1 | //#--------------------------------------------------------------------------- |
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2 | //# STAtmosphere.h: Model of atmospheric opacity |
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3 | //#--------------------------------------------------------------------------- |
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4 | //# Copyright (C) 2004 |
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5 | //# ATNF |
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6 | //# |
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7 | //# The code is based on the Fortran code written by Bob Sault for MIRIAD. |
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8 | //# Converted to C++ by Max Voronkov. This code uses a simple model of the |
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9 | //# atmosphere and Liebe's model (1985) of the complex refractive index of |
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10 | //# air. |
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11 | //# |
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12 | //# The model of the atmosphere is one with an exponential fall-off in |
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13 | //# the water vapour content (scale height of 1540 m) and a temperature lapse |
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14 | //# rate of 6.5 mK/m. Otherwise the atmosphere obeys the ideal gas equation |
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15 | //# and hydrostatic equilibrium. |
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16 | //# |
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17 | //# This program is free software; you can redistribute it and/or modify it |
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18 | //# under the terms of the GNU General Public License as published by the Free |
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19 | //# Software Foundation; either version 2 of the License, or (at your option) |
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20 | //# any later version. |
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21 | //# |
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22 | //# This program is distributed in the hope that it will be useful, but |
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23 | //# WITHOUT ANY WARRANTY; without even the implied warranty of |
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24 | //# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General |
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25 | //# Public License for more details. |
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26 | //# |
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27 | //# You should have received a copy of the GNU General Public License along |
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28 | //# with this program; if not, write to the Free Software Foundation, Inc., |
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29 | //# 675 Massachusetts Ave, Cambridge, MA 02139, USA. |
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30 | //# |
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31 | //# Correspondence concerning this software should be addressed as follows: |
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32 | //# Internet email: Malte.Marquarding@csiro.au |
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33 | //# Postal address: Malte Marquarding, |
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34 | //# Australia Telescope National Facility, |
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35 | //# P.O. Box 76, |
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36 | //# Epping, NSW, 2121, |
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37 | //# AUSTRALIA |
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38 | //# |
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39 | //# $Id: STAtmosphere.h 1346 2007-04-26 03:24:41Z mar637 $ |
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40 | //#--------------------------------------------------------------------------- |
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41 | |
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42 | // own includes |
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43 | #include "STAtmosphere.h" |
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44 | |
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45 | // casa includes |
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46 | #include <casa/Utilities/Assert.h> |
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47 | #include <casa/Quanta.h> |
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48 | |
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49 | // std includes |
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50 | #include <cmath> |
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51 | |
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52 | using namespace casa; |
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53 | using namespace asap; |
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54 | |
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55 | /** |
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56 | * Default Constructor (apart from optional parameters). |
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57 | * The class set up this way will assume International Standard Atmosphere (ISA) conditions, |
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58 | * except for humidity. The latter is assumed to be 50%, which seems more realistic for |
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59 | * Australian telescopes than 0%. |
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60 | * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model |
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61 | * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to |
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62 | * this height, default is 10000m to match MIRIAD. |
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63 | * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration), |
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64 | * default is 50 to match MIRIAD. |
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65 | **/ |
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66 | STAtmosphere::STAtmosphere(double wvScale, double maxAlt, size_t nLayers) : |
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67 | itsGndTemperature(288.), itsGndPressure(101325.), itsGndHumidity(0.5), |
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68 | itsLapseRate(0.0065), itsWVScale(wvScale), itsMaxAlt(maxAlt), |
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69 | itsHeights(nLayers), itsTemperatures(nLayers), |
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70 | itsDryPressures(nLayers), itsVapourPressures(nLayers) |
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71 | { |
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72 | recomputeAtmosphereModel(); |
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73 | } |
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74 | |
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75 | /** |
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76 | * Constructor with explicitly given parameters of the atmosphere |
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77 | * @param[in] temperature air temperature at the observatory (K) |
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78 | * @param[in] pressure air pressure at the observatory (Pascals) |
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79 | * @param[in] humidity air humidity at the observatory (fraction) |
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80 | * @param[in] lapseRate temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA |
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81 | * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model |
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82 | * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to |
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83 | * this height, default is 10000m to match MIRIAD. |
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84 | * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration), |
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85 | * default is 50 to match MIRIAD. |
