar that is handled by syntax in English (and other similar languages) is handled within morphology in Telugu. Phrases including several words (that is, tokens) in English would be mapped on to a single word in Telugu.Telugu language is phonetic in nature in addition to rich in morphology. That is why the speech technology developed for English cannot be applied to Telugu language. This paper highlights the work carried out in an attempt to build a voice enabled text editor with capability of automatic term suggestion. Main claim of the paper is the recognition enhancement process developed by us for suitability of highly inflecting, rich morphological languages. This method results in increased speech recognition accuracy with very much reduction in corpus size. It also adapts Telugu words to the database dynamically, resulting in growth of the corpus.
An Improved Approach for Word Ambiguity RemovalWaqas Tariq
Word ambiguity removal is a task of removing ambiguity from a word, i.e. correct sense of word is identified from ambiguous sentences. This paper describes a model that uses Part of Speech tagger and three categories for word sense disambiguation (WSD). Human Computer Interaction is very needful to improve interactions between users and computers. For this, the Supervised and Unsupervised methods are combined. The WSD algorithm is used to find the efficient and accurate sense of a word based on domain information. The accuracy of this work is evaluated with the aim of finding best suitable domain of word. Keywords: Human Computer Interaction, Supervised Training, Unsupervised Learning, Word Ambiguity, Word sense disambiguation
Parameters Optimization for Improving ASR Performance in Adverse Real World N...Waqas Tariq
From the existing research it has been observed that many techniques and methodologies are available for performing every step of Automatic Speech Recognition (ASR) system, but the performance (Minimization of Word Error Recognition-WER and Maximization of Word Accuracy Rate- WAR) of the methodology is not dependent on the only technique applied in that method. The research work indicates that, performance mainly depends on the category of the noise, the level of the noise and the variable size of the window, frame, frame overlap etc is considered in the existing methods. The main aim of the work presented in this paper is to use variable size of parameters like window size, frame size and frame overlap percentage to observe the performance of algorithms for various categories of noise with different levels and also train the system for all size of parameters and category of real world noisy environment to improve the performance of the speech recognition system. This paper presents the results of Signal-to-Noise Ratio (SNR) and Accuracy test by applying variable size of parameters. It is observed that, it is really very hard to evaluate test results and decide parameter size for ASR performance improvement for its resultant optimization. Hence, this study further suggests the feasible and optimum parameter size using Fuzzy Inference System (FIS) for enhancing resultant accuracy in adverse real world noisy environmental conditions. This work will be helpful to give discriminative training of ubiquitous ASR system for better Human Computer Interaction (HCI). Keywords: ASR Performance, ASR Parameters Optimization, Multi-Environmental Training, Fuzzy Inference System for ASR, ubiquitous ASR system, Human Computer Interaction (HCI)
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The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
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Trend Analysis of Onboard Calibration Data of Terra/ASTER/VNIR and One of the Suspected Causes of Sensitivity Degradation
1. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 71
Trend Analysis of Onboard Calibration Data of
Terra/ASTER/VNIR and One of the Suspected Causes of
Sensitivity Degradation
Kohei Arai arai@is.saga-u.ac.jp
Information Science Department
Saga University
Saga City, 840-8502, Japan
Nagamitsu Ohgi nohgi@jaros.or.jp
Japan Resources Observation System and Space Utilization Organization,
2-24-2 Nichibei Bldg, Hacchobori, Chuo, Tokyo, 104-0032 Japan
Fumihiro Sakuma sakuma@jaros.or.jp
Japan Resources Observation System and Space Utilization Organization,
2-24-2 Nichibei Bldg, Hacchobori, Chuo, Tokyo, 104-0032 Japan
Masakuni Kikuchi kikuchi@jaros.or.jp
Japan Resources Observation System and Space Utilization Organization,
2-24-2 Nichibei Bldg, Hacchobori, Chuo, Tokyo, 104-0032 Japan
Satoshi Tsuchida s.tsuchida@aist.go.jp
Advanced Industrial Science and Engineering,
1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 Japan
Hitomi Inada hinada@bx.jp.nec.com
NEC Corporation,
1-10 Nisshin, Fuchu, Tokyo 183-8501 Japan
Abstract
Sensitivity degradation trend is analyzed for ASTER: Advanced Spaceborne Thermal Emission
and Reflection radiometer/Visible and Near-Infrared Radiometer: VNIR onboard Terra satellite.
