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CE-419 : Principles of RemoteSensing

Subashisa Dutta

Department of Civil Engineering

IIT Guwahati 1

Lecture 14: Remote Sensors An overview and sources ofGeometric distortion

Text Books:1) George Joseph, Fundamentals of Remote Sensing

2) Richards and Jia, Remote sensing Digital image analysis, Springer

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CONCEPT OF RESOLUTION

Quality of information derived from RS images strongly

influenced by spatial, spectral, radiometric and temporalresolution of the sensor

Spatial Resolution

instrument resolving power needed to spatially discriminatethe smallest object

Spectral resolution

encompasses the width of bands used from the wavelengthsof the EM spectrum.

Radiometric resolution

quantify No. of discernible signal levels in a band, {sensors

ability to discriminate radiance differences (NE)} Temporal resolution

time interval between imaging collections over the samegeographic location

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Spatial Resolution

Airy Pattern in an imaging system due to diffraction

Airy disc : the Central disc, about 84% of total energy

The diameter of the first minima is 2.44 (/D) f Where is the wave length of observation, D,

the diameter of the aperture of lens, f is the focal length.

IRS PAN Sensor : D = 22 cm, for 0.5 m wavelength, Altitude = 810km

The spatial resolution limit = 2 m

Same optics for imaging for SWIR, The spatial resolution limit = 8m.

Contrast ratio, Contrast modulation Modulation Transfer Function Concept of Pure and Boundary pixels

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Spectral Resolution

Three aspectslocation of the central wavelengththe bandwidthThe total number of bands

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Hyper-Spectral Imaging

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Electro-opticalImagingInstrument

Spatialfoot-print(Meters)

Swath(Kilometers)

Number ofspectralchannels

Number ofinstruments

No. of daysrequired forglobal coverage

Minimum intervalrequired for revisitinga target (days)

PAN 1 14. 5 1 1 1200 1 to 200

PAN 5.8 74 1 2 48 5

Liss3 23.5 148 3 2 24 24

Liss2 36 140 4 1 22 22

Liss3(SWIR) 70 148 1 2 24 24

Liss1 72 140 4 1 22 22

WiFS 188 810 2 3 5 2

WiFS(swir) 188 810 1 1 5 5

OCM 360 1420 8 1 2 2

CCD P/l 1000 300 3 2Continuous daytimemonitoring of earth

disc

A region of 300km*6000 kmcan be covered every minute

VHRR 2000 Earth Disc 1 2Continuous monitoring

of earth disc

A region of 12000km*8000km can be covered every 7

minutes

VHRR 8000 Earth Disc 2 2Continuous monitoring

of earth disc

A region of 12000km*8000

km can be covered every 7minutes

Current observational capabilities of Electro optical imaging

instruments from Indian satellite platforms

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Engineering Design of the Sensors

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Sources of Geometric Distortion

A number of factors1) Rotation of the earth during image acquisition2) Panoramic effects related to the imaging geometry3) The curvature of the earth4) Variations in platform altitude, attitude and velocity5) The scan rate of some sensors6) Sensor non-idealities

1) Earth Rotation Effects

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Panoramic Distortion

S-bend Distortion

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Effect of Earth Curvature

Satellite

Earth

Rc

Pc

h

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