pkg/radtrans/radtrans_gha2000.F

C $Header: /u/gcmpack/MITgcm_contrib/darwin/pkg/radtrans/radtrans_gha2000.F,v 1.1 2010/06/09 15:59:37 jahn Exp $
C $Name:  $

#include "RADTRANS_OPTIONS.h"

CBOP
C     !ROUTINE: RADTRANS_GHA2000

C     !INTERFACE: ======================================================
      subroutine radtrans_gha2000 (radeg, iyr, imon, day, gha)

C     !DESCRIPTION:
c  This subroutine computes the Greenwich hour angle in degrees for the
c  input time.  It uses the model referenced in The Astronomical Almanac
c  for 1984, Section S (Supplement) and documented in Exact 
c  closed-form geolocation algorithm for Earth survey sensors, by 
c  F.S. Patt and W.W. Gregg, Int. Journal of Remote Sensing, 1993.
c  It includes the correction to mean sideral time for nutation
c  as well as precession.

c  Calling Arguments

c  Name         Type    I/O     Description
c
c  iyr          I*4      I      Year (four digits)
c  day          R*8      I      Day (time of day as fraction)
c  gha          R*8      O      Greenwich hour angle (degrees)


c       Subprograms referenced:
c
c       JD              Computes Julian day from calendar date
c       EPHPARMS        Computes mean solar longitude and anomaly and
c                        mean lunar lontitude and ascending node
c       NUTATE          Compute nutation corrections to lontitude and 
c                        obliquity
c       
c
c       Program written by:     Frederick S. Patt
c                               General Sciences Corporation
c                               November 2, 1992
c
c       Modification History:
c
C     !USES: ===========================================================
      IMPLICIT NONE
#include "RADTRANS_VARS.h"

C     !INPUT PARAMETERS: ===============================================
      INTEGER myThid
      _RL radeg, day
      INTEGER iyr, imon

C     !OUTPUT PARAMETERS: ==============================================
      _RL gha

C     !FUNCTIONS: ======================================================
      INTEGER radtrans_jd
      EXTERNAL radtrans_jd
      
C     !LOCAL VARIABLES: ================================================
      integer iday,jday,nt
      _RL fday, t, gmst, xls, gs, xlm, omega

      data nutime /-99999/
CEOP

c  Compute days since J2000
       iday = int(day)
       fday = day - iday
       jday = radtrans_jd(iyr,imon,iday)
       t = jday - 2451545.5D0 + fday
c  Compute Greenwich Mean Sidereal Time (degrees)
       gmst = 100.4606184D0 + 0.9856473663D0*t + 2.908D-13*t*t

c  Check if need to compute nutation correction for this day
       nt = int(t)
       if (nt.ne.nutime) then
         nutime = nt
         call radtrans_ephparms (t, xls, gs, xlm, omega)
         call radtrans_nutate (radeg, t, xls, gs, xlm, omega, dpsi, eps)
       end if

c  Include apparent time correction and time-of-day
       gha = gmst + dpsi*cos(eps/radeg) + fday*360.0D0
       gha = mod(gha,360.0)
       if (gha.lt.0.0D0) gha = gha + 360.0D0

      return
      end

1	jahn	1.2	C $Header: /u/gcmpack/MITgcm_contrib/darwin/pkg/radtrans/radtrans_gha2000.F,v 1.1 2010/06/09 15:59:37 jahn Exp $
2			C $Name: $
3	jahn	1.1
4			#include "RADTRANS_OPTIONS.h"
5
6			CBOP
7			C !ROUTINE: RADTRANS_GHA2000
8
9			C !INTERFACE: ======================================================
10			subroutine radtrans_gha2000 (radeg, iyr, imon, day, gha)
11
12			C !DESCRIPTION:
13			c This subroutine computes the Greenwich hour angle in degrees for the
14			c input time. It uses the model referenced in The Astronomical Almanac
15			c for 1984, Section S (Supplement) and documented in Exact
16			c closed-form geolocation algorithm for Earth survey sensors, by
17			c F.S. Patt and W.W. Gregg, Int. Journal of Remote Sensing, 1993.
18			c It includes the correction to mean sideral time for nutation
19			c as well as precession.
20
21			c Calling Arguments
22
23			c Name Type I/O Description
24			c
25			c iyr I*4 I Year (four digits)
26			c day R*8 I Day (time of day as fraction)
27			c gha R*8 O Greenwich hour angle (degrees)
28
29
30			c Subprograms referenced:
31			c
32			c JD Computes Julian day from calendar date
33			c EPHPARMS Computes mean solar longitude and anomaly and
34			c mean lunar lontitude and ascending node
35			c NUTATE Compute nutation corrections to lontitude and
36			c obliquity
37			c
38			c
39			c Program written by: Frederick S. Patt
40			c General Sciences Corporation
41			c November 2, 1992
42			c
43			c Modification History:
44			c
45			C !USES: ===========================================================
46			IMPLICIT NONE
47			#include "RADTRANS_VARS.h"
48
49			C !INPUT PARAMETERS: ===============================================
50			INTEGER myThid
51	jahn	1.2	_RL radeg, day
52			INTEGER iyr, imon
53	jahn	1.1
54			C !OUTPUT PARAMETERS: ==============================================
55			_RL gha
56
57			C !FUNCTIONS: ======================================================
58			INTEGER radtrans_jd
59			EXTERNAL radtrans_jd
60
61			C !LOCAL VARIABLES: ================================================
62			integer iday,jday,nt
63			_RL fday, t, gmst, xls, gs, xlm, omega
64
65			data nutime /-99999/
66			CEOP
67
68			c Compute days since J2000
69			iday = int(day)
70			fday = day - iday
71			jday = radtrans_jd(iyr,imon,iday)
72			t = jday - 2451545.5D0 + fday
73			c Compute Greenwich Mean Sidereal Time (degrees)
74			gmst = 100.4606184D0 + 0.9856473663D0t + 2.908D-13t*t
75
76			c Check if need to compute nutation correction for this day
77			nt = int(t)
78			if (nt.ne.nutime) then
79			nutime = nt
80			call radtrans_ephparms (t, xls, gs, xlm, omega)
81			call radtrans_nutate (radeg, t, xls, gs, xlm, omega, dpsi, eps)
82			end if
83
84			c Include apparent time correction and time-of-day
85			gha = gmst + dpsicos(eps/radeg) + fday360.0D0
86			gha = mod(gha,360.0)
87			if (gha.lt.0.0D0) gha = gha + 360.0D0
88
89			return
90			end
91