Fault Tree Analysis is made for sensitivity degradation. Firstly, it is confirmed that the VNIR
detectors are stable enough through dark current and shot noise behavior analysis. Then it is also
confirmed that radiance of calibration lamp equipped VNIR is stable enough through lamp monitor
of photodiode output data analysis. It is confirmed that radiance at the front of VNIR optics is, on
the other hand, degraded in conjunction with sensitivity degradation of VNIR through an analysis
of another photodiode output data which is equipped at the front of VNIR optics, photodiode
output is scale-off at around one year after the launch though. VNIR optics transparency might
not be so degraded due to the fact that VNIR output and the later photodiode output show almost
same degradations. Consequently, it may say that one of possible causes of VNIR sensitivity
degradation is thruster plume.
Keywords: ASTER, Onboard Calibration, Vicarious Calibration, Plume Impingement.
1. INTRODUCTION
Almost all the solar reflection channels of mission instruments onboard Earth observation satellite
carry their own calibration system to maintain consistency of the radiometric fidelity of the
instrument. Thus users may convert from the Digital Number, DN to radiance taking the onboard
calibration system derived calibration coefficient into account. There are some reports on the
calibration issues which include the MOS-1: Marine Observation Satellite-1[1], Landsat-7 ETM+:
Enhanced Thematic Mapper Plus[2], SeaWiFS: Sea-viewing Wide Field-of-view Sensor[3],
2. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 72
SPOT-1 and 2: Satellite Pour l'Observation de la Terre[4], Hyperion[5], and POLDER:
POLarization and Directionality of the Earth's Reflectance[6]. Onboard calibrators cannot provide
results of a higher accuracy than the preflight laboratory calibration. This means that the accuracy
of the in-flight (absolute) calibration is inferior to the preflight results. This is because the preflight
calibration source is used to calibrate the onboard calibrators. In addition, the uncertainty of the
onboard calibrator typically increases with time. Hence, it makes good sense to include additional
calibration approaches that are independent of the preflight calibration. Besides the normal and
expected degradation of the onboard calibrators, they also run the risk of failing or operating
improperly. Therefore, vicarious approaches are employed to provide further checks on the
sensor’s radiometric behavior. Any electro-optical sensor is expected to degrade once in orbit,
and therefore requires a mechanism to monitor the data’s radiometric quality over time. Many
sensors, including ASTER: Advanced Spaceborne Thermal Emission and Reflection radiometer,
employ onboard calibration devices to evaluate temporal changes in the sensor responses.
Onboard calibrators, in general, provide excellent temporal sampling of the sensor’s radiometric
behavior over time. In addition, the repeatability and precision of the onboard systems allow use
of these data in characterizing the sensor’s response trends. Typical approaches for onboard
calibration include lamp-based, diffuser-based, and detector-based methods. ASTER VNIR:
Visible and Near-Infrared Radiometer and SWIR: Short Wave Infrared Radiometer use lamp
based onboard calibrators. The specific design of the ASTER OBC: Onboard Calibrator is
described in the following section. Then the sensor’s response trends and suspected influence
due to plume impingement of contamination of optics entrance of ASTER instrument is followed
by with some evidences. Finally, discussions and concluding remarks are described.
2. ONBOARD CALIBRATION SYSTEM OF TERRA/ASTER/VNIR
2.1 Onboard Calibration System
ASTER VNIR and SWIR channels use lamp-based onboard calibrators for monitoring temporal
changes in the sensor responses. Space restrictions aboard the Terra platform disallow a
solarbased calibration, and therefore, onboard calibration is lamp-based. The VNIR and SWIR
have two onboard calibration lamps, lamp-A and lamp-B. Both are used periodically, and as a
backup system. The VNIR calibration lamp output is monitored by a silicon photo monitor, and is
guided to the calibration optics. The calibration optics output illuminates a portion of the VNIR
aperture’s observation optics and is monitored by a similar photo monitor. Meanwhile, the SWIR
calibration assembly does not have a second silicon photo monitor. In the pre-flight phase, the
onboard calibrators were well characterized with integration spheres calibrated with fixed freezing
point blackbodies of Zn (419.5K). This was accomplished by comparing the VNIR and SWIR
output derived from the integration sphere’s illumination of the two sensors. The same
comparison was made by the calibration lamp’s (A and B) illumination of the two sensors. Next,
the pre-flight gain and offset data (no illumination) were determined. In addition, MTF: Modulation
Transfer Function was measured with slit light from a collimator while stray light effect was
measured with the integration sphere illumination, which is blocked at the full aperture of the
VNIR and SWIR observation optics entrance. The pre-flight calibration data also includes
(1) spectral response,
(2) out-of-band response.
