Converting USGS gage height to match SWOT

[katiemcquillan]

Hi,

I am attempting to convert USGS gage heights to match SWOT heights. I see in the documentation that the SWOT horizontal datum is the equivalent of ITFR2014 epoch 2010 and the vertical datum is EGM2008. I've been having trouble figuring out how to do this conversion in python and was hoping someone in this forum might have advice!

Thanks!
Katie

[katiemcquillan]

I found GDAL was the simplest tool to perform the horizontal and vertical transformations.

It seems the generic EPSG:4326 WGS84 is not recommended to use since it is based on a datum ensemble whose positional accuracy is 2 meters, and instead a realization like WGS84 (G1762) is recommended. WGS84 (G1762) and ITRF 2014 are equivalent for all practical purposes if their epochs are the same. The WGS84 (G1762) standard epoch is typically 2005 and ITRF 2014 standard epoch is 2010.

USGS uses NAD83 (2011) standard epoch is 2010 and NAVD88.

GDAL command that worked:

# EPSG:9057 is wgs84 g1762 which is equivalent to itrf 2014 if they are set to the same epoch
# EPSG: 3855 is EGM2008
# EPSG: 6349 is the compound NAD83(2011) + NAVD88

gdaltransform
-s_coord_epoch "2010.0"
-t_coord_epoch "2010.0"
-s_srs "EPSG:6349"
-t_srs "EPSG:9057+EPSG:3855"
< "gdal_in.txt" >
"gdal_out_6349_9057_3855_2010.txt"

Here is a link to a tutorial:
https://github.com/kmcquil/SWOT_Validation/blob/main/Scripts/usgs_to_swot_tutorial.ipynb

[smu_yoons]

Hello, were you working with the SWOT PIXC or the Raster? I'm trying to compare both the PIXC and the raster with in-situ data and trying to figure out appropriate transformation. Thank you!

[PODAAC - jmcnelis]

Hi Katie,

Thanks a bunch for developing this great resource! I have bookmarked it.

Jack