traceBP

Description

traceBP is a utility designed to analyze sidescan (SS) trace intensities as a function of incidence angle, primarily for EM710 and EM1000 multibeam sonars. It calculates the intensities for individual trace samples, bins them by incidence angle, and then performs a quadratic least-squares fit on the averaged backscatter response of the first and last beams.

The primary outputs are:

  1. A tracepatt file containing coefficients of quadratic equations to normalize outer traces (used by makess -traceBP).
  2. Optionally, a verbose output suitable for plotting traces intensities versus launch angles (for all beams or individual beams).

Usage 

traceBP <merged_file(s)> [OPTIONS]

Arguments

Option Description  
<merged_file(s)> Required. One or more paths to OMG-HDCS merged files (with associated .ss_data files).  
-v Enable verbose output.  
-draft <val> Specifies the draft (in meters) to subtract from observed depths. Auto-calculated from .param or VESSEL_DRAFT (3.46m)
-yoffset <val> Specifies the Y-offset (in meters) to subtract from across-track distances. Auto-calculated from .param or VESSEL_YOFFSET (0.0m)
-plot_log Output backscatter in logarithmic units (dB).  
-plot_linear Output backscatter in linear units.  
-plot_dn Output backscatter in raw Digital Number (DN) units.  
-depth_range <min_m> <max_m> Only process beams within this water depth range (in meters). 0 to 1000

How It Works

  1. Initialization: Initializes various parameters, including draft, offset_y, min_depth, max_depth, and arrays for accumulating backscatter and counts.
  2. File Iteration: Loops through each input merged file:
    • Opens the merged file (infile) and its corresponding sidescan data file (.ss_data).
    • Loads sonar parameters from the .param file to determine draft and offset_y if not overridden.
    • Reads the summary header.
    • Ping Iteration: Loops through each profile (ping) in the merged file:
      • Reads the current profile header and raw beams.
      • Calculates sample_length (pixel size in the sidescan trace).
      • Adjusts depth for draft and acrosstrack for offset_y.
      • Beam and Sample Iteration: For each valid beam within the current ping:
        • Reads the raw sidescan Scan data for the beam from the .ss_data file.
        • Calculates the incAng_centre_trace[j] (incidence angle of the center sample of the beam’s trace).
        • For each sample k within the beam’s sidescan trace:
          • Calculates the incidence_angle for that specific sample (Pythagorean theorem using depth and across-track offset, referencing the center sample’s incidence angle).
          • Determines diff_incidence_angle (difference from the center incidence angle) and a division_index to bin the sample’s backscatter.
          • Accumulates dn_value (Digital Number from the sidescan sample) into sum[j][division_index] and increments count[j][division_index].
          • Calculates avg_BS[j][division_index].
  3. Quadratic Least-Squares Fit:
    • After processing all pings, it identifies the min_sector and max_sector (angle bins with sufficient data) for the first and last valid beams.
    • It then performs a least-squares fit to a quadratic equation (y = c*x^2 + b*x + a) using the avg_BS values as y and binned incidence angles as x. This is done separately for the first and last beams.
    • The coefficients (a, b, c, d, e, f) are printed to standard output.
  4. Output to tracepatt: The calculated coefficients for the first and last beams are written to the tracepatt file.
  5. Plotting Output (if plot flags are used): Prints a formatted table to standard output for plotting, including beam number, file sequence, launch angle, angle offset, average backscatter (converted to log, linear, or DN as requested), and count.

Output Files

  • tracepatt: An ASCII file containing quadratic coefficients for beam pattern normalization.
  • Standard Output: Formatted table for plotting (if plot flags are used).

Dependencies

  • OMG_HDCS_jversion.h: For OMG-HDCS data structures.
  • support.h: For general utility functions and error handling.
  • math.h: For mathematical functions.

Notes

This tool is used to derive empirical corrections for sidescan data based on the angular response of individual trace samples. The quadratic fit provides a smooth representation of this response, which can then be applied by other tools (e.g., makess) to normalize sidescan imagery. The verbose output is useful for diagnosing the angular response of the sonar.