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 | itsHeights(nLayers), itsTemperatures(nLayers), |
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68 | itsDryPressures(nLayers), itsVapourPressures(nLayers), |
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69 | itsGndTemperature(288.), itsPressure(101325.), itsGndHumidity(0.5), |
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70 | itsLapseRate(0.0065), itsWVScale(wvScale), itsMaxAlt(maxAlt), itsObsHeight(200.) |
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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 sea level if the observatory elevation is set |
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79 | * (default is set to 200m) or at the observatory ground level if the elevation |
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80 | * is set to 0 (Pascals) |
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81 | * @param[in] humidity air humidity at the observatory (fraction) |
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82 | * @param[in] lapseRate temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA |
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83 | * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model |
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84 | * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to |
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85 | * this height, default is 10000m to match MIRIAD. |
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86 | * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration), |
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87 | * default is 50 to match MIRIAD. |
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88 | **/ |
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89 | STAtmosphere::STAtmosphere(double temperature, double pressure, double humidity, double lapseRate, |
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90 | double wvScale, double maxAlt, size_t nLayers) : |
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91 | itsHeights(nLayers), itsTemperatures(nLayers), |
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92 | itsDryPressures(nLayers), itsVapourPressures(nLayers), |
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93 | itsGndTemperature(temperature), itsPressure(pressure), itsGndHumidity(humidity), |
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94 | itsLapseRate(lapseRate), itsWVScale(wvScale), itsMaxAlt(maxAlt), itsObsHeight(200.) |
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95 | { |
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96 | recomputeAtmosphereModel(); |
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97 | } |
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98 | |
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99 | /** |
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100 | * Set the new weather station data, recompute the model |
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101 | * @param[in] temperature air temperature at the observatory (K) |
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102 | * @param[in] pressure air pressure at the sea level if the observatory elevation is set to non-zero value |
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103 | * (default is set to 200m) or at the observatory ground level if the elevation |
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104 | * is set to 0 (Pascals) |
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105 | * @param[in] humidity air humidity at the observatory (fraction) |
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106 | **/ |
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107 | void STAtmosphere::setWeather(double temperature, double pressure, double humidity) |
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108 | { |
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109 | itsGndTemperature = temperature; |
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110 | itsPressure = pressure; |
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111 | itsGndHumidity = humidity; |
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112 | recomputeAtmosphereModel(); |
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113 | } |
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114 | |
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115 | /** |
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116 | * Set the elevation of the observatory (height above mean sea level) |
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117 | * It affects only interpretation of the pressure supplied as part of the weather data, if this value |
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118 | * is non-zero, the pressure (e.g. in setWeather or constructor) is that at mean sea level. If the |
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119 | * observatory elevation is set to zero, regardless on real elevation, the pressure is that at the |
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120 | * observatory ground level. |
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121 | * |
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122 | * By default, 200m is assumed and the pressure should be a mean sea level pressure.. |
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123 | * @param[in] elev elevation in metres |
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124 | **/ |
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125 | void STAtmosphere::setObservatoryElevation(double elev) |
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126 | { |
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127 | itsObsHeight = elev; |
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128 | recomputeAtmosphereModel(); |
