Line data    Source code

       1             : #include "AP_Baro.h"
       2             : 
       3             : #include <AP_HAL/AP_HAL.h>
       4             : #include <AP_Math/definitions.h>
       5             : 
       6             : extern const AP_HAL::HAL& hal;
       7             : 
       8             : // ==========================================================================
       9             : // based on tables.cpp from http://www.pdas.com/atmosdownload.html
      10             : 
      11     1117401 : void AP_Baro::SimpleUnderWaterAtmosphere(
      12             :         float alt,            // depth, km.
      13             :         float& rho,           // density/sea-level
      14             :         float& delta,         // pressure/sea-level standard pressure
      15             :         float& theta)         // temperature/sea-level standard temperature
      16             : {
      17             :     // Values and equations based on:
      18             :     // https://en.wikipedia.org/wiki/Standard_sea_level
      19     1117401 :     const float seaDensity = 1.024f;      // g/cm3
      20     1117401 :     const float maxSeaDensity = 1.028f;   // g/cm3
      21     1117401 :     const float pAC = maxSeaDensity - seaDensity; // pycnocline angular coefficient
      22             : 
      23             :     // From: https://www.windows2universe.org/earth/Water/density.html
      24     1117401 :     rho = seaDensity;
      25     1117401 :     if (alt < 1.0f) {
      26             :         // inside pycnocline
      27     1117401 :         rho += pAC*alt;
      28             :     } else {
      29           0 :         rho += pAC;
      30             :     }
      31     1117401 :     rho = rho/seaDensity;
      32             : 
      33             :     // From: https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/fluid_pressure.html
      34             :     // \f$P = \rho (kg) \cdot gravity (m/s2) \cdot depth (m)\f$
      35             :     // \f$P_{atmosphere} = 101.325 kPa\f$
      36             :     // \f$P_{total} = P_{atmosphere} + P_{fluid}\f$
      37     1117401 :     delta = (SSL_AIR_PRESSURE + (seaDensity * 1e3) * GRAVITY_MSS * (alt * 1e3)) / SSL_AIR_PRESSURE;
      38             : 
      39             :     // From: http://residualanalysis.blogspot.com.br/2010/02/temperature-of-ocean-water-at-given.html
      40             :     // \f$T(D)\f$ Temperature underwater at given temperature
      41             :     // \f$S\f$ Surface temperature at the surface
      42             :     // \f$T(D)\approx\frac{S}{1.8 \cdot 10^{-4} \cdot S \cdot T + 1}\f$
      43     1117401 :     const float seaTempSurface = KELVIN_TO_C(SSL_AIR_TEMPERATURE); // Celsius
      44     1117401 :     const float S = seaTempSurface * 0.338f;
      45     1117401 :     theta = 1.0f / ((1.8e-4f) * S * (alt * 1e3f) + 1.0f);
      46     1117401 : }