RangeRateIonosphericDelayModifier.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.RangeRate;
  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-rate measurement with ionospheric delay.
  41.  * The effect of ionospheric correction on the range-rate is directly computed
  42.  * through the computation of the ionospheric delay difference with respect to
  43.  * time.
  44.  *
  45.  * The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
  46.  * For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
  47.  *
  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.     /** Coefficient for measurment configuration (one-way, two-way). */
  57.     private final double fTwoWay;

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

  67.         if (twoWay) {
  68.             fTwoWay = 2.;
  69.         } else {
  70.             fTwoWay = 1.;
  71.         }
  72.     }

  74.     /** Compute the measurement error due to Ionosphere.
  75.      * @param station station
  76.      * @param state spacecraft state
  77.      * @return the measurement error due to Ionosphere
  78.      * @throws OrekitException  if frames transformations cannot be computed
  79.      */
  80.     private double rangeRateErrorIonosphericModel(final GroundStation station, final SpacecraftState state)
  81.         throws OrekitException {
  82.         // The effect of ionospheric correction on the range rate is
  83.         // computed using finite differences.

  85.         final double dt = 10; // s

  87.         //
  88.         final Vector3D position = state.getPVCoordinates().getPosition();

  90.         // elevation
  91.         final double elevation = station.getBaseFrame().getElevation(position,
  92.                                                                      state.getFrame(),
  93.                                                                      state.getDate());

  95.         // only consider measures above the horizon
  96.         if (elevation > 0) {

  98.             // compute azimuth
  99.             final double azimuth = station.getBaseFrame().getAzimuth(position,
  100.                                                                      state.getFrame(),
  101.                                                                      state.getDate());

  103.             // delay in meters
  104.             final double delay1 = ionoModel.pathDelay(state.getDate(),
  105.                                                       station.getBaseFrame().getPoint(),
  106.                                                       elevation,
  107.                                                       azimuth);

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

  112.             // spacecraft position and elevation as seen from the ground station
  113.             final Vector3D position2 = state2.getPVCoordinates().getPosition();
  114.             final double elevation2 = station.getBaseFrame().getElevation(position2,
  115.                                                                           state2.getFrame(),
  116.                                                                           state2.getDate());

  118.             // compute azimuth in degrees
  119.             final double azimuth2 = station.getBaseFrame().getAzimuth(position2,
  120.                                                                       state2.getFrame(),
  121.                                                                       state2.getDate());

  123.             // ionospheric delay dt after in meters
  124.             final double delay2 = ionoModel.pathDelay(state2.getDate(),
  125.                                                       station.getBaseFrame().getPoint(),
  126.                                                       elevation2,
  127.                                                       azimuth2);

  129.             // delay in meters
  130.             return fTwoWay * (delay2 - delay1) / dt;
  131.         }

  133.         return 0;
  134.     }

  136.     /** Compute the Jacobian of the delay term wrt state.
  137.      *
  138.      * @param station station
  139.      * @param refstate reference spacecraft state
  140.      *
  141.      * @return Jacobian of the delay wrt state
  142.      * @throws OrekitException  if frames transformations cannot be computed
  143.      */
  144.     private double[][] rangeErrorJacobianState(final GroundStation station,
  145.                                                final SpacecraftState refstate)
  146.         throws OrekitException {
  147.         final double[][] finiteDifferencesJacobian =
  148.                         Differentiation.differentiate(new StateFunction() {
  149.                             public double[] value(final SpacecraftState state) throws OrekitException {
  150.                                 try {
  151.                                     // evaluate target's elevation with a changed target position
  152.                                     final double value = rangeRateErrorIonosphericModel(station, state);

  154.                                     return new double[] {value };

  156.                                 } catch (OrekitException oe) {
  157.                                     throw new OrekitExceptionWrapper(oe);
  158.                                 }
  159.                             }
  160.                         }, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
  161.                         PositionAngle.TRUE, 15.0, 3).value(refstate);

  163.         return finiteDifferencesJacobian;
  164.     }


  167.     /** Compute the derivative of the delay term wrt parameters.
  168.     *
  169.     * @param station ground station
  170.     * @param driver driver for the station offset parameter
  171.     * @param state spacecraft state
  172.     * @param delay current ionospheric delay
  173.     * @return derivative of the delay wrt station offset parameter
  174.     * @throws OrekitException  if frames transformations cannot be computed
  175.     */
  176.     private double rangeRateErrorParameterDerivative(final GroundStation station,
  177.                                                      final ParameterDriver driver,
  178.                                                      final SpacecraftState state,
  179.                                                      final double delay)
  180.         throws OrekitException {

  182.         final ParameterFunction rangeError = new ParameterFunction() {
  183.             /** {@inheritDoc} */
  184.             @Override
  185.             public double value(final ParameterDriver parameterDriver) throws OrekitException {
  186.                 return rangeRateErrorIonosphericModel(station, state);
  187.             }
  188.         };

  190.         final ParameterFunction rangeErrorDerivative =
  191.                         Differentiation.differentiate(rangeError, driver, 3, 10.0);

  193.         return rangeErrorDerivative.value(driver);

  195.     }

  197.     /** {@inheritDoc} */
  198.     @Override
  199.     public List<ParameterDriver> getParametersDrivers() {
  200.         return Collections.emptyList();
  201.     }

  203.     /** {@inheritDoc} */
  204.     @Override
  205.     public void modify(final EstimatedMeasurement<RangeRate> estimated)
  206.         throws OrekitException {

  208.         final RangeRate       measurement = estimated.getObservedMeasurement();
  209.         final GroundStation   station     = measurement.getStation();
  210.         final SpacecraftState state       = estimated.getStates()[0];

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

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

  216.         // update estimated value taking into account the ionospheric delay.
  217.         // The ionospheric delay is directly added to the range.
  218.         final double[] newValue = oldValue.clone();
  219.         newValue[0] = newValue[0] + delay;
  220.         estimated.setEstimatedValue(newValue);

  222.         // update estimated derivatives with Jacobian of the measure wrt state
  223.         final double[][] djac = rangeErrorJacobianState(station,
  224.                                       state);
  225.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  226.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  227.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  228.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  229.             }
  230.         }
  231.         estimated.setStateDerivatives(0, stateDerivatives);

  233.         for (final ParameterDriver driver : Arrays.asList(station.getEastOffsetDriver(),
  234.                                                           station.getNorthOffsetDriver(),
  235.                                                           station.getZenithOffsetDriver())) {
  236.             if (driver.isSelected()) {
  237.                 // update estimated derivatives with derivative of the modification wrt station parameters
  238.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  239.                 parameterDerivative += rangeRateErrorParameterDerivative(station, driver, state, delay);
  240.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  241.             }
  242.         }

  244.     }

  246. }
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