RangeIonosphericDelayModifier.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.Range;
  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 range measurement with ionospheric delay.
  38.  * The effect of ionospheric correction on the range 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.  * @author Joris Olympio
  49.  * @since 8.0
  50.  */
  51. public class RangeIonosphericDelayModifier implements EstimationModifier<Range> {

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

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

  59.     /** Constructor.
  60.      *
  61.      * @param model Ionospheric delay model appropriate for the current range measurement method.
  62.      * @param freq frequency of the signal in Hz
  63.      */
  64.     public RangeIonosphericDelayModifier(final IonosphericModel model,
  65.                                          final double freq) {
  66.         ionoModel = model;
  67.         frequency = freq;
  68.     }

  70.     /** Compute the measurement error due to ionosphere.
  71.      * @param station station
  72.      * @param state spacecraft state
  73.      * @return the measurement error due to ionosphere
  74.      */
  75.     private double rangeErrorIonosphericModel(final GroundStation station,
  76.                                               final SpacecraftState state) {
  77.         // Base frame associated with the station
  78.         final TopocentricFrame baseFrame = station.getBaseFrame();
  79.         // delay in meters
  80.         final double delay = ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters());
  81.         return delay;
  82.     }

  84.     /** Compute the measurement error due to ionosphere.
  85.      * @param <T> type of the element
  86.      * @param station station
  87.      * @param state spacecraft state
  88.      * @param parameters ionospheric model parameters
  89.      * @return the measurement error due to ionosphere
  90.      */
  91.     private <T extends RealFieldElement<T>> T rangeErrorIonosphericModel(final GroundStation station,
  92.                                                                          final FieldSpacecraftState<T> state,
  93.                                                                          final T[] parameters) {
  94.          // Base frame associated with the station
  95.         final TopocentricFrame baseFrame = station.getBaseFrame();
  96.         // delay in meters
  97.         final T delay = ionoModel.pathDelay(state, baseFrame, frequency, parameters);
  98.         return delay;
  99.     }

  101.     /** Compute the Jacobian of the delay term wrt state using
  102.     * automatic differentiation.
  103.     *
  104.     * @param derivatives ionospheric delay derivatives
  105.     * @param freeStateParameters dimension of the state.
  106.     *
  107.     * @return Jacobian of the delay wrt state
  108.     */
  109.     private double[][] rangeErrorJacobianState(final double[] derivatives, final int freeStateParameters) {
  110.         final double[][] finiteDifferencesJacobian = new double[1][6];
  111.         for (int i = 0; i < freeStateParameters; i++) {
  112.             // First element is the value of the delay
  113.             finiteDifferencesJacobian[0][i] = derivatives[i + 1];
  114.         }
  115.         return finiteDifferencesJacobian;
  116.     }


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

  132.         final ParameterFunction rangeError = new ParameterFunction() {
  133.             /** {@inheritDoc} */
  134.             @Override
  135.             public double value(final ParameterDriver parameterDriver) {
  136.                 return rangeErrorIonosphericModel(station, state);
  137.             }
  138.         };

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

  143.         return rangeErrorDerivative.value(driver);

  145.     }

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

  161.         for (int i = 0; i < dim; i++) {
  162.             rangeError[i] = derivatives[1 + freeStateParameters + i];
  163.         }

  165.         return rangeError;
  166.     }

  168.     /** {@inheritDoc} */
  169.     @Override
  170.     public List<ParameterDriver> getParametersDrivers() {
  171.         return ionoModel.getParametersDrivers();
  172.     }

  174.     @Override
  175.     public void modify(final EstimatedMeasurement<Range> estimated) {
  176.         final Range           measurement = estimated.getObservedMeasurement();
  177.         final GroundStation   station     = measurement.getStation();
  178.         final SpacecraftState state       = estimated.getStates()[0];

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

  182.         // update estimated derivatives with Jacobian of the measure wrt state
  183.         final IonosphericDSConverter converter =
  184.                 new IonosphericDSConverter(state, 6, new InertialProvider(state.getFrame()));
  185.         final FieldSpacecraftState<DerivativeStructure> dsState = converter.getState(ionoModel);
  186.         final DerivativeStructure[] dsParameters = converter.getParameters(dsState, ionoModel);
  187.         final DerivativeStructure dsDelay = rangeErrorIonosphericModel(station, dsState, dsParameters);
  188.         final double[] derivatives = dsDelay.getAllDerivatives();

  190.         final double[][] djac = rangeErrorJacobianState(derivatives, 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] += djac[irow][jcol];
  196.             }
  197.         }
  198.         estimated.setStateDerivatives(0, stateDerivatives);

  200.         int index = 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[] dDelaydP    = rangeErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
  206.                 parameterDerivative += dDelaydP[index];
  207.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  208.                 index = index + 1;
  209.             }

  211.         }

  213.         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
  214.                                                           station.getEastOffsetDriver(),
  215.                                                           station.getNorthOffsetDriver(),
  216.                                                           station.getZenithOffsetDriver())) {
  217.             if (driver.isSelected()) {
  218.                 // update estimated derivatives with derivative of the modification wrt station parameters
  219.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  220.                 parameterDerivative += rangeErrorParameterDerivative(station, driver, state, dsDelay.getValue());
  221.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  222.             }
  223.         }

  225.         // update estimated value taking into account the ionospheric delay.
  226.         // The ionospheric delay is directly added to the range.
  227.         final double[] newValue = oldValue.clone();
  228.         newValue[0] = newValue[0] + dsDelay.getValue();
  229.         estimated.setEstimatedValue(newValue);

  231.     }

  233. }
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