TurnAroundRangeIonosphericDelayModifier.java

  1. /* Copyright 2002-2025 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.CalculusFieldElement;
  23. import org.hipparchus.analysis.differentiation.Gradient;
  24. import org.orekit.attitudes.FrameAlignedProvider;
  25. import org.orekit.estimation.measurements.EstimatedMeasurement;
  26. import org.orekit.estimation.measurements.EstimatedMeasurementBase;
  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.frames.TopocentricFrame;
  31. import org.orekit.models.earth.ionosphere.IonosphericModel;
  32. import org.orekit.propagation.FieldSpacecraftState;
  33. import org.orekit.propagation.SpacecraftState;
  34. import org.orekit.time.AbsoluteDate;
  35. import org.orekit.utils.Differentiation;
  36. import org.orekit.utils.ParameterDriver;
  37. import org.orekit.utils.ParameterFunction;
  38. import org.orekit.utils.TimeSpanMap.Span;

  40. /** Class modifying theoretical TurnAroundRange measurement with ionospheric delay.
  41.  * <p>
  42.  * The effect of ionospheric correction on the TurnAroundRange is directly computed
  43.  * through the computation of the ionospheric delay.
  44.  * </p>
  45.  * <p>
  46.  * The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
  47.  * For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
  48.  * </p>
  49.  * <p>
  50.  * Since 10.0, state derivatives and ionospheric parameters derivates are computed
  51.  * using automatic differentiation.
  52.  * </p>
  53.  * @author Maxime Journot
  54.  * @since 9.0
  55.  */
  56. public class TurnAroundRangeIonosphericDelayModifier implements EstimationModifier<TurnAroundRange> {

  58.     /** Ionospheric delay model. */
  59.     private final IonosphericModel ionoModel;

  61.     /** Frequency [Hz]. */
  62.     private final double frequency;

  64.     /** Constructor.
  65.      *
  66.      * @param model  Ionospheric delay model appropriate for the current TurnAroundRange measurement method.
  67.      * @param freq frequency of the signal in Hz
  68.      */
  69.     public TurnAroundRangeIonosphericDelayModifier(final IonosphericModel model,
  70.                                                    final double freq) {
  71.         ionoModel = model;
  72.         frequency = freq;
  73.     }

  75.     /** {@inheritDoc} */
  76.     @Override
  77.     public String getEffectName() {
  78.         return "ionosphere";
  79.     }

  81.     /** Compute the measurement error due to ionosphere.
  82.      * @param station station
  83.      * @param state spacecraft state
  84.      * @return the measurement error due to ionosphere
  85.      */
  86.     private double rangeErrorIonosphericModel(final GroundStation station,
  87.                                               final SpacecraftState state) {
  88.         // Base frame associated with the station
  89.         final TopocentricFrame baseFrame = station.getBaseFrame();
  90.         // Delay in meters
  91.         return ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters(state.getDate()));
  92.     }

  94.     /** Compute the measurement error due to ionosphere.
  95.      * @param <T> type of the elements
  96.      * @param station station
  97.      * @param state spacecraft state
  98.      * @param parameters ionospheric model parameters
  99.      * @return the measurement error due to ionosphere
  100.      */
  101.     private <T extends CalculusFieldElement<T>> T rangeErrorIonosphericModel(final GroundStation station,
  102.                                                                              final FieldSpacecraftState<T> state,
  103.                                                                              final T[] parameters) {
  104.         // Base frame associated with the station
  105.         final TopocentricFrame baseFrame = station.getBaseFrame();
  106.         // Delay in meters
  107.         return ionoModel.pathDelay(state, baseFrame, frequency, parameters);
  108.     }

  110.     /** Compute the Jacobian of the delay term wrt state using
  111.     * automatic differentiation.
  112.     *
  113.     * @param derivatives ionospheric delay derivatives
  114.     *
  115.     * @return Jacobian of the delay wrt state
  116.     */
  117.     private double[][] rangeErrorJacobianState(final double[] derivatives) {
  118.         final double[][] finiteDifferencesJacobian = new double[1][6];
  119.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  120.         return finiteDifferencesJacobian;
  121.     }


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

  135.         final ParameterFunction rangeError = new ParameterFunction() {
  136.             /** {@inheritDoc} */
  137.             @Override
  138.             public double value(final ParameterDriver parameterDriver, final AbsoluteDate date) {
  139.                 return rangeErrorIonosphericModel(station, state);
  140.             }
  141.         };

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

  146.         return rangeErrorDerivative.value(driver, state.getDate());

  148.     }

  150.     /** Compute the derivative of the delay term wrt parameters using
  151.     * automatic differentiation.
  152.     *
  153.     * @param derivatives ionospheric delay derivatives
  154.     * @param freeStateParameters dimension of the state.
  155.     * @return derivative of the delay wrt ionospheric model parameters
  156.     */
  157.     private double[] rangeErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  158.         // 0 ... freeStateParameters - 1 -> derivatives of the delay wrt state
  159.         // freeStateParameters ... n     -> derivatives of the delay wrt ionospheric parameters
  160.         return Arrays.copyOfRange(derivatives, freeStateParameters, derivatives.length);
  161.     }

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

  169.     @Override
  170.     public void modifyWithoutDerivatives(final EstimatedMeasurementBase<TurnAroundRange> estimated) {

