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| $\sigma^0(f,\theta)$ }}} as a function of frequency and incidence angle. The backscatter coefficient describes how much of the transmitted energy is backscattered from the surface media. |
$\sigma^0(f,p,\theta)$ }}} as a function of frequency, polarization and incidence angle. The backscatter coefficient describes how much of the transmitted energy is backscattered from the surface media. |
Radar backscatter statistics
The received power (intensity) of a radar system is proportional to the (normalized) radar backscatter coefficient
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as a function of frequency, polarization and incidence angle. The backscatter coefficient describes how much of the transmitted energy is backscattered from the surface media.
A (calibrated) ASAR image img(y,x)=I is made of the measured intensities I which can be directly related to the backscatter coefficient. A value of zero means that no energy is reflected from the surface whereas a value of one means the total reflection.
Exercise
This ASAR image shows different sea ice types. Investigate the statistic of normalized backscatter value. What is the mean for the two prevalent sea ice types? Try to fit the image PDF with a superposition of two gamma distributions (ADVANCED EXERCISE).
from pylab import *
img=reshape(fromfile('ASAR_seaice_mixed_20080421_f32_1000x1000.dat',dtype=float32),(1000,1000))
close('all')
ql(img,vmin=0,vmax=0.3)
colorbar()
title('Sea ice radar backscatter intensity')