RangeTroposphericDelayModifier.java

  1. /* Copyright 2002-2020 CS GROUP
  2.  * Licensed to CS GROUP (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.List;

  22. import org.hipparchus.Field;
  23. import org.hipparchus.RealFieldElement;
  24. import org.hipparchus.analysis.differentiation.Gradient;
  25. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  26. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  27. import org.orekit.attitudes.InertialProvider;
  28. import org.orekit.estimation.measurements.EstimatedMeasurement;
  29. import org.orekit.estimation.measurements.EstimationModifier;
  30. import org.orekit.estimation.measurements.GroundStation;
  31. import org.orekit.estimation.measurements.Range;
  32. import org.orekit.models.earth.troposphere.DiscreteTroposphericModel;
  33. import org.orekit.propagation.FieldSpacecraftState;
  34. import org.orekit.propagation.SpacecraftState;
  35. import org.orekit.utils.Differentiation;
  36. import org.orekit.utils.ParameterDriver;
  37. import org.orekit.utils.ParameterFunction;

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

  52.     /** Tropospheric delay model. */
  53.     private final DiscreteTroposphericModel tropoModel;

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

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

  74.     /** Get the station height above mean sea level.
  75.     * @param <T> type of the elements
  76.     * @param field field of the elements
  77.     * @param station  ground station (or measuring station)
  78.     * @return the measuring station height above sea level, m
  79.     */
  80.     private <T extends RealFieldElement<T>> T getStationHeightAMSL(final Field<T> field, final GroundStation station) {
  81.         // FIXME heigth should be computed with respect to geoid WGS84+GUND = EGM2008 for example
  82.         final T height = station.getBaseFrame().getPoint(field).getAltitude();
  83.         return height;
  84.     }

  86.     /** Compute the measurement error due to Troposphere.
  87.      * @param station station
  88.      * @param state spacecraft state
  89.      * @return the measurement error due to Troposphere
  90.      */
  91.     private double rangeErrorTroposphericModel(final GroundStation station, final SpacecraftState state) {
  92.         //
  93.         final Vector3D position = state.getPVCoordinates().getPosition();

  95.         // elevation
  96.         final double elevation = station.getBaseFrame().getElevation(position,
  97.                                                                      state.getFrame(),
  98.                                                                      state.getDate());

  100.         // only consider measures above the horizon
  101.         if (elevation > 0) {
  102.             // altitude AMSL in meters
  103.             final double height = getStationHeightAMSL(station);

  105.             // delay in meters
  106.             final double delay = tropoModel.pathDelay(elevation, height, tropoModel.getParameters(), state.getDate());

  108.             return delay;
  109.         }

  111.         return 0;
  112.     }

  114.     /** Compute the measurement error due to Troposphere.
  115.      * @param <T> type of the element
  116.      * @param station station
  117.      * @param state spacecraft state
  118.      * @param parameters tropospheric model parameters
  119.      * @return the measurement error due to Troposphere
  120.      */
  121.     private <T extends RealFieldElement<T>> T rangeErrorTroposphericModel(final GroundStation station,
  122.                                                                           final FieldSpacecraftState<T> state,
  123.                                                                           final T[] parameters) {

  125.         // Field
  126.         final Field<T> field = state.getDate().getField();
  127.         final T zero         = field.getZero();

  129.         // satellite elevation
  130.         final FieldVector3D<T> position     = state.getPVCoordinates().getPosition();
  131.         final T elevation                   = station.getBaseFrame().getElevation(position,
  132.                                                                                   state.getFrame(),
  133.                                                                                   state.getDate());


  136.         // only consider measures above the horizon
  137.         if (elevation.getReal() > 0) {
  138.             // altitude AMSL in meters
  139.             final T height = getStationHeightAMSL(field, station);

  141.             // delay in meters
  142.             final T delay = tropoModel.pathDelay(elevation, height, parameters, state.getDate());

  144.             return delay;
  145.         }

  147.         return zero;
  148.     }

  150.     /** Compute the Jacobian of the delay term wrt state using
  151.     * automatic differentiation.
  152.     *
  153.     * @param derivatives tropospheric delay derivatives
  154.     *
  155.     * @return Jacobian of the delay wrt state
  156.     */
  157.     private double[][] rangeErrorJacobianState(final double[] derivatives) {
  158.         final double[][] finiteDifferencesJacobian = new double[1][6];
  159.         System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
  160.         return finiteDifferencesJacobian;
  161.     }

