Clarification on extracting Doppler centroid and Doppler FM rate from NISAR sample data

[apulella]

Hello ISCE developers,

I have been playing with the publicly released NISAR sample data, available here:
https://nisar.jpl.nasa.gov/data/sample-data/
So far, it is not clear to me how one should extract or compute the Doppler centroid and the Doppler FM rate from these datasets.
I am aware that for other missions (for example, ESA Sentinel-1) there exist reference documents that describe in detail how users can properly compute Doppler centroid and Doppler rate at mid-swath directly from the metadata.

My questions are:

• Is there an equivalent reference document for NISAR, describing how Doppler centroid and Doppler FM rate should be derived from the sample products?

• Does ISCE2 or ISCE3 currently provide examples for computing these Doppler parameters from NISAR data?

• If such functionality exists in the codebase, could you please point me to the relevant module or workflow?

Any guidance would be greatly appreciated.

Thank you!
Andrea