Earthdata Forum

Hello:
Question: Recently I want to make incidence angle correction for SWOT L2_LR_SSH sigma0 data, but no incidence angle data is included in the .nc file, neither a incidence range is explicitly declared in the related documentation. How can I get the actual incidence angle data or range?
"D-105502_SWOT_ATBD_L2_LR_SSH_20230724a_cite2.pdf" give a "about 4° incidence angle", but no incidence of near range is available, and I prefer more actual data.
If anyone could give any help, I will appreciate it a lot.
I have noticed a similar question at Apr 23, 2025 (viewtopic.php?t=6707&sid=2ba86fb89eff932b8f0ee58191f8136a), unfortunately, nobody answer that question.

Hello,

Here is advice from one of the SWOT algorithm engineers:

The incidence angle can be computed to a pretty good approximation from the cross_track_distance variable in the L2_LR_SSH Expert file using the equations in Sect 8.2.1.2 of the User Handbook (where alpha = cross_track_distance / planet_radius). Assuming a constant spacecraft altitude of 900 km and a constant Earth radius of 6378.137 km works pretty well, although the actual spacecraft altitude is also given in the L2_LR_SSH Expert file as the variable sc_altitude.

Hello:
Thanks a lot for your advice! I foolishly overlooked this chart.

According to my test, the L2_LR_SSH data's incidence angle most fall vetween 0.4° to 4.6° in Greenland Sea and Baffin Bay. Using Unsmoothed_dataset['cross_track_distance'] and expert_dataset['sc_altitude'], here is an example of "SWOT_L2_LR_SSH_Unsmoothed_001_311_20230801T072222_20230801T081349_PGD0_02.npz", left swath:

Glad it helped you, @galasnow !