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88 lines
3.0 KiB
Fortran
88 lines
3.0 KiB
Fortran
SUBROUTINE sla_REFCO ( HM, TDK, PMB, RH, WL, PHI, TLR, EPS,
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: REFA, REFB )
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*+
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* - - - - - -
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* R E F C O
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* - - - - - -
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*
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* Determine the constants A and B in the atmospheric refraction
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* model dZ = A tan Z + B tan**3 Z.
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*
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* Z is the "observed" zenith distance (i.e. affected by refraction)
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* and dZ is what to add to Z to give the "topocentric" (i.e. in vacuo)
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* zenith distance.
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*
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* Given:
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* HM d height of the observer above sea level (metre)
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* TDK d ambient temperature at the observer (K)
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* PMB d pressure at the observer (millibar)
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* RH d relative humidity at the observer (range 0-1)
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* WL d effective wavelength of the source (micrometre)
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* PHI d latitude of the observer (radian, astronomical)
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* TLR d temperature lapse rate in the troposphere (K/metre)
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* EPS d precision required to terminate iteration (radian)
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*
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* Returned:
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* REFA d tan Z coefficient (radian)
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* REFB d tan**3 Z coefficient (radian)
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*
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* Called: sla_REFRO
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*
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* Notes:
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*
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* 1 Typical values for the TLR and EPS arguments might be 0.0065D0 and
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* 1D-10 respectively.
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*
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* 2 The radio refraction is chosen by specifying WL > 100 micrometres.
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*
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* 3 The routine is a slower but more accurate alternative to the
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* sla_REFCOQ routine. The constants it produces give perfect
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* agreement with sla_REFRO at zenith distances arctan(1) (45 deg)
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* and arctan(4) (about 76 deg). It achieves 0.5 arcsec accuracy
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* for ZD < 80 deg, 0.01 arcsec accuracy for ZD < 60 deg, and
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* 0.001 arcsec accuracy for ZD < 45 deg.
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*
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* P.T.Wallace Starlink 22 May 2004
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*
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* Copyright (C) 2004 Rutherford Appleton Laboratory
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*
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* License:
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program (see SLA_CONDITIONS); if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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* Boston, MA 02111-1307 USA
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*
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*-
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IMPLICIT NONE
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DOUBLE PRECISION HM,TDK,PMB,RH,WL,PHI,TLR,EPS,REFA,REFB
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DOUBLE PRECISION ATN1,ATN4,R1,R2
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* Sample zenith distances: arctan(1) and arctan(4)
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PARAMETER (ATN1=0.7853981633974483D0,
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: ATN4=1.325817663668033D0)
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* Determine refraction for the two sample zenith distances
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CALL sla_REFRO(ATN1,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,R1)
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CALL sla_REFRO(ATN4,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,R2)
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* Solve for refraction constants
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REFA = (64D0*R1-R2)/60D0
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REFB = (R2-4D0*R1)/60D0
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END
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