RangeRateIonosphericDelayModifier.java

  1. /* Copyright 2002-2020 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.RealFieldElement;
  23. import org.hipparchus.analysis.differentiation.Gradient;
  24. import org.orekit.attitudes.InertialProvider;
  25. import org.orekit.estimation.measurements.EstimatedMeasurement;
  26. import org.orekit.estimation.measurements.EstimationModifier;
  27. import org.orekit.estimation.measurements.GroundStation;
  28. import org.orekit.estimation.measurements.RangeRate;
  29. import org.orekit.frames.TopocentricFrame;
  30. import org.orekit.models.earth.ionosphere.IonosphericModel;
  31. import org.orekit.propagation.FieldSpacecraftState;
  32. import org.orekit.propagation.SpacecraftState;
  33. import org.orekit.utils.Differentiation;
  34. import org.orekit.utils.ParameterDriver;
  35. import org.orekit.utils.ParameterFunction;

  37. /** Class modifying theoretical range-rate measurement with ionospheric delay.
  38.  * The effect of ionospheric correction on the range-rate is directly computed
  39.  * through the computation of the ionospheric delay difference with respect to
  40.  * time.
  41.  *
  42.  * The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
  43.  * For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
  44.  * <p>
  45.  * Since 10.0, state derivatives and ionospheric parameters derivates are computed
  46.  * using automatic differentiation.
  47.  * </p>
  48.  * @author Joris Olympio
  49.  * @since 8.0
  50.  */
  51. public class RangeRateIonosphericDelayModifier implements EstimationModifier<RangeRate> {

  53.     /** Ionospheric delay model. */
  54.     private final IonosphericModel ionoModel;

  56.     /** Frequency [Hz]. */
  57.     private final double frequency;

  59.     /** Coefficient for measurment configuration (one-way, two-way). */
  60.     private final double fTwoWay;

  62.     /** Constructor.
  63.      *
  64.      * @param model Ionospheric delay model appropriate for the current range-rate measurement method.
  65.      * @param freq frequency of the signal in Hz
  66.      * @param twoWay Flag indicating whether the measurement is two-way.
  67.      */
  68.     public RangeRateIonosphericDelayModifier(final IonosphericModel model,
  69.                                              final double freq, final boolean twoWay) {
  70.         ionoModel = model;
  71.         frequency = freq;

  73.         if (twoWay) {
  74.             fTwoWay = 2.;
  75.         } else {
  76.             fTwoWay = 1.;
  77.         }
  78.     }

  80.     /** Compute the measurement error due to Ionosphere.
  81.      * @param station station
  82.      * @param state spacecraft state
  83.      * @return the measurement error due to Ionosphere
  84.      */
  85.     private double rangeRateErrorIonosphericModel(final GroundStation station, final SpacecraftState state) {
  86.         final double dt = 10; // s
  87.         // Base frame associated with the station
  88.         final TopocentricFrame baseFrame = station.getBaseFrame();
  89.         // delay in meters
  90.         final double delay1 = ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters());
  91.         // propagate spacecraft state forward by dt
  92.         final SpacecraftState state2 = state.shiftedBy(dt);
  93.         // ionospheric delay dt after in meters
  94.         final double delay2 = ionoModel.pathDelay(state2, baseFrame, frequency, ionoModel.getParameters());
  95.         // delay in meters
  96.         return fTwoWay * (delay2 - delay1) / dt;
  97.     }

  99.     /** Compute the measurement error due to Ionosphere.
  100.      * @param <T> type of the elements
  101.      * @param station station
  102.      * @param state spacecraft state
  103.      * @param parameters ionospheric model parameters
  104.      * @return the measurement error due to Ionosphere
  105.      */
  106.     private <T extends RealFieldElement<T>> T rangeRateErrorIonosphericModel(final GroundStation station,
  107.                                                                              final FieldSpacecraftState<T> state,
  108.                                                                              final T[] parameters) {
  109.         final double dt = 10; // s
  110.         // Base frame associated with the station
  111.         final TopocentricFrame baseFrame = station.getBaseFrame();
  112.         // delay in meters
  113.         final T delay1 = ionoModel.pathDelay(state, baseFrame, frequency, parameters);
  114.         // propagate spacecraft state forward by dt
  115.         final FieldSpacecraftState<T> state2 = state.shiftedBy(dt);
  116.         // ionospheric delay dt after in meters
  117.         final T delay2 = ionoModel.pathDelay(state2, baseFrame, frequency, parameters);
  118.         // delay in meters
  119.         return delay2.subtract(delay1).divide(dt).multiply(fTwoWay);
  120.     }

  122.     /** Compute the Jacobian of the delay term wrt state using
  123.     * automatic differentiation.
  124.     *
  125.     * @param derivatives ionospheric delay derivatives
  126.     *
  127.     * @return Jacobian of the delay wrt state
  128.     */
  129.     private double[][] rangeRateErrorJacobianState(final double[] derivatives) {
  130.         final double[][] finiteDifferencesJacobian = new double[1][6];
  131.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  132.         return finiteDifferencesJacobian;
  133.     }

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

  146.         final ParameterFunction rangeError = new ParameterFunction() {
  147.             /** {@inheritDoc} */
  148.             @Override
  149.             public double value(final ParameterDriver parameterDriver) {
  150.                 return rangeRateErrorIonosphericModel(station, state);
  151.             }
  152.         };

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

  157.         return rangeErrorDerivative.value(driver);

  159.     }

  161.     /** Compute the derivative of the delay term wrt parameters using
  162.     * automatic differentiation.
  163.     *
  164.     * @param derivatives ionospheric delay derivatives
  165.     * @param freeStateParameters dimension of the state.
  166.     * @return derivative of the delay wrt ionospheric model parameters
  167.     */
  168.     private double[] rangeRateErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  169.         // 0 ... freeStateParameters - 1 -> derivatives of the delay wrt state
  170.         // freeStateParameters ... n     -> derivatives of the delay wrt ionospheric parameters
  171.         final int dim = derivatives.length - freeStateParameters;
  172.         final double[] rangeError = new double[dim];

  174.         for (int i = 0; i < dim; i++) {
  175.             rangeError[i] = derivatives[freeStateParameters + i];
  176.         }

  178.         return rangeError;
  179.     }

  181.     /** {@inheritDoc} */
  182.     @Override
  183.     public List<ParameterDriver> getParametersDrivers() {
  184.         return ionoModel.getParametersDrivers();
  185.     }

  187.     /** {@inheritDoc} */
  188.     @Override
  189.     public void modify(final EstimatedMeasurement<RangeRate> estimated) {

  191.         final RangeRate       measurement = estimated.getObservedMeasurement();
  192.         final GroundStation   station     = measurement.getStation();
  193.         final SpacecraftState state       = estimated.getStates()[0];

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

  197.         // update estimated derivatives with Jacobian of the measure wrt state
  198.         final IonosphericGradientConverter converter =
  199.                 new IonosphericGradientConverter(state, 6, new InertialProvider(state.getFrame()));
  200.         final FieldSpacecraftState<Gradient> gState = converter.getState(ionoModel);
  201.         final Gradient[] gParameters = converter.getParameters(gState, ionoModel);
  202.         final Gradient gDelay = rangeRateErrorIonosphericModel(station, gState, gParameters);
  203.         final double[] derivatives = gDelay.getGradient();

  205.         // update estimated derivatives with Jacobian of the measure wrt state
  206.         final double[][] djac = rangeRateErrorJacobianState(derivatives);
  207.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  208.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  209.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  210.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  211.             }
  212.         }
  213.         estimated.setStateDerivatives(0, stateDerivatives);

  215.         int index = 0;
  216.         for (final ParameterDriver driver : getParametersDrivers()) {
  217.             if (driver.isSelected()) {
  218.                 // update estimated derivatives with derivative of the modification wrt ionospheric parameters
  219.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  220.                 final double[] dDelaydP    = rangeRateErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
  221.                 parameterDerivative += dDelaydP[index];
  222.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  223.                 index = index + 1;
  224.             }

  226.         }

  228.         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
  229.                                                           station.getEastOffsetDriver(),
  230.                                                           station.getNorthOffsetDriver(),
  231.                                                           station.getZenithOffsetDriver())) {
  232.             if (driver.isSelected()) {
  233.                 // update estimated derivatives with derivative of the modification wrt station parameters
  234.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  235.                 parameterDerivative += rangeRateErrorParameterDerivative(station, driver, state);
  236.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  237.             }
  238.         }

  240.         // update estimated value taking into account the ionospheric delay.
  241.         // The ionospheric delay is directly added to the range.
  242.         final double[] newValue = oldValue.clone();
  243.         newValue[0] = newValue[0] + gDelay.getValue();
  244.         estimated.setEstimatedValue(newValue);

  246.     }

  248. }
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