svpSonar

Description

svpSonar is a utility designed to model the distortion of sonar beams resulting from errors in the assumed sound velocity at the transducer. It simulates various multibeam sonar geometries (line arrays, paired inclined arrays, curved faces) and calculates how an error in the surface sound velocity affects the true steering angle, apparent across-track position, and depth of a beam.

This tool is critical for understanding the sensitivity of multibeam systems to sound velocity profile inaccuracies and for quantifying potential depth and position errors. It generates output data that can be plotted to visualize these distortions.

Usage 

svpSonar (-elac | -em1000 | -line | -em3000d | -isis | -custom <LUT_file>) -out <output_file> [-actual <val>] [-speed_range <min_error> <max_error> <step_error>] [-angle_range <min_angle> <max_angle> <step_angle>]

Arguments

| Option | Description | |—|—| | (-elac | -em1000 | -line | -em3000d | -isis) | Required. Specifies the sonar array geometry type: * -line: Horizontal line array. * -elac: Paired 30 deg inclined line arrays. * -em3000d: Paired 45 deg inclined line arrays. * -isis: Paired 60 deg inclined line arrays. * -em1000: EM1000-like array. | | -custom <LUT_file> | Uses a custom lookup table file (.Time_LUT, .ACROSS_LUT) for ray tracing (currently commented out). | | -out <output_file> | Required. Path for the output ASCII file containing the distortion data. | | -actual <val> | Actual sound speed (m/s) at the transducer. | 1500.0 (assumed) | | -assumed <val> | Assumed sound speed (m/s) for beam steering. | 1500.0 (default) | | -speed_range <min_error> <max_error> <step_error> | Defines a range of sound speed errors (m/s) to simulate. * min_error: Minimum sound speed error. * max_error: Maximum sound speed error. * step_error: Step size for the sound speed error. | -5.0 5.0 0.5 | | -angle_range <min_angle> <max_angle> <step_angle> | Defines the range of beam angles (degrees) to simulate. * min_angle: Minimum beam angle. * max_angle: Maximum beam angle. * step_angle: Step size for the beam angle. | -75.0 75.0 1.0 | | -roll <val> | Simulates a constant vessel roll (degrees). | 0.0 | | -v | Enable verbose output. | |

How It Works

  1. Initialization: Parses command-line arguments, setting the sonar type, sound speed parameters (actual_speed, assumed_speed, min_speed_error, max_speed_error, error_step), and angle range (min_angle, max_angle, angle_step).
  2. Output File Setup: Creates the specified output ASCII file (-out). Writes header information to the file including the number of speed error steps, default Y ranges, and number of angle steps.
  3. Speed Error Loop: Iterates through speed_error values from min_speed_error to max_speed_error with error_step:
    • Calculates actual_speed by adding speed_error to assumed_speed.
    • Writes actual_speed and assumed_speed to the output file.
    • Angle Loop: Iterates through angle values (in degrees) from min_angle to max_angle with angle_step:
      • Steering Calculation: Calls steering() to calculate steered_angle (the angle the sonar system thinks the beam is steered to), taking into account the type of sonar and a simulated roll.
      • True Steering Angle: Calculates true_steered_angle using Snell’s Law, accounting for the actual_speed and assumed_speed.
      • Angle Error: Calculates angle_error as the difference between true_steered_angle and steered_angle.
      • Actual Angle: Calculates actual_angle by adding angle_error to the original angle.
      • Position Calculation:
        • Assumes a true_slant_range of 1.0.
        • Calculates apparent_across and apparent_depth based on actual_angle.
        • Calculates true_across (based on angle).
        • Calculates across_error as true_across - apparent_across.
      • Output Data: Writes all calculated values (angles, across-track, depth, and errors) to the output file.
  4. steering(int type, double roll, double angle) Function:
    • Calculates the effective steered angle based on the sonar array geometry (type) and applied roll.
    • Different sonar types have different relationships between the physical beam angle, roll, and the final steered angle (e.g., simple sum for line array, or offsetting by fixed angles for inclined paired arrays).
  5. Cleanup: Closes the output file.

Output Files

  • <output_file>: An ASCII file containing multiple lines of data. For each speed_error step, it first prints actual_speed and assumed_speed, followed by a series of lines (one for each angle step) containing: angle actual_angle steered_angle angle_error apparent_across apparent_depth true_across across_error

Dependencies

  • support.h: For general utility functions.
  • j_proj.h: For coordinate projection functions.
  • math.h: For mathematical functions.

Notes

svpSonar is a crucial tool for understanding and quantifying the sensitivity of multibeam sonar measurements to sound velocity profile inaccuracies and potential depth/position errors. It helps in assessing the required accuracy of SVPs and in designing mitigation strategies for survey data acquisition and processing. The model supports various sonar geometries for realistic simulation. The tool creates a new file, preserving the original data.