NASA Ocean Color

ocssw V2022
 def gha2000(iyr,day):
     #      converted from gha2000.f
     # This subroutine computes the Greenwich hour angle in degrees for the
     # input time.  It uses the model referenced in The Astronomical Almanac
     # for 1984, Section S (Supplement) and documented in "Exact 
     # closed-form geolocation algorithm for Earth survey sensors", by 
     # F.S. Patt and W.W. Gregg, Int. Journal of Remote Sensing, 1993.
     # It includes the correction to mean sideral time for nutation
     # as well as precession.
     
     # Calling Arguments
     
     # Name         Type    I/O     Description
     # iyr          I*4      I      Year (four digits)
     # day          R*8      I      Day (time of day as fraction)
     # gha          R*8      O      Greenwich hour angle (degrees)
     
     
     #      Subprograms referenced:
     #      JD              Computes Julian day from calendar date
     #      EPHPARMS        Computes mean solar longitude and anomaly and
     #                       mean lunar lontitude and ascending node
     #      NUTATE          Compute nutation corrections to lontitude and 
     #                       obliquity
     #      
     #      Program written by:     Frederick S. Patt
     #                              General Sciences Corporation
     #                              November 2, 1992
     # Liang Hong, 3/24/2020, array calculation
     
     #common /nutcm/dpsi,eps,nutime
     #common /gconst/pi,radeg,re,rem,f,omf2,omegae
     #data imon/1/,nutime/-9999/
     imon = 1
     
     import numpy as np
     from hawknav.jd import jd
     
     # Compute days since J2000
     iday = np.fix(day)
     fday = day - iday
     jday = jd(iyr,imon,iday)
     t = jday - 2451545.5 + fday
     
     # Compute Greenwich Mean Sidereal Time (degrees)
     gmst = 100.4606184 + 0.9856473663*t + 2.908e-13*np.multiply(t,t)
     
     # Check if need to compute nutation correction for this day
     [xls,gs,xlm,omega] = ephparms(t)
     [dpsi,eps,epsm] = nutate(t,xls,gs,xlm,omega)
     
     # Include apparent time correction and time-of-day
     gha = gmst + np.multiply(dpsi, np.cos(np.deg2rad(eps))) + fday*360.0
     gha = gha + 360.0
     gha = np.mod(gha,360)
     
     return gha
  
 def ephparms(t):
  
     # This subroutine computes ephemeris parameters used by other Mission
     # Operations routines:  the solar mean longitude and mean anomaly, and
     # the lunar mean longitude and mean ascending node.  It uses the model
     # referenced in The Astronomical Almanac for 1984, Section S 
     # (Supplement) and documented and documented in "Exact closed-form 
     # geolocation algorithm for Earth survey sensors", by F.S. Patt and 
     # W.W. Gregg, Int. Journal of Remote Sensing, 1993.  These parameters 
     # are used to compute the solar longitude and the nutation in 
     # longitude and obliquity.
  
     # Calling Arguments
  
     # Name         Type    I/O     Description
  
     # t            R*8      I      Time in days since January 1, 2000 at 
     #                               12 hours UT
     # xls          R*8      O      Mean solar longitude (degrees)
     # gs           R*8      O      Mean solar anomaly (degrees)
     # xlm          R*8      O      Mean lunar longitude (degrees)
     # omega        R*8      O      Ascending node of mean lunar orbit 
     #                               (degrees)
  
  
     #      Program written by:     Frederick S. Patt
     #                              General Sciences Corporation
     #                              November 2, 1992
     # Liang Hong, 3/24/2020, array calculation
     
     import numpy as np
     
     # Sun Mean Longitude           
     xls = 280.46592 + 0.9856473516*t
     xls = np.mod(xls,360)
  
     # Sun Mean Anomaly             
     gs = 357.52772 + 0.9856002831*t 
     gs = np.mod(gs,360)
  
     # Moon Mean Longitude          
     xlm = 218.31643 + 13.17639648*t 
     xlm = np.mod(xlm,360)
  
     # Ascending Node of Moon's Mean Orbit  
     omega = 125.04452 - 0.0529537648*t 
     omega = np.mod(omega,360)
  
     return [xls,gs,xlm,omega]
     
 def nutate(t,xls,gs,xlm,omega):
     
     # This subroutine computes the nutation in longitude and the obliquity
     # of the ecliptic corrected for nutation.  It uses the model referenced
     # in The Astronomical Almanac for 1984, Section S (Supplement) and 
     # documented in "Exact closed-form geolocation algorithm for Earth 
     # survey sensors", by F.S. Patt and W.W. Gregg, Int. Journal of 
     # Remote Sensing, 1993.  These parameters are used to compute the 
     # apparent time correction to the Greenwich Hour Angle and for the 
     # calculation of the geocentric Sun vector.  The input ephemeris 
     # parameters are computed using subroutine ephparms.  Terms are 
     # included to 0.1 arcsecond.
  
     # Calling Arguments
  
     # Name         Type    I/O     Description
     
     # t            R*8      I      Time in days since January 1, 2000 at 
     #                               12 hours UT
     # xls          R*8      I      Mean solar longitude (degrees)
     # gs           R*8      I      Mean solar anomaly   (degrees)
     # xlm          R*8      I      Mean lunar longitude (degrees)
     # Omega        R*8      I      Ascending node of mean lunar orbit 
     #                               (degrees)
     # dPsi         R*8      O      Nutation in longitude (degrees)
     # Eps          R*8      O      Obliquity of the Ecliptic (degrees)
     #                               (includes nutation in obliquity)
     
     
     #      Program written by:     Frederick S. Patt
     #                              General Sciences Corporation
     #                              October 21, 1992
     
     #      Modification History:
     
     import numpy as np
     
     xls_rad = np.deg2rad(xls)
     gs_rad = np.deg2rad(gs)
     xlm_rad = np.deg2rad(xlm)
     omega_rad = np.deg2rad(omega)
     
     # Nutation in Longitude
     dpsi = - 17.1996 * np.sin(omega_rad) + 0.2062 * np.sin(2.0*omega_rad) - 1.3187 * np.sin(2.0*xls_rad) + 0.1426 * np.sin(gs_rad) - 0.2274 * np.sin(2.0*xlm_rad)
     
     # Mean Obliquity of the Eclipti#      
     epsm = 23.439291 - 3.560e-7*t 
     
     # Nutation in Obliquity 
     deps = 9.2025 * np.cos(omega_rad) + 0.5736 * np.cos(2.0*xls_rad)
     
     # True Obliquity of the Ecliptic 
     eps = epsm + deps/3600.0
     
     dpsi = dpsi/3600.0
     
     return [dpsi,eps,epsm]
gha2000.gha2000
def gha2000(iyr, day)
Definition: gha2000.py:1
gha2000.ephparms
def ephparms(t)
Definition: gha2000.py:59
gha2000.nutate
def nutate(t, xls, gs, xlm, omega)
Definition: gha2000.py:109
Definition: jd.py:1