refract.c File Reference

Functions
double	novas_inv_refract (RefractionModel model, double jd_tt, const on_surface *restrict loc, enum novas_refraction_type type, double el0)
double	novas_optical_refraction (double jd_tt, const on_surface *loc, enum novas_refraction_type type, double el)
double	novas_radio_refraction (double jd_tt, const on_surface *loc, enum novas_refraction_type type, double el)
double	novas_standard_refraction (double jd_tt, const on_surface *loc, enum novas_refraction_type type, double el)
double	refract (const on_surface *restrict location, enum novas_refraction_model option, double zd_obs)
double	refract_astro (const on_surface *restrict location, enum novas_refraction_model option, double zd_astro)

Detailed Description

Date

Created on Jun 27, 2024

Author

Attila Kovacs and G. Kaplan

A collection of refraction models and utilities to use with novas_app_to_hor() or novas_hor_to_app().

See also

novas_app_to_hor()

novas_hor_to_app().

Function Documentation

novas_inv_refract()

double novas_inv_refract	(	RefractionModel	model,
		double	jd_tt,
		const on_surface *restrict	loc,
		enum novas_refraction_type	type,
		double	el0
	)

Computes the reverse atmospheric refraction for a given refraction model. Thus if a refraction model takes observed elevation as an input, the reverse refraction takes astrometric elevation as its input, and vice versa.

Parameters

model	The original refraction model
jd_tt	[day] Terrestrial Time (TT) based Julian data of observation
loc	Pointer to structure defining the observer's location on earth, and local weather
type	Refraction type to use for the original model: NOVAS_REFRACT_OBSERVED (-1) or NOVAS_REFRACT_ASTROMETRIC (0).
el0	[deg] input elevation for the inverse refraction model.

Returns

[deg] Estimated refraction, or NAN if there was an error (it should also set errno to indicate the type of error).

See also

refract_astro()

itrs_to_hor()

Since

1.1

Author

Attila Kovacs

References novas_inv_max_iter, and NOVAS_REFRACT_OBSERVED.

novas_optical_refraction()

double novas_optical_refraction	(	double	jd_tt,
		const on_surface *	loc,
		enum novas_refraction_type	type,
		double	el
	)

Returns an optical refraction correction using the weather parameters defined for the observer location.

Parameters

jd_tt	[day] Terrestrial Time (TT) based Julian data of observation (unused in this implementation of RefractionModel)
loc	Pointer to structure defining the observer's location on earth, and local weather
type	Whether the input elevation is observed or astrometric: NOVAS_REFRACT_OBSERVED (-1) or NOVAS_REFRACT_ASTROMETRIC (0).
el	[deg] Astrometric (unrefracted) source elevation

Returns

[arcsec] Estimated refraction, or NAN if there was an error (it should also set errno to indicate the type of error).

See also

novas_app_to_hor()

novas_optical_refraction()

NOVAS_STANDARD_ATMOSPHERE()

refract()

refract_astro()

References NOVAS_WEATHER_AT_LOCATION.

novas_radio_refraction()

double novas_radio_refraction	(	double	jd_tt,
		const on_surface *	loc,
		enum novas_refraction_type	type,
		double	el
	)

Atmospheric refraction model for radio wavelengths (Berman & Rockwell 1976). It uses the weather parameters defined for the location, including humidity. As such make sure the weather data is fully defined, and that the humidity was explicitly set after calling make_on_surface().

Adapted from FORTAN code provided by Berman & Rockwell 1976.

REFERENCES:

1. Berman, Allan L., and Rockwell, Stephen T. (1976), NASA JPL Technical Report 32-1601

Parameters

jd_tt	[day] Terrestrial Time (TT) based Julian data of observation (unused in this implementation of RefractionModel)
loc	Pointer to structure defining the observer's location on earth, and local weather. Make sure all weather values, including humidity (added in v1.1), are fully populated.
type	Whether the input elevation is observed or astrometric: NOVAS_REFRACT_OBSERVED (-1) or NOVAS_REFRACT_ASTROMETRIC (0).
el	[deg] source elevation of the specified type.

Returns

[deg] Estimated refraction, or NAN if there was an error (it should also set errno to indicate the type of error).

