PhaseIonosphericDelayModifier.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.  * The ASF 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.gnss.Phase;
  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.utils.Constants;
  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. /**
  41.  * Class modifying theoretical phase measurement with ionospheric delay.
  42.  * The effect of ionospheric correction on the phase is directly computed
  43.  * through the computation of the ionospheric delay.
  44.  * @author David Soulard
  45.  * @author Bryan Cazabonne
  46.  * @since 10.2
  47.  */
  48. public class PhaseIonosphericDelayModifier implements EstimationModifier<Phase> {

  50.     /** Ionospheric delay model. */
  51.     private final IonosphericModel ionoModel;

  53.     /** Frequency [Hz]. */
  54.     private final double frequency;

  56.     /** Constructor.
  57.      *
  58.      * @param model  Ionospheric delay model appropriate for the current range measurement method.
  59.      * @param freq frequency of the signal in Hz
  60.      */
  61.     public PhaseIonosphericDelayModifier(final IonosphericModel model,
  62.                                          final double freq) {
  63.         ionoModel = model;
  64.         frequency = freq;
  65.     }

  67. /** {@inheritDoc} */
  68.     @Override
  69.         public String getEffectName() {
  70.         return "ionosphere";
  71.     }

  73.     /** Compute the measurement error due to ionosphere.
  74.      * @param station station
  75.      * @param state spacecraft state
  76.      * @return the measurement error due to ionosphere
  77.      */
  78.     private double phaseErrorIonosphericModel(final GroundStation station,
  79.                                               final SpacecraftState state) {

  81.         // Base frame associated with the station
  82.         final TopocentricFrame baseFrame = station.getBaseFrame();
  83.         final double wavelength  = Constants.SPEED_OF_LIGHT / frequency;
  84.         // delay in meters
  85.         final double delay = ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters(state.getDate()));
  86.         return delay / wavelength;
  87.     }

  89.     /** Compute the measurement error due to ionosphere.
  90.      * @param <T> type of the element
  91.      * @param station station
  92.      * @param state spacecraft state
  93.      * @param parameters ionospheric model parameters at state date
  94.      * @return the measurement error due to ionosphere
  95.      */
  96.     private <T extends CalculusFieldElement<T>> T phaseErrorIonosphericModel(final GroundStation station,
  97.                                                                              final FieldSpacecraftState<T> state,
  98.                                                                              final T[] parameters) {

  100.         // Base frame associated with the station
  101.         final TopocentricFrame baseFrame = station.getBaseFrame();
  102.         final double wavelength  = Constants.SPEED_OF_LIGHT / frequency;
  103.         // delay in meters
  104.         final T delay = ionoModel.pathDelay(state, baseFrame, frequency, parameters);
  105.         return delay.divide(wavelength);
  106.     }

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


  123.     /** Compute the derivative of the delay term wrt parameters.
  124.      *
  125.      * @param station ground station
  126.      * @param driver driver for the station offset parameter
  127.      * @param state spacecraft state
  128.      * @return derivative of the delay wrt station offset parameter
  129.      */
  130.     private double phaseErrorParameterDerivative(final GroundStation station,
  131.                                                  final ParameterDriver driver,
  132.                                                  final SpacecraftState state) {
  133.         final ParameterFunction phaseError = (parameterDriver, date) -> phaseErrorIonosphericModel(station, state);
  134.         final ParameterFunction phaseErrorDerivative =
  135.                         Differentiation.differentiate(phaseError, 3, 10.0 * driver.getScale());
  136.         return phaseErrorDerivative.value(driver, state.getDate());

  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[] phaseErrorParameterDerivative(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.         return Arrays.copyOfRange(derivatives, freeStateParameters, derivatives.length);
  151.     }

  153.     /** {@inheritDoc} */
  154.     @Override
  155.     public List<ParameterDriver> getParametersDrivers() {
  156.         return ionoModel.getParametersDrivers();
  157.     }

  159.     @Override
  160.     public void modifyWithoutDerivatives(final EstimatedMeasurementBase<Phase> estimated) {

  162.         final Phase           measurement = estimated.getObservedMeasurement();
  163.         final GroundStation   station     = measurement.getStation();
  164.         final SpacecraftState state       = estimated.getStates()[0];

  166.         // Update estimated value taking into account the ionospheric delay.
  167.         // The ionospheric delay is directly subtracted to the phase.
  168.         final double[] newValue = estimated.getEstimatedValue();
  169.         final double delay = phaseErrorIonosphericModel(station, state);
  170.         newValue[0] = newValue[0] - delay;
  171.         estimated.modifyEstimatedValue(this, newValue);

  173.     }

  175.     @Override
  176.     public void modify(final EstimatedMeasurement<Phase> estimated) {

  178.         final Phase           measurement = estimated.getObservedMeasurement();
  179.         final GroundStation   station     = measurement.getStation();
  180.         final SpacecraftState state       = estimated.getStates()[0];

  182.         // Compute ionospheric delay (the division by the wavelength is performed)
  183.         final ModifierGradientConverter converter =
  184.                         new ModifierGradientConverter(state, 6, new FrameAlignedProvider(state.getFrame()));
  185.         final FieldSpacecraftState<Gradient> gState = converter.getState(ionoModel);
  186.         final Gradient[] gParameters = converter.getParametersAtStateDate(gState, ionoModel);
  187.         final Gradient gDelay = phaseErrorIonosphericModel(station, gState, gParameters);
  188.         final double[] derivatives = gDelay.getGradient();

  190.         // Update state derivatives
  191.         final double[][] djac = phaseErrorJacobianState(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.         // Update ionospheric parameter derivatives
  201.         int index = 0;
  202.         for (final ParameterDriver driver : getParametersDrivers()) {
  203.             if (driver.isSelected()) {
  204.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  205.                     // update estimated derivatives with derivative of the modification wrt ionospheric parameters
  206.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  207.                     final double[] dDelaydP    = phaseErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
  208.                     parameterDerivative -= dDelaydP[index];
  209.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  210.                     index = index + 1;
  211.                 }
  212.             }

  214.         }

  216.         // Update station parameter derivatives
  217.         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
  218.                                                           station.getEastOffsetDriver(),
  219.                                                           station.getNorthOffsetDriver(),
  220.                                                           station.getZenithOffsetDriver())) {
  221.             if (driver.isSelected()) {
  222.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  223.                     // update estimated derivatives with derivative of the modification wrt station parameters
  224.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  225.                     parameterDerivative -= phaseErrorParameterDerivative(station, driver, state);
  226.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  227.                 }
  228.             }
  229.         }

  231.         // Update estimated value taking into account the ionospheric delay.
  232.         modifyWithoutDerivatives(estimated);

  234.     }

  236. }
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