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129 | } |
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130 | |
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131 | |
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132 | /** |
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133 | * Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic |
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134 | * equilibrium. The model parameters are taken from the data members of this class. |
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135 | **/ |
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136 | void STAtmosphere::recomputeAtmosphereModel() |
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137 | { |
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138 | AlwaysAssert(itsGndTemperature > 0, AipsError); |
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139 | AlwaysAssert(itsPressure > 0., AipsError); |
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140 | AlwaysAssert((itsGndHumidity >= 0.) && (itsGndHumidity<=1.), AipsError); |
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141 | AlwaysAssert(itsMaxAlt > 0., AipsError); |
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142 | AlwaysAssert(itsWVScale > 0., AipsError); |
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143 | |
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144 | const double heightStep = itsMaxAlt/double(nLayers()); |
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145 | // molar mass of the air |
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146 | const double M = 28.96e-3; |
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147 | // free-fall acceleration |
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148 | const double g = 9.81; |
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149 | |
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150 | const double wvGndSaturationPressure = wvSaturationPressure(itsGndTemperature); |
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151 | const double gndPressure = itsPressure*exp(-M*g/(QC::R.get().getValue()*itsGndTemperature)* |
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152 | (itsObsHeight+0.5*itsLapseRate*itsObsHeight*itsObsHeight/itsGndTemperature)); |
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153 | for (size_t layer = 0; layer < nLayers(); ++layer) { |
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154 | const double height = double(layer)*heightStep; |
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155 | itsHeights[layer] = height; |
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156 | itsTemperatures[layer] = itsGndTemperature/(1.+itsLapseRate*height/itsGndTemperature); |
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157 | const double pressure = gndPressure * exp(-M*g/(QC::R.get().getValue()*itsGndTemperature)* |
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158 | (height+0.5*itsLapseRate*height*height/itsGndTemperature)); |
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159 | itsVapourPressures[layer] = casa::min(itsGndHumidity*exp(-height/itsWVScale)*wvGndSaturationPressure, |
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160 | wvSaturationPressure(itsTemperatures[layer])); |
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161 | itsDryPressures[layer] = pressure - itsVapourPressures[layer]; |
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162 | //std::cout<<"layer="<<layer<<": H="<<itsHeights[layer]<<" T="<<itsTemperatures[layer]<< |
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163 | // " Pvap="<<itsVapourPressures[layer]<<" Pdry="<<itsDryPressures[layer]<<endl; |
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164 | } |
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165 | } |
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166 | |
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167 | /** |
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168 | * Obtain the number of model layers, do consistency check that everything is |
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169 | * resized accordingly |
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170 | * @retrun number of model layers |
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171 | **/ |
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172 | size_t STAtmosphere::nLayers() const |
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173 | { |
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174 | const size_t result = itsHeights.size(); |
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175 | DebugAssert(result > 2, AipsError); |
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176 | DebugAssert(itsTemperatures.size() == result, AipsError); |
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177 | DebugAssert(itsDryPressures.size() == result, AipsError); |
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178 | DebugAssert(itsVapourPressures.size() == result, AipsError); |
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179 | return result; |
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180 | } |
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181 | |
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182 | /** |
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183 | * Determine the saturation pressure of water vapour for the given temperature. |
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184 | * |
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185 | * Reference: |
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186 | * Waters, Refraction effects in the neutral atmosphere. Methods of |
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187 | * Experimental Physics, vol 12B, p 186-200 (1976). |
