TurnAroundRangeIonosphericDelayModifier.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.RealFieldElement;
  23. import org.hipparchus.analysis.differentiation.DerivativeStructure;
  24. import org.orekit.attitudes.InertialProvider;
  25. import org.orekit.estimation.measurements.EstimatedMeasurement;
  26. import org.orekit.estimation.measurements.EstimationModifier;
  27. import org.orekit.estimation.measurements.GroundStation;
  28. import org.orekit.estimation.measurements.TurnAroundRange;
  29. import org.orekit.frames.TopocentricFrame;
  30. import org.orekit.models.earth.ionosphere.IonosphericModel;
  31. import org.orekit.propagation.FieldSpacecraftState;
  32. import org.orekit.propagation.SpacecraftState;
  33. import org.orekit.utils.Differentiation;
  34. import org.orekit.utils.ParameterDriver;
  35. import org.orekit.utils.ParameterFunction;

  37. /** Class modifying theoretical TurnAroundRange measurement with ionospheric delay.
  38.  * The effect of ionospheric correction on the TurnAroundRange is directly computed
  39.  * through the computation of the ionospheric delay.
  40.  *
  41.  * The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
  42.  * For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
  43.  * <p>
  44.  * Since 10.0, state derivatives and ionospheric parameters derivates are computed
  45.  * using automatic differentiation.
  46.  * </p>
  47.  * @author Maxime Journot
  48.  * @since 9.0
  49.  */
  50. public class TurnAroundRangeIonosphericDelayModifier implements EstimationModifier<TurnAroundRange> {

  52.     /** Ionospheric delay model. */
  53.     private final IonosphericModel ionoModel;

  55.     /** Frequency [Hz]. */
  56.     private final double frequency;

  58.     /** Constructor.
  59.      *
  60.      * @param model  Ionospheric delay model appropriate for the current TurnAroundRange measurement method.
  61.      * @param freq frequency of the signal in Hz
  62.      */
  63.     public TurnAroundRangeIonosphericDelayModifier(final IonosphericModel model,
  64.                                                    final double freq) {
  65.         ionoModel = model;
  66.         frequency = freq;
  67.     }

  69.     /** Compute the measurement error due to ionosphere.
  70.      * @param station station
  71.      * @param state spacecraft state
  72.      * @return the measurement error due to ionosphere
  73.      */
  74.     private double rangeErrorIonosphericModel(final GroundStation station,
  75.                                               final SpacecraftState state) {
  76.         // Base frame associated with the station
  77.         final TopocentricFrame baseFrame = station.getBaseFrame();
  78.         // Delay in meters
  79.         final double delay = ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters());
  80.         return delay;
  81.     }

  83.     /** Compute the measurement error due to ionosphere.
  84.      * @param <T> type of the elements
  85.      * @param station station
  86.      * @param state spacecraft state
  87.      * @param parameters ionospheric model parameters
  88.      * @return the measurement error due to ionosphere
  89.      */
  90.     private <T extends RealFieldElement<T>> T rangeErrorIonosphericModel(final GroundStation station,
  91.                                                                          final FieldSpacecraftState<T> state,
  92.                                                                          final T[] parameters) {
  93.         // Base frame associated with the station
  94.         final TopocentricFrame baseFrame = station.getBaseFrame();
  95.         // Delay in meters
  96.         final T delay = ionoModel.pathDelay(state, baseFrame, frequency, parameters);
  97.         return delay;
  98.     }

  100.     /** Compute the Jacobian of the delay term wrt state using
  101.     * automatic differentiation.
  102.     *
  103.     * @param derivatives ionospheric delay derivatives
  104.     * @param freeStateParameters dimension of the state.
  105.     *
  106.     * @return Jacobian of the delay wrt state
  107.     */
  108.     private double[][] rangeErrorJacobianState(final double[] derivatives, final int freeStateParameters) {
  109.         final double[][] finiteDifferencesJacobian = new double[1][6];
  110.         for (int i = 0; i < freeStateParameters; i++) {
  111.             // First element is the value of the delay
  112.             finiteDifferencesJacobian[0][i] = derivatives[i + 1];
  113.         }
  114.         return finiteDifferencesJacobian;
  115.     }


  118.     /** Compute the derivative of the delay term wrt parameters.
  119.      *
  120.      * @param station ground station
  121.      * @param driver driver for the station offset parameter
  122.      * @param state spacecraft state
  123.      * @return derivative of the delay wrt station offset parameter
  124.      */
  125.     private double rangeErrorParameterDerivative(final GroundStation station,
  126.                                                  final ParameterDriver driver,
  127.                                                  final SpacecraftState state) {

  129.         final ParameterFunction rangeError = new ParameterFunction() {
  130.             /** {@inheritDoc} */
  131.             @Override
  132.             public double value(final ParameterDriver parameterDriver) {
  133.                 return rangeErrorIonosphericModel(station, state);
  134.             }
  135.         };

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

  140.         return rangeErrorDerivative.value(driver);

