Yes, you are right. For ERS-1/2, azimuth ambiguity is zero in almost all cases. However you need it for Radarsat-1 or Jers-1.
There is no automatic way of estimating Doppler parameter in eSAR processor. I teach my students how to derive (absolute) Doppler centroid from the image that was azimuth-FFTed after range matched filtering. For Doppler rate, I just let them to use a nominal value derived from the state vector analytically. One reason to do so is that this is an educational SAR processor, rather than automatic easy-going software.
Do you have any plan to open your CDE programme through this Forum?
regards,
Hoonyol
┃[minghui hou said:]
┃N1. I do know that here fdc_middle is the absolute one, right? but the ambiguity should be estimated before you can know it, right? so, here we use the fdc at the middel range as the fdc_middle will give people a misleading as if the ambguity number is calculated from the fdc_middle,but actually it is estimated from the raw data.
┃I have do some work to estimated the fdc and to resolve the ambihuity number, it is prooved that the ambiguity number is 0, actually, ERS has yaw steering to controll that, and the coefficients of the fdc wiht range , i didnt get a good result, maybe this block of data is a litte not such suitable for my CDE algorithm.
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┃about the FFT output order, I will check it again. thank you for your answer:).