dissolved_oxygen_compensation.h

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#include <cmath>
 
double pressure_correction(double pressure_mmhg = 760.0) { return pressure_mmhg / 760.0; }
 
double salinity_correction(double temperature_k, double salinity_ppt)
{
    // base salinity correction
    const double sal_corr_a = 0.017674;
    // adjusts salinity correction based on temperature
    const double sal_corr_b = 10.754;
    // quadratic temp-based adjustment to salinity effect
    const double sal_corr_c = 2140.7;
 
    return std::exp(-salinity_ppt * (sal_corr_a - (sal_corr_b / temperature_k) +
                                     (sal_corr_c / (temperature_k * temperature_k))));
}
 
double calculate_do_saturation_fresh(double temperature_k)
{
    // Constants from Weiss (1970), Equation (7) in USGS WQ.2011.03
    const double a0 = -173.4292;
    const double a1 = 249.6339;
    const double a2 = 143.3483;
    const double a3 = -21.8492;
    const double oxygen_conversion = 1.42905; // mL/L to mg/L at STP
    const double temp_scale = 100.0;
 
    double scaled_temp = temperature_k / temp_scale;
 
    double ln_do =
        a0 + a1 * (temp_scale / temperature_k) + a2 * std::log(scaled_temp) + a3 * scaled_temp;
 
    return oxygen_conversion * std::exp(ln_do);
}
 
double calculate_dissolved_oxygen_solubility(double temperature_celsius, double salinity_ppt,
                                             double pressure_mmhg = 760.0)
{
    const double kelvin_offset = 273.15;
    double temperature_k = temperature_celsius + kelvin_offset;
    double do_saturation = calculate_do_saturation_fresh(temperature_k);
    double salinity_factor = salinity_correction(temperature_k, salinity_ppt);
    double pressure_factor = pressure_correction(pressure_mmhg);
 
    return do_saturation * salinity_factor * pressure_factor;
}
 
double calculate_do_saturation_percent(double do_raw, double do_max)
{
    return (do_raw / do_max) * 100.0;
}