PhaseTroposphericDelayModifier.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.Field;
  24. import org.hipparchus.analysis.differentiation.Gradient;
  25. import org.orekit.attitudes.FrameAlignedProvider;
  26. import org.orekit.estimation.measurements.EstimatedMeasurement;
  27. import org.orekit.estimation.measurements.EstimatedMeasurementBase;
  28. import org.orekit.estimation.measurements.EstimationModifier;
  29. import org.orekit.estimation.measurements.GroundStation;
  30. import org.orekit.estimation.measurements.gnss.Phase;
  31. import org.orekit.models.earth.troposphere.TroposphericModel;
  32. import org.orekit.propagation.FieldSpacecraftState;
  33. import org.orekit.propagation.SpacecraftState;
  34. import org.orekit.utils.Differentiation;
  35. import org.orekit.utils.FieldTrackingCoordinates;
  36. import org.orekit.utils.ParameterDriver;
  37. import org.orekit.utils.ParameterFunction;
  38. import org.orekit.utils.TimeSpanMap.Span;
  39. import org.orekit.utils.TrackingCoordinates;

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

  51.     /** Tropospheric delay model. */
  52.     private final TroposphericModel tropoModel;

  54.     /** Constructor.
  55.      *
  56.      * @param model  Tropospheric delay model appropriate for the current range measurement method.
  57.      * @since 12.1
  58.      */
  59.     public PhaseTroposphericDelayModifier(final TroposphericModel model) {
  60.         tropoModel = model;
  61.     }

  63. /** {@inheritDoc} */
  64.     @Override
  65.         public String getEffectName() {
  66.         return "troposphere";
  67.     }

  69.     /** Compute the measurement error due to Troposphere.
  70.      * @param station station
  71.      * @param state spacecraft state
  72.      * @param wavelength wavelength of the signal
  73.      * @return the measurement error due to Troposphere
  74.      */
  75.     private double phaseErrorTroposphericModel(final GroundStation station, final SpacecraftState state, final double wavelength) {

  77.         // tracking
  78.         final TrackingCoordinates trackingCoordinates =
  79.                         station.getBaseFrame().getTrackingCoordinates(state.getPosition(), state.getFrame(), state.getDate());

  81.         // only consider measures above the horizon
  82.         if (trackingCoordinates.getElevation() > 0) {
  83.             // delay in meters
  84.             final double delay = tropoModel.pathDelay(trackingCoordinates,
  85.                                                       station.getOffsetGeodeticPoint(state.getDate()),
  86.                                                       tropoModel.getParameters(state.getDate()), state.getDate()).
  87.                                  getDelay();

  89.             return delay / wavelength;
  90.         }

  92.         return 0;
  93.     }

  95.     /** Compute the measurement error due to Troposphere.
  96.      * @param <T> type of the element
  97.      * @param station station
  98.      * @param state spacecraft state
  99.      * @param parameters tropospheric model parameters
  100.      * @param wavelength of the measurements
  101.      * @return the measurement error due to Troposphere
  102.      */
  103.     private <T extends CalculusFieldElement<T>> T phaseErrorTroposphericModel(final GroundStation station,
  104.                                                                           final FieldSpacecraftState<T> state,
  105.                                                                           final T[] parameters, final double wavelength) {

  107.         // Field
  108.         final Field<T> field = state.getDate().getField();
  109.         final T zero         = field.getZero();

  111.         // tracking
  112.         final FieldTrackingCoordinates<T> trackingCoordinates =
  113.                         station.getBaseFrame().getTrackingCoordinates(state.getPosition(), state.getFrame(), state.getDate());


  116.         // only consider measures above the horizon
  117.         if (trackingCoordinates.getElevation().getReal() > 0) {
  118.             // delay in meters
  119.             final T delay = tropoModel.pathDelay(trackingCoordinates,
  120.                                                  station.getOffsetGeodeticPoint(state.getDate()),
  121.                                                  parameters, state.getDate()).
  122.                             getDelay();

  124.             return delay.divide(wavelength);
  125.         }

  127.         return zero;
  128.     }

  130.     /** Compute the Jacobian of the delay term wrt state using
  131.     * automatic differentiation.
  132.     *
  133.     * @param derivatives tropospheric delay derivatives
  134.     *
  135.     * @return Jacobian of the delay wrt state
  136.     */
  137.     private double[][] phaseErrorJacobianState(final double[] derivatives) {
  138.         final double[][] finiteDifferencesJacobian = new double[1][6];
  139.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  140.         return finiteDifferencesJacobian;
  141.     }

  143.     /** Compute the derivative of the delay term wrt parameters.
  144.      *
  145.      * @param station ground station
  146.      * @param driver driver for the station offset parameter
  147.      * @param state spacecraft state
  148.      * @param wavelength wavelength of the signal
  149.      * @return derivative of the delay wrt station offset parameter
  150.      */
  151.     private double phaseErrorParameterDerivative(final GroundStation station,
  152.                                                  final ParameterDriver driver,
  153.                                                  final SpacecraftState state,
  154.                                                  final double wavelength) {
  155.         final ParameterFunction rangeError = (parameterDriver, date) -> phaseErrorTroposphericModel(station, state, wavelength);
  156.         final ParameterFunction phaseErrorDerivative =
  157.                         Differentiation.differentiate(rangeError, 3, 10.0 * driver.getScale());
  158.         return phaseErrorDerivative.value(driver, state.getDate());

  160.     }

  162.     /** Compute the derivative of the delay term wrt parameters using
  163.     * automatic differentiation.
  164.     *
  165.     * @param derivatives tropospheric delay derivatives
  166.     * @param freeStateParameters dimension of the state.
  167.     * @return derivative of the delay wrt tropospheric model parameters
  168.     */
  169.     private double[] phaseErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  170.         // 0 ... freeStateParameters - 1   -> derivatives of the delay wrt state
  171.         // freeStateParameters ... n       -> derivatives of the delay wrt tropospheric parameters
  172.         return Arrays.copyOfRange(derivatives, freeStateParameters, derivatives.length);
  173.     }

  175.     /** {@inheritDoc} */
  176.     @Override
  177.     public List<ParameterDriver> getParametersDrivers() {
  178.         return tropoModel.getParametersDrivers();
  179.     }

  181.     /** {@inheritDoc} */
  182.     @Override
  183.     public void modifyWithoutDerivatives(final EstimatedMeasurementBase<Phase> estimated) {

  185.         final Phase           measurement = estimated.getObservedMeasurement();
  186.         final GroundStation   station     = measurement.getStation();
  187.         final SpacecraftState state       = estimated.getStates()[0];

  189.         // Update estimated value taking into account the tropospheric delay.
  190.         // The tropospheric delay is directly added to the phase.
  191.         final double[] newValue = estimated.getEstimatedValue();
  192.         final double delay = phaseErrorTroposphericModel(station, state, measurement.getWavelength());
  193.         newValue[0] = newValue[0] + delay;
  194.         estimated.modifyEstimatedValue(this, newValue);

  196.     }

  198.     /** {@inheritDoc} */
  199.     @Override
  200.     public void modify(final EstimatedMeasurement<Phase> estimated) {
  201.         final Phase           measurement = estimated.getObservedMeasurement();
  202.         final GroundStation   station     = measurement.getStation();
  203.         final SpacecraftState state       = estimated.getStates()[0];

  205.         // update estimated derivatives with Jacobian of the measure wrt state
  206.         final ModifierGradientConverter converter = new ModifierGradientConverter(state, 6, new FrameAlignedProvider(state.getFrame()));
  207.         final FieldSpacecraftState<Gradient> gState = converter.getState(tropoModel);
  208.         final Gradient[] gParameters = converter.getParametersAtStateDate(gState, tropoModel);
  209.         final Gradient gDelay = phaseErrorTroposphericModel(station, gState, gParameters, measurement.getWavelength());
  210.         final double[] derivatives = gDelay.getGradient();

  212.         // Update state derivatives
  213.         final double[][] djac = phaseErrorJacobianState(derivatives);
  214.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  215.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  216.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  217.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  218.             }
  219.         }
  220.         estimated.setStateDerivatives(0, stateDerivatives);


  223.         // Update tropospheric parameter derivatives
  224.         int index = 0;
  225.         for (final ParameterDriver driver : getParametersDrivers()) {
  226.             if (driver.isSelected()) {
  227.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {

  229.                     // update estimated derivatives with derivative of the modification wrt tropospheric parameters
  230.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  231.                     final double[] dDelaydP    = phaseErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
  232.                     parameterDerivative += dDelaydP[index];
  233.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  234.                     index = index + 1;
  235.                 }
  236.             }
  237.         }

  239.         // Update station parameter derivatives
  240.         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
  241.                                                           station.getEastOffsetDriver(),
  242.                                                           station.getNorthOffsetDriver(),
  243.                                                           station.getZenithOffsetDriver())) {
  244.             if (driver.isSelected()) {
  245.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  246.                     // update estimated derivatives with derivative of the modification wrt station parameters
  247.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  248.                     parameterDerivative += phaseErrorParameterDerivative(station, driver, state, measurement.getWavelength());
  249.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  250.                 }
  251.             }
  252.         }

  254.         // Update estimated value taking into account the tropospheric delay.
  255.         modifyWithoutDerivatives(estimated);

  257.     }

  259. }
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