RangeIonosphericDelayModifier.java

  1. /* Copyright 2002-2019 CS Systèmes d'Information
  2.  * Licensed to CS Systèmes d'Information (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.Collections;
  21. import java.util.List;

  23. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  24. import org.orekit.estimation.measurements.EstimatedMeasurement;
  25. import org.orekit.estimation.measurements.EstimationModifier;
  26. import org.orekit.estimation.measurements.GroundStation;
  27. import org.orekit.estimation.measurements.Range;
  28. import org.orekit.models.earth.IonosphericModel;
  29. import org.orekit.orbits.OrbitType;
  30. import org.orekit.orbits.PositionAngle;
  31. import org.orekit.propagation.Propagator;
  32. import org.orekit.propagation.SpacecraftState;
  33. import org.orekit.utils.Differentiation;
  34. import org.orekit.utils.ParameterDriver;
  35. import org.orekit.utils.ParameterFunction;
  36. import org.orekit.utils.StateFunction;

  38. /** Class modifying theoretical range measurement with ionospheric delay.
  39.  * The effect of ionospheric correction on the range is directly computed
  40.  * through the computation of the ionospheric delay.
  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.  *
  45.  * @author Maxime Journot
  46.  * @author Joris Olympio
  47.  * @since 8.0
  48.  */
  49. public class RangeIonosphericDelayModifier implements EstimationModifier<Range> {

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

  54.     /** Constructor.
  55.      *
  56.      * @param model  Ionospheric delay model appropriate for the current range measurement method.
  57.      */
  58.     public RangeIonosphericDelayModifier(final IonosphericModel model) {
  59.         ionoModel = model;
  60.     }

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

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

  77.         // only consider measures above the horizon
  78.         if (elevation > 0) {

  80.             // compute azimuth
  81.             final double azimuth = station.getBaseFrame().getAzimuth(position,
  82.                                                                      state.getFrame(),
  83.                                                                      state.getDate());

  85.             // delay in meters
  86.             final double delay = ionoModel.pathDelay(state.getDate(),
  87.                                                      station.getBaseFrame().getPoint(),
  88.                                                      elevation, azimuth);
  89.             return delay;
  90.         }

  92.         return 0;
  93.     }

  95.     /** Compute the Jacobian of the delay term wrt state.
  96.      *
  97.      * @param station station
  98.      * @param refstate reference spacecraft state
  99.      *
  100.      * @return Jacobian of the delay wrt state
  101.      */
  102.     private double[][] rangeErrorJacobianState(final GroundStation station,
  103.                                                final SpacecraftState refstate) {
  104.         final double[][] finiteDifferencesJacobian =
  105.                         Differentiation.differentiate(new StateFunction() {
  106.                             public double[] value(final SpacecraftState state) {
  107.                                 // evaluate target's elevation with a changed target position
  108.                                 final double value = rangeErrorIonosphericModel(station, state);

  110.                                 return new double[] {
  111.                                     value
  112.                                 };
  113.                             }
  114.                         }, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
  115.                         PositionAngle.TRUE, 15.0, 3).value(refstate);

  117.         return finiteDifferencesJacobian;
  118.     }


  121.     /** Compute the derivative of the delay term wrt parameters.
  122.      *
  123.      * @param station ground station
  124.      * @param driver driver for the station offset parameter
  125.      * @param state spacecraft state
  126.      * @param delay current ionospheric delay
  127.      * @return derivative of the delay wrt station offset parameter
  128.      */
  129.     private double rangeErrorParameterDerivative(final GroundStation station,
  130.                                                  final ParameterDriver driver,
  131.                                                  final SpacecraftState state,
  132.                                                  final double delay) {

  134.         final ParameterFunction rangeError = new ParameterFunction() {
  135.             /** {@inheritDoc} */
  136.             @Override
  137.             public double value(final ParameterDriver parameterDriver) {
  138.                 return rangeErrorIonosphericModel(station, state);
  139.             }
  140.         };

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

  145.         return rangeErrorDerivative.value(driver);

  147.     }

  149.     /** {@inheritDoc} */
  150.     @Override
  151.     public List<ParameterDriver> getParametersDrivers() {
  152.         return Collections.emptyList();
  153.     }

  155.     @Override
  156.     public void modify(final EstimatedMeasurement<Range> estimated) {
  157.         final Range           measurement = estimated.getObservedMeasurement();
  158.         final GroundStation   station     = measurement.getStation();
  159.         final SpacecraftState state       = estimated.getStates()[0];

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

  163.         final double delay = rangeErrorIonosphericModel(station, state);

  165.         // update estimated value taking into account the ionospheric delay.
  166.         // The ionospheric delay is directly added to the range.
  167.         final double[] newValue = oldValue.clone();
  168.         newValue[0] = newValue[0] + delay;
  169.         estimated.setEstimatedValue(newValue);

  171.         // update estimated derivatives with Jacobian of the measure wrt state
  172.         final double[][] djac = rangeErrorJacobianState(station, state);
  173.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  174.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  175.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  176.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  177.             }
  178.         }
  179.         estimated.setStateDerivatives(0, stateDerivatives);

  181.         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
  182.                                                           station.getEastOffsetDriver(),
  183.                                                           station.getNorthOffsetDriver(),
  184.                                                           station.getZenithOffsetDriver())) {
  185.             if (driver.isSelected()) {
  186.                 // update estimated derivatives with derivative of the modification wrt station parameters
  187.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  188.                 parameterDerivative += rangeErrorParameterDerivative(station, driver, state, delay);
  189.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  190.             }
  191.         }

  193.     }

  195. }
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