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.Gradient;
  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.     *
  105.     * @return Jacobian of the delay wrt state
  106.     */
  107.     private double[][] rangeErrorJacobianState(final double[] derivatives) {
  108.         final double[][] finiteDifferencesJacobian = new double[1][6];
  109.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  110.         return finiteDifferencesJacobian;
  111.     }


  114.     /** Compute the derivative of the delay term wrt parameters.
  115.      *
  116.      * @param station ground station
  117.      * @param driver driver for the station offset parameter
  118.      * @param state spacecraft state
  119.      * @return derivative of the delay wrt station offset parameter
  120.      */
  121.     private double rangeErrorParameterDerivative(final GroundStation station,
  122.                                                  final ParameterDriver driver,
  123.                                                  final SpacecraftState state) {

  125.         final ParameterFunction rangeError = new ParameterFunction() {
  126.             /** {@inheritDoc} */
  127.             @Override
  128.             public double value(final ParameterDriver parameterDriver) {
  129.                 return rangeErrorIonosphericModel(station, state);
  130.             }
  131.         };

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

  136.         return rangeErrorDerivative.value(driver);

  138.     }

  140.     /** Compute the derivative of the delay term wrt parameters using
  141.     * automatic differentiation.
  142.     *
  143.     * @param derivatives ionospheric delay derivatives
  144.     * @param freeStateParameters dimension of the state.
  145.     * @return derivative of the delay wrt ionospheric model parameters
  146.     */
  147.     private double[] rangeErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  148.         // 0 ... freeStateParameters - 1 -> derivatives of the delay wrt state
  149.         // freeStateParameters ... n     -> derivatives of the delay wrt ionospheric parameters
  150.         final int dim = derivatives.length - freeStateParameters;
  151.         final double[] rangeError = new double[dim];

  153.         for (int i = 0; i < dim; i++) {
  154.             rangeError[i] = derivatives[freeStateParameters + i];
  155.         }

  157.         return rangeError;
  158.     }

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

  166.     @Override
  167.     public void modify(final EstimatedMeasurement<TurnAroundRange> estimated) {
  168.         final TurnAroundRange measurement   = estimated.getObservedMeasurement();
  169.         final GroundStation   masterStation = measurement.getMasterStation();
  170.         final GroundStation   slaveStation  = measurement.getSlaveStation();
  171.         final SpacecraftState state         = estimated.getStates()[0];

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

  175.         // Update estimated derivatives with Jacobian of the measure wrt state
  176.         final IonosphericGradientConverter converter =
  177.                 new IonosphericGradientConverter(state, 6, new InertialProvider(state.getFrame()));
  178.         final FieldSpacecraftState<Gradient> gState = converter.getState(ionoModel);
  179.         final Gradient[] gParameters = converter.getParameters(gState, ionoModel);
  180.         final Gradient masterGDelay = rangeErrorIonosphericModel(masterStation, gState, gParameters);
  181.         final Gradient slaveGDelay = rangeErrorIonosphericModel(slaveStation, gState, gParameters);
  182.         final double[] masterDerivatives = masterGDelay.getGradient();
  183.         final double[] slaveDerivatives  = masterGDelay.getGradient();

  185.         final double[][] masterDjac = rangeErrorJacobianState(masterDerivatives);
  186.         final double[][] slaveDjac  = rangeErrorJacobianState(slaveDerivatives);
  187.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  188.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  189.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  190.                 stateDerivatives[irow][jcol] += masterDjac[irow][jcol] + slaveDjac[irow][jcol];
  191.             }
  192.         }
  193.         estimated.setStateDerivatives(0, stateDerivatives);

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

  206.         }

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

  219.         }

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

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

  244.         // Update estimated value taking into account the ionospheric delay.
  245.         // The ionospheric delay is directly added to the TurnAroundRange.
  246.         final double[] newValue = oldValue.clone();
  247.         newValue[0] = newValue[0] + masterGDelay.getReal() + slaveGDelay.getReal();
  248.         estimated.setEstimatedValue(newValue);
  249.     }

  251. }
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