Digital Image Processing: A Remote Sensing
Perspective
FW5560
Lecture 7
Radiometric Correction
Radiometric correction
Improving the accuracy of surface spectral reflectance or
emittance. Would like to obtain measurements of absolute
reflectance or emittance at the earth’s surface. Must consider
contributions and subtraction imposed by atmospheric
components.
Also consider gains and bias of the sensors themselves.
DN
Relationship between DN and Spectral Radiance
Slope = channel gain
Intercept =
channel offset
RMIN
L = spectral radiance
(watts/cm2/sr)
RMAX
= spectral radiance of internal calibration lamps
Radiometric Correction Steps
Output values for malfunctioning detectors are replaced by DNs
of adjacent detectors in the same band
Band responses to the calibration bands are use to characterize
the in-orbit response functions of the individual channels.
Functions are updated every 11,520 scan lines
Histogram equalization procedure is performed
Radiometric LUTs are calculated to convert the DNs to units of
absolute radiance
Used to measure difference in sscen rediance in a quantitative
fashion within and between scense
Histogram equalization- minimize residual line to line striping
DN frequency histogram for each sensor of each band, calculate
the mean and std dev. Convert this numbers to absolute units
using the original estimates of gain and offset.
G’c,b = Gc.b (Sc,b/Sb )
B’c,b = Bc,b + Gc.b (Mc,b – (SbMb/Sc,b))
Gc.b and Bc,b = original estimates of gain and offset respectively
Mc,b = mean associate the histogram for sensor c and band b in
units of absolute radiance
Sc,b= std dev. of the histogram
Sb= avg of the standard deviations for a band
Atmospheric Correction
Optical characteristics of the atmosphere are estimated either by
using special features of the ground surface or by direct
measurements of the atmospheric constituents or by using
theoretical models. Various quantities related to the atmospheric
correction can then be computed by the radiative transfer
algorithms given the atmospheric optical properties. Second, the
remotely sensed imagery can be corrected by inversion procedures
that derive the surface reflectance.
Single Image Normalization Using Dark Image Adjustment
ATCOR3 is atmospheric correction and haze removal software
used to correct changes in the spectral reflectance of materials on
the earth's surface. ATCOR3 can be integrated with a DEM for
atmospheric correction in images of rugged terrain.
Features:
Produce sharp and brilliant satellite images
Reduce the shadow effect in mountainous terrain
Obtain better classification results by using real reflectance
values
Compare multi-temporal and multi-sensoral values
Calculate value added products such as sky view factor and cast
shadow calculation