Introduction to RS Lecture 2avikb/GNR401/RS/RS_401_lecture_2.pdf · Intro. to RS The Sun is the most important source of EM radiation used in passive optical remote sensing. The Sun’s

NR401 Dr. Avik Bhattacharya 1

Introduction to RSLecture 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.




Intro. to RS

Passive system:

EM Energy source- the SUN


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.


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.


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


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


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


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


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


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.


Spectral Signatures


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

)(| fER ff


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


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


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


Intro. to RS

Not impossible to generate continuous spectra for identifying objects.

Practical solution Observation in discrete spectral region

Spectral bands

Documents

Introduction to RS Lecture 2avikb/GNR401/RS/RS_401_lecture_2.pdf · Intro. to RS The Sun is the most important source of EM radiation used in passive optical remote sensing. The Sun’s