This class implements opacity/atmospheric brightness temperature model equivalent to the model available in MIRIAD. More...

#include <ATAtmosphere.h>

Public Member Functions
	ATAtmosphere (Double wvScale=1540., Double maxAlt=10000.0, Int nLayers=50)
	Default Constructor (apart from optional parameters). More...

	ATAtmosphere (Double temperature, Double pressure, Double humidity, Double lapseRate=0.0065, Double wvScale=1540., Double maxAlt=10000.0, Int nLayers=50)
	Constructor with explicitly given parameters of the atmosphere. More...

void	setWeather (Double temperature, Double pressure, Double humidity)
	Set the new weather station data, recompute the model. More...

void	setObservatoryElevation (Double elev)
	Set the elevation of the observatory (height above mean sea level) More...

Double	zenithOpacity (Double freq) const
	Calculate zenith opacity at the given frequency. More...

Vector< Double >	zenithOpacities (const Vector< Double > &freqs) const
	Calculate zenith opacity for the range of frequencies. More...

Double	opacity (Double freq, Double el) const
	Calculate opacity at the given frequency and elevation. More...

Vector< Double >	opacities (const Vector< Double > &freqs, Double el) const
	Calculate opacities for the range of frequencies at the given elevation. More...

Protected Member Functions
void	recomputeAtmosphereModel ()
	Build the atmosphere model based on exponential fall-off, ideal gas and hydrostatic equilibrium. More...

Int	nLayers () const
	Obtain the number of model layers, do consistency check that everything is resized accordingly number of model layers. More...

Static Protected Member Functions
static Double	wvSaturationPressure (Double temperature)
	Determine the saturation pressure of water vapour for the given temperature. More...

static DComplex	dryRefractivity (Double freq, Double temperature, Double pDry, Double pVapour)
	Compute the complex refractivity of the dry components of the atmosphere (oxygen lines) at the given frequency. More...

static DComplex	vapourRefractivity (Double freq, Double temperature, Double pDry, Double pVapour)
	Compute the complex refractivity of the water vapour monomers at the given frequency. More...

Private Attributes
Vector< Double >	itsHeights
	heights of all model layers More...

Vector< Double >	itsTemperatures
	temperatures of all model layers More...

Vector< Double >	itsDryPressures
	partial pressures of dry component for all model layers More...

Vector< Double >	itsVapourPressures
	partial pressure of water vapour for all model layers More...

Double	itsGndTemperature
	Atmosphere parameters. More...

Double	itsPressure
	sea level pressure (Pascals) More...

Double	itsGndHumidity
	ground level humidity (fraction) More...

Double	itsLapseRate
	lapse rate (K/m) More...

Double	itsWVScale
	water vapour scale height (m) More...

Double	itsMaxAlt
	altitude of the highest layer of the model (m) More...

Double	itsObsHeight
	observatory elevation (m) More...

Detailed Description

This class implements opacity/atmospheric brightness temperature model equivalent to the model available in MIRIAD.

The actual math is a conversion 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.

The ASAP atmosphere opacity model

Author: Max Voronkov

Date

Date:: 2010-03-17 14:55:17 +1000 (Thu, 26 Apr 2007)

Version

Definition at line 60 of file ATAtmosphere.h.

Constructor & Destructor Documentation

casa::ATAtmosphere::ATAtmosphere	(	Double	wvScale = `1540.`,
		Double	maxAlt = `10000.0`,
		Int	nLayers = `50`
	)

explicit

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%.

Parameters

[in]	wvScale	water vapour scale height (m), default is 1540m to match MIRIAD's model
[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.
[in]	nLayers	number of plane parallel layers in the model (essentially for a numberical integration), default is 50 to match MIRIAD.

casa::ATAtmosphere::ATAtmosphere	(	Double	temperature,
		Double	pressure,
		Double	humidity,
		Double	lapseRate = `0.0065`,
		Double	wvScale = `1540.`,
		Double	maxAlt = `10000.0`,
		Int	nLayers = `50`
	)

Constructor with explicitly given parameters of the atmosphere.

Parameters

[in]	temperature	air temperature at the observatory (K)
[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)
[in]	pressure	air pressure at the observatory (Pascals)
[in]	humidity	air humidity at the observatory (fraction)
[in]	lapseRate	temperature lapse rate (K/m), default is 0.0065 K/m to match MIRIAD and ISA
[in]	wvScale	water vapour scale height (m), default is 1540m to match MIRIAD's model
[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.
[in]	nLayers	number of plane parallel layers in the model (essentially for a numberical integration), default is 50 to match MIRIAD.

Member Function Documentation

static DComplex casa::ATAtmosphere::dryRefractivity	(	Double	freq,
		Double	temperature,
		Double	pDry,
		Double	pVapour
	)

staticprotected

Compute the complex refractivity of the dry components of the atmosphere (oxygen lines) at the given frequency.

