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 sea level if the observatory elevation |
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92 | * is set to non-zero value (note, by default is set to 200m) or at the |
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93 | * observatory ground level if the elevation is set to 0. (The value is in Pascals) |
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94 | * @param[in] pressure air pressure at the observatory (Pascals) |
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95 | * @param[in] humidity air humidity at the observatory (fraction) |
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96 | * @param[in] lapseRate temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA |
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97 | * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model |
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98 | * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to |
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99 | * this height, default is 10000m to match MIRIAD. |
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100 | * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration), |
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101 | * default is 50 to match MIRIAD. |
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102 | **/ |
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103 | STAtmosphere(double temperature, double pressure, double humidity, double lapseRate = 0.0065, |
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104 | double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50); |
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105 | |
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106 | /** |
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107 | * Set the new weather station data, recompute the model |
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108 | * @param[in] temperature air temperature at the observatory (K) |
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109 | * @param[in] pressure air pressure at the sea level if the observatory elevation |
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110 | * is set to non-zero value (note, by default is set to 200m) or at the |
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111 | * observatory ground level if the elevation is set to 0. (The value is in Pascals) |
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112 | * @param[in] humidity air humidity at the observatory (fraction) |
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113 | **/ |
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114 | void setWeather(double temperature, double pressure, double humidity); |
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115 | |
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116 | /** |
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117 | * Set the elevation of the observatory (height above mean sea level) |
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118 | * |
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119 | * The observatory elevation affects only interpretation of the pressure supplied as part |
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120 | * of the weather data, if this value is non-zero, the pressure (e.g. in setWeather or |
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121 | * constructor) is that at mean sea level. If the observatory elevation is set to zero, |
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122 | * regardless on real elevation, the pressure is that at the observatory ground level. |
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123 | * |
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124 | * By default, 200m is assumed. |
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125 | * @param[in] elev elevation in metres |
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126 | **/ |
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127 | void setObservatoryElevation(double elev); |
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128 | |
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129 | /** |
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130 | * Calculate zenith opacity at the given frequency. This is a simplified version |
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131 | * of the routine implemented in MIRIAD, which calculates just zenith opacity and |
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132 | * nothing else. Note, that if the opacity is high, 1/sin(el) law is not correct |
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133 | * even in the plane parallel case due to refraction. |
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134 | * @param[in] freq frequency of interest in Hz |
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135 | * @return zenith opacity (nepers, i.e. dimensionless) |
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136 | **/ |
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137 | double zenithOpacity(double freq) const; |
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138 | |
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139 | /** |
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140 | * Calculate zenith opacity for the range of frequencies. Same as zenithOpacity, but |
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141 | * for a vector of frequencies. |
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142 | * @param[in] freqs vector of frequencies in Hz |
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143 | * @return vector of zenith opacities, one value per frequency (nepers, i.e. dimensionless) |
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144 | **/ |
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145 | std::vector<double> zenithOpacities(const std::vector<double> &freqs) const; |
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146 | |
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147 | /** |
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148 | * Calculate opacity at the given frequency and elevation. This is a simplified |
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149 | * version of the routine implemented in MIRIAD, which calculates just the opacity and |
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150 | * nothing else. In contract to zenithOpacity, this method takes into account refraction |
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151 | * and is more accurate than if one assumes 1/sin(el) factor. |
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152 | * @param[in] freq frequency of interest in Hz |
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153 | * @param[in] el elevation in radians |
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154 | * @return zenith opacity (nepers, i.e. dimensionless) |
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155 | **/ |
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156 | double opacity(double freq, double el) const; |
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157 | |
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158 | /** |
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159 | * Calculate opacities for the range of frequencies at the given elevation. Same as |
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160 | * opacity, but for a vector of frequencies. |
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161 | * @param[in] freqs vector of frequencies in Hz |
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162 | * @param[in] el elevation in radians |
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163 | * @return vector of opacities, one value per frequency (nepers, i.e. dimensionless) |
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164 | **/ |
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165 | std::vector<double> opacities(const std::vector<double> &freqs, double el) const; |
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166 | |
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167 | protected: |
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168 | /** |
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169 | * Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic |
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170 | * equilibrium. The model parameters are taken from the data members of this class. |
