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Reject Bragg Peaks Far from Expected Bragg Index

Source: R/SeaSondeRCS_FOR.R
seasonder_rejectDistantBraggPeakTest.Rd

This function evaluates Bragg peaks based on their proximity to expected Bragg index bins. If the boundaries of a peak are farther from all Bragg indices than the width of the peak itself, the peak is rejected by returning an empty integer vector.

Usage

seasonder_rejectDistantBraggPeakTest(
  seasonder_cs_object,
  peak,
  range = NA,
  peak_name = ""
)

Arguments

seasonder_cs_object

A SeaSondeRCS object containing the spectral data and Bragg indices.

peak

A numeric vector indicating the Doppler bin positions of the peak under evaluation.

range

Optional; A numeric or integer value representing the range cell corresponding to the peak. Defaults to NA.

peak_name

Optional; A character string representing the name or identifier of the peak (e.g., "positive_FOR" or "negative_FOR"). Defaults to an empty string.

Value

A possibly modified version of the peak argument, where a rejected peak is returned as integer(0), indicating that it does not pass the proximity test.

Details

Reason for the Test: The test ensures that peaks identified as part of the first-order Bragg region are reasonably close to the expected Bragg index. Peaks that are distant from the Bragg index are likely caused by noise, interference, or other sources unrelated to first-order Bragg scatter. These invalid peaks, if included, can lead to erroneous current velocity vectors and degrade the quality of radar-derived measurements.

Specifically, the test rejects peaks when:

  • The distance from the left or right boundary of the peak to the nearest Bragg index exceeds the width of the peak.

  • This condition ensures that peaks with excessively large offsets from the Bragg index are excluded.

Steps:

  1. If the peak is empty, the function does nothing.

  2. Calculates the width of the peak as the difference between its maximum and minimum Doppler bin indices.

  3. Computes the left and right boundaries of the peak.

  4. Calculates the distance from each boundary to all Bragg indices.

  5. Rejects the peak if both boundary distances exceed the peak width.

  6. Logs the rejection information if applicable.

This test is particularly important in scenarios where strong non-Bragg signals, such as those from ships or other high-intensity noise sources, might otherwise be misclassified as first-order Bragg.

References

COS. SpectraPlotterMap 12 User Guide. CODAR Ocean Sensors (COS), Mountain View, CA, USA, 2016.

See also