EarthPoleTide.cpp

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#pragma ident "$Id: EarthPoleTide.cpp 2457 2010-08-18 14:20:12Z coandrei $"

//============================================================================
//
//  This file is part of GPSTk, the GPS Toolkit.
//
//  The GPSTk is free software; you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published
//  by the Free Software Foundation; either version 2.1 of the License, or
//  any later version.
//
//  The GPSTk is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with GPSTk; if not, write to the Free Software Foundation,
//  Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
//  Wei Yan - Chinese Academy of Sciences . 2009, 2010
//
//============================================================================


#include "EarthPoleTide.hpp"
#include "ASConstant.hpp"
#include "IERS.hpp"

namespace gpstk
{

      /* Solid pole tide to normalized earth potential coefficients
       *
       * @param mjdUtc   UTC in MJD
       * @param dC21     correction to normalized coefficients dC21
       * @param dS21     correction to normalized coefficients dS21
       */
   void EarthPoleTide::getPoleTide(double mjdUtc, double& dC21, double& dS21 )
   {
      // See IERS Conventions 2003 section 7.1.4, P84

      // x offset and it's rate in 2000
      const double xp0 = 0.054;      // in arcsec
      const double dxp0 = 0.00083;   // in arcsec/year

      // y offset and it's rate in 2000
      const double yp0 = 0.357;      // in arcsec
      const double dyp0 = 0.00395;   // in arcsec/year

      // UTC time
      double leapYear = (mjdUtc-ASConstant::MJD_J2000)/365.25;
      
      double xpm = xp0 + leapYear * dxp0;
      double ypm = yp0 + leapYear * dyp0;
      
      double xp = IERS::xPole(mjdUtc);   // in arcsec
      double yp = IERS::yPole(mjdUtc);    // in arcsec
      
      double m1 =  xp - xpm;
      double m2 = -yp + ypm;
      
      // See IERS Conventions 2003 section 6.2, P65
      // Correction to normalized earth potential coefficients
      // C21 and S21
      dC21 = -1.333e-9 * ( m1 - 0.0115 * m2 );
      dS21 = -1.333e-9 * ( m2 + 0.0115 * m1 );

   }  // End of method 'EarthPoleTide::getPoleTide()'

}  // End of namespace 'gpstk'

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