mirror of https://github.com/ArduPilot/ardupilot
73 lines
2.8 KiB
C++
73 lines
2.8 KiB
C++
#include "AP_Baro.h"
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#include <AP_HAL/AP_HAL.h>
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extern const AP_HAL::HAL& hal;
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// ==========================================================================
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// based on tables.cpp from http://www.pdas.com/atmosdownload.html
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/*
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Compute the temperature, density, and pressure in the standard atmosphere
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Correct to 20 km. Only approximate thereafter.
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*/
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void AP_Baro::SimpleAtmosphere(
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const float alt, // geometric altitude, km.
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float& sigma, // density/sea-level standard density
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float& delta, // pressure/sea-level standard pressure
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float& theta) // temperature/sea-level standard temperature
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{
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const float REARTH = 6369.0f; // radius of the Earth (km)
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const float GMR = 34.163195f; // gas constant
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float h=alt*REARTH/(alt+REARTH); // geometric to geopotential altitude
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if (h < 11.0f) {
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// Troposphere
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theta = (SSL_AIR_TEMPERATURE - 6.5f * h) / SSL_AIR_TEMPERATURE;
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delta = powf(theta, GMR / 6.5f);
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} else {
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// Stratosphere
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theta = 216.65f / SSL_AIR_TEMPERATURE;
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delta = 0.2233611f * expf(-GMR * (h - 11.0f) / 216.65f);
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}
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sigma = delta/theta;
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}
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void AP_Baro::SimpleUnderWaterAtmosphere(
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float alt, // depth, km.
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float& rho, // density/sea-level
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float& delta, // pressure/sea-level standard pressure
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float& theta) // temperature/sea-level standard temperature
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{
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// Values and equations based on:
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// https://en.wikipedia.org/wiki/Standard_sea_level
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const float seaDensity = 1.024f; // g/cm3
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const float maxSeaDensity = 1.028f; // g/cm3
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const float pAC = maxSeaDensity - seaDensity; // pycnocline angular coefficient
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// From: https://www.windows2universe.org/earth/Water/density.html
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rho = seaDensity;
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if (alt < 1.0f) {
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// inside pycnocline
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rho += pAC*alt;
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} else {
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rho += pAC;
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}
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rho = rho/seaDensity;
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// From: https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/fluid_pressure.html
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// \f$P = \rho (kg) \cdot gravity (m/s2) \cdot depth (m)\f$
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// \f$P_{atmosphere} = 101.325 kPa\f$
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// \f$P_{total} = P_{atmosphere} + P_{fluid}\f$
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delta = (SSL_AIR_PRESSURE + (seaDensity * 1e3) * GRAVITY_MSS * (alt * 1e3)) / SSL_AIR_PRESSURE;
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// From: http://residualanalysis.blogspot.com.br/2010/02/temperature-of-ocean-water-at-given.html
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// \f$T(D)\f$ Temperature underwater at given temperature
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// \f$S\f$ Surface temperature at the surface
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// \f$T(D)\approx\frac{S}{1.8 \cdot 10^{-4} \cdot S \cdot T + 1}\f$
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const float seaTempSurface = KELVIN_TO_C(SSL_AIR_TEMPERATURE); // Celsius
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const float S = seaTempSurface * 0.338f;
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theta = 1.0f / ((1.8e-4f) * S * (alt * 1e3f) + 1.0f);
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}
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