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171 | **/ |
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172 | void recomputeAtmosphereModel(); |
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173 | |
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174 | /** |
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175 | * Obtain the number of model layers, do consistency check that everything is |
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176 | * resized accordingly |
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177 | * @retrun number of model layers |
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178 | **/ |
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179 | size_t nLayers() const; |
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180 | |
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181 | /** |
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182 | * Determine the saturation pressure of water vapour for the given temperature. |
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183 | * |
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184 | * Reference: |
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185 | * Waters, Refraction effects in the neutral atmosphere. Methods of |
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186 | * Experimental Physics, vol 12B, p 186-200 (1976). |
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187 | * |
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188 | * @param[in] temperature temperature in K |
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189 | * @return vapour saturation pressure (Pascals) |
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190 | **/ |
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191 | static double wvSaturationPressure(double temperature); |
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192 | |
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193 | /** |
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194 | * Compute the complex refractivity of the dry components of the atmosphere |
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195 | * (oxygen lines) at the given frequency. |
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196 | * @param[in] freq frequency (Hz) |
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197 | * @param[in] temperature air temperature (K) |
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198 | * @param[in] pDry partial pressure of dry components (Pascals) |
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199 | * @param[in] pVapour partial pressure of water vapour (Pascals) |
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200 | * @return complex refractivity |
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201 | * |
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202 | * Reference: |
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203 | * Liebe, An updated model for millimeter wave propogation in moist air, |
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204 | * Radio Science, 20, 1069-1089 (1985). |
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205 | **/ |
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206 | static std::complex<double> dryRefractivity(double freq, double temperature, |
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207 | double pDry, double pVapour); |
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208 | |
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209 | /** |
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210 | * Compute the complex refractivity of the water vapour monomers |
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211 | * at the given frequency. |
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212 | * @param[in] freq frequency (Hz) |
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213 | * @param[in] temperature air temperature (K) |
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214 | * @param[in] pDry partial pressure of dry components (Pascals) |
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215 | * @param[in] pVapour partial pressure of water vapour (Pascals) |
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216 | * @return complex refractivity |
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217 | * |
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218 | * Reference: |
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219 | * Liebe, An updated model for millimeter wave propogation in moist air, |
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220 | * Radio Science, 20, 1069-1089 (1985). |
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221 | **/ |
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222 | static std::complex<double> vapourRefractivity(double freq, double temperature, |
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223 | double pDry, double pVapour); |
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224 | |
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225 | private: |
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226 | |
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227 | // heights of all model layers |
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228 | std::vector<double> itsHeights; |
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229 | |
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230 | // temperatures of all model layers |
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231 | std::vector<double> itsTemperatures; |
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232 | |
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233 | // partial pressures of dry component for all model layers |
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234 | std::vector<double> itsDryPressures; |
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235 | |
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236 | // partial pressure of water vapour for all model layers |
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237 | std::vector<double> itsVapourPressures; |
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238 | |
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239 | /** |
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240 | * Atmosphere parameters |
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241 | **/ |
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242 | |
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243 | // ground level temperature (K) |
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244 | double itsGndTemperature; |
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245 | |
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246 | // sea level pressure (Pascals) |
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247 | double itsPressure; |
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248 | |
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249 | // ground level humidity (fraction) |
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250 | double itsGndHumidity; |
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251 | |
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252 | // lapse rate (K/m) |
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253 | double itsLapseRate; |
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254 | |
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255 | // water vapour scale height (m) |
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256 | double itsWVScale; |
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257 | |
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258 | // altitude of the highest layer of the model (m) |
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259 | double itsMaxAlt; |
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260 | |
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261 | // observatory elevation (m) |
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262 | double itsObsHeight; |
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263 | }; |
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264 | |
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265 | } // namespace asap |
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266 | |
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267 | #endif // #ifndef STATMOSPHERE_H |
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268 | |
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