RangeRateIonosphericDelayModifier.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.RangeRate;
  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-rate measurement with ionospheric delay.
  39.  * The effect of ionospheric correction on the range-rate is directly computed
  40.  * through the computation of the ionospheric delay difference with respect to
  41.  * time.
  42.  *
  43.  * The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
  44.  * For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
  45.  *
  46.  * @author Joris Olympio
  47.  * @since 8.0
  48.  */
  49. public class RangeRateIonosphericDelayModifier implements EstimationModifier<RangeRate> {

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

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

  57.     /** Constructor.
  58.      *
  59.      * @param model Ionospheric delay model appropriate for the current range-rate measurement method.
  60.      * @param twoWay Flag indicating whether the measurement is two-way.
  61.      */
  62.     public RangeRateIonosphericDelayModifier(final IonosphericModel model, final boolean twoWay) {
  63.         ionoModel = model;

  65.         if (twoWay) {
  66.             fTwoWay = 2.;
  67.         } else {
  68.             fTwoWay = 1.;
  69.         }
  70.     }

  72.     /** Compute the measurement error due to Ionosphere.
  73.      * @param station station
  74.      * @param state spacecraft state
  75.      * @return the measurement error due to Ionosphere
  76.      */
  77.     private double rangeRateErrorIonosphericModel(final GroundStation station, final SpacecraftState state) {
  78.         // The effect of ionospheric correction on the range rate is
  79.         // computed using finite differences.

  81.         final double dt = 10; // s

  83.         //
  84.         final Vector3D position = state.getPVCoordinates().getPosition();

  86.         // elevation
  87.         final double elevation = station.getBaseFrame().getElevation(position,
  88.                                                                      state.getFrame(),
  89.                                                                      state.getDate());

  91.         // only consider measures above the horizon
  92.         if (elevation > 0) {

  94.             // compute azimuth
  95.             final double azimuth = station.getBaseFrame().getAzimuth(position,
  96.                                                                      state.getFrame(),
  97.                                                                      state.getDate());

  99.             // delay in meters
  100.             final double delay1 = ionoModel.pathDelay(state.getDate(),
  101.                                                       station.getBaseFrame().getPoint(),
  102.                                                       elevation,
  103.                                                       azimuth);

  105.             // propagate spacecraft state forward by dt
  106.             final SpacecraftState state2 = state.shiftedBy(dt);

  108.             // spacecraft position and elevation as seen from the ground station
  109.             final Vector3D position2 = state2.getPVCoordinates().getPosition();
  110.             final double elevation2 = station.getBaseFrame().getElevation(position2,
  111.                                                                           state2.getFrame(),
  112.                                                                           state2.getDate());

  114.             // compute azimuth in degrees
  115.             final double azimuth2 = station.getBaseFrame().getAzimuth(position2,
  116.                                                                       state2.getFrame(),
  117.                                                                       state2.getDate());

  119.             // ionospheric delay dt after in meters
  120.             final double delay2 = ionoModel.pathDelay(state2.getDate(),
  121.                                                       station.getBaseFrame().getPoint(),
  122.                                                       elevation2,
  123.                                                       azimuth2);

  125.             // delay in meters
  126.             return fTwoWay * (delay2 - delay1) / dt;
  127.         }

  129.         return 0;
  130.     }

  132.     /** Compute the Jacobian of the delay term wrt state.
  133.      *
  134.      * @param station station
  135.      * @param refstate reference spacecraft state
  136.      *
  137.      * @return Jacobian of the delay wrt state
  138.      */
  139.     private double[][] rangeErrorJacobianState(final GroundStation station,
  140.                                                final SpacecraftState refstate) {
  141.         final double[][] finiteDifferencesJacobian =
  142.                         Differentiation.differentiate(new StateFunction() {
  143.                             public double[] value(final SpacecraftState state) {
  144.                                 // evaluate target's elevation with a changed target position
  145.                                 final double value = rangeRateErrorIonosphericModel(station, state);

  147.                                 return new double[] {value };
  148.                             }
  149.                         }, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
  150.                         PositionAngle.TRUE, 15.0, 3).value(refstate);

  152.         return finiteDifferencesJacobian;
  153.     }


  156.     /** Compute the derivative of the delay term wrt parameters.
  157.     *
  158.     * @param station ground station
  159.     * @param driver driver for the station offset parameter
  160.     * @param state spacecraft state
  161.     * @param delay current ionospheric delay
  162.     * @return derivative of the delay wrt station offset parameter
  163.     */
  164.     private double rangeRateErrorParameterDerivative(final GroundStation station,
  165.                                                      final ParameterDriver driver,
  166.                                                      final SpacecraftState state,
  167.                                                      final double delay) {

  169.         final ParameterFunction rangeError = new ParameterFunction() {
  170.             /** {@inheritDoc} */
  171.             @Override
  172.             public double value(final ParameterDriver parameterDriver) {
  173.                 return rangeRateErrorIonosphericModel(station, state);
  174.             }
  175.         };

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

  180.         return rangeErrorDerivative.value(driver);

  182.     }

  184.     /** {@inheritDoc} */
  185.     @Override
  186.     public List<ParameterDriver> getParametersDrivers() {
  187.         return Collections.emptyList();
  188.     }

  190.     /** {@inheritDoc} */
  191.     @Override
  192.     public void modify(final EstimatedMeasurement<RangeRate> estimated) {

  194.         final RangeRate       measurement = estimated.getObservedMeasurement();
  195.         final GroundStation   station     = measurement.getStation();
  196.         final SpacecraftState state       = estimated.getStates()[0];

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

  200.         final double delay = rangeRateErrorIonosphericModel(station, state);

  202.         // update estimated value taking into account the ionospheric delay.
  203.         // The ionospheric delay is directly added to the range.
  204.         final double[] newValue = oldValue.clone();
  205.         newValue[0] = newValue[0] + delay;
  206.         estimated.setEstimatedValue(newValue);

  208.         // update estimated derivatives with Jacobian of the measure wrt state
  209.         final double[][] djac = rangeErrorJacobianState(station,
  210.                                       state);
  211.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  212.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  213.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  214.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  215.             }
  216.         }
  217.         estimated.setStateDerivatives(0, stateDerivatives);

  219.         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
  220.                                                           station.getEastOffsetDriver(),
  221.                                                           station.getNorthOffsetDriver(),
  222.                                                           station.getZenithOffsetDriver())) {
  223.             if (driver.isSelected()) {
  224.                 // update estimated derivatives with derivative of the modification wrt station parameters
  225.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  226.                 parameterDerivative += rangeRateErrorParameterDerivative(station, driver, state, delay);
  227.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  228.             }
  229.         }

  231.     }

  233. }
Created with JaCoCo 0.8.2.201808211720