source: trunk/src/STAtmosphere.h@ 1711

Last change on this file since 1711 was 1711, checked in by Max Voronkov, 15 years ago

added model of water vapour refractivity

File size: 8.1 KB
Line 
1//#---------------------------------------------------------------------------
2//# STAtmosphere.h: Model of atmospheric opacity
3//#---------------------------------------------------------------------------
4//# Copyright (C) 2004
5//# ATNF
6//#
7//# The code is based on the Fortran code written by Bob Sault for MIRIAD.
8//# Converted to C++ by Max Voronkov. This code uses a simple model of the
9//# atmosphere and Liebe's model (1985) of the complex refractive index of
10//# air.
11//#
12//# The model of the atmosphere is one with an exponential fall-off in
13//# the water vapour content (scale height of 1540 m) and a temperature lapse
14//# rate of 6.5 mK/m. Otherwise the atmosphere obeys the ideal gas equation
15//# and hydrostatic equilibrium.
16//#
17//# This program is free software; you can redistribute it and/or modify it
18//# under the terms of the GNU General Public License as published by the Free
19//# Software Foundation; either version 2 of the License, or (at your option)
20//# any later version.
21//#
22//# This program is distributed in the hope that it will be useful, but
23//# WITHOUT ANY WARRANTY; without even the implied warranty of
24//# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
25//# Public License for more details.
26//#
27//# You should have received a copy of the GNU General Public License along
28//# with this program; if not, write to the Free Software Foundation, Inc.,
29//# 675 Massachusetts Ave, Cambridge, MA 02139, USA.
30//#
31//# Correspondence concerning this software should be addressed as follows:
32//# Internet email: Malte.Marquarding@csiro.au
33//# Postal address: Malte Marquarding,
34//# Australia Telescope National Facility,
35//# P.O. Box 76,
36//# Epping, NSW, 2121,
37//# AUSTRALIA
38//#
39//# $Id: STAtmosphere.h 1346 2007-04-26 03:24:41Z mar637 $
40//#---------------------------------------------------------------------------
41
42#ifndef STATMOSPHERE_H
43#define STATMOSPHERE_H
44
45// std includes
46#include <vector>
47#include <complex>
48
49namespace asap {
50
51/**
52 * This class implements opacity/atmospheric brightness temperature model
53 * equivalent to the model available in MIRIAD. The actual math is a
54 * convertion of the Fortran code written by Bob Sault for MIRIAD.
55 * It implements a simple model of the atmosphere and Liebe's model (1985)
56 * of the complex refractive index of air.
57 *
58 * The model of the atmosphere is one with an exponential fall-off in
59 * the water vapour content (scale height of 1540 m) and a temperature lapse
60 * rate of 6.5 mK/m. Otherwise the atmosphere obeys the ideal gas equation
61 * and hydrostatic equilibrium.
62 *
63 * Note, the model includes atmospheric lines up to 800 GHz, but was not
64 * rigorously tested above 100 GHz and for instruments located at
65 * a significant elevation. For high-elevation sites it may be necessary to
66 * adjust scale height and lapse rate.
67 *
68 * @brief The ASAP atmosphere opacity model
69 * @author Max Voronkov
70 * @date $Date: 2010-03-17 14:55:17 +1000 (Thu, 26 Apr 2007) $
71 * @version
72 */
73class STAtmosphere {
74public:
75 /**
76 * Default Constructor (apart from optional parameters).
77 * The class set up this way will assume International Standard Atmosphere (ISA) conditions,
78 * except for humidity. The latter is assumed to be 50%, which seems more realistic for
79 * Australian telescopes than 0%.
80 * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model
81 * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to
82 * this height, default is 10000m to match MIRIAD.
83 * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration),
84 * default is 50 to match MIRIAD.
85 **/
86 explicit STAtmosphere(double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50);
87
88 /**
89 * Constructor with explicitly given parameters of the atmosphere
90 * @param[in] temperature air temperature at the observatory (K)
