What are the Range and Azimuth Shift Dependency Coregistration Default Values in ENVI SARScape?

In the Coregistration Default Values in SARScape, what are the "Range Shift Dependency" and "Azimuth Shift Dependency" and what is their influence on the coregistration result?


The range or azimuth shift dependency (R.D.) reprensents the degree of freedom you want to leave when computing the shift in range (or azimuth) during the coregistration process.  This value does not correspond directly to the polynomial degree of the polynomial coregistration but rather to the number of coefficients of the coregistration equation:    

Δrange (or azimuth) = K₁ + K₂X + K₃Y + K₄X² + K₅Y²

For R.D. = 1, the shift is a constant value for the whole image.
For R.D. = 2, the shift is also a function of range position.
For R.D. = 3, the shift is also a function of azimuth position
For R.D. = 4, the shift is also a function of the square range position.
For R.D. = 5, the shift is also function of square azimuth position.

In most cases, a linear dependency from the range and azimuth position is enough (i.e. R.D. = 2 for only a range dependency or R.D. = 3 for range and azimuth dependency).  The constant (R.D. = 1) is usually too little.

It makes sense to have this value set to 4 (or 5) especially in the case of non-zero doppler focalized data (i.e. squinted geometry data) or for very large baseline data. In these cases, the shift dependency (mostly the azimuth shift) is affected by non-linear effects.  For example, if you examine these types of images you may note that the image is distorted along the range in the azimuth direction.  So to perform coregistration, you will need a second degree polynomial.

Review on 12/31/2013 MM