RangeTroposphericDelayModifier.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.TroposphericModel;
  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 tropospheric delay.
  41.  * The effect of tropospheric correction on the range is directly computed
  42.  * through the computation of the tropospheric delay.
  43.  *
  44.  * In general, for GNSS, VLBI, ... there is hardly any frequency dependence in the delay.
  45.  * For SLR techniques however, the frequency dependence is sensitive.
  46.  *
  47.  * @author Maxime Journot
  48.  * @author Joris Olympio
  49.  * @since 8.0
  50.  */
  51. public class RangeTroposphericDelayModifier implements EstimationModifier<Range> {

  53.     /** Tropospheric delay model. */
  54.     private final TroposphericModel tropoModel;

  56.     /** Constructor.
  57.      *
  58.      * @param model  Tropospheric delay model appropriate for the current range measurement method.
  59.      */
  60.     public RangeTroposphericDelayModifier(final TroposphericModel model) {
  61.         tropoModel = model;
  62.     }

  64.     /** Get the station height above mean sea level.
  65.      *
  66.      * @param station  ground station (or measuring station)
  67.      * @return the measuring station height above sea level, m
  68.      */
  69.     private double getStationHeightAMSL(final GroundStation station) {
  70.         // FIXME heigth should be computed with respect to geoid WGS84+GUND = EGM2008 for example
  71.         final double height = station.getBaseFrame().getPoint().getAltitude();
  72.         return height;
  73.     }

  75.     /** Compute the measurement error due to Troposphere.
  76.      * @param station station
  77.      * @param state spacecraft state
  78.      * @return the measurement error due to Troposphere
  79.      * @throws OrekitException  if frames transformations cannot be computed
  80.      */
  81.     private double rangeErrorTroposphericModel(final GroundStation station, final SpacecraftState state)
  82.         throws OrekitException {
  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) {
  93.             // altitude AMSL in meters
  94.             final double height = getStationHeightAMSL(station);

  96.             // delay in meters
  97.             final double delay = tropoModel.pathDelay(elevation, height);

  99.             return delay;
  100.         }

  102.         return 0;
  103.     }

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

  122.                                     return new double[] {value };

  124.                                 } catch (OrekitException oe) {
  125.                                     throw new OrekitExceptionWrapper(oe);
  126.                                 }
  127.                             }
  128.                         }, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
  129.                         PositionAngle.TRUE, 15.0, 3).value(refstate);

  131.         return finiteDifferencesJacobian;
  132.     }


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

  150.         final ParameterFunction rangeError = new ParameterFunction() {
  151.             /** {@inheritDoc} */
  152.             @Override
  153.             public double value(final ParameterDriver parameterDriver) throws OrekitException {
  154.                 return rangeErrorTroposphericModel(station, state);
  155.             }
  156.         };

  158.         final ParameterFunction rangeErrorDerivative =
  159.                         Differentiation.differentiate(rangeError, driver, 3, 10.0);

  161.         return rangeErrorDerivative.value(driver);

  163.     }

  165.     /** {@inheritDoc} */
  166.     @Override
  167.     public List<ParameterDriver> getParametersDrivers() {
  168.         return Collections.emptyList();
  169.     }

  171.     /** {@inheritDoc} */
  172.     @Override
  173.     public void modify(final EstimatedMeasurement<Range> estimated)
  174.         throws OrekitException {
  175.         final Range           measurement = estimated.getObservedMeasurement();
  176.         final GroundStation   station     = measurement.getStation();
  177.         final SpacecraftState state       = estimated.getStates()[0];

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

  181.         final double delay = rangeErrorTroposphericModel(station, state);

  183.         // update estimated value taking into account the tropospheric delay.
  184.         // The tropospheric delay is directly added to the range.
  185.         final double[] newValue = oldValue.clone();
  186.         newValue[0] = newValue[0] + delay;
  187.         estimated.setEstimatedValue(newValue);

  189.         // update estimated derivatives with Jacobian of the measure wrt state
  190.         final double[][] djac = rangeErrorJacobianState(station,
  191.                                       state);
  192.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  193.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  194.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  195.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  196.             }
  197.         }
  198.         estimated.setStateDerivatives(0, stateDerivatives);

  200.         for (final ParameterDriver driver : Arrays.asList(station.getEastOffsetDriver(),
  201.                                                           station.getNorthOffsetDriver(),
  202.                                                           station.getZenithOffsetDriver())) {
  203.             if (driver.isSelected()) {
  204.                 // update estimated derivatives with derivative of the modification wrt station parameters
  205.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  206.                 parameterDerivative += rangeErrorParameterDerivative(station, driver, state, delay);
  207.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  208.             }
  209.         }

  211.     }

  213. }
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