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86 | **/ |
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87 | STAtmosphere::STAtmosphere(double temperature, double pressure, double humidity, double lapseRate, |
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88 | double wvScale, double maxAlt, size_t nLayers) : |
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89 | itsGndTemperature(temperature), itsGndPressure(pressure), itsGndHumidity(humidity), |
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90 | itsLapseRate(lapseRate), itsWVScale(wvScale), itsMaxAlt(maxAlt), |
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91 | itsHeights(nLayers), itsTemperatures(nLayers), |
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92 | itsDryPressures(nLayers), itsVapourPressures(nLayers) |
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93 | { |
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94 | recomputeAtmosphereModel(); |
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95 | } |
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96 | |
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97 | /** |
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98 | * Set the new weather station data, recompute the model |
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99 | * @param[in] temperature air temperature at the observatory (K) |
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100 | * @param[in] pressure air pressure at the observatory (Pascals) |
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101 | * @param[in] humidity air humidity at the observatory (fraction) |
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102 | **/ |
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103 | void STAtmosphere::setWeather(double temperature, double pressure, double humidity) |
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104 | { |
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105 | itsGndTemperature = temperature; |
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106 | itsGndPressure = pressure; |
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107 | itsGndHumidity = humidity; |
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108 | recomputeAtmosphereModel(); |
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109 | } |
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110 | |
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111 | /** |
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112 | * Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic |
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113 | * equilibrium. The model parameters are taken from the data members of this class. |
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114 | **/ |
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115 | void STAtmosphere::recomputeAtmosphereModel() |
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116 | { |
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117 | AlwaysAssert(itsGndTemperature > 0, AipsError); |
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118 | AlwaysAssert(itsGndPressure > 0., AipsError); |
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119 | AlwaysAssert((itsGndHumidity >= 0.) && (itsGndHumidity<=1.), AipsError); |
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120 | AlwaysAssert(itsMaxAlt > 0., AipsError); |
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121 | AlwaysAssert(itsWVScale > 0., AipsError); |
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122 | |
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123 | const double heightStep = itsMaxAlt/double(nLayers()); |
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124 | // molar mass of the air |
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125 | const double M = 28.96e-3; |
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126 | // free-fall acceleration |
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127 | const double g = 9.81; |
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128 | const double wvGndSaturationPressure = wvSaturationPressure(itsGndTemperature); |
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129 | for (size_t layer = 0; layer < nLayers(); ++layer) { |
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130 | const double height = double(layer)*heightStep; |
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131 | itsHeights[layer] = height; |
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132 | itsTemperatures[layer] = itsGndTemperature/(1.+itsLapseRate*height/itsGndTemperature); |
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133 | const double pressure = itsGndPressure * exp(-M*g/(QC::R.get().getValue()*itsGndTemperature)* |
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134 | (height+0.5*itsLapseRate*height*height/itsGndTemperature)); |
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135 | itsVapourPressures[layer] = casa::min(itsGndHumidity*exp(-height/itsWVScale)*wvGndSaturationPressure, |
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136 | wvSaturationPressure(itsTemperatures[layer])); |
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137 | itsDryPressures[layer] = pressure - itsVapourPressures[layer]; |
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138 | } |
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139 | } |
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140 | |
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141 | /** |
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142 | * Obtain the number of model layers, do consistency check that everything is |
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143 | * resized accordingly |
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144 | * @retrun number of model layers |
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145 | **/ |
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146 | size_t STAtmosphere::nLayers() const |
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147 | { |
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148 | const size_t result = itsHeights.size(); |
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149 | DebugAssert(result > 0, AipsError); |
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150 | DebugAssert(itsTemperatures.size() == result, AipsError); |
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151 | DebugAssert(itsDryPressures.size() == result, AipsError); |
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152 | DebugAssert(itsVapourPressures.size() == result, AipsError); |
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153 | return result; |
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154 | } |
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155 | |
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156 | /** |
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157 | * Determine the saturation pressure of water vapour for the given temperature. |
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158 | * |
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159 | * Reference: |
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160 | * Waters, Refraction effects in the neutral atmosphere. Methods of |
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161 | * Experimental Physics, vol 12B, p 186-200 (1976). |
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162 | * |
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163 | * @param[in] temperature temperature in K |
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164 | * @return vapour saturation pressure (Pascals) |
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165 | **/ |
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166 | double STAtmosphere::wvSaturationPressure(double temperature) |
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167 | { |
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168 | if (temperature > 215.) { |
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169 | return 0.; |
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170 | } |
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171 | const double theta = 300.0/temperature; |
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172 | return 1e5/(41.51/std::pow(theta,5)*std::pow(10.,9.834*theta-10.0)); |
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173 | } |
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174 | |
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