pkg/radtrans/radtrans_gha2000.F

C $Header: /u/gcmpack/MITgcm_contrib/darwin2/pkg/radtrans/radtrans_gha2000.F,v 1.1 2011/04/13 18:56:26 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	C $Header: /u/gcmpack/MITgcm_contrib/darwin2/pkg/radtrans/radtrans_gha2000.F,v 1.1 2011/04/13 18:56:26 jahn Exp $
2	C $Name: $
3
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	_RL radeg, day
52	INTEGER iyr, imon
53
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