//#--------------------------------------------------------------------------- //# STAtmosphere.h: Model of atmospheric opacity //#--------------------------------------------------------------------------- //# Copyright (C) 2004 //# ATNF //# //# The code is based on the Fortran code written by Bob Sault for MIRIAD. //# Converted to C++ by Max Voronkov. This code uses a simple model of the //# atmosphere and Liebe's model (1985) of the complex refractive index of //# air. //# //# The model of the atmosphere is one with an exponential fall-off in //# the water vapour content (scale height of 1540 m) and a temperature lapse //# rate of 6.5 mK/m. Otherwise the atmosphere obeys the ideal gas equation //# and hydrostatic equilibrium. //# //# This program is free software; you can redistribute it and/or modify it //# under the terms of the GNU General Public License as published by the Free //# Software Foundation; either version 2 of the License, or (at your option) //# any later version. //# //# This program is distributed in the hope that it will be useful, but //# WITHOUT ANY WARRANTY; without even the implied warranty of //# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General //# Public License for more details. //# //# You should have received a copy of the GNU General Public License along //# with this program; if not, write to the Free Software Foundation, Inc., //# 675 Massachusetts Ave, Cambridge, MA 02139, USA. //# //# Correspondence concerning this software should be addressed as follows: //# Internet email: Malte.Marquarding@csiro.au //# Postal address: Malte Marquarding, //# Australia Telescope National Facility, //# P.O. Box 76, //# Epping, NSW, 2121, //# AUSTRALIA //# //# $Id: STAtmosphere.h 1346 2007-04-26 03:24:41Z mar637 $ //#--------------------------------------------------------------------------- #ifndef STATMOSPHERE_H #define STATMOSPHERE_H // std includes #include #include namespace asap { /** * This class implements opacity/atmospheric brightness temperature model * equivalent to the model available in MIRIAD. The actual math is a * convertion of the Fortran code written by Bob Sault for MIRIAD. * It implements a simple model of the atmosphere and Liebe's model (1985) * of the complex refractive index of air. * * The model of the atmosphere is one with an exponential fall-off in * the water vapour content (scale height of 1540 m) and a temperature lapse * rate of 6.5 mK/m. Otherwise the atmosphere obeys the ideal gas equation * and hydrostatic equilibrium. * * Note, the model includes atmospheric lines up to 800 GHz, but was not * rigorously tested above 100 GHz and for instruments located at * a significant elevation. For high-elevation sites it may be necessary to * adjust scale height and lapse rate. * * @brief The ASAP atmosphere opacity model * @author Max Voronkov * @date $Date: 2010-03-17 14:55:17 +1000 (Thu, 26 Apr 2007) $ * @version */ class STAtmosphere { public: /** * Default Constructor (apart from optional parameters). * The class set up this way will assume International Standard Atmosphere (ISA) conditions, * except for humidity. The latter is assumed to be 50%, which seems more realistic for * Australian telescopes than 0%. * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to * this height, default is 10000m to match MIRIAD. * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration), * default is 50 to match MIRIAD. **/ explicit STAtmosphere(double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50); /** * Constructor with explicitly given parameters of the atmosphere * @param[in] temperature air temperature at the observatory (K) * @param[in] pressure air pressure at the sea level if the observatory elevation * is set to non-zero value (note, by default is set to 200m) or at the * observatory ground level if the elevation is set to 0. (The value is in Pascals) * @param[in] pressure air pressure at the observatory (Pascals) * @param[in] humidity air humidity at the observatory (fraction) * @param[in] lapseRate temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA * @param[in] wvScale water vapour scale height (m), default is 1540m to match MIRIAD's model * @param[in] maxAlt maximum altitude of the model atmosphere (m), plane parallel layers are spread linearly up to * this height, default is 10000m to match MIRIAD. * @param[in] nLayers number of plane parallel layers in the model (essentially for a numberical integration), * default is 50 to match MIRIAD. **/ STAtmosphere(double temperature, double pressure, double humidity, double lapseRate = 0.0065, double wvScale = 1540., double maxAlt = 10000.0, size_t nLayers = 50); /** * Set the new weather station data, recompute the model * @param[in] temperature air temperature at the observatory (K) * @param[in] pressure air pressure at the sea level if the observatory elevation * is set to non-zero value (note, by default is set to 200m) or at the * observatory ground level if the elevation is set