Parameters

[in]	freq	frequency (Hz)
[in]	temperature	air temperature (K)
[in]	pDry	partial pressure of dry components (Pascals)
[in]	pVapour	partial pressure of water vapour (Pascals)

Returns: complex refractivity

Reference: Liebe, An updated model for millimeter wave propogation in moist air, Radio Science, 20, 1069-1089 (1985).

Int casa::ATAtmosphere::nLayers ( ) const

protected

Obtain the number of model layers, do consistency check that everything is resized accordingly number of model layers.

Vector<Double> casa::ATAtmosphere::opacities	(	const Vector< Double > &	freqs,
		Double	el
	)		const

Calculate opacities for the range of frequencies at the given elevation.

Same as opacity, but for a Vector of frequencies.

Parameters

[in]	freqs	Vector of frequencies in Hz
[in]	el	elevation in radians

Returns: Vector of opacities, one value per frequency (nepers, i.e. dimensionless)

Double casa::ATAtmosphere::opacity	(	Double	freq,
		Double	el
	)		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.

Parameters

[in]	freq	frequency of interest in Hz
[in]	el	elevation in radians

Returns: zenith opacity (nepers, i.e. dimensionless)

void casa::ATAtmosphere::recomputeAtmosphereModel ( )

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 casa::ATAtmosphere::setObservatoryElevation ( Double elev )

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.

Parameters

[in] elev elevation in metres

void casa::ATAtmosphere::setWeather	(	Double	temperature,
		Double	pressure,
		Double	humidity
	)

Set the new weather station data, recompute the model.

Parameters

[in]	temperature	air temperature at the observatory (K)
[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)
[in]	humidity	air humidity at the observatory (fraction)

static DComplex casa::ATAtmosphere::vapourRefractivity	(	Double	freq,
		Double	temperature,
		Double	pDry,
		Double	pVapour
	)

staticprotected

Compute the complex refractivity of the water vapour monomers at the given frequency.

Parameters

[in]	freq	frequency (Hz)
[in]	temperature	air temperature (K)
[in]	pDry	partial pressure of dry components (Pascals)
[in]	pVapour	partial pressure of water vapour (Pascals)

Returns: complex refractivity

Reference: Liebe, An updated model for millimeter wave propogation in moist air, Radio Science, 20, 1069-1089 (1985).

static Double casa::ATAtmosphere::wvSaturationPressure ( Double temperature )

staticprotected

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).

Parameters

[in] temperature temperature in K

Returns: vapour saturation pressure (Pascals)

Vector<Double> casa::ATAtmosphere::zenithOpacities ( const Vector< Double > & freqs ) const

Calculate zenith opacity for the range of frequencies.

Same as zenithOpacity, but for a Vector of frequencies.

Parameters

[in] freqs Vector of frequencies in Hz

Returns: Vector of zenith opacities, one value per frequency (nepers, i.e. dimensionless)

Double casa::ATAtmosphere::zenithOpacity ( Double freq ) const

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.

Parameters

[in] freq frequency of interest in Hz

Returns: zenith opacity (nepers, i.e. dimensionless)

Member Data Documentation

Vector<Double> casa::ATAtmosphere::itsDryPressures

private

partial pressures of dry component for all model layers

Definition at line 221 of file ATAtmosphere.h.

Double casa::ATAtmosphere::itsGndHumidity

private

ground level humidity (fraction)

Definition at line 237 of file ATAtmosphere.h.

Double casa::ATAtmosphere::itsGndTemperature

private

Atmosphere parameters.

ground level temperature (K)

Definition at line 231 of file ATAtmosphere.h.

Vector<Double> casa::ATAtmosphere::itsHeights

private

heights of all model layers

Definition at line 215 of file ATAtmosphere.h.

Double casa::ATAtmosphere::itsLapseRate

private

lapse rate (K/m)

Definition at line 240 of file ATAtmosphere.h.

Double casa::ATAtmosphere::itsMaxAlt

private

altitude of the highest layer of the model (m)

Definition at line 246 of file ATAtmosphere.h.

Double casa::ATAtmosphere::itsObsHeight

private

observatory elevation (m)

Definition at line 249 of file ATAtmosphere.h.

Double casa::ATAtmosphere::itsPressure

private

sea level pressure (Pascals)

Definition at line 234 of file ATAtmosphere.h.

Vector<Double> casa::ATAtmosphere::itsTemperatures

private

temperatures of all model layers

Definition at line 218 of file ATAtmosphere.h.

Vector<Double> casa::ATAtmosphere::itsVapourPressures

private

partial pressure of water vapour for all model layers

Definition at line 224 of file ATAtmosphere.h.

Double casa::ATAtmosphere::itsWVScale

private

water vapour scale height (m)

Definition at line 243 of file ATAtmosphere.h.

The documentation for this class was generated from the following file:

casa/code/atnf/atca/ATAtmosphere.h

Public Member Functions

Protected Member Functions

Static Protected Member Functions

Private Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation