RangeRate.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;

  19. import java.util.Arrays;
  20. import java.util.HashMap;
  21. import java.util.Map;

  23. import org.hipparchus.Field;
  24. import org.hipparchus.analysis.differentiation.DSFactory;
  25. import org.hipparchus.analysis.differentiation.DerivativeStructure;
  26. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  27. import org.orekit.errors.OrekitException;
  28. import org.orekit.frames.FieldTransform;
  29. import org.orekit.propagation.SpacecraftState;
  30. import org.orekit.time.AbsoluteDate;
  31. import org.orekit.time.FieldAbsoluteDate;
  32. import org.orekit.utils.ParameterDriver;
  33. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  34. import org.orekit.utils.TimeStampedPVCoordinates;

  36. /** Class modeling one-way or two-way range rate measurement between two vehicles.
  37.  * One-way range rate (or Doppler) measurements generally apply to specific satellites
  38.  * (e.g. GNSS, DORIS), where a signal is transmitted from a satellite to a
  39.  * measuring station.
  40.  * Two-way range rate measurements are applicable to any system. The signal is
  41.  * transmitted to the (non-spinning) satellite and returned by a transponder
  42.  * (or reflected back)to the same measuring station.
  43.  * The Doppler measurement can be obtained by multiplying the velocity by (fe/c), where
  44.  * fe is the emission frequency.
  45.  *
  46.  * @author Thierry Ceolin
  47.  * @author Joris Olympio
  48.  * @since 8.0
  49.  */
  50. public class RangeRate extends AbstractMeasurement<RangeRate> {

  52.     /** Ground station from which measurement is performed. */
  53.     private final GroundStation station;

  55.     /** Flag indicating whether it is a two-way measurement. */
  56.     private final boolean twoway;

  58.     /** Simple constructor.
  59.      * <p>
  60.      * This constructor uses 0 as the index of the propagator related
  61.      * to this measurement, thus being well suited for mono-satellite
  62.      * orbit determination.
  63.      * </p>
  64.      * @param station ground station from which measurement is performed
  65.      * @param date date of the measurement
  66.      * @param rangeRate observed value, m/s
  67.      * @param sigma theoretical standard deviation
  68.      * @param baseWeight base weight
  69.      * @param twoway if true, this is a two-way measurement
  70.      * @exception OrekitException if a {@link org.orekit.utils.ParameterDriver}
  71.      * name conflict occurs
  72.      */
  73.     public RangeRate(final GroundStation station, final AbsoluteDate date,
  74.                      final double rangeRate,
  75.                      final double sigma,
  76.                      final double baseWeight,
  77.                      final boolean twoway)
  78.         throws OrekitException {
  79.         this(station, date, rangeRate, sigma, baseWeight, twoway, 0);
  80.     }

  82.     /** Simple constructor.
  83.      * @param station ground station from which measurement is performed
  84.      * @param date date of the measurement
  85.      * @param rangeRate observed value, m/s
  86.      * @param sigma theoretical standard deviation
  87.      * @param baseWeight base weight
  88.      * @param twoway if true, this is a two-way measurement
  89.      * @param propagatorIndex index of the propagator related to this measurement
  90.      * @exception OrekitException if a {@link org.orekit.utils.ParameterDriver}
  91.      * name conflict occurs
  92.      * @since 9.0
  93.      */
  94.     public RangeRate(final GroundStation station, final AbsoluteDate date,
  95.                      final double rangeRate,
  96.                      final double sigma,
  97.                      final double baseWeight,
  98.                      final boolean twoway,
  99.                      final int propagatorIndex)
  100.         throws OrekitException {
  101.         super(date, rangeRate, sigma, baseWeight, Arrays.asList(propagatorIndex),
  102.               station.getEastOffsetDriver(),
  103.               station.getNorthOffsetDriver(),
  104.               station.getZenithOffsetDriver(),
  105.               station.getPrimeMeridianOffsetDriver(),
  106.               station.getPrimeMeridianDriftDriver(),
  107.               station.getPolarOffsetXDriver(),
  108.               station.getPolarDriftXDriver(),
  109.               station.getPolarOffsetYDriver(),
  110.               station.getPolarDriftYDriver());
  111.         this.station = station;
  112.         this.twoway  = twoway;
  113.     }