The VNIR has two onboard calibration halogen lamps (A and B) as is shown in Figure1. The light
from these lamps is led to the VNIR optics via a set of calibration optics. Filters and
photomonitors are located fore and aft of the calibration optics to monitor the output of the lamps
as well as any possible degradation in the calibration optics. Lamp output and photo monitor data
are collected every 33 days (primarily it was 16 days of the Terra orbital revisit cycle plus one day
= 17 days and is 49 days now a day), and RCC: Radiometric Calibration Coefficients are
calculated from the VNIR output taking into account the photo-monitor output. The RCC values
are normalized by the pre-flight data to determine their final estimate. This procedure is the same
for the SWIR RCC calculation except that the SWIR OBC does include a photo monitor system at
the lamp but does not include a photo monitor system for entrance of the optics. Thus, only data
3. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 73
from a photo monitor that is aft of the calibration lamp is taken into account.
FIGURE 1: Onboard calibration system of the ASTER/VNIR
2.2 Onboard Calibration Trend
Figure2 shows the RCC trends for VNIR.
OBC RCC
FIGURE 2: OBC RCC trends for Band 1(Blue), Band 2(Green) and Band 3(Red)
The RCC were changed relatively rapidly in the early stage of the launch, and is changed
gradually for the time being. These are approximated with an exponential function with a bias and
a negative coefficient. If the trend is approximated with the function of RCC = B exp (-At) + C,
then A, B, and C equal the following values: Band1 (560nm): A = 0.00190, B = 0.360, C = 0.735
Band2 (660nm): A = 0.00168, B = 0.282, C = 0.807Band3 (810nm): A = 0.00150, B = 0.216, C =
0.860 During 2500 days after the launch, VNIR OBC RCC were degraded about 10% for Band3,
16% for Band2 and 23 % for Band1, respectively while SWIR OBC RCC were degraded
approximately 2.0 to 3.5% depending on bands[7]. These trends are very similar to the vicarious
calibration derived RCC, and also look similar to the OBC RCC trend of the OPS: Optical Sensor
onboard the JERS-1: Japanese Earth Resources Satellite, a legacy precursor to the ASTER
instrument. There are two major trends in OBC RCC trends, at the first 800 days and at the 2100
4. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 74
days after the launch as is shown in Figure2. It is suspected that out-gas from the materials of
VNIR instrument and thruster plume in the initial phase. Each of the VNIR bands is shown, as are
the onboard calibrator results for these bands in a fashion similar to that shown in Figure 2. On
the other hand, Figure 3 shows vicarious calibration trend [8]. Although both onboard and
vicarious calibration trends are similar, there are small biases, a few percents for Band 1 to 3N as
is indicated in Figure 3. Therefore, VNIR sensitivity degradation is confirmed with the different two
sources. VNIR sensitivity degradation can be expressed with exponential function so that one of
the possible causes of the degradation is contamination. The other causes are degradation of
optical transparency of the calibration optics, sensitivity degradation of photo-monitor,
degradation of photmonitor filter, etc.
FIGURE 3: OBC and Vicarious RCC Trends
2.3 Photo-Monitor Output Trend
As is shown in Figure 1, VNIR has two photo-monitors, one (PD2) is set at lamp output and the
other one (PD1) is set at the optics entrance, just in front of the collecting mirror.
Although PD1 output shows scale-off at around 370 days after launch as is shown in Figure 4, the
degradation of the degradation ratio shows almost same trend as OBC and vicarious RCC trends.
Also PD2 output shows stable lamp illumination so that one of possible causes for the sensitivity
degradation is contamination at the optics entrance because the calibration optics is composed
with browning lenses (less degradation of transparency due to radiation from solar flare). From
the PD1 output data, approximated exponential function is estimated with least square method.
