source: branches/asap-3.x/src/STAtmosphere.h@ 2607

Last change on this file since 2607 was 1718, checked in by Max Voronkov, 15 years ago

updated documentation to reflect better interpretation of the pressure

File size: 10.9 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 sea level if the observatory elevation
92 * is set to non-zero value (note, by default is set to 200m) or at the
93 * observatory ground level if the elevation is set to 0. (The value is in Pascals)
94 * @param[in] pressure air pressure at the observatory (Pascals)
95 * @param[in] humidity air humidity at the observatory (fraction)
96 * @param[in] lapseRate temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA
97 * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model
98 * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to
99 * this height, default is 10000m to match MIRIAD.
100 * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration),
101 * default is 50 to match MIRIAD.
102 **/
103 STAtmosphere(double temperature, double pressure, double humidity, double lapseRate = 0.0065,
104 double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50);
105
106 /**
107 * Set the new weather station data, recompute the model
108 * @param[in] temperature air temperature at the observatory (K)
109 * @param[in] pressure air pressure at the sea level if the observatory elevation
110 * is set to non-zero value (note, by default is set to 200m) or at the
111 * observatory ground level if the elevation is set to 0. (The value is in Pascals)
112 * @param[in] humidity air humidity at the observatory (fraction)
113 **/
114 void setWeather(double temperature, double pressure, double humidity);
115
116 /**
117 * Set the elevation of the observatory (height above mean sea level)
118 *
119 * The observatory elevation affects only interpretation of the pressure supplied as part
120 * of the weather data, if this value is non-zero, the pressure (e.g. in setWeather or
121 * constructor) is that at mean sea level. If the observatory elevation is set to zero,
122 * regardless on real elevation, the pressure is that at the observatory ground level.
123 *
124 * By default, 200m is assumed.
125 * @param[in] elev elevation in metres
126 **/
127 void setObservatoryElevation(double elev);
128
129 /**
130 * Calculate zenith opacity at the given frequency. This is a simplified version
131 * of the routine implemented in MIRIAD, which calculates just zenith opacity and
132 * nothing else. Note, that if the opacity is high, 1/sin(el) law is not correct
133 * even in the plane parallel case due to refraction.
134 * @param[in] freq frequency of interest in Hz
135 * @return zenith opacity (nepers, i.e. dimensionless)
136 **/
137 double zenithOpacity(double freq) const;
138
139 /**
140 * Calculate zenith opacity for the range of frequencies. Same as zenithOpacity, but
141 * for a vector of frequencies.
142 * @param[in] freqs vector of frequencies in Hz
143 * @return vector of zenith opacities, one value per frequency (nepers, i.e. dimensionless)
144 **/
145 std::vector<double> zenithOpacities(const std::vector<double> &freqs) const;
146
147 /**
148 * Calculate opacity at the given frequency and elevation. This is a simplified
149 * version of the routine implemented in MIRIAD, which calculates just the opacity and
150 * nothing else. In contract to zenithOpacity, this method takes into account refraction
151 * and is more accurate than if one assumes 1/sin(el) factor.
152 * @param[in] freq frequency of interest in Hz
153 * @param[in] el elevation in radians
154 * @return zenith opacity (nepers, i.e. dimensionless)
155 **/
156 double opacity(double freq, double el) const;
157
158 /**
159 * Calculate opacities for the range of frequencies at the given elevation. Same as
160 * opacity, but for a vector of frequencies.
161 * @param[in] freqs vector of frequencies in Hz
162 * @param[in] el elevation in radians
163 * @return vector of opacities, one value per frequency (nepers, i.e. dimensionless)
164 **/
165 std::vector<double> opacities(const std::vector<double> &freqs, double el) const;
166
167protected:
168 /**
169 * Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic
170 * equilibrium. The model parameters are taken from the data members of this class.
171 **/
172 void recomputeAtmosphereModel();
173
174 /**
175 * Obtain the number of model layers, do consistency check that everything is
176 * resized accordingly
177 * @retrun number of model layers
178 **/
179 size_t nLayers() const;
180
181 /**
182 * Determine the saturation pressure of water vapour for the given temperature.
183 *
184 * Reference:
185 * Waters, Refraction effects in the neutral atmosphere. Methods of
186 * Experimental Physics, vol 12B, p 186-200 (1976).
187 *
188 * @param[in] temperature temperature in K
189 * @return vapour saturation pressure (Pascals)
190 **/
191 static double wvSaturationPressure(double temperature);
192
193 /**
194 * Compute the complex refractivity of the dry components of the atmosphere
195 * (oxygen lines) at the given frequency.
196 * @param[in] freq frequency (Hz)
197 * @param[in] temperature air temperature (K)
198 * @param[in] pDry partial pressure of dry components (Pascals)
199 * @param[in] pVapour partial pressure of water vapour (Pascals)
200 * @return complex refractivity
201 *
202 * Reference:
203 * Liebe, An updated model for millimeter wave propogation in moist air,
204 * Radio Science, 20, 1069-1089 (1985).
205 **/
206 static std::complex<double> dryRefractivity(double freq, double temperature,
207 double pDry, double pVapour);
208
209 /**
210 * Compute the complex refractivity of the water vapour monomers
211 * at the given frequency.
212 * @param[in] freq frequency (Hz)
213 * @param[in] temperature air temperature (K)
214 * @param[in] pDry partial pressure of dry components (Pascals)
215 * @param[in] pVapour partial pressure of water vapour (Pascals)
216 * @return complex refractivity
217 *
218 * Reference:
219 * Liebe, An updated model for millimeter wave propogation in moist air,
220 * Radio Science, 20, 1069-1089 (1985).
221 **/
222 static std::complex<double> vapourRefractivity(double freq, double temperature,
223 double pDry, double pVapour);
224
225private:
226
227 // heights of all model layers
228 std::vector<double> itsHeights;
229
230 // temperatures of all model layers
231 std::vector<double> itsTemperatures;
232
233 // partial pressures of dry component for all model layers
234 std::vector<double> itsDryPressures;
235
236 // partial pressure of water vapour for all model layers
237 std::vector<double> itsVapourPressures;
238
239 /**
240 * Atmosphere parameters
241 **/
242
243 // ground level temperature (K)
244 double itsGndTemperature;
245
246 // sea level pressure (Pascals)
247 double itsPressure;
248
249 // ground level humidity (fraction)
250 double itsGndHumidity;
251
252 // lapse rate (K/m)
253 double itsLapseRate;
254
255 // water vapour scale height (m)
256 double itsWVScale;
257
258 // altitude of the highest layer of the model (m)
259 double itsMaxAlt;
260
261 // observatory elevation (m)
262 double itsObsHeight;
263};
264
265} // namespace asap
266
267#endif // #ifndef STATMOSPHERE_H
268
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