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Hello good time.
I wanted to be proud of my work. I would like to investigate two lakes in the Caspian and Urmia in Iran using one or two satellites. (Preferably jason and sentinel)
A. Which data format is suitable for my use?
R: Both SAR (Sentinel-3 & CryoSat-2) and LRM (e.g. Jason-2 & ENVISAT) altimetry can be used but shall be filtered properly. Please read peer review papers on the topic to understand how to properly select & filter the data over water bodies.
B- Is your suggestion for analysis using maps software or brat?
R: BRAT can surely be used for a preliminary analysis, filters can be used to select just points acquired over the river and flags can be used to discard invalid measurements. Mean values of valid points of each pass can also be calculated using the statistics button.
c – Altimeter data formats are very wide and varied. Which is more appropriate for work on lakes and why?
R: altimetry posting rates are typically at 1Hz (7 km spacing between two estimates) or 20Hz (300 m spacing between two estimates). Resolution is instead dictated by the processing scheme (SAR 300 m in along-track direction & LRM: 2-10 km in along-track direction depending on SWH) Moreover, the ESA GPOD SARvatore service (see info below) also offers Cryosat-2 and Sentinel-3 data at 80 Hz (80 m spacing between two estimates & SAR resolution in along-track). This is an excellent posting rate for investigating small inland water bodies.
d – Can the lake depth be measured with maps or brat?
R: With the altimeter you derive a water level above and ellipsoid or a geoid. The waveform typically does not penetrate the water and is mostly reflected at the water surface. Try checking for peer-review papers. For the open ocean please check: https://www.aviso.altimetry.fr/applications/geodesy-and-geophysics/bathymetry.html
e-How accurate is this?
R: It is not easy to provide a value here. It depends by the quality of the data selection process and by the quality of the estimates and gauges measurements used for validation. Typically, good validation values can have an RMSE of around 20 cm, but this is just an example. Again please check peer-review papers.
What is your suggestion ?
R: Read peer-review papers on similar water bodies & datasets you want to use and start by reapplying consolidated approaches. Master the theory before starting using BRAT.
Useful resources about altimetry and SARvatore:
(Training page to be updated soon with the material presented, material presented the past year is available at: https://nikal.eventsair.com/QuickEventWebsitePortal/11th-coastal-altimetry-workshop/esa/ExtraContent/ContentPage?page=8)
For a tutorial on altimetry and BRAT please check:
and he associated material here:
Thank you very much and appreciate your response
R: I wish you all the best with your research,
Marco Restano (SERCO c/o ESA-ESRIN)