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slalib/atmdsp.f

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+      SUBROUTINE sla_ATMDSP (TDK, PMB, RH, WL1, A1, B1, WL2, A2, B2)
+*+
+*     - - - - - - -
+*      A T M D S P
+*     - - - - - - -
+*
+*  Apply atmospheric-dispersion adjustments to refraction coefficients.
+*
+*  Given:
+*     TDK       d       ambient temperature, K
+*     PMB       d       ambient pressure, millibars
+*     RH        d       ambient relative humidity, 0-1
+*     WL1       d       reference wavelength, micrometre (0.4D0 recommended)
+*     A1        d       refraction coefficient A for wavelength WL1 (radians)
+*     B1        d       refraction coefficient B for wavelength WL1 (radians)
+*     WL2       d       wavelength for which adjusted A,B required
+*
+*  Returned:
+*     A2        d       refraction coefficient A for wavelength WL2 (radians)
+*     B2        d       refraction coefficient B for wavelength WL2 (radians)
+*
+*  Notes:
+*
+*  1  To use this routine, first call sla_REFCO specifying WL1 as the
+*     wavelength.  This yields refraction coefficients A1,B1, correct
+*     for that wavelength.  Subsequently, calls to sla_ATMDSP specifying
+*     different wavelengths will produce new, slightly adjusted
+*     refraction coefficients which apply to the specified wavelength.
+*
+*  2  Most of the atmospheric dispersion happens between 0.7 micrometre
+*     and the UV atmospheric cutoff, and the effect increases strongly
+*     towards the UV end.  For this reason a blue reference wavelength
+*     is recommended, for example 0.4 micrometres.
+*
+*  3  The accuracy, for this set of conditions:
+*
+*        height above sea level    2000 m
+*                      latitude    29 deg
+*                      pressure    793 mb
+*                   temperature    17 degC
+*                      humidity    50%
+*                    lapse rate    0.0065 degC/m
+*          reference wavelength    0.4 micrometre
+*                star elevation    15 deg
+*
+*     is about 2.5 mas RMS between 0.3 and 1.0 micrometres, and stays
+*     within 4 mas for the whole range longward of 0.3 micrometres
+*     (compared with a total dispersion from 0.3 to 20.0 micrometres
+*     of about 11 arcsec).  These errors are typical for ordinary
+*     conditions and the given elevation;  in extreme conditions values
+*     a few times this size may occur, while at higher elevations the
+*     errors become much smaller.
+*
+*  4  If either wavelength exceeds 100 micrometres, the radio case
+*     is assumed and the returned refraction coefficients are the
+*     same as the given ones.  Note that radio refraction coefficients
+*     cannot be turned into optical values using this routine, nor
+*     vice versa.
+*
+*  5  The algorithm consists of calculation of the refractivity of the
+*     air at the observer for the two wavelengths, using the methods
+*     of the sla_REFRO routine, and then scaling of the two refraction
+*     coefficients according to classical refraction theory.  This
+*     amounts to scaling the A coefficient in proportion to (n-1) and
+*     the B coefficient almost in the same ratio (see R.M.Green,
+*     "Spherical Astronomy", Cambridge University Press, 1985).
+*
+*  Last revision   2 December 2005
+*
+*  Copyright P.T.Wallace.  All rights reserved.
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the 
+*    Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
+*    Boston, MA  02111-1307  USA
+*
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION TDK,PMB,RH,WL1,A1,B1,WL2,A2,B2
+
+      DOUBLE PRECISION F,TDKOK,PMBOK,RHOK,
+     :                 PSAT,PWO,W1,WLOK,WLSQ,W2,DN1,DN2
+
+
+*  Check for radio wavelengths
+      IF (WL1.GT.100D0.OR.WL2.GT.100D0) THEN
+
+*     Radio: no dispersion
+         A2 = A1
+         B2 = B1
+      ELSE
+
+*     Optical: keep arguments within safe bounds
+         TDKOK = MIN(MAX(TDK,100D0),500D0)
+         PMBOK = MIN(MAX(PMB,0D0),10000D0)
+         RHOK = MIN(MAX(RH,0D0),1D0)
+
+*     Atmosphere parameters at the observer
+         PSAT = 10D0**(-8.7115D0+0.03477D0*TDKOK)
+         PWO = RHOK*PSAT
+         W1 = 11.2684D-6*PWO
+
+*     Refractivity at the observer for first wavelength
+         WLOK = MAX(WL1,0.1D0)
+         WLSQ = WLOK*WLOK
+         W2 = 77.5317D-6+(0.43909D-6+0.00367D-6/WLSQ)/WLSQ
+         DN1 = (W2*PMBOK-W1)/TDKOK
+
+*     Refractivity at the observer for second wavelength
+         WLOK = MAX(WL2,0.1D0)
+         WLSQ = WLOK*WLOK
+         W2 = 77.5317D-6+(0.43909D-6+0.00367D-6/WLSQ)/WLSQ
+         DN2 = (W2*PMBOK-W1)/TDKOK
+
+*     Scale the refraction coefficients (see Green 4.31, p93)
+         IF (DN1.NE.0D0) THEN
+            F = DN2/DN1
+            A2 = A1*F
+            B2 = B1*F
+            IF (DN1.NE.A1) B2=B2*(1D0+DN1*(DN1-DN2)/(2D0*(DN1-A1)))
+         ELSE
+            A2 = A1
+            B2 = B1
+         END IF
+      END IF
+
+      END