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188 | * |
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189 | * @param[in] temperature temperature in K |
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190 | * @return vapour saturation pressure (Pascals) |
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191 | **/ |
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192 | double STAtmosphere::wvSaturationPressure(double temperature) |
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193 | { |
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194 | if (temperature <= 215.) { |
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195 | return 0.; |
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196 | } |
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197 | const double theta = 300.0/temperature; |
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198 | return 1e5/(41.51/std::pow(theta,5)*std::pow(10.,9.834*theta-10.0)); |
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199 | } |
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200 | |
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201 | /** |
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202 | * Compute the complex refractivity of the dry components of the atmosphere |
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203 | * (oxygen lines) at the given frequency. |
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204 | * @param[in] freq frequency (Hz) |
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205 | * @param[in] temperature air temperature (K) |
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206 | * @param[in] pDry partial pressure of dry components (Pascals) |
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207 | * @param[in] pVapour partial pressure of water vapour (Pascals) |
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208 | * @return complex refractivity |
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209 | * |
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210 | * Reference: |
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211 | * Liebe, An updated model for millimeter wave propogation in moist air, |
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212 | * Radio Science, 20, 1069-1089 (1985). |
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213 | **/ |
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214 | std::complex<double> STAtmosphere::dryRefractivity(double freq, double temperature, |
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215 | double pDry, double pVapour) |
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216 | { |
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217 | // the number of parameters per atmospheric line and the number of lines taken into account |
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218 | const size_t nLineParams = 7; |
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219 | const size_t nLines = 48; |
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220 | // actual tabulated values |
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221 | const double lines[nLines][nLineParams] = |
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222 | {{49.452379, 0.12E-6, 11.830, 8.40E-3, 0.0, 5.60E-3, 1.7}, |
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223 | {49.962257, 0.34E-6, 10.720, 8.50E-3, 0.0, 5.60E-3, 1.7}, |
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224 | {50.474238, 0.94E-6, 9.690, 8.60E-3, 0.0, 5.60E-3, 1.7}, |
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225 | {50.987748, 2.46E-6, 8.690, 8.70E-3, 0.0, 5.50E-3, 1.7}, |
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226 | {51.503350, 6.08E-6, 7.740, 8.90E-3, 0.0, 5.60E-3, 1.8}, |
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227 | {52.021409, 14.14E-6, 6.840, 9.20E-3, 0.0, 5.50E-3, 1.8}, |
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228 | {52.542393, 31.02E-6, 6.000, 9.40E-3, 0.0, 5.70E-3, 1.8}, |
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229 | {53.066906, 64.10E-6, 5.220, 9.70E-3, 0.0, 5.30E-3, 1.9}, |
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230 | {53.595748, 124.70E-6, 4.480, 10.00E-3, 0.0, 5.40E-3, 1.8}, |
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231 | {54.129999, 228.00E-6, 3.810, 10.20E-3, 0.0, 4.80E-3, 2.0}, |
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232 | {54.671157, 391.80E-6, 3.190, 10.50E-3, 0.0, 4.80E-3, 1.9}, |
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233 | {55.221365, 631.60E-6, 2.620, 10.79E-3, 0.0, 4.17E-3, 2.1}, |
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234 | {55.783800, 953.50E-6, 2.115, 11.10E-3, 0.0, 3.75E-3, 2.1}, |
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235 | {56.264777, 548.90E-6, 0.010, 16.46E-3, 0.0, 7.74E-3, 0.9}, |
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236 | {56.363387, 1344.00E-6, 1.655, 11.44E-3, 0.0, 2.97E-3, 2.3}, |
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237 | {56.968180, 1763.00E-6, 1.255, 11.81E-3, 0.0, 2.12E-3, 2.5}, |
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238 | {57.612481, 2141.00E-6, 0.910, 12.21E-3, 0.0, 0.94E-3, 3.7}, |
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239 | {58.323874, 2386.00E-6, 0.621, 12.66E-3, 0.0, -0.55E-3, -3.1}, |
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240 | {58.446589, 1457.00E-6, 0.079, 14.49E-3, 0.0, 5.97E-3, 0.8}, |
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241 | {59.164204, 2404.00E-6, 0.386, 13.19E-3, 0.0, -2.44E-3, 0.1}, |
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242 | {59.590982, 2112.00E-6, 0.207, 13.60E-3, 0.0, 3.44E-3, 0.5}, |
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243 | {60.306057, 2124.00E-6, 0.207, 13.82E-3, 0.0, -4.13E-3, 0.7}, |
