find Saral ssh using brat

[marjan]

hi every one
i am a beginner in Altimetry issue and i want to work with Saral satellite data on a small lake to find ssh for monitoring the sea level changes from 2013
i dont know how to set data
i set long for x ,lat for y but i cant find ssh for saral in the insert formula menu to set expression for ssh
please help me .
with best regards

[bratKeymaster]

Dear Marjan,

Yes, there is not a specific expression for SSH in SARAL, so you can use the default one.

All the formulas are stored in a file in your machine called formulas.ini. In the same folder you can find the aliases.xml that links similar variables from different missions with the same tag.

In the formulas.ini you can see that the SSH formula is just using the alias for the ssh written as “%{ssh}”. In the aliases.xml file you can see for the SARAL case you can see that the ssh is %{sla} + %{mean_sea_surface}, so in the end ssha + mss_dtu13 .

My advice is that you don’t use the ssh formula to compute the water level for a lake. The SSHA is probably using the range computed with the ocean retracker, and the Mean Sea Surface model DTU 13 is not probably the best over land.

You can compute the water level for the lake by using a variation of the WSH_Inland_Waters formula
%{altitude} – %{range} – %{iono_corr} – %{dry_tropo_corr} – %{wet_tropo_corr}

For SARAL you have to write
alt – range – model_wet_tropo_corr – model_dry_tropo_corr

As the wet and dry tropospheric corrections are at 1Hz you should use “alt” and “range” that are also at 1Hz. Also, the variable in your axis should have the same dimensions, so put “lat” and “lon” variables and don’t use “lat_40Hz” or “lon_40Hz”. If your lake is too small you will need to go to 40Hz measurements making the retrievals a bit more tricky as the corrections are not provided at 40Hz.

Additionally, you can consider using the PEACHI products based on the SARAL mission. They are product oriented to get better results over inland waters. You can get them from the ODES service

Also, take into account that the orbit for SARAL is drifting since July 2016 so the revisit time over your lake will change.

Depending on the size of the lake the measurements will be contaminated and special processing will be needed. You can check if your lake is listed in one of the services providing water levels from altimetry.

Services
Rivers and Lakes (ESA)
Hydroweb (LEGOS)
Global Reservoir and Lake Monitoring (US Dept. of Agriculture)
DAHITI project

Development projects
CRUCIAL project
SHAPE project

Let us know if you have any other issue,

Regards,

Albert, BRAT Team

• This reply was modified 9 months ago by  brat.

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