Flood Mask GeoTIFFs produced by flood mapping don't represent associated Flood Depth GeoTIFFs

[jhkennedy]

The flood mapping code currently requires three input GeoTIFFs:

• _VV.tif -- RTC amplitude image, in VV polarization
• _HAND.tif -- Height Above Nearest Drainage data
• _WM.tif -- Surface water extent mask (True if water, False if not)

and currently produces four GeoTIFFs:

• _PW.tif -- Perennial (permanent) water mask (True if water, False if not)
• _WaterDepth.tif -- Depth of water "where there is water" (WM or PW)
• _FloodMask.tif -- Currently is "where there is water" (WM or PW)
• _FloodDepth.tif Depth of flooded areas (WaterDepth with Perennial water removed)

In it's current iteration, FloodMask would be better called WaterMask as it's the combination WM and PW and has the same extent as WaterDepth. To illustrate, the water depth looks like:

Overlaying PW looks like:

and then the FloodDepth looks like the difference of the two (WaterDepth - PW):

But FloodMask looks like:

So we should either:

1. Rename it to _WaterMask.tif
2. Write out aa _FloodMask.tif that matches the FloodDepth

For 1, I think it will be really hard to communicate the differences between the SM GeoTIFF and the WaterMask GeoTIFF as they are very similarly named and scoped.

For 2, it we'd just have to move where we write the FloodMask GeoTIFF
https://github.com/ASFHyP3/asf-tools/blob/develop/asf_tools/flood_map.py#L215-L216

To below this line (where we've removed the perennial water):
https://github.com/ASFHyP3/asf-tools/blob/develop/asf_tools/flood_map.py#L218

[jhkennedy]

We'll need to ask the HydroSAR team their intent for this mask.

I did confirm it's being written in the same way in the source HydroSAR notebooks. See the "Export Your Flood Depth Map as GeoTIFF" section near the bottom:
https://github.com/fjmeyer/HydroSAR/blob/master/Flood_Depth_Estimation_with_Flood_Extent_Maps.ipynb