PhaseTroposphericDelayModifier.java

  1. /* Copyright 2002-2024 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.DiscreteTroposphericModel;
  32. import org.orekit.propagation.FieldSpacecraftState;
  33. import org.orekit.propagation.SpacecraftState;
  34. import org.orekit.utils.Differentiation;
  35. import org.orekit.utils.ParameterDriver;
  36. import org.orekit.utils.ParameterFunction;
  37. import org.orekit.utils.TimeSpanMap.Span;

  39. /**
  40.  * Class modifying theoretical phase measurement with tropospheric delay.
  41.  * The effect of tropospheric correction on the phase is directly computed
  42.  * through the computation of the tropospheric delay.
  43.  * @author David Soulard
  44.  * @author Bryan Cazabonne
  45.  * @since 10.2
  46.  */
  47. public class PhaseTroposphericDelayModifier implements EstimationModifier<Phase> {

  49.     /** Tropospheric delay model. */
  50.     private final DiscreteTroposphericModel tropoModel;

  52.     /** Constructor.
  53.      *
  54.      * @param model  Tropospheric delay model appropriate for the current range measurement method.
  55.      */
  56.     public PhaseTroposphericDelayModifier(final DiscreteTroposphericModel model) {
  57.         tropoModel = model;
  58.     }

  60.     /** Compute the measurement error due to Troposphere.
  61.      * @param station station
  62.      * @param state spacecraft state
  63.      * @param wavelength wavelength of the signal
  64.      * @return the measurement error due to Troposphere
  65.      */
  66.     private double phaseErrorTroposphericModel(final GroundStation station, final SpacecraftState state, final double wavelength) {

  68.         // elevation
  69.         final double elevation =
  70.                         station.getBaseFrame().getTrackingCoordinates(state.getPosition(), state.getFrame(), state.getDate()).
  71.                         getElevation();

  73.         // only consider measures above the horizon
  74.         if (elevation > 0) {
  75.             // delay in meters
  76.             final double delay = tropoModel.pathDelay(elevation, station.getBaseFrame().getPoint(), tropoModel.getParameters(state.getDate()), state.getDate());

  78.             return delay / wavelength;
  79.         }

  81.         return 0;
  82.     }

  84.     /** Compute the measurement error due to Troposphere.
  85.      * @param <T> type of the element
  86.      * @param station station
  87.      * @param state spacecraft state
  88.      * @param parameters tropospheric model parameters
  89.      * @param wavelength of the measurements
  90.      * @return the measurement error due to Troposphere
  91.      */
  92.     private <T extends CalculusFieldElement<T>> T phaseErrorTroposphericModel(final GroundStation station,
  93.                                                                           final FieldSpacecraftState<T> state,
  94.                                                                           final T[] parameters, final double wavelength) {

  96.         // Field
  97.         final Field<T> field = state.getDate().getField();
  98.         final T zero         = field.getZero();

  100.         // satellite elevation
  101.         final T elevation =
  102.                         station.getBaseFrame().getTrackingCoordinates(state.getPosition(), state.getFrame(), state.getDate()).
  103.                         getElevation();


  106.         // only consider measures above the horizon
  107.         if (elevation.getReal() > 0) {
  108.             // delay in meters
  109.             final T delay = tropoModel.pathDelay(elevation, station.getBaseFrame().getPoint(field), parameters, state.getDate());

  111.             return delay.divide(wavelength);
  112.         }

  114.         return zero;
  115.     }

  117.     /** Compute the Jacobian of the delay term wrt state using
  118.     * automatic differentiation.
  119.     *
  120.     * @param derivatives tropospheric delay derivatives
  121.     *
  122.     * @return Jacobian of the delay wrt state
  123.     */
  124.     private double[][] phaseErrorJacobianState(final double[] derivatives) {
  125.         final double[][] finiteDifferencesJacobian = new double[1][6];
  126.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  127.         return finiteDifferencesJacobian;
  128.     }

  130.     /** Compute the derivative of the delay term wrt parameters.
  131.      *
  132.      * @param station ground station
  133.      * @param driver driver for the station offset parameter
  134.      * @param state spacecraft state
  135.      * @param wavelength wavelength of the signal
  136.      * @return derivative of the delay wrt station offset parameter
  137.      */
  138.     private double phaseErrorParameterDerivative(final GroundStation station,
  139.                                                  final ParameterDriver driver,
  140.                                                  final SpacecraftState state,
  141.                                                  final double wavelength) {
  142.         final ParameterFunction rangeError = (parameterDriver, date) -> phaseErrorTroposphericModel(station, state, wavelength);
  143.         final ParameterFunction phaseErrorDerivative =
  144.                         Differentiation.differentiate(rangeError, 3, 10.0 * driver.getScale());
  145.         return phaseErrorDerivative.value(driver, state.getDate());

  147.     }

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

  162.         for (int i = 0; i < dim; i++) {
  163.             rangeError[i] = derivatives[freeStateParameters + i];
  164.         }

  166.         return rangeError;
  167.     }

  169.     /** {@inheritDoc} */
  170.     @Override
  171.     public List<ParameterDriver> getParametersDrivers() {
  172.         return tropoModel.getParametersDrivers();
  173.     }

  175.     /** {@inheritDoc} */
  176.     @Override
  177.     public void modifyWithoutDerivatives(final EstimatedMeasurementBase<Phase> estimated) {

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

  183.         // Update estimated value taking into account the tropospheric delay.
  184.         // The tropospheric delay is directly added to the phase.
  185.         final double[] newValue = estimated.getEstimatedValue();
  186.         final double delay = phaseErrorTroposphericModel(station, state, measurement.getWavelength());
  187.         newValue[0] = newValue[0] + delay;
  188.         estimated.setEstimatedValue(newValue);

  190.     }

  192.     /** {@inheritDoc} */
  193.     @Override
  194.     public void modify(final EstimatedMeasurement<Phase> estimated) {
  195.         final Phase           measurement = estimated.getObservedMeasurement();
  196.         final GroundStation   station     = measurement.getStation();
  197.         final SpacecraftState state       = estimated.getStates()[0];

  199.         // update estimated derivatives with Jacobian of the measure wrt state
  200.         final ModifierGradientConverter converter = new ModifierGradientConverter(state, 6, new FrameAlignedProvider(state.getFrame()));
  201.         final FieldSpacecraftState<Gradient> gState = converter.getState(tropoModel);
  202.         final Gradient[] gParameters = converter.getParametersAtStateDate(gState, tropoModel);
  203.         final Gradient gDelay = phaseErrorTroposphericModel(station, gState, gParameters, measurement.getWavelength());
  204.         final double[] derivatives = gDelay.getGradient();

  206.         // Update state derivatives
  207.         final double[][] djac = phaseErrorJacobianState(derivatives);
  208.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  209.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  210.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  211.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  212.             }
  213.         }
  214.         estimated.setStateDerivatives(0, stateDerivatives);


  217.         // Update tropospheric parameter derivatives
  218.         int index = 0;
  219.         for (final ParameterDriver driver : getParametersDrivers()) {
  220.             if (driver.isSelected()) {
  221.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {

  223.                     // update estimated derivatives with derivative of the modification wrt tropospheric parameters
  224.                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
  225.                     final double[] dDelaydP    = phaseErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
  226.                     parameterDerivative += dDelaydP[index];
  227.                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
  228.                     index = index + 1;
  229.                 }
  230.             }
  231.         }

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

  248.         // Update estimated value taking into account the tropospheric delay.
  249.         modifyWithoutDerivatives(estimated);

  251.     }

  253. }
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