refract.c File Reference

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

Macros
#define	NOVAS_DEFAULT_WAVELENGTH   0.55
	[μm] Median wavelength of visible light.

Functions
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.
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.
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).
int	novas_refract_wavelength (double microns)
	Sets the observing wavelength for which refraction is to be calculated when using a wavelength-depenendent model, such as novas_wave_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.
double	novas_wave_refraction (double jd_tt, const on_surface *loc, enum novas_refraction_type type, double el)
	The wavelength-dependent IAU atmospheric refraction model, based on the SOFA iauRefco() function, in compliance to the 'SOFA Software License' terms of the original source.
double	refract (const on_surface *restrict location, enum novas_refraction_model model, double zd_obs)
	Computes atmospheric optical refraction for an observed (already refracted!) zenith distance through the atmosphere.
double	refract_astro (const on_surface *restrict location, enum novas_refraction_model model, double zd_astro)
	Computes atmospheric optical refraction for a source at an astrometric zenith distance (e.g.

Detailed Description

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

Date

Created on Jun 27, 2024

Author

Attila Kovacs and G. Kaplan

See also

novas_app_to_hor(), novas_hor_to_app()

Macro Definition Documentation

NOVAS_DEFAULT_WAVELENGTH

#define NOVAS_DEFAULT_WAVELENGTH   0.55

[μm] Median wavelength of visible light.

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.

Referenced by novas_radio_refraction(), and novas_wave_refraction().

refract()

double refract	(	const on_surface *restrict	location,
		enum novas_refraction_model	model,
		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. Some, but not all, refraction models will use location-based (e.g. weather) information. For models that do not need it, it may be NULL.
model	The built in refraction model to use. E.g. NOVAS_STANDARD_ATMOSPHERE (1), or NOVAS_WEATHER_AT_LOCATION (2)...
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_RADIO_REFRACTION, novas_radio_refraction(), NOVAS_REFRACT_OBSERVED, NOVAS_REFRACTION_MODELS, novas_set_default_weather(), NOVAS_WAVE_REFRACTION, novas_wave_refraction(), NOVAS_WEATHER_AT_LOCATION, novas_on_surface::pressure, and novas_on_surface::temperature.

Referenced by refract_astro().

refract_astro()

double refract_astro	(	const on_surface *restrict	location,
		enum novas_refraction_model	model,
		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. Some, but not all, refraction models will use location-based (e.g. weather) information. For models that do not need it, it may be NULL.
model	The built in refraction model to use. E.g. NOVAS_STANDARD_ATMOSPHERE (1), or NOVAS_WEATHER_AT_LOCATION (2)...
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, NOVAS_RADIO_REFRACTION, novas_radio_refraction(), NOVAS_REFRACT_ASTROMETRIC, and refract().

Referenced by equ2hor().