Sentinel-1 VV VH backscatter DA (REWORKED)

[cmclaug2]

Description

This PR is a reworked version of #1208
This PR:

• Extracts the testcase that was added to the source code
• Updates documentation
• Reverts Config.pl to the Main branch
• Removes unnecessary NaN check in LIS_historyMod.F90

Addresses #1192
Addresses #1012

Testcase

I have confirmed this replicates the testcase in #1208
I have confirmed this compiles with strict checks.

[jvgeiger]

When compiled with GNU compilers, LIS crashes in enkf_Mod.F90 at line 319 with the message:

Error in `./LIS': malloc(): memory corruption:

When compiled with Intel compilers with additional debugging enabled, LIS crashes in LIS_DAobservationsMod.F90 at line 2051 with the message:

forrtl: severe (408): fort: (3): Subscript #2 of the array LIS_OBS_NGRIDS has value -1 which is less than the lower bound of 0

In S1_sigmaVVVHSMLAI/S1_sigmaVVVHSMLAI_Mod.F90, flist is used uninitialized. This file also uses ls to create a list of files. This should be replaced with a call to create_filelist.

[mbechtold]

Hi @jvgeiger
I addressed the issues that you raised in this PR cmclaug2#1 for the branch of @cmclaug2. Results are zero-diff.
The only thing I could not test is the compilation with the GNU compiler. Hope the memory corruption is fixed as well. Let me know if there is anything else I can do to finalize this PR.
Thanks!

[mbechtold]

@dmocko @sujayvkumar @cmclaug2 @jvgeiger
In February, I added this note to the PR. Would be great if this PR could eventually be merged soon to make this DA instance easily accessible for other LIS users.

[jvgeiger]

Hello. I apologize for the delay. We get to pull requests, issues, and discussions when time permits. Unfortunately, other tasks kept coming up. I will review your bug fixes and finish this pull request as soon as possible.