new_speedtosalinity

Description

new_speedtosalinity is a utility that calculates salinity from sound velocity, temperature, and depth (converted to pressure) using empirical equations. It reads a file containing depth, sound velocity, and temperature data, then iterates through possible salinity values to find the best fit for the observed sound velocity using either the Wilson (1962) or Chen-Millero-Li (1977) equations.

This tool is essential for oceanographic applications where direct salinity measurements are unavailable, but sound velocity, temperature, and depth are known. It allows for the reconstruction of salinity profiles for use in various oceanographic models.

Usage 

new_speedtosalinity -in <infile> -out <outfile> (-wilson | -cml) [-v] [-test]

Arguments

Option Description
-in <infile> Required. Path to the input ASCII file containing depth, sound_velocity, temperature data.
-out <outfile> Required. Path for the output ASCII file containing depth, sound_velocity, temperature, salinity data.
-wilson Required (choose one). Uses the Wilson (1962) empirical equation to calculate sound velocity.
-cml Required (choose one). Uses the Chen-Millero-Li (1977) empirical equation to calculate sound velocity.
-v Enable verbose output.
-test Runs a hardcoded test case for vchemilli and exits.

Input File Format (ASCII)

The input file (-in) is expected to be a comma-separated ASCII file with three columns: depth, sound_velocity, temperature

How It Works

  1. Initialization: Parses command-line arguments to get input/output filenames, select the empirical equation (-wilson or -cml), and set verbose/test modes.
  2. File Opening: Opens the input ASCII file (-in) for reading and the output ASCII file (-out) for writing.
  3. Data Processing Loop: Reads depth, sound_velocity, and temperature from each line of the input file:
    • Pressure Calculation: Converts depth to pressure (in kg/cm²) by adding atmospheric pressure and accounting for density.
    • Salinity Iteration:
      • Initializes salinity to 0 and minDiff to a large value.
      • Iterates salinity from 0 up to max_salinity (400, representing 0 to 40.0 ppt in 0.1 ppt increments).
      • For each salinity value, it calculates temp_velocity using either vsw() (Wilson) or vchemilli() (Chen-Millero-Li) function.
      • Compares temp_velocity with the observed sound_velocity to find the best_guess_salinity that minimizes the absolute difference.
    • Output: Writes depth, sound_velocity, temperature, and best_guess_salinity to the output file.
  4. vsw(double t, double p, double s) (Wilson 1962 Equation):
    • Calculates sound velocity based on temperature (t), pressure (p), and salinity (s) using Wilson’s empirical formula.
  5. vchemilli(double t, double p, double s) (Chen-Millero-Li 1977 Equation):
    • Calculates sound velocity based on temperature (t), pressure (p), and salinity (s) using the Chen-Millero-Li empirical formula, which is generally more accurate.
  6. Cleanup: Closes input and output files.

Output Files

  • <outfile>: An ASCII file containing depth, sound_velocity, temperature, best_guess_salinity data.

Dependencies

  • support.h: For general utility functions.
  • math.h: For mathematical functions.

Notes

This tool is a valuable component in oceanographic data analysis, particularly when direct salinity measurements are missing or unreliable. By leveraging the empirical relationships between sound velocity, temperature, salinity, and pressure, it enables the reconstruction of crucial oceanographic parameters. The two available equations (Wilson and Chen-Millero-Li) provide options for different accuracy requirements. The tool creates a new file, preserving the original input.