Intensity ratio is the ratio of the powers (intensities) of the two polarization channels. The intensity ratio (or its inverse) can be computed for all pairs of polarization channels.
The ratio should be computed for multilook data (number of looks >= 25), because the ratio is too noisy when computed for single samples of single-look data. You can use the ratio to assess the quality of the calibration of polarimetric SAR data.
Phase difference is the angle between two elements of the scattering matrix in a multipolarized or polarimetric radar. With SAR Polarimetry Target Analysis, it is computed from the elements of the covariance matrix.
To obtain a reliable estimate of the phase difference with single-look data, the data should first be averaged spatially over a delineated target using multilooking, filtering, or averaging. A phase-difference image derived from single-look data or multilook data with insufficient looks will be very noisy. Therefore, the recommended effective number of looks is 25 or greater.
Phase difference provides no useful information with data that has mutually incoherent channels, such as the ENVISAT ASAR dual-pol images.
You can use phase difference to assess the quality of the calibration of polarimetric SAR data. In perfectly calibrated data, the response to a trihedral reflector shows a phase difference of zero for any pair of polarization channels.
With HH and VV polarizations, the correlation coefficient is the average of the product between the complex HH channel and the conjugate of the complex VV channel. It is normalized by the square root of the product of the powers in the HH and VV channels. With other polarizations, it is calculated similarly.
The value of the correlation coefficient is one when the received signals from the two channels are linearly related.
A value less than one can indicate noise on one or both of the channels or a partial polarization of the received EM waves if the target is known to have a linear relationship between polarization channels. An example is the backscatter received from an ideal trihedral corner reflector.
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