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OSOceanAcoustics / echopype

Enabling interoperability and scalability in ocean sonar data analysis
https://echopype.readthedocs.io/
Apache License 2.0
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Fix/nasc #1149

Closed simedroniraluca closed 1 year ago

simedroniraluca commented 1 year ago

NASC (Nautical Area Scattering Coefficient) Computation Correction

This PR is opened to propose a solution for https://github.com/OSOceanAcoustics/echopype/pull/1136

Changes Made:

  1. Conversion Factors: Conversion factors have been incorporated to facilitate the conversion from backscattering cross-section to scattering cross-section and from meters to nautical miles (nmi).

  2. Computation Approach:

    • Cells Selection: Cells are chosen based on their depth and distance. The distance calculation is based on latitude and longitude coordinates.
    • NASC Calculation: For each channel and cell, the NASC is computed using the following steps:
      • Multiply the Sv (in linear units) with the height of the samples. The sample height is determined as the difference between consecutive depth values.
      • Compute the mean of the obtained values.
      • Multiply the mean value by the number of samples within the selected cell per the number of pings in the same cell.
      • Further multiply the result by $4 \times \pi \times 1852^2$
      • Finally, divide the obtained result by the percentage of non-NaN samples present in the analysis.