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244 | {60.434775, 2461.00E-6, 0.386, 12.97E-3, 0.0, 1.32E-3, -1.0}, |
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245 | {61.150558, 2504.00E-6, 0.621, 12.48E-3, 0.0, -0.36E-3, 5.8}, |
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246 | {61.800152, 2298.00E-6, 0.910, 12.07E-3, 0.0, -1.59E-3, 2.9}, |
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247 | {62.411212, 1933.00E-6, 1.255, 11.71E-3, 0.0, -2.66E-3, 2.3}, |
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248 | {62.486253, 1517.00E-6, 0.078, 14.68E-3, 0.0, -4.77E-3, 0.9}, |
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249 | {62.997974, 1503.00E-6, 1.660, 11.39E-3, 0.0, -3.34E-3, 2.2}, |
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250 | {63.568515, 1087.00E-6, 2.110, 11.08E-3, 0.0, -4.17E-3, 2.0}, |
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251 | {64.127764, 733.50E-6, 2.620, 10.78E-3, 0.0, -4.48E-3, 2.0}, |
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252 | {64.678900, 463.50E-6, 3.190, 10.50E-3, 0.0, -5.10E-3, 1.8}, |
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253 | {65.224067, 274.80E-6, 3.810, 10.20E-3, 0.0, -5.10E-3, 1.9}, |
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254 | {65.764769, 153.00E-6, 4.480, 10.00E-3, 0.0, -5.70E-3, 1.8}, |
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255 | {66.302088, 80.09E-6, 5.220, 9.70E-3, 0.0, -5.50E-3, 1.8}, |
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256 | {66.836827, 39.46E-6, 6.000, 9.40E-3, 0.0, -5.90E-3, 1.7}, |
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257 | {67.369595, 18.32E-6, 6.840, 9.20E-3, 0.0, -5.60E-3, 1.8}, |
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258 | {67.900862, 8.01E-6, 7.740, 8.90E-3, 0.0, -5.80E-3, 1.7}, |
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259 | {68.431001, 3.30E-6, 8.690, 8.70E-3, 0.0, -5.70E-3, 1.7}, |
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260 | {68.960306, 1.28E-6, 9.690, 8.60E-3, 0.0, -5.60E-3, 1.7}, |
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261 | {69.489021, 0.47E-6, 10.720, 8.50E-3, 0.0, -5.60E-3, 1.7}, |
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262 | {70.017342, 0.16E-6, 11.830, 8.40E-3, 0.0, -5.60E-3, 1.7}, |
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263 | {118.750341, 945.00E-6, 0.000, 15.92E-3, 0.0, -0.44E-3, 0.9}, |
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264 | {368.498350, 67.90E-6, 0.020, 19.20E-3, 0.6, 0.00E00, 1.0}, |
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265 | {424.763120, 638.00E-6, 0.011, 19.16E-3, 0.6, 0.00E00, 1.0}, |
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266 | {487.249370, 235.00E-6, 0.011, 19.20E-3, 0.6, 0.00E00, 1.0}, |
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267 | {715.393150, 99.60E-6, 0.089, 18.10E-3, 0.6, 0.00E00, 1.0}, |
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268 | {773.838730, 671.00E-6, 0.079, 18.10E-3, 0.6, 0.00E00, 1.0}, |
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269 | {834.145330, 180.00E-6, 0.079, 18.10E-3, 0.6, 0.00E00, 1.0}}; |
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270 | |
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271 | // convert to the units of Liebe |
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272 | const double theta = 300./temperature; |
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273 | const double kPaPVap = 0.001*pVapour; |
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274 | const double kPaPDry = 0.001*pDry; |
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275 | const double fGHz = freq * 1e-9; |
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276 | |
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277 | // some coefficients |
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278 | const double ap = 1.4e-10*(1-1.2e-5*std::pow(fGHz,1.5)); |
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279 | const double gamma0 = 5.6e-3*(kPaPDry + 1.1*kPaPVap)*std::pow(theta,0.8); |
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280 | // initial refractivity |
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281 | std::complex<double> result(2.588*kPaPDry*theta + |
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282 | 3.07e-4*(1.0/(1.0+std::pow(fGHz/gamma0,2))-1)*kPaPDry*theta*theta, |
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283 | (2*3.07e-4/(gamma0*(1+std::pow(fGHz/gamma0,2))*(1+std::pow(fGHz/60,2))) + |
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284 | ap*kPaPDry*std::pow(theta,2.5))*fGHz*kPaPDry*theta*theta); |
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285 | |
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286 | // sum the contributions of all the lines |
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287 | for (size_t l = 0; l < nLines; ++l) { |
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288 | const double S = lines[l][1]*kPaPDry*std::pow(theta,3)*exp(lines[l][2]*(1.-theta)); |
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289 | const double gamma = lines[l][3]*(kPaPDry*std::pow(theta,0.8-lines[l][4]) + 1.1*kPaPVap*theta); |
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290 | const double delta = lines[l][5]*kPaPDry*std::pow(theta,lines[l][6]); |
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291 | const double x = (lines[l][0]-fGHz)*(lines[l][0]-fGHz) + gamma*gamma; |
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292 | const double y = (lines[l][0]+fGHz)*(lines[l][0]+fGHz) + gamma*gamma; |
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293 | const double z = (lines[l][0]+gamma*gamma/lines[l][0]); |
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294 | result += std::complex<double> (S*( (z-fGHz)/x + (z+fGHz)/y - 2./lines[l][0] + |
