RangeIonosphericDelayModifier.java

  1. /* Copyright 2002-2018 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.errors.OrekitException;
  25. import org.orekit.errors.OrekitExceptionWrapper;
  26. import org.orekit.estimation.measurements.EstimatedMeasurement;
  27. import org.orekit.estimation.measurements.EstimationModifier;
  28. import org.orekit.estimation.measurements.GroundStation;
  29. import org.orekit.estimation.measurements.Range;
  30. import org.orekit.models.earth.IonosphericModel;
  31. import org.orekit.orbits.OrbitType;
  32. import org.orekit.orbits.PositionAngle;
  33. import org.orekit.propagation.Propagator;
  34. import org.orekit.propagation.SpacecraftState;
  35. import org.orekit.utils.Differentiation;
  36. import org.orekit.utils.ParameterDriver;
  37. import org.orekit.utils.ParameterFunction;
  38. import org.orekit.utils.StateFunction;

  40. /** Class modifying theoretical range measurement with ionospheric delay.
  41.  * The effect of ionospheric correction on the range is directly computed
  42.  * through the computation of the ionospheric delay.
  43.  *
  44.  * The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
  45.  * For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
  46.  *
  47.  * @author Maxime Journot
  48.  * @author Joris Olympio
  49.  * @since 8.0
  50.  */
  51. public class RangeIonosphericDelayModifier implements EstimationModifier<Range> {

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

  56.     /** Constructor.
  57.      *
  58.      * @param model  Ionospheric delay model appropriate for the current range measurement method.
  59.      */
  60.     public RangeIonosphericDelayModifier(final IonosphericModel model) {
  61.         ionoModel = model;
  62.     }

  64.     /** Compute the measurement error due to ionosphere.
  65.      * @param station station
  66.      * @param state spacecraft state
  67.      * @return the measurement error due to ionosphere
  68.      * @throws OrekitException  if frames transformations cannot be computed
  69.      */
  70.     private double rangeErrorIonosphericModel(final GroundStation station,
  71.                                               final SpacecraftState state)
  72.         throws OrekitException {
  73.         //
  74.         final Vector3D position = state.getPVCoordinates().getPosition();

  76.         // elevation
  77.         final double elevation = station.getBaseFrame().getElevation(position,
  78.                                                                      state.getFrame(),
  79.                                                                      state.getDate());

  81.         // only consider measures above the horizon
  82.         if (elevation > 0) {

  84.             // compute azimuth
  85.             final double azimuth = station.getBaseFrame().getAzimuth(position,
  86.                                                                      state.getFrame(),
  87.                                                                      state.getDate());

  89.             // delay in meters
  90.             final double delay = ionoModel.pathDelay(state.getDate(),
  91.                                                      station.getBaseFrame().getPoint(),
  92.                                                      elevation, azimuth);
  93.             return delay;
  94.         }

  96.         return 0;
  97.     }

  99.     /** Compute the Jacobian of the delay term wrt state.
  100.      *
  101.      * @param station station
  102.      * @param refstate reference spacecraft state
  103.      *
  104.      * @return Jacobian of the delay wrt state
  105.      * @throws OrekitException  if frames transformations cannot be computed
  106.      */
  107.     private double[][] rangeErrorJacobianState(final GroundStation station,
  108.                                                final SpacecraftState refstate)
  109.         throws OrekitException {
  110.         final double[][] finiteDifferencesJacobian =
  111.                         Differentiation.differentiate(new StateFunction() {
  112.                             public double[] value(final SpacecraftState state) throws OrekitException {
  113.                                 try {
  114.                                     // evaluate target's elevation with a changed target position
  115.                                     final double value = rangeErrorIonosphericModel(station, state);

  117.                                     return new double[] {
  118.                                         value
  119.                                     };

  121.                                 } catch (OrekitException oe) {
  122.                                     throw new OrekitExceptionWrapper(oe);
  123.                                 }
  124.                             }
  125.                         }, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
  126.                         PositionAngle.TRUE, 15.0, 3).value(refstate);

  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.      * @param delay current ionospheric delay
  138.      * @return derivative of the delay wrt station offset parameter
  139.      * @throws OrekitException  if frames transformations cannot be computed
  140.      */
  141.     private double rangeErrorParameterDerivative(final GroundStation station,
  142.                                                  final ParameterDriver driver,
  143.                                                  final SpacecraftState state,
  144.                                                  final double delay)
  145.         throws OrekitException {

  147.         final ParameterFunction rangeError = new ParameterFunction() {
  148.             /** {@inheritDoc} */
  149.             @Override
  150.             public double value(final ParameterDriver parameterDriver) throws OrekitException {
  151.                 return rangeErrorIonosphericModel(station, state);
  152.             }
  153.         };

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

  158.         return rangeErrorDerivative.value(driver);

  160.     }

  162.     /** {@inheritDoc} */
  163.     @Override
  164.     public List<ParameterDriver> getParametersDrivers() {
  165.         return Collections.emptyList();
  166.     }

  168.     @Override
  169.     public void modify(final EstimatedMeasurement<Range> estimated)
  170.         throws OrekitException {
  171.         final Range           measurement = estimated.getObservedMeasurement();
  172.         final GroundStation   station     = measurement.getStation();
  173.         final SpacecraftState state       = estimated.getStates()[0];

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

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

  179.         // update estimated value taking into account the ionospheric delay.
  180.         // The ionospheric delay is directly added to the range.
  181.         final double[] newValue = oldValue.clone();
  182.         newValue[0] = newValue[0] + delay;
  183.         estimated.setEstimatedValue(newValue);

  185.         // update estimated derivatives with Jacobian of the measure wrt state
  186.         final double[][] djac = rangeErrorJacobianState(station, state);
  187.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  188.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  189.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  190.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  191.             }
  192.         }
  193.         estimated.setStateDerivatives(0, stateDerivatives);

  195.         for (final ParameterDriver driver : Arrays.asList(station.getEastOffsetDriver(),
  196.                                                           station.getNorthOffsetDriver(),
  197.                                                           station.getZenithOffsetDriver())) {
  198.             if (driver.isSelected()) {
  199.                 // update estimated derivatives with derivative of the modification wrt station parameters
  200.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  201.                 parameterDerivative += rangeErrorParameterDerivative(station, driver, state, delay);
  202.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  203.             }
  204.         }

  206.     }

  208. }
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