homepage Forums Altimetry Forum The formula to calculate inland water level in BRAT?

This topic contains 6 replies, has 2 voices, and was last updated by  Long Trinh 3 weeks, 1 day ago.

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  • #16810

    Long Trinh
    Participant

    As my question, I just start use BRAT and I also download the image from Sentinel-3 and use this tool to calculate the water level (WL). I use the formula:
    ((((((alt_01 – range_ocean_01_ku) – mod_dry_tropo_cor_meas_altitude_01) – mod_wet_tropo_cor_meas_altitude_01) – iono_cor_alt_01_ku) – pole_tide_01) – solid_earth_tide_01) – geoid_01
    However, when I check with the WL in hydroweb, it quite different, so can someone show me the correct formula.
    Thanks!!!

  • #16814

    aambrozio
    Participant

    The formula is correct. What might be happening is that you are trying to measure the water level of a small water body in relation to the ground footprint, leading to contamination from land.

    For example, with the very same formula and a larger inland water body, specifically Lake Ladoga, you can obtain values similar (product S3B_SR_2_LAN____20220619T084551_20220619T093620_20220713T131442_3029_067_164______PS2_O_NT_004)

    Number of valid data = 15.000000
    Mean = 4.507873
    Standard deviation = 0.387836
    Minimum = 3.098700
    Maximum = 4.768200

    to ones you can find at Hydroweb

    # data file format
    # (1): decimal year (2) date = yyyy/mm/dd (3): time = hh:mm
    # (4): height above surface of ref (m), (5): standard deviation from height (m)
    # (6): area (km2), (7): volume with respect to volume of first date (km3)
    # (8): flag
    #
    #
    2022.43662671 ; 2022/06/09 ; 08:51 ; 4.94 ; 0.04 ; 9999.999 ; 9999.999 ; ;
    2022.47774353 ; 2022/06/24 ; 09:02 ; 4.83 ; 0.06 ; 9999.999 ; 9999.999 ; ;

    Screenshots of BRAT’s and Hydroweb’s plots

    • This reply was modified 4 weeks, 1 day ago by  aambrozio.
    • #16816

      Long Trinh
      Participant

      Thanks!! 1 more question, how can I determine the exact location of the virtual station, I know VS is the cross-section bwt the satellite path and the water body, but for the large reservoir how can I determine the location

  • #16817

    aambrozio
    Participant

    The exact location of a virtual station can be any point within the intersection of a water body with a satellite ground track. Nonetheless, you have to take into account that the topography around the virtual station has a large influence on the measurements and that you want your virtual station to be as close as possible to in situ gauges, or in the case of above, to other virtual stations.

    Bear in mind that in my previous post, specifically the part with the water level values obtained from a S3B product, I did not analyze the measurements as a function of a distance along the ground track in relation to a virtual station, so the accuracy can be improved.

    For further information on the current methodologies concerning virtual stations I advise you to check the available literature.

    • #16818

      Long Trinh
      Participant

      When I apply thIS formula for the reservoir but why there are missing path like the imgage 1 and the varion is so large? and how to fix this
      https://drive.google.com/file/d/1YpBq7UoFB-jALtADhpYl0XhWmtHY4Opj/view?usp=sharing
      And when I apply the other formula to calculate water level which I found in a paper
      “elevation_ocog_20_ku – mean_sea_surf_sol1_20_ku”
      Why the varion of water level in a reveroir is so large? Image 2
      https://drive.google.com/file/d/13kxERcJW3JJRdfU9AEQjhbCFL88Ltl2M/view?usp=sharing
      P/s: The latitude from 11.09 to 11.14

    • #16820

      aambrozio
      Participant

      What’s the longitude(s)? In the images and in your post there is no precise information about it. One of the images has the coordinates 101° 38′ 42.22″ E,14° 0′ 18.11″ N, which is relatively close to the interval of latitudes you mentioned, but I need the full coordinates so that I can help you.

      Also, any additional information about the water body itself, besides the coordinates, would be helpful.

      • This reply was modified 3 weeks, 1 day ago by  aambrozio.
    • #16822

      Long Trinh
      Participant

      Sorry, I forgot
      Its name: Tri An Lake in Vietnam ( you can found in Hydroweb with its incorrect name is Tri Han lake)
      Latitude of the lake is 11.18 and Longtitude: 107.14
      and the sentinel 3B cut through this location (from 11.08 degree to 11.14 (lat) and 107.08 to 107.07 (lon))
      Can you see it for me and explain for me why, sorry to bother you

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