TurnAroundRangeTroposphericDelayModifier.java

  1. /* Copyright 2002-2022 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.Field;
  23. import org.hipparchus.CalculusFieldElement;
  24. import org.hipparchus.analysis.differentiation.Gradient;
  25. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  26. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  27. import org.orekit.attitudes.InertialProvider;
  28. import org.orekit.estimation.measurements.EstimatedMeasurement;
  29. import org.orekit.estimation.measurements.EstimationModifier;
  30. import org.orekit.estimation.measurements.GroundStation;
  31. import org.orekit.estimation.measurements.TurnAroundRange;
  32. import org.orekit.models.earth.troposphere.DiscreteTroposphericModel;
  33. import org.orekit.propagation.FieldSpacecraftState;
  34. import org.orekit.propagation.SpacecraftState;
  35. import org.orekit.utils.Differentiation;
  36. import org.orekit.utils.ParameterDriver;
  37. import org.orekit.utils.ParameterFunction;

  39. /** Class modifying theoretical turn-around TurnAroundRange measurement with tropospheric delay.
  40.  * The effect of tropospheric correction on the TurnAroundRange is directly computed
  41.  * through the computation of the tropospheric delay.
  42.  *
  43.  * In general, for GNSS, VLBI, ... there is hardly any frequency dependence in the delay.
  44.  * For SLR techniques however, the frequency dependence is sensitive.
  45.  *
  46.  * @author Maxime Journot
  47.  * @since 9.0
  48.  */
  49. public class TurnAroundRangeTroposphericDelayModifier implements EstimationModifier<TurnAroundRange> {

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

  54.     /** Constructor.
  55.      *
  56.      * @param model  Tropospheric delay model appropriate for the current TurnAroundRange measurement method.
  57.      */
  58.     public TurnAroundRangeTroposphericDelayModifier(final DiscreteTroposphericModel model) {
  59.         tropoModel = model;
  60.     }

  62.     /** Compute the measurement error due to Troposphere.
  63.      * @param station station
  64.      * @param state spacecraft state
  65.      * @return the measurement error due to Troposphere
  66.      */
  67.     private double rangeErrorTroposphericModel(final GroundStation station, final SpacecraftState state) {
  68.         //
  69.         final Vector3D position = state.getPVCoordinates().getPosition();

  71.         // elevation
  72.         final double elevation = station.getBaseFrame().getElevation(position,
  73.                                                                      state.getFrame(),
  74.                                                                      state.getDate());

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

  81.             return delay;
  82.         }

  84.         return 0;
  85.     }

  87.     /** Compute the measurement error due to Troposphere.
  88.      * @param <T> type of the element
  89.      * @param station station
  90.      * @param state spacecraft state
  91.      * @param parameters tropospheric model parameters
  92.      * @return the measurement error due to Troposphere
  93.      */
  94.     private <T extends CalculusFieldElement<T>> T rangeErrorTroposphericModel(final GroundStation station,
  95.                                                                           final FieldSpacecraftState<T> state,
  96.                                                                           final T[] parameters) {
  97.         // Field
  98.         final Field<T> field = state.getDate().getField();
  99.         final T zero         = field.getZero();

  101.         //
  102.         final FieldVector3D<T> position = state.getPVCoordinates().getPosition();
  103.         final T dsElevation             = station.getBaseFrame().getElevation(position,
  104.                                                                               state.getFrame(),
  105.                                                                               state.getDate());

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

  112.             return delay;
  113.         }

  115.         return zero;
  116.     }

  118.     /** Compute the Jacobian of the delay term wrt state using
  119.     * automatic differentiation.
  120.     *
  121.     * @param derivatives tropospheric delay derivatives
  122.     *
  123.     * @return Jacobian of the delay wrt state
  124.     */
  125.     private double[][] rangeErrorJacobianState(final double[] derivatives) {
  126.         final double[][] finiteDifferencesJacobian = new double[1][6];
  127.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  128.         return finiteDifferencesJacobian;
  129.     }


  132.     /** Compute the derivative of the delay term wrt parameters.
  133.      *
  134.      * @param station ground station
  135.      * @param driver driver for the station offset parameter
  136.      * @param state spacecraft state
  137.      * @return derivative of the delay wrt station offset parameter
  138.      */
  139.     private double rangeErrorParameterDerivative(final GroundStation station,
  140.                                                  final ParameterDriver driver,
  141.                                                  final SpacecraftState state) {

  143.         final ParameterFunction rangeError = new ParameterFunction() {
  144.             /** {@inheritDoc} */
  145.             @Override
  146.             public double value(final ParameterDriver parameterDriver) {
  147.                 return rangeErrorTroposphericModel(station, state);
  148.             }
  149.         };

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

  153.         return rangeErrorDerivative.value(driver);

