NR401 Dr. Avik Bhattacharya 1
Introduction to RSLecture 2
NR401 Dr. Avik Bhattacharya 2
Intro. to RS
This course is about electromagnetic energy sensors – other types of remote sensing such as geophysical will be disregarded.
For proper analysis and interpretation of remote sensing data, it is important to understand the source of electromagnetic energy, its nature, its propagation, and its interaction with atmosphere and other matter.
NR401 Dr. Avik Bhattacharya 3
NR401 Dr. Avik Bhattacharya 4
NR401 Dr. Avik Bhattacharya 5
Intro. to RS
Passive system:
EM Energy source- the SUN
NR401 Dr. Avik Bhattacharya 6
Intro. to RS
The Sun is the most important source of EM radiation used in passive optical remote sensing.
The Sun’s radiation covers Ultraviolet Visible Infrared Microwave Radio waves
Maximum radiation occurs around 0.55 µm Visible region of the EM spectra.
NR401 Dr. Avik Bhattacharya 7
http://stereo.gsfc.nasa.gov/
Surface regions of the Sun Surface regions of the Sun -- the the photosphere, the chromosphere, and photosphere, the chromosphere, and the corona. the corona.
The photosphere corresponds to the The photosphere corresponds to the bright region normally visible to the bright region normally visible to the naked naked eye. (`Temperature ~ 6000 K). (`Temperature ~ 6000 K)
The chromosphere lies ~5,000 km The chromosphere lies ~5,000 km above the photosphere. Shortabove the photosphere. Short--lived, lived, projections may extend for several projections may extend for several thousands of kms from the thousands of kms from the chromosphere. (Temperature ~ chromosphere. (Temperature ~ 20,000 K)20,000 K)
The corona is the outermost layer of The corona is the outermost layer of the Sun; this region extends into the the Sun; this region extends into the region of the planets.region of the planets.
NR401 Dr. Avik Bhattacharya 8
Intro. to RS
Solar radiation reaching the Earth’s surface is modified by the atmospheric effects
All bodies at temperature above absolute zero degree emit EM radiation at different wavelengths Planck’s Law
Earth as blackbody at 300 K emits radiation at around 9.5 µm
NR401 Dr. Avik Bhattacharya 9
Intro. to RS
Solar radiation has to pass through the atmosphere before it interacts with Earth’s surface.
Radiation is scattered/absorbed by gases and particulates.
The strongest absorption occurs at wavelength < 0.3 µm Ozone Layer
NR401 Dr. Avik Bhattacharya 10
Intro. to RS
Certain spectral regions of the EM radiation pass through the atmosphere without much attenuation Atmospheric Windows
In the region of atmospheric windows Scattering by atmospheric molecules and aerosols
produces spatial redistribution of energy The scattered/diffused radiance entering the field of
view of a remote sensor other than that from the target Path Radiance
NR401 Dr. Avik Bhattacharya 11
Intro. to RS
Atmospheric haze/cloud is much more transparent to microwave than optical and Infrared region of the EM spectrum
Microwave remote sensing Side Looking Airborne Radar (SLAR) Synthetic Aperture Radar (SAR)
Active and Passive Microwave RS
NR401 Dr. Avik Bhattacharya 12
Intro. to RS (Concept of Signatures)
Incident EM on a surface either gets Reflected/Absorbed/Re-radiated/Transmitted
Dependence upon the nature of the object and wavelength of the incident radiation
Study of interaction understanding of the object under observation
NR401 Dr. Avik Bhattacharya 13
Intro. to RS (Concept of Signatures)
The basic property which allows identification of an object Signature
Spectral/Spatial/Temporal/Polarization4 major characteristics of the target which facilitates discrimination.
NR401 Dr. Avik Bhattacharya 14
Spectral Signatures
NR401 Dr. Avik Bhattacharya 15
Intro. to RS
Spectral variation are changes in the reflectance/emittance of an object
Colour of an object is a manifestation of spectral variance in reflectance in the visible region
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NR401 Dr. Avik Bhattacharya 16
Intro. to RS
Spatial variation Spatial arrangement of terrain features
providing attributes such as shape/size/texture of objects
Temporal variation Changes in reflectivity/emissivity with time.
They can be diurnal/seasonal
NR401 Dr. Avik Bhattacharya 17
Intro. to RS
Polarization variation Changes in polarization of the EM radiation
reflected/emitted by an object.
The degree of polarization is a characteristic of the object and hence can be used to distinguished the object.
Useful in the microwave region
NR401 Dr. Avik Bhattacharya 18
Intro. to RS
Signatures are not completely deterministic
Statistical in nature with certain mean value with some dispersion around it
Spectral variation is the most often used signature in the Optical/IR region
NR401 Dr. Avik Bhattacharya 19
Intro. to RS
Not impossible to generate continuous spectra for identifying objects.
Practical solution Observation in discrete spectral region
Spectral bands