Remote sensing

Syllabus
1. Introduction of Remote Sensing.
1.1 Definition
1.2 Principle
1.3 History
1.4 Indian Remote Sensing
2. Types Of Remote Sensing Sensor Systems.
2.1 Active Systems.
2.2 Passive Systems.
3. Remote Sensing Platforms.
4. Remote Sensing Systems.
4.1 Ideal
4.2 Real
4.3 Optimal
4.4 Thermal
4.5 Microwave.
5. Electromagnetic energy.
6. Electromagnetic Spectrum.
7. Electromagnetic radiation.
7.1 Effects of Atmosphere
7.1.2 Scattering.
7.1.2 Absorption.
8. Energy Interaction.
9. Image Resolution In Remote Sensing.
9.1 Intro
9.2 Types Of image Resolution.
10. Applications of Remote Sensing.
11. Advantages & Disadvantages of Remote
Sensing
2

INTRODUCTION TO REMOTE
SENSING
Definition of Remote Sensing
• Remote sensing is the science and art of obtaining information
about an object, area, or phenomenon through the analysis of
data acquired by a device that is not in contact with the object,
area or phenomenon under investigation (Lillesand & Kiefer,
2000).
• Remote sensing is the science of obtaining and interpreting
information from a distance using sensors that are not in
physical contact with the object being observed (Randall B.
Smith, 2001).
3

What is the principle???
Components of a Remote Sensing System
Target
Energy source
Transmission path
Sensor
4

• Target– the object or material that is
being studied. The components in the system
work together to measure and record
information about the target without actually
coming into physical contact with it.
• Energy source - Illuminates or provides
electromagnetic energy to the target. The
energy interacts with the target, depending on
the properties of the target and the radiation,
and will act as a medium for transmitting
information from the target to the sensor.
5

• Sensor - a remote device that will
collect and record the electromagnetic
radiation. Sensors can be used to measure
energy that is given off (or emitted) by the
target, reflected off of the target, or transmitted
through the target.
• The resulting set of data is transmitted to a
receiving station where the data are processed
into a usable format, which is most often as an
image. The image is then interpreted in order
to extract information about the target.
• This interpretation can be done visually or
electronically with the aid of computers and
image processing software.
6

Familiar forms of remote
sensing
• medical imaging technologies
− Magnetic Resonance Imaging (MRI)
− sonograms
− X-Ray imaging.
• technologies use forms of energy to produce
images of the inside of the human body.
8

• Remote sensing is not limited to investigations
within our own planet.
• Most forms of astronomy are examples of
remote sensing, since the targets under
investigation are such vast distances from
Earth
• Astronomers collect and analyze the energy
given off by these objects in space by using
telescopes and other sensing devices.
• This information is recorded and used to draw
conclusions about space and our universe
9

Other Examples :-
• ocean and atmospheric observing
• Magnetic resonance Imaging (MRI)
• Positron Emission Tomography (PET)
• Space probes
10

HISTORY OF REMOTE SENSING :
 Remote sensing starts
with the invention of
camera more than 150
years ago(1840s)
 The idea and practice
looking down the earth
surface emerged in
1840s cameras secured
to tethered balloon
11

 Famed pigeons are used
for remote sensing
12

 In the first world war
cameras mounted on
airplanes are used to
provide images of large
surface areas
13

 In 1960s and 1970s primary platform changed to
satellites
14

 Sensors become available to record the earth surface
in several bands what human’s eye couldn’t see
15

Starts in 1960s
First Indian satellites
• Aryabhata (19-April-1975 ) launched
in LEO by USSR rocket
• Bhaskara I & II carrying two TV
cameras
• Rohini siries (experimental)
INDIAN REMOTE SENSING
16

First Indian Remote Sensing Satellites
 IRS-1A (17-March-1988), 904 km
 IRS-1B (29-August-1991)
Both carrying
LISS-1A (Resolution 72.5 m)
LISS-2A,LISS-2B (Resolution 36.25 m)
 IRS-1C (1995), 817 km
 IRS-1D (1997)
17

Ground Control Stations
 Located at Bangalore( tracking and
monitoring)
 National Remote Sensing Centre
located at Hyderabad (Balanagar
&Shadnagar) to process data
18