91 * @param[in] pressure air pressure at the observatory (Pascals)
92 * @param[in] humidity air humidity at the observatory (fraction)
93 * @param[in] lapseRate temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA
94 * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model
95 * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to
96 * this height, default is 10000m to match MIRIAD.
97 * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration),
98 * default is 50 to match MIRIAD.
99 **/
100 STAtmosphere(double temperature, double pressure, double humidity, double lapseRate = 0.0065,
101 double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50);
102
103 /**
104 * Set the new weather station data, recompute the model
105 * @param[in] temperature air temperature at the observatory (K)
106 * @param[in] pressure air pressure at the observatory (Pascals)
107 * @param[in] humidity air humidity at the observatory (fraction)
108 **/
109 void setWeather(double temperature, double pressure, double humidity);
110
111protected:
112 /**
113 * Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic
114 * equilibrium. The model parameters are taken from the data members of this class.
115 **/
116 void recomputeAtmosphereModel();
117
118 /**
119 * Obtain the number of model layers, do consistency check that everything is
120 * resized accordingly
121 * @retrun number of model layers
122 **/
123 size_t nLayers() const;
124
125 /**
126 * Determine the saturation pressure of water vapour for the given temperature.
127 *
128 * Reference:
129 * Waters, Refraction effects in the neutral atmosphere. Methods of
130 * Experimental Physics, vol 12B, p 186-200 (1976).
131 *
132 * @param[in] temperature temperature in K
133 * @return vapour saturation pressure (Pascals)
134 **/
135 static double wvSaturationPressure(double temperature);
136
137 /**
138 * Compute the complex refractivity of the dry components of the atmosphere
139 * (oxygen lines) at the given frequency.
140 * @param[in] freq frequency (Hz)
141 * @param[in] temperature air temperature (K)
142 * @param[in] pDry partial pressure of dry components (Pascals)
143 * @param[in] pVapour partial pressure of water vapour (Pascals)
144 * @return complex refractivity
145 *
146 * Reference:
147 * Liebe, An updated model for millimeter wave propogation in moist air,
148 * Radio Science, 20, 1069-1089 (1985).
149 **/
150 static std::complex<double> dryRefractivity(double freq, double temperature,
151 double pDry, double pVapour);
152
153 /**
154 * Compute the complex refractivity of the water vapour monomers
155 * at the given frequency.
156 * @param[in] freq frequency (Hz)
157 * @param[in] temperature air temperature (K)
158 * @param[in] pDry partial pressure of dry components (Pascals)
159 * @param[in] pVapour partial pressure of water vapour (Pascals)
160 * @return complex refractivity
161 *
162 * Reference:
163 * Liebe, An updated model for millimeter wave propogation in moist air,
164 * Radio Science, 20, 1069-1089 (1985).
165 **/
166 static std::complex<double> vapourRefractivity(double freq, double temperature,
167 double pDry, double pVapour);
168
169private:
170
171 // heights of all model layers
172 std::vector<double> itsHeights;
173
174 // temperatures of all model layers
175 std::vector<double> itsTemperatures;
176
177 // partial pressures of dry component for all model layers
178 std::vector<double> itsDryPressures;
179
180 // partial pressure of water vapour for all model layers
181 std::vector<double> itsVapourPressures;
182
183 /**
184 * Atmosphere parameters
185 **/
186
187 // ground level temperature (K)
188 double itsGndTemperature;
189
190 // ground level pressure (Pascals)
191 double itsGndPressure;
192
193 // ground level humidity (fraction)
194 double itsGndHumidity;
195
196 // lapse rate (K/m)
197 double itsLapseRate;
198
199 // water vapour scale height (m)
200 double itsWVScale;
201
202 // altitude of the highest layer of the model (m)
203 double itsMaxAlt;
204};
205
206} // namespace asap
207
208#endif // #ifndef STATMOSPHERE_H
209
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