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SUBROUTINE sla__ATMT (R0, T0, ALPHA, GAMM2, DELM2,
: C1, C2, C3, C4, C5, C6, R, T, DN, RDNDR)
*+
* - - - - -
* A T M T
* - - - - -
*
* Internal routine used by REFRO
*
* Refractive index and derivative with respect to height for the
* troposphere.
*
* Given:
* R0 d height of observer from centre of the Earth (metre)
* T0 d temperature at the observer (deg K)
* ALPHA d alpha )
* GAMM2 d gamma minus 2 ) see HMNAO paper
* DELM2 d delta minus 2 )
* C1 d useful term )
* C2 d useful term )
* C3 d useful term ) see source
* C4 d useful term ) of sla_REFRO
* C5 d useful term )
* C6 d useful term )
* R d current distance from the centre of the Earth (metre)
*
* Returned:
* T d temperature at R (deg K)
* DN d refractive index at R
* RDNDR d R * rate the refractive index is changing at R
*
* Note that in the optical case C5 and C6 are zero.
*
* P.T.Wallace Starlink 30 May 1997
*
* Copyright (C) 1997 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
DOUBLE PRECISION R0,T0,ALPHA,GAMM2,DELM2,C1,C2,C3,C4,C5,C6,
: R,T,DN,RDNDR
DOUBLE PRECISION TT0,TT0GM2,TT0DM2
T = MAX(MIN(T0-ALPHA*(R-R0),320D0),100D0)
TT0 = T/T0
TT0GM2 = TT0**GAMM2
TT0DM2 = TT0**DELM2
DN = 1D0+(C1*TT0GM2-(C2-C5/T)*TT0DM2)*TT0
RDNDR = R*(-C3*TT0GM2+(C4-C6/TT0)*TT0DM2)
END
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