Various Forms Of Collected Data
 Acoustic Wave Distribution (Ion based)
 Force Distribution (Force based)
 Electromagnetic Energy (Wavelength
based) and
REMOTE SENSING DEALS WITH DATA
COLLECTED BY ELECTROMAGNETIC
ENERGY
PHYSICS OF REMOTE SENSING
19

Types of Remote Sensing Sensor Systems.
Based on Source of energy
Active Passive
20

Passive System
• The sun provides a very convenient source of
energy for remote sensing.
• The sun's energy is either reflected, or
absorbed and then reemitted.
• Remote sensing systems which measure
energy that is naturally available are called
passive sensors.
• Passive sensors can only be used to detect
energy when the naturally occurring energy is
available.
21

• Passive sensors can only be used to detect energy
when the naturally occurring energy is available.
• For all reflected energy, this can only take place
during the time when the sun is illuminating the
Earth.
• There is no reflected energy available from the sun at
night.
• Energy that is naturally emitted (such as thermal
infrared) can be detected day or night.
22

Active System
• The sensor emits radiation which is directed
toward the target to be investigated.
• The radiation reflected from that target is
detected and measured by the sensor.
• Advantages :- the ability to obtain
measurements anytime, regardless of the time
of day or season.
• require the generation of a fairly large amount
of energy to adequately illuminate targets.
• E.g. a laser fluorosensor and
a synthetic aperture radar (SAR)
23

Remote Sensing Platforms
Remote sensing platforms can be classified as follows, based on the elevation from the Earth’s
surface at which these platforms are placed.
Ground level remote sensing
o Ground level remote sensors are very close to the ground
o They are basically used to develop and calibrate sensors for different features on the Earth’s
surface.
Aerial remote sensing
o Low altitude aerial remote sensing
o High altitude aerial remote sensing
Space borne remote sensing
o Space shuttles
o Polar orbiting satellites
o Geo-stationary satellites
From each of these platforms, remote sensing can be done either in passive or active mode.24

IDEAL Remote Sensing System
The basic components of an ideal remote sensing system include:
i. A Uniform Energy Source which provides energy over all
wavelengths, at a constant, known, high level of output
ii. A Non-interfering Atmosphere which will not modify either the
energy transmitted from the source or emitted (or reflected) from the
object in any manner.
iii. A Series of Unique Energy/Matter Interactions at the Earth's
Surface which generate reflected and/or emitted signals that are selective
with respect to wavelength and also unique to each object or earth
surface feature type.
26

Components of an ideal remote sensing system
27

iv. A Super Sensor which is highly sensitive to all wavelengths. A super
sensor would be simple, reliable, accurate, economical, and requires no
power or space. This sensor yields data on the absolute brightness (or
radiance) from a scene as a function of wavelength.
v. A Real-Time Data Handling System which generates the instance
radiance versus wavelength response and processes into an interpretable
format in real time. The data derived is unique to a particular terrain and
hence provide insight into its physical-chemical-biological state.
vi. Multiple Data Users having knowledge in their respective disciplines
and also in remote sensing data acquisition and analysis techniques. The
information collected will be available to them faster and at less expense.
This information will aid the users in various decision making processes
and also further in implementing these decisions.
28

Real Remote Sensing System
Real remote sensing systems employed in general operation and utility have many
shortcomings when compared with an ideal system explained above.
i. Energy Source: The energy sources for real systems are usually non-uniform over
various wavelengths and also vary with time and space. This has major effect on the
passive remote sensing systems. The spectral distribution of reflected sunlight varies
both temporally and spatially. Earth surface materials also emit energy to varying
degrees of efficiency. A real remote sensing system needs calibration for source
characteristics.
ii. The Atmosphere: The atmosphere modifies the spectral distribution and strength of
the energy received or emitted (Fig. 8). The effect of atmospheric interaction varies
with the wavelength associated, sensor used and the sensing application. Calibration is
required to eliminate or compensate these atmospheric effects.
29