See also

novas_optical_refraction()

make_on_surface()

on_surface

References on_surface::humidity, novas_inv_refract(), novas_radio_refraction(), NOVAS_REFRACT_ASTROMETRIC, NOVAS_REFRACT_OBSERVED, on_surface::pressure, and on_surface::temperature.

novas_standard_refraction()

double novas_standard_refraction	(	double	jd_tt,
		const on_surface *	loc,
		enum novas_refraction_type	type,
		double	el
	)

Returns an optical refraction correction for a standard atmosphere.

Parameters

jd_tt	[day] Terrestrial Time (TT) based Julian data of observation (unused in this implementation of RefractionModel)
loc	Pointer to structure defining the observer's location on earth, and local weather
type	Whether the input elevation is observed or astrometric: NOVAS_REFRACT_OBSERVED (-1) or NOVAS_REFRACT_ASTROMETRIC (0).
el	[deg] Astrometric (unrefracted) source elevation

Returns

[deg] Estimated refraction, or NAN if there was an error (it should also set errno to indicate the type of error).

See also

novas_app_to_hor()

novas_optical_refraction()

NOVAS_STANDARD_ATMOSPHERE()

refract()

refract_astro()

References NOVAS_STANDARD_ATMOSPHERE.

refract()

double refract	(	const on_surface *restrict	location,
		enum novas_refraction_model	option,
		double	zd_obs
	)

Computes atmospheric optical refraction for an observed (already refracted!) zenith distance through the atmosphere. In other words this is suitable to convert refracted zenith angles to astrometric (unrefracted) zenith angles. For the reverse, see refract_astro().

The returned value is the approximate refraction for optical wavelengths. This function can be used for planning observations or telescope pointing, but should not be used for precise positioning.

NOTES:

1. The standard temeperature model includes a very rough estimate of the mean annual temeprature for the ovserver's latitude and elevation, rather than the 10 C everywhere assumption in NOVAS C 3.1.<.li>

REFERENCES:

1. Explanatory Supplement to the Astronomical Almanac, p. 144.
2. Bennett, G. (1982), Journal of Navigation (Royal Institute) 35, pp. 255-259.

Parameters

location	Pointer to structure containing observer's location. It may also contains weather data (optional) for the observer's location.
option	NOVAS_STANDARD_ATMOSPHERE (1), or NOVAS_WEATHER_AT_LOCATION (2) if to use the weather values contained in the 'location' data structure.
zd_obs	[deg] Observed (already refracted!) zenith distance through the atmosphere.

Returns

[deg] the calculated optical refraction or 0.0 if the location is NULL or the option is invalid or the 'zd_obs' is invalid (<90°).

See also

refract_astro()

hor_to_itrs()

References NOVAS_NO_ATMOSPHERE, NOVAS_STANDARD_ATMOSPHERE, and NOVAS_WEATHER_AT_LOCATION.

refract_astro()

double refract_astro	(	const on_surface *restrict	location,
		enum novas_refraction_model	option,
		double	zd_astro
	)

Computes atmospheric optical refraction for a source at an astrometric zenith distance (e.g. calculated without accounting for an atmosphere). This is suitable for converting astrometric (unrefracted) zenith angles to observed (refracted) zenith angles. See refract() for the reverse correction.

The returned value is the approximate refraction for optical wavelengths. This function can be used for planning observations or telescope pointing, but should not be used for precise positioning.

REFERENCES:

1. Explanatory Supplement to the Astronomical Almanac, p. 144.
2. Bennett, G. (1982), Journal of Navigation (Royal Institute) 35, pp. 255-259.

Parameters

location	Pointer to structure containing observer's location. It may also contains weather data (optional) for the observer's location.
option	NOVAS_STANDARD_ATMOSPHERE (1), or NOVAS_WEATHER_AT_LOCATION (2) if to use the weather values contained in the 'location' data structure.
zd_astro	[deg] Astrometric (unrefracted) zenith distance angle of the source.

Returns

[deg] the calculated optical refraction. (to ~0.1 arcsec accuracy), or 0.0 if the location is NULL or the option is invalid.

See also

refract()

itrs_to_hor()

Since

1.0

Author

Attila Kovacs

References novas_inv_max_iter, and refract().