RangeRateTroposphericDelayModifier.java

  1. /* Copyright 2002-2018 CS Systèmes d'Information
  2.  * Licensed to CS Systèmes d'Information (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.estimation.measurements.modifiers;

  19. import java.util.Arrays;
  20. import java.util.Collections;
  21. import java.util.List;

  23. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  24. import org.orekit.errors.OrekitException;
  25. import org.orekit.errors.OrekitExceptionWrapper;
  26. import org.orekit.estimation.measurements.EstimatedMeasurement;
  27. import org.orekit.estimation.measurements.EstimationModifier;
  28. import org.orekit.estimation.measurements.GroundStation;
  29. import org.orekit.estimation.measurements.RangeRate;
  30. import org.orekit.models.earth.TroposphericModel;
  31. import org.orekit.orbits.OrbitType;
  32. import org.orekit.orbits.PositionAngle;
  33. import org.orekit.propagation.Propagator;
  34. import org.orekit.propagation.SpacecraftState;
  35. import org.orekit.utils.Differentiation;
  36. import org.orekit.utils.ParameterDriver;
  37. import org.orekit.utils.ParameterFunction;
  38. import org.orekit.utils.StateFunction;

  40. /** Class modifying theoretical range-rate measurements with tropospheric delay.
  41.  * The effect of tropospheric correction on the range-rate is directly computed
  42.  * through the computation of the tropospheric delay difference with respect to
  43.  * time.
  44.  *
  45.  * In general, for GNSS, VLBI, ... there is hardly any frequency dependence in the delay.
  46.  * For SLR techniques however, the frequency dependence is sensitive.
  47.  *
  48.  * @author Joris Olympio
  49.  * @since 8.0
  50.  */
  51. public class RangeRateTroposphericDelayModifier implements EstimationModifier<RangeRate> {

  53.     /** Tropospheric delay model. */
  54.     private final TroposphericModel tropoModel;

  56.     /** Two-way measurement factor. */
  57.     private final double fTwoWay;

  59.     /** Constructor.
  60.      *
  61.      * @param model  Tropospheric delay model appropriate for the current range-rate measurement method.
  62.      * @param tw     Flag indicating whether the measurement is two-way.
  63.      */
  64.     public RangeRateTroposphericDelayModifier(final TroposphericModel model, final boolean tw) {
  65.         tropoModel = model;
  66.         if (tw) {
  67.             fTwoWay = 2.;
  68.         } else {
  69.             fTwoWay = 1.;
  70.         }
  71.     }

  73.     /** Get the station height above mean sea level.
  74.      *
  75.      * @param station  ground station (or measuring station)
  76.      * @return the measuring station height above sea level, m
  77.      */
  78.     private double getStationHeightAMSL(final GroundStation station) {
  79.         // FIXME heigth should be computed with respect to geoid WGS84+GUND = EGM2008 for example
  80.         final double height = station.getBaseFrame().getPoint().getAltitude();
  81.         return height;
  82.     }

  84.     /** Compute the measurement error due to Troposphere.
  85.      * @param station station
  86.      * @param state spacecraft state
  87.      * @return the measurement error due to Troposphere
  88.      * @throws OrekitException  if frames transformations cannot be computed
  89.      */
  90.     public double rangeRateErrorTroposphericModel(final GroundStation station,
  91.                                                   final SpacecraftState state)
  92.         throws OrekitException {
  93.         // The effect of tropospheric correction on the range rate is
  94.         // computed using finite differences.

  96.         final double dt = 10; // s

  98.         // station altitude AMSL in meters
  99.         final double height = getStationHeightAMSL(station);

  101.         // spacecraft position and elevation as seen from the ground station
  102.         final Vector3D position = state.getPVCoordinates().getPosition();

  104.         // elevation
  105.         final double elevation1 = station.getBaseFrame().getElevation(position,
  106.                                                                       state.getFrame(),
  107.                                                                       state.getDate());

  109.         // only consider measures above the horizon
  110.         if (elevation1 > 0) {
  111.             // tropospheric delay in meters
  112.             final double d1 = tropoModel.pathDelay(elevation1, height);

  114.             // propagate spacecraft state forward by dt
  115.             final SpacecraftState state2 = state.shiftedBy(dt);

  117.             // spacecraft position and elevation as seen from the ground station
  118.             final Vector3D position2 = state2.getPVCoordinates().getPosition();

  120.             // elevation
  121.             final double elevation2 = station.getBaseFrame().getElevation(position2,
  122.                                                                           state2.getFrame(),
  123.                                                                           state2.getDate());