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295 | delta*(1/x-1/y)*gamma*fGHz/lines[l][0]), |
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296 | S*( (1/x+1/y)*gamma*fGHz/lines[l][0] - |
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297 | delta*((lines[l][0]-fGHz)/x + (lines[l][0]+fGHz)/y)*fGHz/lines[l][0])); |
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298 | } |
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299 | |
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300 | return result; |
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301 | } |
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302 | |
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303 | /** |
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304 | * Compute the complex refractivity of the water vapour monomers |
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305 | * at the given frequency. |
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306 | * @param[in] freq frequency (Hz) |
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307 | * @param[in] temperature air temperature (K) |
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308 | * @param[in] pDry partial pressure of dry components (Pascals) |
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309 | * @param[in] pVapour partial pressure of water vapour (Pascals) |
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310 | * @return complex refractivity |
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311 | * |
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312 | * Reference: |
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313 | * Liebe, An updated model for millimeter wave propogation in moist air, |
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314 | * Radio Science, 20, 1069-1089 (1985). |
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315 | **/ |
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316 | std::complex<double> STAtmosphere::vapourRefractivity(double freq, double temperature, |
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317 | double pDry, double pVapour) |
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318 | { |
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319 | // the number of parameters per atmospheric line and the number of lines taken into account |
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320 | const size_t nLineParams = 4; |
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321 | const size_t nLines = 30; |
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322 | // actual tabulated values |
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323 | const double lines[nLines][nLineParams] = |
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324 | {{22.235080, 0.1090, 2.143, 27.84E-3}, |
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325 | {67.813960, 0.0011, 8.730, 27.60E-3}, |
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326 | {119.995940, 0.0007, 8.347, 27.00E-3}, |
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327 | {183.310117, 2.3000, 0.653, 28.35E-3}, |
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328 | {321.225644, 0.0464, 6.156, 21.40E-3}, |
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329 | {325.152919, 1.5400, 1.515, 27.00E-3}, |
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330 | {336.187000, 0.0010, 9.802, 26.50E-3}, |
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331 | {380.197372, 11.9000, 1.018, 27.60E-3}, |
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332 | {390.134508, 0.0044, 7.318, 19.00E-3}, |
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333 | {437.346667, 0.0637, 5.015, 13.70E-3}, |
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334 | {439.150812, 0.9210, 3.561, 16.40E-3}, |
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335 | {443.018295, 0.1940, 5.015, 14.40E-3}, |
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336 | {448.001075, 10.6000, 1.370, 23.80E-3}, |
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337 | {470.888947, 0.3300, 3.561, 18.20E-3}, |
---|
338 | {474.689127, 1.2800, 2.342, 19.80E-3}, |
---|
339 | {488.491133, 0.2530, 2.814, 24.90E-3}, |
---|
340 | {503.568532, 0.0374, 6.693, 11.50E-3}, |
---|
341 | {504.482692, 0.0125, 6.693, 11.90E-3}, |
---|
342 | {556.936002, 510.000, 0.114, 30.00E-3}, |
---|
343 | {620.700807, 5.0900, 2.150, 22.30E-3}, |
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344 | {658.006500, 0.2740, 7.767, 30.00E-3}, |
---|
345 | {752.033227, 250.000, 0.336, 28.60E-3}, |
---|
346 | {841.073593, 0.0130, 8.113, 14.10E-3}, |
---|
347 | {859.865000, 0.1330, 7.989, 28.60E-3}, |
---|
348 | {899.407000, 0.0550, 7.845, 28.60E-3}, |
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349 | {902.555000, 0.0380, 8.360, 26.40E-3}, |
---|
350 | {906.205524, 0.1830, 5.039, 23.40E-3}, |
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351 | {916.171582, 8.5600, 1.369, 25.30E-3}, |
---|
352 | {970.315022, 9.1600, 1.842, 24.00E-3}, |
---|
353 | {987.926764, 138.000, 0.178, 28.60E-3}}; |
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354 | |
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355 | // convert to the units of Liebe |
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356 | const double theta = 300./temperature; |
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357 | const double kPaPVap = 0.001*pVapour; |
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358 | const double kPaPDry = 0.001*pDry; |
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359 | const double fGHz = freq * 1e-9; |
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360 | |
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361 | // initial refractivity |
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362 | std::complex<double> result(2.39*kPaPVap*theta + 41.6*kPaPVap*theta*theta + |
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363 | 6.47e-6*std::pow(fGHz,2.05)*kPaPVap*std::pow(theta,2.4), |
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364 | (0.915*1.40e-6*kPaPDry + 5.41e-5*kPaPVap*theta*theta*theta)* |
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365 | fGHz*kPaPVap*std::pow(theta,2.5)); |
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366 | |
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367 | // sum contributions of all the lines |
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368 | for (size_t l = 0; l < nLines; ++l) { |
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369 | const double S = lines[l][1]*kPaPVap*std::pow(theta,3.5)*exp(lines[l][2]*(1.-theta)); |
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370 | const double gamma = lines[l][3]*(kPaPDry*std::pow(theta,0.8) + 4.80*kPaPVap*theta); |
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371 | const double x = (lines[l][0]-fGHz)*(lines[l][0]-fGHz) + gamma*gamma; |
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372 | const double y = (lines[l][0]+fGHz)*(lines[l][0]+fGHz) + gamma*gamma; |
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373 | const double z = (lines[l][0]+gamma*gamma/lines[l][0]); |
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374 | result += std::complex<double>(S*((z-fGHz)/x + (z+fGHz)/y - 2./lines[l][0]), |
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375 | S*((1./x+1./y)*gamma*fGHz/lines[l][0])); |
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376 | } |
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377 | |
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378 | return result; |
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379 | } |
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380 | |
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381 | /** |
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382 | * Calculate zenith opacity at the given frequency. This is a simplified version |
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383 | * of the routine implemented in MIRIAD, which calculates just zenith opacity and |
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384 | * nothing else. Note, that if the opacity is high, 1/sin(el) law is not correct |
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385 | * even in the plane parallel case due to refraction. |
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386 | * @param[in] freq frequency of interest in Hz |
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387 | * @return zenith opacity (nepers, i.e. dimensionless) |
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388 | **/ |
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389 | double STAtmosphere::zenithOpacity(double freq) const |
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390 | { |
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391 | // essentially a numerical integration with the Trapezium method |
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392 | double tau = 0.; |
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393 | for (int layer = int(nLayers()) - 1; layer>=0; --layer) { |
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394 | double dH = 0.; |
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395 | if (layer == 0) { |
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396 | dH = 0.5*(itsHeights[1]-itsHeights[0]); |
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397 | } else if (layer + 1 == int(nLayers())) { |
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398 | dH = 0.5*(itsHeights[nLayers()-1]-itsHeights[nLayers()-2]); |
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399 | } else { |
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400 | dH = 0.5*(itsHeights[layer+1]-itsHeights[layer-1]); |
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401 | } |
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402 | // imaginary part of the total complex refractivity |
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403 | const double nImag = 1e-6*std::imag(dryRefractivity(freq,itsTemperatures[layer],itsDryPressures[layer], |
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404 | itsVapourPressures[layer])+vapourRefractivity(freq,itsTemperatures[layer],itsDryPressures[layer], |
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405 | itsVapourPressures[layer])); |
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406 | tau += dH*4.*casa::C::pi/QC::c.get().getValue()*freq*nImag; |
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407 | } |
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408 | return tau; |
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409 | } |
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410 | |
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411 | /** |
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412 | * Calculate zenith opacity for the range of frequencies. Same as zenithOpacity, but |
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413 | * for a vector of frequencies. |
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414 | * @param[in] freqs vector of frequencies in Hz |
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415 | * @return vector of zenith opacities, one value per frequency (nepers, i.e. dimensionless) |
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416 | **/ |
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417 | std::vector<double> STAtmosphere::zenithOpacities(const std::vector<double> &freqs) const |
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418 | { |
