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 | #ifndef STATMOSPHERE_H
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43 | #define STATMOSPHERE_H
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44 |
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45 | // std includes
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46 | #include <vector>
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47 | #include <complex>
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48 |
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49 | namespace asap {
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50 |
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51 | /**
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52 | * This class implements opacity/atmospheric brightness temperature model
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53 | * equivalent to the model available in MIRIAD. The actual math is a
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54 | * convertion of the Fortran code written by Bob Sault for MIRIAD.
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55 | * It implements a simple model of the atmosphere and Liebe's model (1985)
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56 | * of the complex refractive index of air.
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57 | *
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58 | * The model of the atmosphere is one with an exponential fall-off in
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59 | * the water vapour content (scale height of 1540 m) and a temperature lapse
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60 | * rate of 6.5 mK/m. Otherwise the atmosphere obeys the ideal gas equation
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61 | * and hydrostatic equilibrium.
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62 | *
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63 | * Note, the model includes atmospheric lines up to 800 GHz, but was not
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64 | * rigorously tested above 100 GHz and for instruments located at
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65 | * a significant elevation. For high-elevation sites it may be necessary to
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66 | * adjust scale height and lapse rate.
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67 | *
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68 | * @brief The ASAP atmosphere opacity model
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69 | * @author Max Voronkov
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70 | * @date $Date: 2010-03-17 14:55:17 +1000 (Thu, 26 Apr 2007) $
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71 | * @version
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72 | */
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73 | class STAtmosphere {
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74 | public:
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75 | /**
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76 | * Default Constructor (apart from optional parameters).
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77 | * The class set up this way will assume International Standard Atmosphere (ISA) conditions,
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78 | * except for humidity. The latter is assumed to be 50%, which seems more realistic for
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79 | * Australian telescopes than 0%.
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80 | * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model
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81 | * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to
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82 | * this height, default is 10000m to match MIRIAD.
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83 | * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration),
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84 | * default is 50 to match MIRIAD.
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85 | **/
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86 | explicit STAtmosphere(double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50);
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87 |
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88 | /**
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89 | * Constructor with explicitly given parameters of the atmosphere
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90 | * @param[in] temperature air temperature at the observatory (K)
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91 | * @param[in] pressure air pressure at the observatory (Pascals)
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92 | * @param[in] humidity air humidity at the observatory (fraction)
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93 | * @param[in] lapseRate temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA
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94 | * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model
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95 | * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to
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96 | * this height, default is 10000m to match MIRIAD.
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97 | * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration),
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98 | * default is 50 to match MIRIAD.
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99 | **/
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100 | STAtmosphere(double temperature, double pressure, double humidity, double lapseRate = 0.0065,
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101 | double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50);
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102 |
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103 | /**
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104 | * Set the new weather station data, recompute the model
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105 | * @param[in] temperature air temperature at the observatory (K)
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106 | * @param[in] pressure air pressure at the observatory (Pascals)
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107 | * @param[in] humidity air humidity at the observatory (fraction)
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108 | **/
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109 | void setWeather(double temperature, double pressure, double humidity);
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110 |
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111 | protected:
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112 | /**
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113 | * Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic
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114 | * equilibrium. The model parameters are taken from the data members of this class.
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115 | **/
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116 | void recomputeAtmosphereModel();
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117 |
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118 | /**
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119 | * Obtain the number of model layers, do consistency check that everything is
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120 | * resized accordingly
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121 | * @retrun number of model layers
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122 | **/
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123 | size_t nLayers() const;
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124 |
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125 | /**
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126 | * Determine the saturation pressure of water vapour for the given temperature.
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127 | *
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128 | * Reference:
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129 | * Waters, Refraction effects in the neutral atmosphere. Methods of
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130 | * Experimental Physics, vol 12B, p 186-200 (1976).
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131 | *
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132 | * @param[in] temperature temperature in K
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133 | * @return vapour saturation pressure (Pascals)
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134 | **/
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135 | static double wvSaturationPressure(double temperature);
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136 |
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137 | /**
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138 | * Compute the complex refractivity of the dry components of the atmosphere
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139 | * (oxygen lines) at the given frequency.
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140 | * @param[in] freq frequency (Hz)
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141 | * @param[in] temperature air temperature (K)
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142 | * @param[in] pDry partial pressure of dry components (Pascals)
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143 | * @param[in] pVapour partial pressure of water vapour (Pascals)
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144 | * @return complex refractivity
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145 | *
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146 | * Reference:
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147 | * Liebe, An updated model for millimeter wave propogation in moist air,
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148 | * Radio Science, 20, 1069-1089 (1985).
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149 | **/
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150 | static std::complex<double> dryRefractivity(double freq, double temperature,
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151 | double pDry, double pVapour);
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152 |
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153 | /**
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154 | * Compute the complex refractivity of the water vapour monomers
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155 | * at the given frequency.
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156 | * @param[in] freq frequency (Hz)
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157 | * @param[in] temperature air temperature (K)
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158 | * @param[in] pDry partial pressure of dry components (Pascals)
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159 | * @param[in] pVapour partial pressure of water vapour (Pascals)
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160 | * @return complex refractivity
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161 | *
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162 | * Reference:
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163 | * Liebe, An updated model for millimeter wave propogation in moist air,
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164 | * Radio Science, 20, 1069-1089 (1985).
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165 | **/
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166 | static std::complex<double> vapourRefractivity(double freq, double temperature,
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167 | double pDry, double pVapour);
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168 |
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169 | private:
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170 |
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171 | // heights of all model layers
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172 | std::vector<double> itsHeights;
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173 |
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174 | // temperatures of all model layers
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175 | std::vector<double> itsTemperatures;
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176 |
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177 | // partial pressures of dry component for all model layers
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178 | std::vector<double> itsDryPressures;
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179 |
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180 | // partial pressure of water vapour for all model layers
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181 | std::vector<double> itsVapourPressures;
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182 |
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183 | /**
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184 | * Atmosphere parameters
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185 | **/
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186 |
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187 | // ground level temperature (K)
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188 | double itsGndTemperature;
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189 |
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190 | // ground level pressure (Pascals)
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191 | double itsGndPressure;
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192 |
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193 | // ground level humidity (fraction)
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194 | double itsGndHumidity;
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195 |
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196 | // lapse rate (K/m)
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197 | double itsLapseRate;
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198 |
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199 | // water vapour scale height (m)
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200 | double itsWVScale;
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201 |
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202 | // altitude of the highest layer of the model (m)
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203 | double itsMaxAlt;
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204 | };
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205 |
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206 | } // namespace asap
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207 |
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208 | #endif // #ifndef STATMOSPHERE_H
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209 |
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