  172.         final TurnAroundRange measurement      = estimated.getObservedMeasurement();
  173.         final GroundStation   primaryStation   = measurement.getPrimaryStation();
  174.         final GroundStation   secondaryStation = measurement.getSecondaryStation();
  175.         final SpacecraftState state            = estimated.getStates()[0];

  177.         // Update estimated value taking into account the ionospheric delay.
  178.         // The ionospheric delay is directly added to the TurnAroundRange.
  179.         final double[] newValue     = estimated.getEstimatedValue();
  180.         final double primaryDelay   = rangeErrorIonosphericModel(primaryStation, state);
  181.         final double secondaryDelay = rangeErrorIonosphericModel(secondaryStation, state);
  182.         newValue[0] = newValue[0] + primaryDelay + secondaryDelay;
  183.         estimated.modifyEstimatedValue(this, newValue);

  185.     }

  187.     @Override
  188.     public void modify(final EstimatedMeasurement<TurnAroundRange> estimated) {
  189.         final TurnAroundRange measurement      = estimated.getObservedMeasurement();
  190.         final GroundStation   primaryStation   = measurement.getPrimaryStation();
  191.         final GroundStation   secondaryStation = measurement.getSecondaryStation();
  192.         final SpacecraftState state            = estimated.getStates()[0];

  194.         // Update estimated derivatives with Jacobian of the measure wrt state
  195.         final ModifierGradientConverter converter =
  196.                 new ModifierGradientConverter(state, 6, new FrameAlignedProvider(state.getFrame()));
  197.         final FieldSpacecraftState<Gradient> gState = converter.getState(ionoModel);
  198.         final Gradient[] gParameters        = converter.getParametersAtStateDate(gState, ionoModel);
  199.         final Gradient primaryGDelay        = rangeErrorIonosphericModel(primaryStation, gState, gParameters);
  200.         final Gradient secondaryGDelay      = rangeErrorIonosphericModel(secondaryStation, gState, gParameters);
  201.         final double[] primaryDerivatives   = primaryGDelay.getGradient();
  202.         final double[] secondaryDerivatives = secondaryGDelay.getGradient();

  204.         final double[][] primaryDjac      = rangeErrorJacobianState(primaryDerivatives);
  205.         final double[][] secondaryDjac    = rangeErrorJacobianState(secondaryDerivatives);
  206.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  207.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  208.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  209.                 stateDerivatives[irow][jcol] += primaryDjac[irow][jcol] + secondaryDjac[irow][jcol];
  210.             }
  211.         }
  212.         estimated.setStateDerivatives(0, stateDerivatives);

  214.         int indexPrimary = 0;
  215.         for (final ParameterDriver driver : getParametersDrivers()) {
  216.             if (driver.isSelected()) {
  217.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  218.                     // update estimated derivatives with derivative of the modification wrt ionospheric parameters
  219.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  220.                     final double[] derivatives = rangeErrorParameterDerivative(primaryDerivatives, converter.getFreeStateParameters());
  221.                     parameterDerivative += derivatives[indexPrimary];
  222.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  223.                     indexPrimary += 1;
  224.                 }
  225.             }

  227.         }

  229.         int indexSecondary = 0;
  230.         for (final ParameterDriver driver : getParametersDrivers()) {
  231.             if (driver.isSelected()) {
  232.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  233.                     // update estimated derivatives with derivative of the modification wrt ionospheric parameters
  234.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  235.                     final double[] derivatives = rangeErrorParameterDerivative(secondaryDerivatives, converter.getFreeStateParameters());
  236.                     parameterDerivative += derivatives[indexSecondary];
  237.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  238.                     indexSecondary += 1;
  239.                 }
  240.             }

  242.         }

  244.         // Update derivatives with respect to primary station position
  245.         for (final ParameterDriver driver : Arrays.asList(primaryStation.getClockOffsetDriver(),
  246.                                                           primaryStation.getEastOffsetDriver(),
  247.                                                           primaryStation.getNorthOffsetDriver(),
  248.                                                           primaryStation.getZenithOffsetDriver())) {
  249.             if (driver.isSelected()) {
  250.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {

  252.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  253.                     parameterDerivative += rangeErrorParameterDerivative(primaryStation, driver, state);
  254.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  255.                 }
  256.             }
  257.         }

  259.         // Update derivatives with respect to secondary station position
  260.         for (final ParameterDriver driver : Arrays.asList(secondaryStation.getEastOffsetDriver(),
  261.                                                           secondaryStation.getNorthOffsetDriver(),
  262.                                                           secondaryStation.getZenithOffsetDriver())) {
  263.             if (driver.isSelected()) {
  264.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {

  266.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  267.                     parameterDerivative += rangeErrorParameterDerivative(secondaryStation, driver, state);
  268.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  269.                 }
  270.             }
  271.         }

  273.         // Update estimated value taking into account the ionospheric delay.
  274.         // The ionospheric delay is directly added to the TurnAroundRange.
  275.         final double[] newValue = estimated.getEstimatedValue();
  276.         newValue[0] = newValue[0] + primaryGDelay.getReal() + secondaryGDelay.getReal();
  277.         estimated.modifyEstimatedValue(this, newValue);
  278.     }

  280. }
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