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419 | std::vector<double> result(freqs.size()); |
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420 | for (size_t ch = 0; ch<freqs.size(); ++ch) { |
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421 | result[ch] = zenithOpacity(freqs[ch]); |
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422 | } |
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423 | return result; |
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424 | } |
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425 | |
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426 | /** |
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427 | * Calculate opacity at the given frequency and elevation. This is a simplified |
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428 | * version of the routine implemented in MIRIAD, which calculates just the opacity and |
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429 | * nothing else. In contract to zenithOpacity, this method takes into account refraction |
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430 | * and is more accurate than if one assumes 1/sin(el) factor. |
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431 | * @param[in] freq frequency of interest in Hz |
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432 | * @param[in] el elevation in radians |
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433 | * @return zenith opacity (nepers, i.e. dimensionless) |
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434 | **/ |
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435 | double STAtmosphere::opacity(double freq, double el) const |
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436 | { |
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437 | // essentially a numerical integration with the Trapezium method |
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438 | double tau = 0.; |
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439 | const double sineEl = sin(el); |
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440 | for (int layer = int(nLayers()) - 1; layer>=0; --layer) { |
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441 | double dH = 0.; |
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442 | if (layer == 0) { |
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443 | dH = 0.5*(itsHeights[1]-itsHeights[0]); |
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444 | } else if (layer + 1 == int(nLayers())) { |
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445 | dH = 0.5*(itsHeights[nLayers()-1]-itsHeights[nLayers()-2]); |
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446 | } else { |
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447 | dH = 0.5*(itsHeights[layer+1]-itsHeights[layer-1]); |
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448 | } |
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449 | // total complex refractivity |
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450 | const std::complex<double> n = dryRefractivity(freq,itsTemperatures[layer],itsDryPressures[layer], |
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451 | itsVapourPressures[layer]) + |
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452 | vapourRefractivity(freq,itsTemperatures[layer],itsDryPressures[layer], |
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453 | itsVapourPressures[layer]); |
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454 | // real and imaginary part of the total complex refractivity scaled appropriately |
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455 | const double nImag = 1e-6*std::imag(n); |
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456 | const double nReal = 1. + 1e-6*std::real(n); |
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457 | // length increment |
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458 | const double dL = dH*nReal/sqrt(nReal*nReal+sineEl*sineEl-1.); |
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459 | tau += dL*4.*casa::C::pi/QC::c.get().getValue()*freq*nImag; |
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460 | } |
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461 | return tau; |
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462 | } |
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463 | |
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464 | /** |
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465 | * Calculate opacities for the range of frequencies at the given elevation. Same as |
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466 | * opacity, but for a vector of frequencies. |
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467 | * @param[in] freqs vector of frequencies in Hz |
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468 | * @param[in] el elevation in radians |
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469 | * @return vector of opacities, one value per frequency (nepers, i.e. dimensionless) |
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470 | **/ |
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471 | std::vector<double> STAtmosphere::opacities(const std::vector<double> &freqs, double el) const |
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472 | { |
---|
473 | std::vector<double> result(freqs.size()); |
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474 | for (size_t ch = 0; ch<freqs.size(); ++ch) { |
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475 | result[ch] = opacity(freqs[ch],el); |
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476 | } |
---|
477 | return result; |
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478 | } |
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479 | |
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