  163.     /** Compute the derivative of the delay term wrt parameters.
  164.      *
  165.      * @param station ground station
  166.      * @param driver driver for the station offset parameter
  167.      * @param state spacecraft state
  168.      * @return derivative of the delay wrt station offset parameter
  169.      */
  170.     private double rangeErrorParameterDerivative(final GroundStation station,
  171.                                                  final ParameterDriver driver,
  172.                                                  final SpacecraftState state) {

  174.         final ParameterFunction rangeError = new ParameterFunction() {
  175.             /** {@inheritDoc} */
  176.             @Override
  177.             public double value(final ParameterDriver parameterDriver) {
  178.                 return rangeErrorTroposphericModel(station, state);
  179.             }
  180.         };

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

  185.         return rangeErrorDerivative.value(driver);

  187.     }

  189.     /** Compute the derivative of the delay term wrt parameters using
  190.     * automatic differentiation.
  191.     *
  192.     * @param derivatives tropospheric delay derivatives
  193.     * @param freeStateParameters dimension of the state.
  194.     * @return derivative of the delay wrt tropospheric model parameters
  195.     */
  196.     private double[] rangeErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
  197.         // 0 ... freeStateParameters - 1 -> derivatives of the delay wrt state
  198.         // freeStateParameters ... n     -> derivatives of the delay wrt tropospheric parameters
  199.         final int dim = derivatives.length - freeStateParameters;
  200.         final double[] rangeError = new double[dim];

  202.         for (int i = 0; i < dim; i++) {
  203.             rangeError[i] = derivatives[freeStateParameters + i];
  204.         }

  206.         return rangeError;
  207.     }

  209.     /** {@inheritDoc} */
  210.     @Override
  211.     public List<ParameterDriver> getParametersDrivers() {
  212.         return tropoModel.getParametersDrivers();
  213.     }

  215.     /** {@inheritDoc} */
  216.     @Override
  217.     public void modify(final EstimatedMeasurement<Range> estimated) {
  218.         final Range           measurement = estimated.getObservedMeasurement();
  219.         final GroundStation   station     = measurement.getStation();
  220.         final SpacecraftState state       = estimated.getStates()[0];

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

  224.         // update estimated derivatives with Jacobian of the measure wrt state
  225.         final TroposphericGradientConverter converter =
  226.                 new TroposphericGradientConverter(state, 6, new InertialProvider(state.getFrame()));
  227.         final FieldSpacecraftState<Gradient> gState = converter.getState(tropoModel);
  228.         final Gradient[] gParameters = converter.getParameters(gState, tropoModel);
  229.         final Gradient gDelay = rangeErrorTroposphericModel(station, gState, gParameters);
  230.         final double[] derivatives = gDelay.getGradient();

  232.         final double[][] djac = rangeErrorJacobianState(derivatives);

  234.         final double[][] stateDerivatives = estimated.getStateDerivatives(0);
  235.         for (int irow = 0; irow < stateDerivatives.length; ++irow) {
  236.             for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
  237.                 stateDerivatives[irow][jcol] += djac[irow][jcol];
  238.             }
  239.         }
  240.         estimated.setStateDerivatives(0, stateDerivatives);

  242.         int index = 0;
  243.         for (final ParameterDriver driver : getParametersDrivers()) {
  244.             if (driver.isSelected()) {
  245.                 // update estimated derivatives with derivative of the modification wrt tropospheric parameters
  246.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  247.                 final double[] dDelaydP    = rangeErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
  248.                 parameterDerivative += dDelaydP[index];
  249.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  250.                 index = index + 1;
  251.             }

  253.         }

  255.         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
  256.                                                           station.getEastOffsetDriver(),
  257.                                                           station.getNorthOffsetDriver(),
  258.                                                           station.getZenithOffsetDriver())) {
  259.             if (driver.isSelected()) {
  260.                 // update estimated derivatives with derivative of the modification wrt station parameters
  261.                 double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
  262.                 parameterDerivative += rangeErrorParameterDerivative(station, driver, state);
  263.                 estimated.setParameterDerivatives(driver, parameterDerivative);
  264.             }
  265.         }

  267.         // update estimated value taking into account the tropospheric delay.
  268.         // The tropospheric delay is directly added to the range.
  269.         final double[] newValue = oldValue.clone();
  270.         newValue[0] = newValue[0] + gDelay.getReal();
  271.         estimated.setEstimatedValue(newValue);

  273.     }

  275. }
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