iii. The Energy/Matter Interactions at the Earth's Surface: Remote sensing is based
on the principle that each and every material reflects or emits energy in a unique,
known way. However, spectral signatures may be similar for different material types.
This makes differentiation difficult. Also, the knowledge of most of the energy/matter
interactions for earth surface features is either at elementary level or even completely
unknown.
iv. The Sensor: Real sensors have fixed limits of spectral sensitivity i.e., they are not
sensitive to all wavelengths. Also, they have limited spatial resolution (efficiency in
recording spatial details). Selection of a sensor requires a trade-off between spatial
resolution and spectral sensitivity. For example, while photographic systems have very
good spatial resolution and poor spectral sensitivity, non-photographic systems have
poor spatial resolution.
v. The Data Handling System: Human intervention is necessary for processing sensor
data; even though machines are also included in data handling. This makes the idea of
real time data handling almost impossible. The amount of data generated by the sensors
far exceeds the data handling capacity.
vi. The Multiple Data Users: The success of any remote sensing mission lies on the
user who ultimately transforms the data into information. This is possible only if the
user understands the problem thoroughly and has a wide knowledge in the data
generation. The user should know how to interpret the data generated and should know
how best to use them. 30

Electromagnetic Spectrum
Remote Sensing
• Based on Range of Electromagnetic Spectrum
− Optical Remote Sensing
− Thermal Remote Sensing
− Microwave Remote Sensing
31

Optical Remote Sensing
• wavelength range: 300 nm to 3000 nm.
• The optical remote sensing devices
operate in the visible, near infrared,
middle infrared and short wave infrared
portion of the electromagnetic spectrum.
• Most of the remote sensors record the
EMR in this range
32

Thermal Remote Sensing
• the wavelength range :
3000 nm to 5000 nm
8000 nm to 14000 nm
• Record the energy emitted from the earth
• The previous range is related to high
temperature phenomenon like forest fire, and
later with the general earth features having
lower temperatures.
33

Microwave Remote Sensing
• wavelength range : 1 mm to 1 m
• Most of the microwave sensors are active
sensors, having there own sources of energy,
e. g, RADARSAT.
• Longer wavelength microwave radiation can
penetrate through cloud cover, haze, dust
• as the longer wavelengths are not susceptible
to atmospheric scattering which affects
shorter optical wavelengths.
• This property allows detection of microwave
energy under almost all weather and
environmental conditions so that data can be
collected at any time. 34

 Combination of Electric
and Magnetic fields
both are mutually
perpendicular to each
other passes
perpendicular to the
light
 Travels with a speed of
light (3 x 10ᶺ8 m/sec)
ELECTROMAGNETIC ENERGY
35

ELECTROMAGNETIC RADIATION
 EMR is originated from billions of vibrating
electrons, atoms , and molecules which emits EMR
in unique combination of wave lengths
 All the objects above -273˚C (0˚K) Reflects, Emits
and Absorbs EMR
 Amount of EMR radiation depends on the
Temperature of the Object
36

Data Acquisition:
 Source of EM energy
 Propagation of EM energy through atmosphere
 Interaction of EM energy with earth surface features
 Re-transmission of the EM energy through
atmosphere
 Recording of the reflected EM energy by the sensing
systems
 Generation of the sensor data in pictorial or digital
form
GENERAL PROCESS OF REMOTE
SENSNG
37

Data Analysis:
 Interpretation and analysis of the generated data
 Generation of information products
 Users
GENERAL PROCESS OF REMOTE
SENSNG
39

BASIC WAVE THEORY
 EM Energy travels in a harmonic sinusoidal fashion
(3 x 10ᴧ8 m/sec)
 EM wave consists of two fluctuating fields
40

 WAVE LENGTH :- is defined as the distance between
two successive wave peaks (λ)usually expressed in
micrometers(µm) or manometers (nm).
 Frequency:- It is defined as the no of cycles of
passing a fixed point in space is called frequency
Waves obey the equation
c = νλ ----(1.0)
ν = frequency
λ = wave length
c= (3*10^8 m/s)
BASIC WAVE THEORY
41

It tells about how the EM Energy interacts with matter
The smallest possible unit is photon
Each possesses a certain quantity of energy.
The Energy of a quanta/photon is given as under:-
Q= h.f ------- (1.1)
Where
Q= energy of quanta(J).
h = Planck’s constant 6.626x10ᶺ-34 J-sec
f= frequency.
From Equation 1.0 &1.1
Q = hc/λ
h = Planck’s constant 6.626x10ᶺ-34 J-sec
c = velocity of wave = 3*10^8 (m/s)
λ = wave length
PARTICLE THEORY
42