  142.     }

  144.     /** Compute the derivative of the delay term wrt parameters using
  145.     * automatic differentiation.
  146.     *
  147.     * @param derivatives ionospheric delay derivatives
  148.     * @param freeStateParameters dimension of the state.
  149.     * @return derivative of the delay wrt ionospheric model parameters
  150.     */
  151.     private double[] rangeErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  152.         // 0                               -> value of the delay
  153.         // 1 ... freeStateParameters       -> derivatives of the delay wrt state
  154.         // freeStateParameters + 1 ... n   -> derivatives of the delay wrt ionospheric parameters
  155.         final int dim = derivatives.length - 1 - freeStateParameters;
  156.         final double[] rangeError = new double[dim];

  158.         for (int i = 0; i < dim; i++) {
  159.             rangeError[i] = derivatives[1 + freeStateParameters + i];
  160.         }

  162.         return rangeError;
  163.     }

  165.     /** {@inheritDoc} */
  166.     @Override
  167.     public List<ParameterDriver> getParametersDrivers() {
  168.         return ionoModel.getParametersDrivers();
  169.     }

  171.     @Override
  172.     public void modify(final EstimatedMeasurement<TurnAroundRange> estimated) {
  173.         final TurnAroundRange measurement   = estimated.getObservedMeasurement();
  174.         final GroundStation   masterStation = measurement.getMasterStation();
  175.         final GroundStation   slaveStation  = measurement.getSlaveStation();
  176.         final SpacecraftState state         = estimated.getStates()[0];

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

  180.         // Update estimated derivatives with Jacobian of the measure wrt state
  181.         final IonosphericDSConverter converter =
  182.                 new IonosphericDSConverter(state, 6, new InertialProvider(state.getFrame()));
  183.         final FieldSpacecraftState<DerivativeStructure> dsState = converter.getState(ionoModel);
  184.         final DerivativeStructure[] dsParameters = converter.getParameters(dsState, ionoModel);
  185.         final DerivativeStructure masterDSDelay = rangeErrorIonosphericModel(masterStation, dsState, dsParameters);
  186.         final DerivativeStructure slaveDSDelay = rangeErrorIonosphericModel(slaveStation, dsState, dsParameters);
  187.         final double[] masterDerivatives = masterDSDelay.getAllDerivatives();
  188.         final double[] slaveDerivatives  = masterDSDelay.getAllDerivatives();

  190.         final double[][] masterDjac = rangeErrorJacobianState(masterDerivatives, converter.getFreeStateParameters());
  191.         final double[][] slaveDjac  = rangeErrorJacobianState(slaveDerivatives, converter.getFreeStateParameters());
  192.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  193.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  194.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  195.                 stateDerivatives[irow][jcol] += masterDjac[irow][jcol] + slaveDjac[irow][jcol];
  196.             }
  197.         }
  198.         estimated.setStateDerivatives(0, stateDerivatives);

  200.         int indexMaster = 0;
  201.         for (final ParameterDriver driver : getParametersDrivers()) {
  202.             if (driver.isSelected()) {
  203.                 // update estimated derivatives with derivative of the modification wrt ionospheric parameters
  204.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  205.                 final double[] derivatives = rangeErrorParameterDerivative(masterDerivatives, converter.getFreeStateParameters());
  206.                 parameterDerivative += derivatives[indexMaster];
  207.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  208.                 indexMaster += 1;
  209.             }

  211.         }

  213.         int indexSlave = 0;
  214.         for (final ParameterDriver driver : getParametersDrivers()) {
  215.             if (driver.isSelected()) {
  216.                 // update estimated derivatives with derivative of the modification wrt ionospheric parameters
  217.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  218.                 final double[] derivatives = rangeErrorParameterDerivative(slaveDerivatives, converter.getFreeStateParameters());
  219.                 parameterDerivative += derivatives[indexSlave];
  220.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  221.                 indexSlave += 1;
  222.             }

  224.         }

  226.         // Update derivatives with respect to master station position
  227.         for (final ParameterDriver driver : Arrays.asList(masterStation.getClockOffsetDriver(),
  228.                                                           masterStation.getEastOffsetDriver(),
  229.                                                           masterStation.getNorthOffsetDriver(),
  230.                                                           masterStation.getZenithOffsetDriver())) {
  231.             if (driver.isSelected()) {
  232.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  233.                 parameterDerivative += rangeErrorParameterDerivative(masterStation, driver, state);
  234.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  235.             }
  236.         }

  238.         // Update derivatives with respect to slave station position
  239.         for (final ParameterDriver driver : Arrays.asList(slaveStation.getEastOffsetDriver(),
  240.                                                           slaveStation.getNorthOffsetDriver(),
  241.                                                           slaveStation.getZenithOffsetDriver())) {
  242.             if (driver.isSelected()) {
  243.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  244.                 parameterDerivative += rangeErrorParameterDerivative(slaveStation, driver, state);
  245.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  246.             }
  247.         }

  249.         // Update estimated value taking into account the ionospheric delay.
  250.         // The ionospheric delay is directly added to the TurnAroundRange.
  251.         final double[] newValue = oldValue.clone();
  252.         newValue[0] = newValue[0] + masterDSDelay.getReal() + slaveDSDelay.getReal();
  253.         estimated.setEstimatedValue(newValue);
  254.     }

  256. }
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