The degradation rate is confirmed to be almost same as OBC and vicarious RCC trends as is
shown in Figure 5.
5. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 75
FIGURE 4 : Photomonitor output for both calibration system A and B of PD1 and PD2.
FIGURE 5 : Approximated exponential function of PD1 output using PD1 data taken in 370 days
after launch together with the other photomonitor output trends.
R square for this exponential approximation for PD1A is 0.9963 so that exterpolation might be
possible accurately. OBC RCC trends with reference to the calibration systems (Lamp A and B as
well as photo-monitor PD1 and 2) are shown in Figure 6. In the figure, exterpolation curve is
shown as “pd1a(Exterpolation)”, photomonitor output voltage shows negative for the period 370
days after launch though.
6. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 76
-20
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000 3500 4000
D ays after launchRCCandphotomonitoroutput(V)
pd1a(Exterpolation)
pd2a
pd1b(Exterpolation)
pd2b
band1
band2
band3N
FIGURE 6 : OBC RCC trend together with photo-monitor output trend.
The first three lines are for Band 3, 2 and 1, respectively, of RCC ranges from 105 (just after the
launch) to 76 at around 3600 days after launch while the last four lines are for photo-monitor
output. As is mentioned before, photo-monitor PD1 for both lamp A and B were in scale off at 370
days after launch so that PD1 (lamp A and B) trend were extrapolated by the exponential function
with coefficients determined from the PD1 output data of the first 370 days. As is shown in Figure
6, the coefficients of exponential function of RCC trend is almost same as that of exterpolation
function of PD1. Thus it might be concluded that one of the possible causes of the RCC
degradation would be contamination at the optics entrance of VNIR due to plume impingement.
Thruster plume of hydrazine hydrate has not only absorption band at around 12mm but also
continuous absorption in the visible region (absorption coefficient is not large though)
1
. Also
hydrazine absorption in visible wavelength region is reported [9]. They measured spectral
absorption of liquid as a product of hydrazine [10] with several chemicals. Consequently, they
found the very calm peak absorption at around 460-480nm. For these reasons, there is a little
absorption in visible wavelength region due to hydrazine hydrate of thruster plume which may
affect to degradation of optics transparency of mission instruments onboard satellites.
2.4 Possible Causes of Sensitivity Degradation and Fault Tree Analysis
Firstly, it is shown that VNIR detector sensitivity is stable. As is shown in Figure 7 and 8, dark
signal (Output signal when no input from the VNIR optics entrance (Night time observation)) and
detector temperature is very stable so that it may say that detector sensitivity is stable enough.
B and 1 Dark (pix=2500,2501)B and 1 Dark (pix=2500,2501)B and 1 Dark (pix=2500,2501)B and 1 Dark (pix=2500,2501)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
1999/12/6 2001/4/19 2002/9/1 2004/1/14 2005/5/28 2006/10/10 2008/2/22 2009/7/6 2010/11/18 2012/4/1
DN
2500-Low
2501-Low
2500-Norm al
2501-Norm al
2500-High
2501-High
1 http://www.coe.ou.edu/sserg/web/Results/EPA%20Spectra/N2H4%20etc.pdf
7. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 77
B and 2 D ark (pix=2500,2501)B and 2 D ark (pix=2500,2501)B and 2 D ark (pix=2500,2501)B and 2 D ark (pix=2500,2501)
0.00
1.00
2.00
3.00
4.00
5.00
1999/12/6 2001/4/19 2002/9/1 2004/1/14 2005/5/28 2006/10/10 2008/2/22 2009/7/6 2010/11/18 2012/4/1
DN
2500-Low
2501-Low
2500-N orm al
2501-N orm al
2500-H igh
2501-H igh
B and 3N D ark (pix=2500,2501)B and 3N D ark (pix=2500,2501)B and 3N D ark (pix=2500,2501)B and 3N D ark (pix=2500,2501)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
11.00
12.00
13.00
14.00
15.00
16.00
17.00
18.00
1999/12/6 2001/4/19 2002/9/1 2004/1/14 2005/5/28 2006/10/10 2008/2/22 2009/7/6 2010/11/18 2012/4/1
DN
2500-Low
2501-Low
2500-Norm al
2501-Norm al
2500-High
2501-High
FIGURE 7: Dark signals for Bands 1(Top), 2(Middle), 3(Bottom)
FIGURE 8: Detector temperature for Bands 1,2,3.