ELECTROMAGNETIC SPECTRUM
Distribution of the continuum of radiant energy
can be plotted as a function of wavelength (or
frequency) and is known as the electromagnetic
radiation (EMR) spectrum
43

ENERGY SOURCES AND RADIATION
PRINCIPLES
• Primary source of energy that illuminates different
features on the earth surface is the Sun.
• Although the Sun produces electromagnetic
radiation in a wide range of wavelengths, the
amount of energy it produces is not uniform across
all wavelengths.
• Other than the solar radiation, the Earth and the
terrestrial objects also are the sources of
electromagnetic radiation. All matter at
temperature above absolute zero (0oK or -273˚C)
emits electromagnetic radiations continuously.
46

Stephan Boltzmann’s law
M = σΤᶺ4
M = Total radiant existence of material,
Watts/mᶺ2
σ = Stephan boltzmann’s constant
5.6697x10ᶺ-8 W/mᶺ2/˚K
T = Temperature in ˚K
PRINCIPLES
47

Black body Radiation:
A blackbody is a hypothetical, ideal radiator. It
absorbs and reemits the entire energy incident upon
it.
• No body in space is perfectly blackbody
• As the temperature increases, the peak shifts
towards the left. This is explained by the Wien’s
displacement law. It states that the dominant
wavelength at which a black body radiates “ λm ” is
inversely proportional to the absolute temperature
of the black body
PRINCIPLES
48

PRINCIPLES
49

E= Black body spectral radiance measued in w/mᶺ2/m
h= Planck’s constant
K= Boltzmann’s constant
c= speed of light
e= base of the logarithm
λ= wave length in ‘m’
T= temperature in ˚K
PRINCIPLES
50

Wien’s displacement law
λmax = b/T
λmax = wave length of maximum emitted energy
measured in, μm
b = Wien's displacement constant
T = Temperature in ˚K
PRINCIPLES
51

EARTH’S ATMOSPHERE
Composition Of The Atmosphere
Atmosphere is the gaseous envelop
that surrounds the Earth’s surface.
Much of the gases are concentrated
within the lower 100km of the
atmosphere. Only 3x10-5 percent
of the gases are found above 100
km (Gibbson, 2000).
52

Gaseous Composition of The Earth’s Atmosphere
53

The radiation from the
energy source passes
through some distance
of atmosphere before
being detected by the
remote sensor
EFFECTS OF ATMOSPHERE ON
54

SCATTERING :
Atmospheric scattering is
the process by which
small particles in the
atmosphere diffuse a
portion of the incident
radiation in all directions
TYPES OF SCATTERING:-
a). Selective Scattering.
b). Non-selective Scattering.
55

TYPES OF SELECTIVE SCATTERING :
1. Rayleigh scattering
2. Mie scattering.
56

Rayleigh scattering :
This occurs when the
particles causing the
scattering are much
smaller in diameter
(less than one tenth)
than the wavelengths of
radiation interacting
with them.
57

Mie Scattering :
• which occurs when the wavelengths of the
energy is almost equal to the diameter of the
atmospheric particles
• longer wavelengths also get scattered compared
to Rayleigh scatter
58

Non-selective scattering :
• which occurs when the diameters of the
atmospheric particles are much larger
(approximately 10 times) than the wavelengths
being sensed
• This scattering is non-selective with respect to
wavelength since all visible and IR wavelengths get
scattered equally
59

Absorption
• Absorption : Process in which the incident energy is retained by particles in the
atmosphere
• Energy is transformed into other forms
• Unlike scattering, atmospheric absorption causes an effective loss of energy
• Absorption depends on
– Wavelength of the energy
– Atmospheric composition
– Arrangement of the gaseous molecules and their energy level
• The absorbing medium will not only absorb a portion of the total energy, but will also
reflect, refract or scatter the energy. The absorbed energy may also be transmitted back
to the atmosphere.
60

Absorption….
• The most efficient absorbers of solar radiation are
 Water vapour, carbon dioxide, and ozone
• Gaseous components are selective absorbers of the electromagnetic radiation
 Absorb electromagnetic energy in specific wavelength bands
 Depends on the arrangement of the gaseous molecules and their energy levels
Atmospheric window
• The ranges of wavelength that are partially or wholly transmitted through the
atmosphere
• Remote sensing data acquisition is limited through these atmospheric
windows
61