  125.             // tropospheric delay dt after
  126.             final double d2 = tropoModel.pathDelay(elevation2, height);

  128.             return fTwoWay * (d2 - d1) / dt;
  129.         }

  131.         return 0;
  132.     }


  135.     /** Compute the Jacobian of the delay term wrt state.
  136.      *
  137.      * @param station station
  138.      * @param refstate spacecraft state
  139.      * @param delay current tropospheric delay
  140.      * @return Jacobian of the delay wrt state
  141.      * @throws OrekitException  if frames transformations cannot be computed
  142.      */
  143.     private double[][] rangeRateErrorJacobianState(final GroundStation station,
  144.                                                    final SpacecraftState refstate,
  145.                                                    final double delay)
  146.         throws OrekitException {
  147.         final double[][] finiteDifferencesJacobian =
  148.                         Differentiation.differentiate(new StateFunction() {
  149.                             public double[] value(final SpacecraftState state) throws OrekitException {
  150.                                 try {
  151.                                     // evaluate target's elevation with a changed target position
  152.                                     final double value = rangeRateErrorTroposphericModel(station, state);

  154.                                     return new double[] {value };

  156.                                 } catch (OrekitException oe) {
  157.                                     throw new OrekitExceptionWrapper(oe);
  158.                                 }
  159.                             }
  160.                         }, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
  161.                         PositionAngle.TRUE, 15.0, 3).value(refstate);

  163.         return finiteDifferencesJacobian;
  164.     }

  166.     /** Compute the derivative of the delay term wrt parameters.
  167.     *
  168.     * @param station ground station
  169.     * @param driver driver for the station offset parameter
  170.     * @param state spacecraft state
  171.     * @param delay current ionospheric delay
  172.     * @return derivative of the delay wrt station offset parameter
  173.     * @throws OrekitException  if frames transformations cannot be computed
  174.     */
  175.     private double rangeRateErrorParameterDerivative(final GroundStation station,
  176.                                                      final ParameterDriver driver,
  177.                                                      final SpacecraftState state,
  178.                                                      final double delay)
  179.         throws OrekitException {

  181.         final ParameterFunction rangeError = new ParameterFunction() {
  182.             /** {@inheritDoc} */
  183.             @Override
  184.             public double value(final ParameterDriver parameterDriver) throws OrekitException {
  185.                 return rangeRateErrorTroposphericModel(station, state);
  186.             }
  187.         };

  189.         final ParameterFunction rangeErrorDerivative =
  190.                         Differentiation.differentiate(rangeError, driver, 3, 10.0);

  192.         return rangeErrorDerivative.value(driver);

  194.     }

  196.     /** {@inheritDoc} */
  197.     @Override
  198.     public List<ParameterDriver> getParametersDrivers() {
  199.         return Collections.emptyList();
  200.     }

  202.     /** {@inheritDoc} */
  203.     @Override
  204.     public void modify(final EstimatedMeasurement<RangeRate> estimated)
  205.         throws OrekitException {
  206.         final RangeRate       measurement = estimated.getObservedMeasurement();
  207.         final GroundStation   station     = measurement.getStation();
  208.         final SpacecraftState state       = estimated.getStates()[0];

  210.         final double[] oldValue = estimated.getEstimatedValue();

  212.         final double delay = rangeRateErrorTroposphericModel(station, state);

  214.         // update estimated value taking into account the tropospheric delay.
  215.         // The tropospheric delay is directly added to the range.
  216.         final double[] newValue = oldValue.clone();
  217.         newValue[0] = newValue[0] + delay;
  218.         estimated.setEstimatedValue(newValue);

  220.         // update estimated derivatives with Jacobian of the measure wrt state
  221.         final double[][] djac = rangeRateErrorJacobianState(station,
  222.                                       state,
  223.                                       delay);
  224.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  225.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  226.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  227.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  228.             }
  229.         }
  230.         estimated.setStateDerivatives(0, stateDerivatives);

  232.         for (final ParameterDriver driver : Arrays.asList(station.getEastOffsetDriver(),
  233.                                                           station.getNorthOffsetDriver(),
  234.                                                           station.getZenithOffsetDriver())) {
  235.             if (driver.isSelected()) {
  236.                 // update estimated derivatives with derivative of the modification wrt station parameters
  237.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  238.                 parameterDerivative += rangeRateErrorParameterDerivative(station, driver, state, delay);
  239.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  240.             }
  241.         }

  243.     }

  245. }
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