As is shown in Figure 4, radiance from the calibration lamp is also stable so that optical
transparency of VNIR optics might be degraded. There are some possible causes of the VNIR
optical transparency degradation those are (1) Initial phase and (2) Long term sensitivity
degradations. In the initial phase, out-gas from materials of VNIR is one of them followed by
thruster plume contamination. For the long term degradation, optical transparency degradation
due to ultra-violet and solar radiation as well as thruster plume is major causes. Optical
transparency degradation due to ultra-violet light polymerization of optics is one of those followed
by browning of optics. Fault Tree is shown in Figure 9.
8. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 78
FIGURE 9: Fault Tree for VNIR sensitivity degradation
VNIR optics employs non-browning materials so that it may not occur browning in the optics.
Ultra-violet light polymerization of optics might be occurred. It used to be occurred due to organic
gas contamination on optics surface, in particular, coating material of the sensor optics onboard
satellite
11
.
Although VNIR does not employ such coating material at all, it is difficult to say it is not a cause.
Thus thruster plume is one of possible causes.
During hydrazine is burning from thruster, plume includes not only hydrazine, N2H4, but also NH3,
H2O, N2, H2. Mass fraction of N2 is dominant followed by NH3. Terra satellite carries two types of
monopropellant of thruster, 5lbf and 1lbf. Plume impingement rate at aperture of NH3 is dominant
followed by H2O and N2H4. Re-emission rate for these molecules are greater than impingement
rate so that the surface of the VNIR optics is not accumulate anything. Hydrazine hydrate stick
2
on the surface of optics would occur so that it is suspected that some mixture of hydrazine such
as H4N2・H2O is remained on the surface of VNIR optics (sticking fraction of N2H4 is 0.1% in
accordance with the site of footnote below 2).
Although hydrazine hydrate has no absorption in visible and near infrared wavelength region,
transparency in that region is not 100%. Transparency of H4N2・H2O is 96% at around VNIR
Band 1, 97% at around Band 2 and 98% at around Band 3, respectively. This situation is much
severe for short wave infrared region, SWIR. Sensitivity degradation of SWIR is not so significant
and is much less than VNIR. One of the reasons for this is that thruster plume is situated in front
of optics as a particle, it is not realistic though. Thus sticking hydrazine hydrate on the optics
might not be a suspect so that ultra-violet light polymerization of optics might be a suspect.
Further investigation is needed.
2.5 Size Distribution of Thruster Plume
From the wavelength dependency of OBC RCC trend, it is possible to estimate size distribution if
it is assumed that plume impingement is one of possible causes of the RCC degradation [12],[13].
Figure 10 shows wavelength dependency of the RCC degradations. From this spectral
dependency, size distribution is estimated with the assumption that the size distribution is
followed by the power law as well as the accumulated number of particles is normalized by one.
Figure 11 shows the estimated size distribution. The size distribution estimation has not been
validated yet.
2 http://www.gps.caltech.edu/genesis/Thrusters.html
9. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 79
y = -0.4297x - 1.6158
-4.52
-4.5
-4.48
-4.46
-4.44
-4.42
-4.4
-4.38
-4.36
-4.34
-4.32
-4.3
6.30 6.35 6.40 6.45 6.50 6.55 6.60 6.65 6.70 6.75
ln(W avelength)
-ln(RCC)
FIGURE10: Spectral characteristics of RCC and its linearly approximated function.
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
0.010 0.100 1.000 10.000
radius(m icrom eter)
Thenumberofparticles
FIGURE11: Estimated size distribution of plume impingement that is one of causes of the
RCC degradation
2.6 Size Distribution and SWIR Sensitivity Degradation
From Figure 11, it can be assumed that hydrazine hydrate is distributed at the optics surface
sparsely because most of hydrazine hydrate particle size is smaller than 1 micrometer and the
number of the particles with 0.1 micrometer of radius is around 2000 while the number of particle
with 0.01 micrometer of radius is 2 million. On the other hand, SWIR sensitivity degradation for
each band is around 1.2%, 2.7%, 2.7%, 2.5%, 2.4%, and 2.7% for Band 4-9 within the first 7 and
half years after the launch. Meanwhile, the center wavelength of SWIR of each band is 1.65,
2.165, 2.205, 2.26, 2.33 and 2.395 micrometer for Band 4-9 so that hydrazine hydrate particles
are small enough for influencing to optics transparency through scattering. It is said that
hydrazine hydrate particles do not affect to the sensitivity degradation for SWIR wavelength
regions.
