Support SNAP `.znap` input reading

[Simon-van-Diepen]

SNAP outputs per epoch:

• A .znap (SNAP-specific .zarr)-archive, one per acquisition (currently named YYYYMMDD-coreg.znap, can be altered if necessary/preferred), containing the following layers:
  * h2ph_<polarisation>_<epoch>: height-to-phase screen with the reference DEM subtracted cropped to the AoI (e.g. h2ph_VV_06Jan2023)
  * i_<polarisation>_<epoch>: real component of the reduced SLCs cropped to the AoI (e.g. i_VV_06Jan2023)
  * q_<polarisation>_<epoch>: imaginary component of the reduced SLCs cropped to the AoI (e.g. q_VV_06Jan2023)
  * incident_angle: incidence angle at each pixel
  * slant_range_time: slant range time at each pixel
  * elevation: DEM (only at the mother epoch)
  - coordinates:
  * latitude: latitude coordinates cropped to the AoI
  * latitude_<polarisation>: latitude coordinates cropped to the AoI (only at the mother epoch, difference unclear) (e.g. latitude_VV)
  * longitude: longitude coordinates cropped to the AoI
  * longitude_<polarisation>: longitude coordinates cropped to the AoI (only at the mother epoch, difference unclear) (e.g. longitude_VV)
  - metadata:
  * product metadata (in a JSON file located in *.znap/SNAP/product_metadata.json, related to Support reading metadata from SNAP corregistration results #82 )
  * ground control points (empty)
  * pins (empty)

This collection of .znap archives needs to be read into sarxarray, but the existing implementation does not allow for such a collection of .zarr archives (and real and imag do not exist in the variables as they have different names).

[rogerkuou]

Hi @Simon-van-Diepen, thanks for summarize this! Super useful. Can you point me to an example dataset you are working with? Maybe a link on Spider?

[Simon-van-Diepen]

@rogerkuou the example stack I generated using SNAP is located at /project/caroline/Share/users/caroline-admin/caroline-test/test_nl_amsterdam_v3/stack-snap/nl_amsterdam_s1_dsc_t037 on Spider, should've included that indeed

EDIT: I have moved it to /project/caroline/Share/users/caroline-admin/caroline-test/test_nl_amsterdam_v3/stack-snap/nl_amsterdam_s1_dsc_t037_backup so I can continue testing the SNAP-caroline implementation

[Simon-van-Diepen]

This is probably very closely related to #31 as well, maybe that should be a sub-issue

[Simon-van-Diepen]

Hi @rogerkuou since you're running low on hours on this project and I need this functionality for Caroline I am planning to take over the development of this ticket (as well as the related #31 and #82). Then you can focus on the final parts of the JOSS paper and I can continue my work for Caroline. Is that okay with you?

[rogerkuou]

Hi @Simon-van-Diepen , it's a nice idea! Thanks!