TurnAroundRangeTroposphericDelayModifier.java

  1. /* Copyright 2002-2020 CS GROUP
  2.  * Licensed to CS GROUP (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.List;

  22. import org.hipparchus.Field;
  23. import org.hipparchus.RealFieldElement;
  24. import org.hipparchus.analysis.differentiation.Gradient;
  25. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  26. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  27. import org.orekit.attitudes.InertialProvider;
  28. import org.orekit.estimation.measurements.EstimatedMeasurement;
  29. import org.orekit.estimation.measurements.EstimationModifier;
  30. import org.orekit.estimation.measurements.GroundStation;
  31. import org.orekit.estimation.measurements.TurnAroundRange;
  32. import org.orekit.models.earth.troposphere.DiscreteTroposphericModel;
  33. import org.orekit.propagation.FieldSpacecraftState;
  34. import org.orekit.propagation.SpacecraftState;
  35. import org.orekit.utils.Differentiation;
  36. import org.orekit.utils.ParameterDriver;
  37. import org.orekit.utils.ParameterFunction;

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

  51.     /** Tropospheric delay model. */
  52.     private final DiscreteTroposphericModel tropoModel;

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

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

  73.     /** Get the station height above mean sea level.
  74.     * @param <T> type of the elements
  75.     * @param field field of the elements
  76.     * @param station  ground station (or measuring station)
  77.     * @return the measuring station height above sea level, m
  78.     */
  79.     private <T extends RealFieldElement<T>> T getStationHeightAMSL(final Field<T> field,
  80.                                                                    final GroundStation station) {
  81.         // FIXME heigth should be computed with respect to geoid WGS84+GUND = EGM2008 for example
  82.         final T height = station.getBaseFrame().getPoint(field).getAltitude();
  83.         return height;
  84.     }

  86.     /** Compute the measurement error due to Troposphere.
  87.      * @param station station
  88.      * @param state spacecraft state
  89.      * @return the measurement error due to Troposphere
  90.      */
  91.     private double rangeErrorTroposphericModel(final GroundStation station, final SpacecraftState state) {
  92.         //
  93.         final Vector3D position = state.getPVCoordinates().getPosition();

  95.         // elevation
  96.         final double elevation = station.getBaseFrame().getElevation(position,
  97.                                                                      state.getFrame(),
  98.                                                                      state.getDate());

  100.         // only consider measures above the horizon
  101.         if (elevation > 0) {
  102.             // altitude AMSL in meters
  103.             final double height = getStationHeightAMSL(station);

  105.             // Delay in meters
  106.             final double delay = tropoModel.pathDelay(elevation, height, tropoModel.getParameters(), state.getDate());

  108.             return delay;
  109.         }

  111.         return 0;
  112.     }

  114.     /** Compute the measurement error due to Troposphere.
  115.      * @param <T> type of the element
  116.      * @param station station
  117.      * @param state spacecraft state
  118.      * @param parameters tropospheric model parameters
  119.      * @return the measurement error due to Troposphere
  120.      */
  121.     private <T extends RealFieldElement<T>> T rangeErrorTroposphericModel(final GroundStation station,
  122.                                                                           final FieldSpacecraftState<T> state,
  123.                                                                           final T[] parameters) {
  124.         // Field
  125.         final Field<T> field = state.getDate().getField();
  126.         final T zero         = field.getZero();

  128.         //
  129.         final FieldVector3D<T> position = state.getPVCoordinates().getPosition();
  130.         final T dsElevation             = station.getBaseFrame().getElevation(position,
  131.                                                                               state.getFrame(),
  132.                                                                               state.getDate());

  134.         // only consider measures above the horizon
  135.         if (dsElevation.getReal() > 0) {
  136.             // altitude AMSL in meters
  137.             final T height = getStationHeightAMSL(field, station);

  139.             // Delay in meters
  140.             final T delay = tropoModel.pathDelay(dsElevation, height, parameters, state.getDate());

  142.             return delay;
  143.         }

  145.         return zero;
  146.     }

  148.     /** Compute the Jacobian of the delay term wrt state using
  149.     * automatic differentiation.
  150.     *
  151.     * @param derivatives tropospheric delay derivatives
  152.     *
  153.     * @return Jacobian of the delay wrt state
  154.     */
  155.     private double[][] rangeErrorJacobianState(final double[] derivatives) {
  156.         final double[][] finiteDifferencesJacobian = new double[1][6];
  157.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  158.         return finiteDifferencesJacobian;
  159.     }


  162.     /** Compute the derivative of the delay term wrt parameters.
  163.      *
  164.      * @param station ground station
  165.      * @param driver driver for the station offset parameter
  166.      * @param state spacecraft state
  167.      * @return derivative of the delay wrt station offset parameter
  168.      */
  169.     private double rangeErrorParameterDerivative(final GroundStation station,
  170.                                                  final ParameterDriver driver,
  171.                                                  final SpacecraftState state) {

  173.         final ParameterFunction rangeError = new ParameterFunction() {
  174.             /** {@inheritDoc} */
  175.             @Override
  176.             public double value(final ParameterDriver parameterDriver) {
  177.                 return rangeErrorTroposphericModel(station, state);
  178.             }
  179.         };

  181.         final ParameterFunction rangeErrorDerivative = Differentiation.differentiate(rangeError, 3, 10.0 * driver.getScale());