to 0. (The value is in Pascals) * @param[in] humidity air humidity at the observatory (fraction) **/ void setWeather(double temperature, double pressure, double humidity); /** * Set the elevation of the observatory (height above mean sea level) * * The observatory elevation affects only interpretation of the pressure supplied as part * of the weather data, if this value is non-zero, the pressure (e.g. in setWeather or * constructor) is that at mean sea level. If the observatory elevation is set to zero, * regardless on real elevation, the pressure is that at the observatory ground level. * * By default, 200m is assumed. * @param[in] elev elevation in metres **/ void setObservatoryElevation(double elev); /** * Calculate zenith opacity at the given frequency. This is a simplified version * of the routine implemented in MIRIAD, which calculates just zenith opacity and * nothing else. Note, that if the opacity is high, 1/sin(el) law is not correct * even in the plane parallel case due to refraction. * @param[in] freq frequency of interest in Hz * @return zenith opacity (nepers, i.e. dimensionless) **/ double zenithOpacity(double freq) const; /** * Calculate zenith opacity for the range of frequencies. Same as zenithOpacity, but * for a vector of frequencies. * @param[in] freqs vector of frequencies in Hz * @return vector of zenith opacities, one value per frequency (nepers, i.e. dimensionless) **/ std::vector zenithOpacities(const std::vector &freqs) const; /** * Calculate opacity at the given frequency and elevation. This is a simplified * version of the routine implemented in MIRIAD, which calculates just the opacity and * nothing else. In contract to zenithOpacity, this method takes into account refraction * and is more accurate than if one assumes 1/sin(el) factor. * @param[in] freq frequency of interest in Hz * @param[in] el elevation in radians * @return zenith opacity (nepers, i.e. dimensionless) **/ double opacity(double freq, double el) const; /** * Calculate opacities for the range of frequencies at the given elevation. Same as * opacity, but for a vector of frequencies. * @param[in] freqs vector of frequencies in Hz * @param[in] el elevation in radians * @return vector of opacities, one value per frequency (nepers, i.e. dimensionless) **/ std::vector opacities(const std::vector &freqs, double el) const; protected: /** * Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic * equilibrium. The model parameters are taken from the data members of this class. **/ void recomputeAtmosphereModel(); /** * Obtain the number of model layers, do consistency check that everything is * resized accordingly * @retrun number of model layers **/ size_t nLayers() const; /** * Determine the saturation pressure of water vapour for the given temperature. * * Reference: * Waters, Refraction effects in the neutral atmosphere. Methods of * Experimental Physics, vol 12B, p 186-200 (1976). * * @param[in] temperature temperature in K * @return vapour saturation pressure (Pascals) **/ static double wvSaturationPressure(double temperature); /** * Compute the complex refractivity of the dry components of the atmosphere * (oxygen lines) at the given frequency. * @param[in] freq frequency (Hz) * @param[in] temperature air temperature (K) * @param[in] pDry partial pressure of dry components (Pascals) * @param[in] pVapour partial pressure of water vapour (Pascals) * @return complex refractivity * * Reference: * Liebe, An updated model for millimeter wave propogation in moist air, * Radio Science, 20, 1069-1089 (1985). **/ static std::complex dryRefractivity(double freq, double temperature, double pDry, double pVapour); /** * Compute the complex refractivity of the water vapour monomers * at the given frequency. * @param[in] freq frequency (Hz) * @param[in] temperature air temperature (K) * @param[in] pDry partial pressure of dry components (Pascals) * @param[in] pVapour partial pressure of water vapour (Pascals) * @return complex refractivity * * Reference: * Liebe, An updated model for millimeter wave propogation in moist air, * Radio Science, 20, 1069-1089 (1985). **/ static std::complex vapourRefractivity(double freq, double temperature, double pDry, double pVapour); private: // heights of all model layers std::vector itsHeights; // temperatures of all model layers std::vector itsTemperatures; // partial pressures of dry component for all model layers std::vector itsDryPressures; // partial pressure of water vapour for all model layers std::vector itsVapourPressures; /** * Atmosphere parameters **/ // ground level temperature (K) double itsGndTemperature; // sea level pressure (Pascals) double itsPressure; // ground level humidity (fraction) double itsGndHumidity; // lapse rate (K/m) double itsLapseRate; // water vapour scale height (m) double itsWVScale; // altitude of the highest layer of the model (m) double itsMaxAlt; // observatory elevation (m) double itsObsHeight; }; } // namespace asap #endif // #ifndef STATMOSPHERE_H