| 1 | #include "slalib.h"
|
|---|
| 2 | #include "slamac.h"
|
|---|
| 3 | void slaRefco ( double hm, double tdk, double pmb, double rh,
|
|---|
| 4 | double wl, double phi, double tlr, double eps,
|
|---|
| 5 | double *refa, double *refb )
|
|---|
| 6 | /*
|
|---|
| 7 | ** - - - - - - - - -
|
|---|
| 8 | ** s l a R e f c o
|
|---|
| 9 | ** - - - - - - - - -
|
|---|
| 10 | **
|
|---|
| 11 | ** Determine constants A and B in atmospheric refraction model
|
|---|
| 12 | ** dz = A tan z + B tan^3 z.
|
|---|
| 13 | **
|
|---|
| 14 | ** z is the "observed" zenith distance (i.e. affected by
|
|---|
| 15 | ** refraction) and dz is what to add to z to give the "topocentric"
|
|---|
| 16 | ** (i.e. in vacuo) zenith distance.
|
|---|
| 17 | **
|
|---|
| 18 | ** Given:
|
|---|
| 19 | ** hm double height of the observer above sea level (metre)
|
|---|
| 20 | ** tdk double ambient temperature at the observer (deg k)
|
|---|
| 21 | ** pmb double pressure at the observer (millibar)
|
|---|
| 22 | ** rh double relative humidity at the observer (range 0-1)
|
|---|
| 23 | ** wl double effective wavelength of the source (micrometre)
|
|---|
| 24 | ** phi double latitude of the observer (radian, astronomical)
|
|---|
| 25 | ** tlr double temperature lapse rate in the troposphere (degk/metre)
|
|---|
| 26 | ** eps double precision required to terminate iteration (radian)
|
|---|
| 27 | **
|
|---|
| 28 | ** Returned:
|
|---|
| 29 | ** *refa double tan z coefficient (radian)
|
|---|
| 30 | ** *refb double tan^3 z coefficient (radian)
|
|---|
| 31 | **
|
|---|
| 32 | ** Called: slaRefro
|
|---|
| 33 | **
|
|---|
| 34 | ** Notes:
|
|---|
| 35 | **
|
|---|
| 36 | ** 1 Typical values for the tlr and eps arguments might be 0.0065 and
|
|---|
| 37 | ** 1e-10 respectively.
|
|---|
| 38 | **
|
|---|
| 39 | ** 2 The radio refraction is chosen by specifying wl > 100 micrometres.
|
|---|
| 40 | **
|
|---|
| 41 | ** 3 The routine is a slower but more accurate alternative to the
|
|---|
| 42 | ** slaRefcoq routine. The constants it produces give perfect
|
|---|
| 43 | ** agreement with slaRefro at zenith distances arctan(1) (45 deg)
|
|---|
| 44 | ** and arctan(4) (about 76 deg). It achieves 0.5 arcsec accuracy
|
|---|
| 45 | ** for ZD < 80 deg, 0.01 arcsec accuracy for ZD < 60 deg, and
|
|---|
| 46 | ** 0.001 arcsec accuracy for ZD < 45 deg.
|
|---|
| 47 | **
|
|---|
| 48 | ** Last revision: 4 June 1997
|
|---|
| 49 | **
|
|---|
| 50 | ** Copyright P.T.Wallace. All rights reserved.
|
|---|
| 51 | */
|
|---|
| 52 | {
|
|---|
| 53 | double r1,r2;
|
|---|
| 54 |
|
|---|
| 55 | /* Sample zenith distances: arctan(1) and arctan(4) */
|
|---|
| 56 | static double atn1 = 0.7853981633974483;
|
|---|
| 57 | static double atn4 = 1.325817663668033;
|
|---|
| 58 |
|
|---|
| 59 | /* Determine refraction for the two sample zenith distances. */
|
|---|
| 60 | slaRefro ( atn1, hm, tdk, pmb, rh, wl, phi, tlr, eps, &r1 );
|
|---|
| 61 | slaRefro ( atn4, hm, tdk, pmb, rh, wl, phi, tlr, eps, &r2 );
|
|---|
| 62 |
|
|---|
| 63 | /* Solve for refraction constants. */
|
|---|
| 64 | *refa = ( 64.0 * r1 - r2 ) / 60.0;
|
|---|
| 65 | *refb = ( r2 - 4.0 * r1 ) / 60.0;
|
|---|
| 66 | }
|
|---|
