SWOT: need to set ref_frame_offset

[remkos]

The values for ref_frame_offset, ref_frame_offset_mle3, and ref_frame_offset_adaptive for SWOT have not been set yet (i.e. they are zero). They need to be determined and added to the data base, probably allow with #194

[remkos]

Based on cyles 301-314 (all available Phase B cycles until present), I determined the following numbers:

• ref_frame_offset: -6.0 mm
• ref_frame_offset_mle3: +1.5 mm

Based on cycle 301-307 (all available Phase B cycles with GDRs), I determined the following numbers:

• ref_frame_offset_adaptive: -36.0 mm

These values align the MLE4 results with other altimeters and align the MLE3 and Adaptive results with MLE4.

[remkos]

All SWOT data has been updated and uploaded, along with the fix for issue #194

[remkos]

This fix is part of release v4.6.3 (/~https://github.com/remkos/rads/releases/tag/v4.6.3)