TurnAroundRangeTroposphericDelayModifier.java

  1. /* Copyright 2002-2017 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.TurnAroundRange;
  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 turn-around TurnAroundRange measurement with tropospheric delay.
  41.  * The effect of tropospheric correction on the TurnAroundRange is directly computed
  42.  * through the computation of the tropospheric delay.
  43.  *
  44.  * In general, for GNSS, VLBI, ... there is hardly any frequency dependence in the delay.
  45.  * For SLR techniques however, the frequency dependence is sensitive.
  46.  *
  47.  * @author Maxime Journot
  48.  * @since 9.0
  49.  */
  50. public class TurnAroundRangeTroposphericDelayModifier implements EstimationModifier<TurnAroundRange> {

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

  55.     /** Constructor.
  56.      *
  57.      * @param model  Tropospheric delay model appropriate for the current TurnAroundRange measurement method.
  58.      */
  59.     public TurnAroundRangeTroposphericDelayModifier(final TroposphericModel model) {
  60.         tropoModel = model;
  61.     }

  63.     /** Get the station height above mean sea level.
  64.      *
  65.      * @param station  ground station (or measuring station)
  66.      * @return the measuring station height above sea level, m
  67.      */
  68.     private double getStationHeightAMSL(final GroundStation station) {
  69.         // FIXME height should be computed with respect to geoid WGS84+GUND = EGM2008 for example
  70.         final double height = station.getBaseFrame().getPoint().getAltitude();
  71.         return height;
  72.     }

  74.     /** Compute the measurement error due to Troposphere.
  75.      * @param station station
  76.      * @param state spacecraft state
  77.      * @return the measurement error due to Troposphere
  78.      * @throws OrekitException  if frames transformations cannot be computed
  79.      */
  80.     private double rangeErrorTroposphericModel(final GroundStation station, final SpacecraftState state)
  81.         throws OrekitException {
  82.         //
  83.         final Vector3D position = state.getPVCoordinates().getPosition();

  85.         // elevation
  86.         final double elevation = station.getBaseFrame().getElevation(position,
  87.                                                                      state.getFrame(),
  88.                                                                      state.getDate());

  90.         // only consider measures above the horizon
  91.         if (elevation > 0) {
  92.             // altitude AMSL in meters
  93.             final double height = getStationHeightAMSL(station);

  95.             // Delay in meters
  96.             final double delay = tropoModel.pathDelay(elevation, height);

  98.             return delay;
  99.         }

  101.         return 0;
  102.     }

  104.     /** Compute the Jacobian of the delay term wrt state.
  105.      *
  106.      * @param station station
  107.      * @param refstate reference spacecraft state
  108.      *
  109.      * @return Jacobian of the delay wrt state
  110.      * @throws OrekitException  if frames transformations cannot be computed
  111.      */
  112.     private double[][] rangeErrorJacobianState(final GroundStation station, final SpacecraftState refstate)
  113.         throws OrekitException {
  114.         final double[][] finiteDifferencesJacobian =
  115.                         Differentiation.differentiate(new StateFunction() {
  116.                             public double[] value(final SpacecraftState state) throws OrekitException {
  117.                                 try {
  118.                                     // evaluate target's elevation with a changed target position
  119.                                     final double value = rangeErrorTroposphericModel(station, state);

  121.                                     return new double[] {value };

  123.                                 } catch (OrekitException oe) {
  124.                                     throw new OrekitExceptionWrapper(oe);
  125.                                 }
  126.                             }
  127.                         }, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
  128.                         PositionAngle.TRUE, 15.0, 3).value(refstate);

  130.         return finiteDifferencesJacobian;
  131.     }


  134.     /** Compute the derivative of the delay term wrt parameters.
  135.      *
  136.      * @param station ground station
  137.      * @param driver driver for the station offset parameter
  138.      * @param state spacecraft state
  139.      * @return derivative of the delay wrt station offset parameter
  140.      * @throws OrekitException  if frames transformations cannot be computed
  141.      */
  142.     private double rangeErrorParameterDerivative(final GroundStation station,
  143.                                                  final ParameterDriver driver,
  144.                                                  final SpacecraftState state)
  145.         throws OrekitException {

  147.         final ParameterFunction rangeError = new ParameterFunction() {
  148.             /** {@inheritDoc} */
  149.             @Override
  150.             public double value(final ParameterDriver parameterDriver) throws OrekitException {
  151.                 return rangeErrorTroposphericModel(station, state);
  152.             }
  153.         };

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

  157.         return rangeErrorDerivative.value(driver);

  159.     }

  161.     /** {@inheritDoc} */
  162.     @Override
  163.     public List<ParameterDriver> getParametersDrivers() {
  164.         return Collections.emptyList();
  165.     }

  167.     /** {@inheritDoc} */
  168.     @Override
  169.     public void modify(final EstimatedMeasurement<TurnAroundRange> estimated)
  170.         throws OrekitException {
  171.         final TurnAroundRange measurement   = estimated.getObservedMeasurement();
  172.         final GroundStation   masterStation = measurement.getMasterStation();
  173.         final GroundStation   slaveStation  = measurement.getSlaveStation();
  174.         final SpacecraftState state         = estimated.getStates()[0];

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

  178.         // Update estimated value taking into account the tropospheric delay.
  179.         // The tropospheric delay is directly added to the TurnAroundRange.
  180.         final double masterDelay = rangeErrorTroposphericModel(masterStation, state);
  181.         final double slaveDelay = rangeErrorTroposphericModel(slaveStation, state);
  182.         final double[] newValue = oldValue.clone();
  183.         newValue[0] = newValue[0] + masterDelay + slaveDelay;
  184.         estimated.setEstimatedValue(newValue);

  186.         // Update estimated derivatives with Jacobian of the measure wrt state
  187.         final double[][] masterDjac = rangeErrorJacobianState(masterStation, state);
  188.         final double[][] slaveDjac = rangeErrorJacobianState(slaveStation, state);
  189.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  190.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  191.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  192.                 stateDerivatives[irow][jcol] += masterDjac[irow][jcol] + slaveDjac[irow][jcol];
  193.             }
  194.         }
  195.         estimated.setStateDerivatives(0, stateDerivatives);

  197.         // Update derivatives with respect to master station position
  198.         for (final ParameterDriver driver : Arrays.asList(masterStation.getEastOffsetDriver(),
  199.                                                           masterStation.getNorthOffsetDriver(),
  200.                                                           masterStation.getZenithOffsetDriver())) {
  201.             if (driver.isSelected()) {
  202.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  203.                 parameterDerivative += rangeErrorParameterDerivative(masterStation, driver, state);
  204.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  205.             }
  206.         }

  208.         // Update derivatives with respect to slave station position
  209.         for (final ParameterDriver driver : Arrays.asList(slaveStation.getEastOffsetDriver(),
  210.                                                           slaveStation.getNorthOffsetDriver(),
  211.                                                           slaveStation.getZenithOffsetDriver())) {
  212.             if (driver.isSelected()) {
  213.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  214.                 parameterDerivative += rangeErrorParameterDerivative(slaveStation, driver, state);
  215.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  216.             }
  217.         }
  218.     }

  220. }
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