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HPRSTATN

HPRSTATN

Name


  HPRSTATN

Author


  Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
  craigm@lheamail.gsfc.nasa.gov
  UPDATED VERSIONs can be found on my WEB PAGE:
      http://cow.physics.wisc.edu/~craigm/idl/idl.html

Purpose


  Compute high precision earth station positions in inertial coordinates

Major Topics


  Geometry

Calling Sequence


  HPRSTATN, JDTT, R_ITRF, R_ECI, V_ECI, $
            [ /JPL, /USE_EOP, /NO_UT1, TBASE= ]

Description



  The procedure HPRSTATN computes the coordinates and velocities of
  an earth station in J2000 equatorial earth-centered inertial
  coordinates (ECI). This may be useful in any application where an
  earthbound observatory is used to collect data on a non-terrestrial
  phenomenon.
  The user must have the following routines involved: HPRNUTANG;
  Markwardt Quaternion Library; JPLEPHREAD and JPLEPHINTERP (if JPL
  keyword is used); EOPDATA (if USE_EOP keyword is set); and TAI_UTC.
  Also, the appropriate data files for TAI-UTC and Earth Orientation
  Parameters must be installed.
  The user must specify the position of the earth station in
  earth-centered, earth-fixed, cartesian coordinates of the ITRF.
  The Z-axis points to terrestrial north, the X-axis lies in the
  terrestrial equator pointing towards the Greenwich meridian, and
  the Y-axis forms the right handed coordinate system. Any
  positional units may be specified.
  For the highest precision, the preferred method is to know the
  coordinates from a direct IRTF reduction, i.e., via VLBI. If you
  have geodetic longitude/latitude, a procedure is given below which
  can covert geodetic coordinates referred to WGS84 to ITRF cartesian
  coordinates.
  The values returned are the earth-centered inertial J2000
  coordinates and velocities of the station. All the effects of
  earth rotation, precession, nutation, and polar motion can be
  included. The user has a choice of the kinds of transformations
  that are included (see JPL, USE_EOP and NO_UT1 keywords).
  The returned positional units are the same as the input units. The
  returned velocity units are (units of input) PER SECOND.
  It is possible specify more than one time, or more than one station
  position, or both. If both more than one time and position are
  specified, then there must be an equal quantity of both.
  CARTESIAN COORDINATES FROM GEODETIC COORDINATES
  For a station whose geodetic latitude LAT, longitude LON (where
  positive is east) and elevation H specified relative to the
  ellipsoid, the cartesian coordinates are:
        R_ITRF = [ (A*C + H)*COS(LAT)*COS(LON), $
                    (A*C + H)*COS(LAT)*SIN(LON), $
                    (A*S + H)*SIN(LAT) ]
  where for the WGS84 reference ellipsoid, the equatorial radius is
  set to A = 6378.137 km, and the flattening factor F =
  1/298.257223563, and
      C = 1.0/SQRT(COS(LAT)^2 + (1 - F)^2*SIN(LAT)^2)
      S = (1 - F)^2 * C
  Reference: Explanatory Supplement to the Astronomical Almanac,
  eqns. 3.351-1 and 3.352-2.

Inputs



  JDTT - a scalar or N-vector, the TT epoch time(s) for which
          station coordinates are to be computed.
          For reference, JDTT = JDTAI + 32.184/86400d, where JDTAI is
          the international atomic time measured in days. The value
          of the keyword TBASE is added to JDTT to arrive at the
          actual Julian date.
  R_ITRF - cartesian coordinates of earth station. Either a
            3-vector, or a 3xN array. Units can be any positional
            units.

Outputs



  R_ECI - upon output, the coordinates of the station at the given
          time(s), referred to the earth-centered J2000 coordinate
          system. Either a 3-vector or 3xN array depending on the
          input. Units are the same as for R_ITRF.
  V_ECI - upon output, the velocities of the station at the given
          time(s), referred to the earth-centered J2000 coordinate
          system. Either a 3-vector or 3xN array depending on the
          input. Units are (units of R_ITRF) PER SECOND.

Keyword Parameters



  TBASE - a fixed epoch time (Julian days) to be added to each value
          of JDTT. Since subtraction of large numbers occurs with
          TBASE first, the greatest precision is achieved when TBASE
          is expressed as a nearby julian epoch, JDTT is expressed
          as a small offset from the fixed epoch.
          Default: 0
  JPL - if set, then the JPL ephemeris is used to compute nutation
        angles. Otherwise the series representation of HPRNUTANG is
        used.
  USE_EOP - if set, then use earth orientation parameters, returned
            by EOPDATA, to further refine the station coordinates.
            Otherwise, only precession and nutation are used.
  NO_UT1 - if set, then do not use the UT1-UTC conversion.
  NO_PRECESSION - disable precession calculation.
  NO_NUTATION - disable nutation calculation.
  NO_POLAR_MOTION - disable polar motion calculation.

Example



  ;; ITRF coordinates of Deep Space Network Antenna 63 (METERS)
  R_DSN63 = [+4849092.647d, -0360180.569d, +4115109.113d]
  ;; Time: 2000/01/01 01:30 TT
  JDTT = jday(2000d,1,1) + 1.5/24
  ;; Compute position of antenna in J2000 coordinate system using
  ;; full Earth Orientation Parameters.
  HPRSTATN, JDTT, R_DSN63, R_ECI, V_ECI, /USE_EOP

See Also



  HPRNUTANG, TAI_UTC (Markwardt Library)
  EOPDATA, JPLEPHREAD, JPLEPHINTERP

References



  McCarthy, D. D. (ed.) 1996: IERS Conventions, IERS T.N. 21.
    http://maia.usno.navy.mil/conventions.html
  Seidelmann, P.K. 1992, *Explanatory Supplement to the Astronomical
    Almanac*, ISBN 0-935702-68-7

Modification History


  Written, 6 May 2002, CM
  Documented, 12 May 2002, CM
  Corrected discussion of geodetic coordinates, 26 May 2002, CM
  Add NO_POLAR_MOTION keyword; only compute V_ECI if the variable
    is passed, 07 Mar 2007, CM
  Save some memory by deleting variables that are no longer used,
    19 Dec 2008, CM
  Some small documentation improvements, 16 Jan 2010, CM
  Correct error in calculation of conversion from geodetic lat/lon
    to cartesian, and add references, 2010-05-12, CM
  $Id: hprstatn.pro,v 1.8 2010/05/12 22:17:32 craigm Exp $



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