  155.     }

  157.     /** Compute the derivative of the delay term wrt parameters using
  158.     * automatic differentiation.
  159.     *
  160.     * @param derivatives tropospheric delay derivatives
  161.     * @param freeStateParameters dimension of the state.
  162.     * @return derivative of the delay wrt tropospheric model parameters
  163.     */
  164.     private double[] rangeErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  165.         // 0 ... freeStateParameters - 1 -> derivatives of the delay wrt state
  166.         // freeStateParameters ... n     -> derivatives of the delay wrt tropospheric parameters
  167.         final int dim = derivatives.length - freeStateParameters;
  168.         final double[] rangeError = new double[dim];

  170.         for (int i = 0; i < dim; i++) {
  171.             rangeError[i] = derivatives[freeStateParameters + i];
  172.         }

  174.         return rangeError;
  175.     }

  177.     /** {@inheritDoc} */
  178.     @Override
  179.     public List<ParameterDriver> getParametersDrivers() {
  180.         return tropoModel.getParametersDrivers();
  181.     }

  183.     /** {@inheritDoc} */
  184.     @Override
  185.     public void modify(final EstimatedMeasurement<TurnAroundRange> estimated) {
  186.         final TurnAroundRange measurement      = estimated.getObservedMeasurement();
  187.         final GroundStation   primaryStation   = measurement.getPrimaryStation();
  188.         final GroundStation   secondaryStation = measurement.getSecondaryStation();
  189.         final SpacecraftState state            = estimated.getStates()[0];

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

  193.         // Update estimated derivatives with Jacobian of the measure wrt state
  194.         final TroposphericGradientConverter converter =
  195.                 new TroposphericGradientConverter(state, 6, new InertialProvider(state.getFrame()));
  196.         final FieldSpacecraftState<Gradient> gState = converter.getState(tropoModel);
  197.         final Gradient[] gParameters = converter.getParameters(gState, tropoModel);
  198.         final Gradient   primaryGDelay        = rangeErrorTroposphericModel(primaryStation, gState, gParameters);
  199.         final Gradient   secondaryGDelay      = rangeErrorTroposphericModel(secondaryStation, gState, gParameters);
  200.         final double[]   primaryDerivatives   = primaryGDelay.getGradient();
  201.         final double[]   secondaryDerivatives = secondaryGDelay.getGradient();

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

  213.         int indexPrimary = 0;
  214.         for (final ParameterDriver driver : getParametersDrivers()) {
  215.             if (driver.isSelected()) {
  216.                 // update estimated derivatives with derivative of the modification wrt tropospheric parameters
  217.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  218.                 final double[] derivatives = rangeErrorParameterDerivative(primaryDerivatives, converter.getFreeStateParameters());
  219.                 parameterDerivative += derivatives[indexPrimary];
  220.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  221.                 indexPrimary += 1;
  222.             }

  224.         }

  226.         int indexSecondary = 0;
  227.         for (final ParameterDriver driver : getParametersDrivers()) {
  228.             if (driver.isSelected()) {
  229.                 // update estimated derivatives with derivative of the modification wrt tropospheric parameters
  230.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  231.                 final double[] derivatives = rangeErrorParameterDerivative(secondaryDerivatives, converter.getFreeStateParameters());
  232.                 parameterDerivative += derivatives[indexSecondary];
  233.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  234.                 indexSecondary += 1;
  235.             }

  237.         }

  239.         // Update derivatives with respect to primary station position
  240.         for (final ParameterDriver driver : Arrays.asList(primaryStation.getClockOffsetDriver(),
  241.                                                           primaryStation.getEastOffsetDriver(),
  242.                                                           primaryStation.getNorthOffsetDriver(),
  243.                                                           primaryStation.getZenithOffsetDriver())) {
  244.             if (driver.isSelected()) {
  245.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  246.                 parameterDerivative += rangeErrorParameterDerivative(primaryStation, driver, state);
  247.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  248.             }
  249.         }

  251.         // Update derivatives with respect to secondary station position
  252.         for (final ParameterDriver driver : Arrays.asList(secondaryStation.getEastOffsetDriver(),
  253.                                                           secondaryStation.getNorthOffsetDriver(),
  254.                                                           secondaryStation.getZenithOffsetDriver())) {
  255.             if (driver.isSelected()) {
  256.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  257.                 parameterDerivative += rangeErrorParameterDerivative(secondaryStation, driver, state);
  258.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  259.             }
  260.         }

  262.         // Update estimated value taking into account the tropospheric delay.
  263.         // The tropospheric delay is directly added to the TurnAroundRange.
  264.         final double[] newValue = oldValue.clone();
  265.         newValue[0] = newValue[0] + primaryGDelay.getReal() + secondaryGDelay.getReal();
  266.         estimated.setEstimatedValue(newValue);

  268.     }

  270. }
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