Basic’s of Remote Sensing Praveen Vishwakarma Diploma in Remote Sensing & GeoinformaticsDept. of Remote Sensing & Geoinformatics MDS University, Ajmer Submitted to:: Dr. Sarvesh Palriya H.O.D. Remote Sensing Dept.
DefinitionsRemote Sensing can be defined as the acquisition and recording of information about anobject without being indirect contact with that object.Remote Sensing, process of obtaining information about land, water, or an object withoutany physical contact between the sensor and the subject of analysis.Remote Sensing is an extensive science, drawing from many areas for support anddevelopment. It depends greatly on the support of governments and private industriesworldwide. Satellite and digital imagery play an important role in remote sensing;providing information about the land studiedThe benefits of remote sensing continue to arise. It can be used to access hard toreach areas for fieldwork, and provides a more detailed, permanent and objectivesurvey that offers a different perspective. Air photos are still favored and easilyaccessible sources of information for classification
Remote Sensing means acquiring information about a phenomena, object or surface while at a distance from it. This name isattributed to recent technology in which Satellite and space craftare used from collecting information to it.
1. Energy Source or Illumination – The first requirement for remote sensing is tohave an energy source which illuminates or provides electromagnetic energy to thetarget of interest.2. Radiation and the Atmosphere– As the energy travels from its source to thetarget, it will come in contact with and interact with the atmosphere it passesthrough. This interaction may take place a second time as the energy travels fromthe target to the sensor.3. Interaction with the Target - Once the energy makes its way to the targetthrough the atmosphere, it interacts with the target depending on the properties ofboth the target and the radiation.4. Recording of Energy by the Sensor - After the energy has been scattered by, oremitted from the target, we require a sensor (remote - not in contact with the target)to collect and record the electromagnetic radiation.5. Transmission, Reception, and Processing - The energy recorded by the sensorhas to be transmitted, often in electronic form, to a receiving and processing stationwhere the data are processed into an image (hardcopy and/or digital).
Data Analysis1. Interpretation and Analysis - The processed image is interpreted, visuallyand/or digitally or electronically, to extract information about the target which wasilluminated.2. Application - The final element of the remote sensing process is achievedwhen we apply the information we have been able to extract from the imageryabout the target in order to better understand it, reveal some new information, orassist in solving a particular problem.These seven elements comprise the remote sensing process from beginning toend. We will be covering all of these in sequential order
Two characteristics of electromagnetic radiation are particularly importantfor understanding remote sensing. These are the wavelength and frequency.
Interaction with THE AtmosphereBefore radiation used for remote sensing reaches the Earths surface it has to travel throughsome distance of the Earths atmosphere. Particles and gases in the atmosphere can affectthe incoming light and radiation. These effects are caused by the mechanisms of scatteringand absorption.Scattering occurs when particles or large gas molecules present in the atmosphere interactwith and cause the electromagnetic radiation to be redirected from its original path. Howmuch scattering takes place depends on several factors including the wavelength of theradiation, the abundance of particles or gases, and the distance the radiation travels throughthe atmosphere. There are three (3) types of scattering which take place.
ScatteringAtmospheric scattering is accomplished through absorption and re-emission ofradiation by atoms or molecules.Rayleigh scattering : occurs when particles are very small compared tothe wavelength of the radiation. These could be particles such as small specks ofdust or nitrogen and oxygen molecules. Rayleigh scattering causes shorterwavelengths of energy to be scattered much more than longer wavelengths.Rayleigh scattering is the dominant scattering mechanism in the upper atmosphere.The fact that the sky appears "blue" during the day is because of this phenomenon. Mie scattering :occurs when the particles are just about the same size as the wavelength of the radiation. Dust, pollen, smoke and water vapor are common causes of Mie scattering which tends to affect longer wavelengths than those affected by Rayleigh scattering. Non-selective scattering: This occurs when the particles are much larger than the wavelength of the radiation. Water droplets and large dust particles can cause this type of scattering. Nonselective scattering gets its name from the fact that all wavelengths are scattered about equally.
Absorption Absorption is the process by which radiant energy is absorbed and converted into other forms of energy. An absorption band is a range of wavelengths (or frequencies) in the electromagnetic spectrum within which radiant energy is absorbed by substances such as water carbon dioxide (CO2), oxygen (O2), ozone (O3), and nitrous oxide (N2O). Ozone, carbon dioxide, and water vapor are the three main atmospheric constituents which absorb radiation. Ozone : Ozone serves to absorb the harmful (to most living things) ultraviolet radiation from the sun. Without this protective layer in the atmosphere our skin would burn when exposed to sunlight.carbon dioxide: Carbon dioxide referred to as a greenhouse gas. This is because it tendsto absorb radiation strongly in the far infrared portion of the spectrum - that areaassociated with thermal heating – which serves to trap this heat inside the atmosphere.Water vapor: Water vapor in the atmosphere absorbs much of the incoming long waveinfrared and shortwave microwave radiation (between 22 m and 1 m ). The presenceof water vapor in the lower atmosphere varies greatly from location to location and atdifferent times of the year. For example, the air mass above a desert would have verylittle water vapor to absorb energy, while the tropics would have high concentrations ofwater vapor.
Atmospheric Windows In the spectrum we can "look" for remote sensing purposes. Those areas of the spectrum which arenot severely influenced by atmospheric absorption and thus, are useful to remote sensors, arecalled atmospheric windows. we can define those wavelengths that we cause most effectively forremote sensing. The visible portion of the spectrum, to which our eyes are most sensitive, correspondsto both an atmospheric window and the peak energy level of the sun. Note also that heat energyemitted by the Earth corresponds to a window around 10 μm in the thermal IR portion of the spectrum,while the large window at wavelengths beyond 1 mm is associated with the Now that we understandhow electromagnetic energy makes its journey from its source to the surface (and it is a difficultjourney, as you can see) we will next examine what happens to that radiation when it does arrive at theEarths surface.
Spectral SignatureAny Remotely sensed parameter , which directly or indirectly characterizes thenature and or condition of the object under observation , as defined as t spectralsignature.
Platform & orbitsTwo Satellite orbits are important for Remote sensing observation of the earth :1.Geo-stationary orbit 2.Sunsynchronous - polar orbit1.Geo-stationary Orbit : The Geo-Stationary orbit is such a position for a satellite that it keeps place of with the rotation of earth. These Platform are covering the same place and give continues near hemispheric coverage over the same area day and night. These Geostationary Satellite , at altitudes of approximately 36,000 km. revolve at speeds which match the rotations of the earth so they seem stationary , relative to the earth’s surface. This allows the Satellites to observe and collect information continuously over specific areas. These are the main used for communications and metrological application.
Polar orbit :The second important Remote sensing orbit is Polar orbit. Satellite in apolar orbit cycle from north pole to south pole . The polar orbit have an inclination