2.7 Fuel Consumption and RCC Trend
Another evidence of the causes of RCC degradation is the relation between fuel consumption and
RCC degradation. Figure 12 shows the fuel consumption of Terra satellite which carries
ASTER/VNIR. Figure 12 also shows approximated function of the fuel consumption together with
approximated function of RCC degradation. As is well known that the fuel consumption in just
after launch is relatively large, there is bias between the two approximated functions of fuel
consumption and RCC degradation. Both functions, however, show almost same trend.
Figure 13 also shows the OBC RCC trends, with the reference to the two calibration systems,
Lamp A and B as well as PD2, for Band 1, 2 and 3. Figure13 also shows the fuel consumption
and its approximated function with exponential function. It may say that theses show almost same
trend.
10. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 80
y = 302.44e
-0.0002x
R
2
= 0.9633
150
170
190
210
230
250
270
290
310
330
350
0 500 1000 1500 2000 2500 3000 3500 4000
Days after launch, x
Fuelconsumptionandapprox.functionwith
exponetialfunction
Fuel comsumption
340Exp(- 0.0002x)
Exponetial Approx.
FIGURE 12: The relation between fuel consumption and RCC degradation.
0.7
0.75
0.8
0.85
0.9
0.95
1
0 1000 2000 3000 4000
D ays after launch,x
RCC,approximatedfunctionandfuel
consumption
0.7+0.3Exp(-0.001x)
Ab12500
Ab12501
Ab22500
Ab22501
Ab32500
Ab32501
B b12500
B b12501
B b22500
B b22501
B b32500
B b32501
Fuel
FIGURE 13: Relations between OBC RCC trend and fuel consumption as well as the
approximated function of fuel consumption.
2.8 Comparison between Terra/MODIS and VNIR Sensitivity Degradations
Also sensitivity degradation of VNIR is compared to that of Terra/MODIS: Moderate Resolution
Imaging Spectroradiometer because ASTER/VNIR and MODIS is onboard and their optics is
equipped at Earth pointed plane on the same satellite, Terra so that almost same thruster plume
influence may occur for both optics.
Sensitivity degradation of MODIS is well reported
13
so that it is compared to that of VNIR. There
are three obvious epochs on around 520, 900 days and 1400 days after launch in terms of
coincidence between fuel consumption and sensitivity degradation. These are common to both
mission instruments, VNIR and MODIS.
Also these sensitivity degradations for both show coincident to the fuel consumption. Also
according to X. Xiong et.al (2006), sensitivity degradation ratio between MODIS bands 8(412nm)
and 4(554nm) as well as bands 4 and 17(905nm) are approximately 5.5 and 6.0, respectively.
Meanwhile, sensitivity degradation ratio between VNIR and 1(560nm) and 3(810nm) is around
2.2. On the other hand, sensitivity degradation of MODIS band 4 is around 6% at 1500 days after
launch while that of VNIR band 1 is 24%. Sensitivity degradation of VNIR is much significant than
MODIS.
2.9 RCC Comparison between VNIR Band 3N and 3B
VNIR has two telescopes, band 1, 2 and 3N (Nadir looking) and band 3B (Backward looking) as
is illustrated in Figure 14. Both telescope are equipped at the different location with the different
angle (3N is pointing to the nadir while 3B is pointing to off-nadir with 27.6 degree).
Contamination situations for both telescopes, therefore, are different. For this reason, sensitivity
degradations for these two may be different. Figure 15 shows the difference between vicarious
calibration data derived RCC for both. Because Band 3B does not have any onboard calibration
system so that only vicarious calibration data derived RCC is discussed. If the thruster plume
comes from the front of optics uniformly, then contamination of backward optics is 11.38%
11. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 81
(cos(27.6 degree)) less than nadir optics. Both degradations show 8.54% difference between
Band 3N and Band 3B so that it is close to 11.38% of less contamination of backward telescope
of Band 3B due to thruster plume.