Atmospheric Window
• Wavelengths shorted than 0.1 μm
– Absorbed by Nitrogen and other
gaseous components
• Wavelengths shorter than 0.3μm
(X-rays, Gamma rays and part of
ultraviolet rays)
– Mostly absorbed by the ozone
(O3)
• Visible part of the spectrum
– Little absorption occurs
• Oxygen in the atmosphere causes
absorption centered at 6.3μm.
• Infrared (IR) radiation
– Mainly absorbed by water
vapour and carbon dioxide
molecules
• Far infrared region
– Mostly absorbed by the
atmosphere
• Microwave region
– Absorption is almost nil 62

Absorption……
• The most common sources of energy are
 Incident solar energy
– Maximum energy in the visible region
 Radiation from the Earth
• Maximum energy in the thermal IR region
• Two atmospheric windows
– at 3 to 5μm and at 8 to 14μm
• Radar & Passive microwave systems operate through a window in the region
1 mm-1 m
Major atmospheric windows used in remote sensing and their characteristics
Atmospheric window Wavelength band
(μm)
Characteristics
Upper ultraviolet, Visible and
photographic IR
0.3-1 apprx. 95% transmission
Reflected infrared 1.3, 1.6, 2.2 Three narrow bands
Thermal infrared 3.0-5.0
8.0-14.0
Two broad bands
Microwave >5000 Atmosphere is mostly transparent 63

Sensor Selection For Remote Sensing
• The spectral sensitivity of the available sensors
• The available atmospheric windows in the spectral
range(s) considered. The spectral range of the sensor is
selected by considering the energy interactions with the
features under investigation.
• The source, magnitude, and spectral composition of the
energy available in the particular range.
• Multi Spectral Sensors sense simultaneously through
multiple, narrow wavelength ranges that can be located at
various points in visible through the thermal spectral
regions
ENERGY INTERACTIONS IN THE
64

Energy Interactions
• Electromagnetic energy interactions with the surface features
Reflection
Absorption
Transmission
Incident radiation
Earth
Absorption
Reflection
Transmission
65

REFLECTION :
• Reflection is the process in which the incident energy is
redirected in such a way that the angle of incidence is
equal to the angle of reflection
• Electromagnetic energy is incident on the surface, it may
get reflected or scattered depending upon the
roughness of the surface relative to the wavelength of
the incident energy
ENERGY INTERACTIONS WITH
EARTH’S SURFACE FEATURES
66

Reflection
Interaction with the earth surface
67

Types Of Reflections:
Diffuse Reflection
• It occurs when the surface is smooth and flat
• A mirror-like or smooth reflection is obtained
where complete or nearly complete incident energy
is reflected in one direction
Specular Reflection
• It occurs when the surface is rough.
• The energy is reflected uniformly in all directions
68

69

Spectral Reflectance :
Spectral signature :
70

 Absorption
 Radiation is absorbed by the target
 A portion absorbed by the Earth’s surface is available for
emission as thermal radiation
71

ENERGY INTERACTIONS WITH EARTH’S
SURFACE FEATURES
• Transmission
Radiation is allowed to pass through the target
Changes the velocity and wavelength of the radiation
Transmitted energy may be further scattered or absorbed in
the medium
72

Transmission and Refraction
73

ENERGY INTERACTIONS WITH EARTH’S
SURFACE FEATURES
• Reflection, Absorption or Transmission ?
 Energy incident on a surface may be partially reflected, absorbed or transmitted
 Which process takes place on a surface depends on the following factors:
• Wavelength of the radiation
• Angle at which the radiation intersects the surface
• Composition and physical properties of the surface
• Relationship between reflection, absorption and transmission
 Principle of conservation of energy as a function of wavelength
EI (λ) = ER (λ) + EA(λ) + ET (λ)
OR
ER (λ) = EI (λ) - EA(λ) - ET (λ)
EI = Incident energy
ER = Reflected energy
EA = Absorbed energy
ET = Transmitted energy
74

REFLECTION VS SCATTERING
Reflection
• Incident energy is redirected
• Angle of incidence = Angle of reflection
 The reflected radiation leaves the surface at
the same angle as it approached
Scattering
 A special type of reflection
 Incident energy is diffused in many directions
 Often called Diffuse Reflection
75