  183.         return rangeErrorDerivative.value(driver);

  185.     }

  187.     /** Compute the derivative of the delay term wrt parameters using
  188.     * automatic differentiation.
  189.     *
  190.     * @param derivatives tropospheric delay derivatives
  191.     * @param freeStateParameters dimension of the state.
  192.     * @return derivative of the delay wrt tropospheric model parameters
  193.     */
  194.     private double[] rangeErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  195.         // 0 ... freeStateParameters - 1 -> derivatives of the delay wrt state
  196.         // freeStateParameters ... n     -> derivatives of the delay wrt tropospheric parameters
  197.         final int dim = derivatives.length - freeStateParameters;
  198.         final double[] rangeError = new double[dim];

  200.         for (int i = 0; i < dim; i++) {
  201.             rangeError[i] = derivatives[freeStateParameters + i];
  202.         }

  204.         return rangeError;
  205.     }

  207.     /** {@inheritDoc} */
  208.     @Override
  209.     public List<ParameterDriver> getParametersDrivers() {
  210.         return tropoModel.getParametersDrivers();
  211.     }

  213.     /** {@inheritDoc} */
  214.     @Override
  215.     public void modify(final EstimatedMeasurement<TurnAroundRange> estimated) {
  216.         final TurnAroundRange measurement   = estimated.getObservedMeasurement();
  217.         final GroundStation   masterStation = measurement.getMasterStation();
  218.         final GroundStation   slaveStation  = measurement.getSlaveStation();
  219.         final SpacecraftState state         = estimated.getStates()[0];

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

  223.         // Update estimated derivatives with Jacobian of the measure wrt state
  224.         final TroposphericGradientConverter converter =
  225.                 new TroposphericGradientConverter(state, 6, new InertialProvider(state.getFrame()));
  226.         final FieldSpacecraftState<Gradient> gState = converter.getState(tropoModel);
  227.         final Gradient[] gParameters = converter.getParameters(gState, tropoModel);
  228.         final Gradient masterGDelay = rangeErrorTroposphericModel(masterStation, gState, gParameters);
  229.         final Gradient slaveGDelay = rangeErrorTroposphericModel(slaveStation, gState, gParameters);
  230.         final double[] masterDerivatives = masterGDelay.getGradient();
  231.         final double[] slaveDerivatives  = masterGDelay.getGradient();

  233.         final double[][] masterDjac = rangeErrorJacobianState(masterDerivatives);
  234.         final double[][] slaveDjac  = rangeErrorJacobianState(slaveDerivatives);
  235.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  236.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  237.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  238.                 stateDerivatives[irow][jcol] += masterDjac[irow][jcol] + slaveDjac[irow][jcol];
  239.             }
  240.         }
  241.         estimated.setStateDerivatives(0, stateDerivatives);

  243.         int indexMaster = 0;
  244.         for (final ParameterDriver driver : getParametersDrivers()) {
  245.             if (driver.isSelected()) {
  246.                 // update estimated derivatives with derivative of the modification wrt tropospheric parameters
  247.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  248.                 final double[] derivatives = rangeErrorParameterDerivative(masterDerivatives, converter.getFreeStateParameters());
  249.                 parameterDerivative += derivatives[indexMaster];
  250.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  251.                 indexMaster += 1;
  252.             }

  254.         }

  256.         int indexSlave = 0;
  257.         for (final ParameterDriver driver : getParametersDrivers()) {
  258.             if (driver.isSelected()) {
  259.                 // update estimated derivatives with derivative of the modification wrt tropospheric parameters
  260.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  261.                 final double[] derivatives = rangeErrorParameterDerivative(slaveDerivatives, converter.getFreeStateParameters());
  262.                 parameterDerivative += derivatives[indexSlave];
  263.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  264.                 indexSlave += 1;
  265.             }

  267.         }

  269.         // Update derivatives with respect to master station position
  270.         for (final ParameterDriver driver : Arrays.asList(masterStation.getClockOffsetDriver(),
  271.                                                           masterStation.getEastOffsetDriver(),
  272.                                                           masterStation.getNorthOffsetDriver(),
  273.                                                           masterStation.getZenithOffsetDriver())) {
  274.             if (driver.isSelected()) {
  275.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  276.                 parameterDerivative += rangeErrorParameterDerivative(masterStation, driver, state);
  277.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  278.             }
  279.         }

  281.         // Update derivatives with respect to slave station position
  282.         for (final ParameterDriver driver : Arrays.asList(slaveStation.getEastOffsetDriver(),
  283.                                                           slaveStation.getNorthOffsetDriver(),
  284.                                                           slaveStation.getZenithOffsetDriver())) {
  285.             if (driver.isSelected()) {
  286.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  287.                 parameterDerivative += rangeErrorParameterDerivative(slaveStation, driver, state);
  288.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  289.             }
  290.         }

  292.         // Update estimated value taking into account the tropospheric delay.
  293.         // The tropospheric delay is directly added to the TurnAroundRange.
  294.         final double[] newValue = oldValue.clone();
  295.         newValue[0] = newValue[0] + masterGDelay.getReal() + slaveGDelay.getReal();
  296.         estimated.setEstimatedValue(newValue);

  298.     }

  300. }
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