FIGURE 14: Illustrative view of VNIR instrument.
(a) OBC and vicarious RCC trends for Band 3N
(b) Vicarious RCC trend for Band 3B
FIGURE 15: Difference of OBC RCC and vicarious calibration data derived RCC for both Band
3N and Band 3B.
Consequently, optics transparency seems to be most suspected cause of the RCC (sensitivity)
degradation due to plume impingement by hydrazine hydrate from the thrusters.
2.10 Another Evidence of Contamination of ASTER/TIR Optics With Thruster Plume
ASTER composed with three mission instruments, VNIR, SWIR and Thermal Infrared Radiometer
(TIR) which has five spectral channels in the atmospheric window. Sensitivity degradation of TIR
Band 12 (9.1 micrometer of spectral channel) is significant followed by the Band 10, 11 as well as
Band 13 and 14 as is shown in Table 1. Table 1 shows wavelength coverage and annual
degradation of sensitivity.
During thruster burns hydrazine, hydrazine + water will be plumed. Hydrazine Hydrate
(N2H4+H2O) has an absorption line at around 9.1µm11 so that it is understandable that
sensitivity degradation is significant [15]. Also sensitivity degradation of Band 12 is much
12. Kohei Arai, Nagamitsu Ohgi, Fumihiro Sakuma, Masakuni Kikuchi, Satoshi Tsuchida & Hitomi Inada
International Journal of Applied Science (IJAS), Volume (2) : Issue (3) : 2011 82
significant in comparison to the other bands. Therefore, it is confirmed that hydrazine hydrate
contaminated at the optics surface TIR as well as VNIR and SWIR.
Band No. Wavelength
10 8.125~8.475µm
11 8.475~8.825µm
12 8.925~9.275µm
13 10.25~10.95µm
14 10.95~11.65µm
TABLE 1: Spectral channels of ASTER/TIR
3. CONCLUDING REMARKS
Due to the fact that dark signal and shot noise as well as circumstances of the VNIR such as
detector temperature are stable so that detector of the VNIR is stable. Calibration lamp radiance
monitor of photodiode output is stable so that calibration lamp is stable. Optics entrance monitor
of photodiode which measures calibration lamp radiance shows a remarkable degradation. It was
terminated 370 days after the launch, though. The degradation trend is almost same as
OBC/RCC degradation (VNIR sensitivity degradation) if exterpolated degradation of optics
entrance calibration radiance is compared to OBC/RCC. VNIR optics transparency is not so
degraded. One of the possible causes of OBC/RCC degradation comes from contamination or
ultra-violet light polymerization on the surface of VNIR optics entrance.
Assumption of which RCC degradation is caused by contamination of optics entrance of VNIR
due to plume impingement from gas jet for attitude control seems to be reasonable. Sticking
fraction of hydrazine is 0.1 while absorption coefficients at 500, 600, 700nm are 0.4, 0.3, 0.2%.
Vicarious calibration shows difference sensitivity degradations between VNIR Band 3N and 3B.
This may be caused by the fact that the optics for Band 3N is pointing to nadir while for Band 3B
is pointing to 27.6 degree off-nadir because contamination situation due to thruster plume is
different each other. Optics component are same for Band 3N and 3B so that both of the ultra-
violet light polymerization and the sticking hydrazine hydrate are suspected. Similarly, MODIS
sensitivity degradation shows a coincidence to VNIR OBC/RCC trend in terms of three obvious
epochs on 520, 900 and 1400 days after the launch.
These three epochs are similar to the fuel consumption epochs. Using wavelength dependency of
RCC degradation, size distribution is estimated with the relation between ln(wavelength) and
ln(RCC degradation) based on power low distribution function. It has to be validated though. In a
realistic case, thruster plume sticks to the optics but not situated as a particle. There is an
evidence of sticking hydrazine hydrate on the TIR optics due to the fact that absorption
wavelength of hydrazine hydrate corresponds to the most significant sensitivity degradation band
of TIR. Consequently, optics transparency would be a most suspected cause of the RCC
(sensitivity) degradation due to plume impingement by hydrazine hydrate from the thrusters or
ultra-violet light polymerization of optics. Further investigation is needed.
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