REFLECTION VS SCATTERING…….
Reflection or Scattering?
• Depends on the roughness of the surface with respect to the incident wavelength
Roughness of the surface < Incident wavelength  Smooth surface  Reflection
Roughness of the surface > Incident wavelength  Rough surface  Scattering
• Roughness of the surface controls how the energy is reflected
• Mainly two types
 Specular reflection
 Diffuse (Lambertian) reflection
76

Image Resolution
• Image resolution refers to the number of pixels in an unit area
of a digital photo or image.
• The term resolution used in both traditional and digital
photography to describe the quality of the image.
77

Image Resolution (Cont...)
• Types of Resolution
1. Spatial Resolution
2. Temporal Resolution
3. Spectral Resolution
4. Radiometric Resolution
78

Spatial Resolution (cont.)
The spatial resolution specifies the pixel size of satellite images
covering the earth surface.
High spatial resolution: 0.41 - 4 m
Low spatial resolution: 30 - > 1000 m
1 pixel in image
= 30mx30m in land
1 pixel in image
= 1mx1m in land
79

Below is an illustration of how the same image might appear at different
pixel resolutions (practical aspect)
80

40 x 40
320 x 320
80 x 80
81

Temporal Resolution
• The temporal resolution specifies the revisiting
frequency of a satellite sensor for a specific location.
• High temporal resolution: < 24 hours - 3 days
Medium temporal resolution: 4 - 16 days
Low temporal resolution: > 16 days
82

Temporal Resolution
Time
July 1 July 12 July 23 August 3
11 days
16 days
July 2 July 18 August 3
83

Spectral Resolution
• The ability of a sensor to detect small differences in wavelength
• It specifies the number of spectral bands in which the sensor can
collect reflected radiance.
• High spectral resolution: 220 bands
Medium spectral resolution: 3 - 15 bands
Low spectral resolution: 3 bands
84

• Example: Black and
white image
- Single sensing device
- Intensity is sum of
intensity of all
visible wavelengths
Can you tell the color of the
platform top?
How about her sash?
Spectral Resolution
(Cont.)
0.4 mm 0.7 mm
Black &
White
Images
Blue + Green + Red
85

Spectral Resolution (Cont.)
• Example: Color image
- Color images need
least three sensing
devices, e.g., red, green,
and blue; RGB
Using increased spectral
resolution (three sensing
wavelengths) adds
information
In this case by “sensing”
RGB can combine to
get full color rendition
0.4 mm 0.7 mm
Color
Images
Blue Green Red
86

Radiometric Resolution
• It measures of a sensor's ability to discriminate small differences in
the magnitude of radiation within the ground area that
corresponds to a single raster cell.
• The greater the bit depth (number of data bits per pixel) of the
images that a sensor records, the higher its radiometric resolution.
• The AVHRR sensor, for example, stores 210 (1024) bits per pixel, as
opposed to the 28 bits per pixel that the Landsat sensors record.
Computer
store
everything in
0 or 1
87

Radiometric Resolution (Cont.)
2 88

Comparison of Satellites based on
Resolution
89

Remote sensing application
• a software application that processes
remote sensing data
• enable generating geographic information
from satellite and airborne sensor data
• read specialized file formats that contain
sensor image data, georeferencing
information, and sensor metadata.
• Some of the more popular remote sensing
file formats include: GeoTIFF, NITF, HDF,
and NetCDF. 90

APPLICATION OF REMOTE SENSING
 Flood estimation
91

 Earthquake Estimation
92

 Weather Maps
93

 Crop Yielding
 Tsunamis
 Forest Fires
 Regional Planning
 Surveying in Inaccessible Areas
 Flood and Drought Warnings
94

Advantages and Disadvantages
of Remote Sensing
Advantages of remote sensing are:
a) Provides data of large areas
b) Provides data of very remote and inaccessible regions
c) Able to obtain imagery of any area over a continuous period of time through which
the any anthropogenic or natural changes in the landscape can be analyzed
d) Relatively inexpensive when compared to employing a team of surveyors
e) Easy and rapid collection of data
f) Rapid production of maps for interpretation
Disadvantages of remote sensing are:
a) The interpretation of imagery requires a certain skill level
b) Needs cross verification with ground (field) survey data
c) Data from multiple sources may create confusion
d) Objects can be misclassified or confused
e) Distortions may occur in an image due to the relative motion of sensor and source95

Remote sensing

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