[1757] | 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}, |
---|
| 326 | {119.995940, 0.0007, 8.347, 27.00E-3}, |
---|
| 327 | {183.310117, 2.3000, 0.653, 28.35E-3}, |
---|
| 328 | {321.225644, 0.0464, 6.156, 21.40E-3}, |
---|
| 329 | {325.152919, 1.5400, 1.515, 27.00E-3}, |
---|
| 330 | {336.187000, 0.0010, 9.802, 26.50E-3}, |
---|
| 331 | {380.197372, 11.9000, 1.018, 27.60E-3}, |
---|
| 332 | {390.134508, 0.0044, 7.318, 19.00E-3}, |
---|
| 333 | {437.346667, 0.0637, 5.015, 13.70E-3}, |
---|
| 334 | {439.150812, 0.9210, 3.561, 16.40E-3}, |
---|
| 335 | {443.018295, 0.1940, 5.015, 14.40E-3}, |
---|
| 336 | {448.001075, 10.6000, 1.370, 23.80E-3}, |
---|
| 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}, |
---|
| 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}, |
---|
| 349 | {902.555000, 0.0380, 8.360, 26.40E-3}, |
---|
| 350 | {906.205524, 0.1830, 5.039, 23.40E-3}, |
---|
| 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 |
---|
| 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 | } |
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| 477 | return result; |
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| 478 | } |
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| 479 | |
---|