  115.     /** Check if the instance represents a two-way measurement.
  116.      * @return true if the instance represents a two-way measurement
  117.      */
  118.     public boolean isTwoWay() {
  119.         return twoway;
  120.     }

  122.     /** Get the ground station from which measurement is performed.
  123.      * @return ground station from which measurement is performed
  124.      */
  125.     public GroundStation getStation() {
  126.         return station;
  127.     }

  129.     /** {@inheritDoc} */
  130.     @Override
  131.     protected EstimatedMeasurement<RangeRate> theoreticalEvaluation(final int iteration, final int evaluation,
  132.                                                                     final SpacecraftState[] states)
  133.         throws OrekitException {

  135.         final SpacecraftState state = states[getPropagatorsIndices().get(0)];

  137.         // Range-rate derivatives are computed with respect to spacecraft state in inertial frame
  138.         // and station position in station's offset frame
  139.         // -------
  140.         //
  141.         // Parameters:
  142.         //  - 0..2 - Position of the spacecraft in inertial frame
  143.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  144.         //  - 6..n - station parameters (station offsets, pole, prime meridian...)
  145.         int nbParams = 6;
  146.         final Map<String, Integer> indices = new HashMap<>();
  147.         for (ParameterDriver driver : getParametersDrivers()) {
  148.             if (driver.isSelected()) {
  149.                 indices.put(driver.getName(), nbParams++);
  150.             }
  151.         }
  152.         final DSFactory factory = new DSFactory(nbParams, 1);
  153.         final Field<DerivativeStructure> field = factory.getDerivativeField();
  154.         final FieldVector3D<DerivativeStructure> zero = FieldVector3D.getZero(field);

  156.         // Coordinates of the spacecraft expressed as a derivative structure
  157.         final TimeStampedFieldPVCoordinates<DerivativeStructure> pvaDS = getCoordinates(state, 0, factory);

  159.         // transform between station and inertial frame, expressed as a derivative structure
  160.         // The components of station's position in offset frame are the 3 last derivative parameters
  161.         final AbsoluteDate downlinkDate = getDate();
  162.         final FieldAbsoluteDate<DerivativeStructure> downlinkDateDS =
  163.                         new FieldAbsoluteDate<>(field, downlinkDate);
  164.         final FieldTransform<DerivativeStructure> offsetToInertialDownlink =
  165.                         station.getOffsetToInertial(state.getFrame(), downlinkDateDS, factory, indices);

  167.         // Station position in inertial frame at end of the downlink leg
  168.         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationDownlink =
  169.                         offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
  170.                                                                                                             zero, zero, zero));

  172.         // Compute propagation times
  173.         // (if state has already been set up to pre-compensate propagation delay,
  174.         //  we will have delta == tauD and transitState will be the same as state)

  176.         // Downlink delay
  177.         final DerivativeStructure tauD = signalTimeOfFlight(pvaDS, stationDownlink.getPosition(), downlinkDateDS);

  179.         // Transit state
  180.         final double                delta        = downlinkDate.durationFrom(state.getDate());
  181.         final DerivativeStructure   deltaMTauD   = tauD.negate().add(delta);
  182.         final SpacecraftState       transitState = state.shiftedBy(deltaMTauD.getValue());

  184.         // Transit state (re)computed with derivative structures
  185.         final TimeStampedFieldPVCoordinates<DerivativeStructure> transitPV = pvaDS.shiftedBy(deltaMTauD);

  187.         // one-way (downlink) range-rate
  188.         final EstimatedMeasurement<RangeRate> evalOneWay1 =
  189.                         oneWayTheoreticalEvaluation(iteration, evaluation, true,
  190.                                                     stationDownlink, transitPV, transitState, indices);
  191.         final EstimatedMeasurement<RangeRate> estimated;
  192.         if (twoway) {
  193.             // one-way (uplink) light time correction
  194.             final AbsoluteDate approxUplinkDate = downlinkDate.shiftedBy(-2 * tauD.getValue());
  195.             final FieldAbsoluteDate<DerivativeStructure> approxUplinkDateDS = new FieldAbsoluteDate<>(field, approxUplinkDate);
  196.             final FieldTransform<DerivativeStructure> offsetToInertialApproxUplink =
  197.                             station.getOffsetToInertial(state.getFrame(), approxUplinkDateDS, factory, indices);

  199.             final TimeStampedFieldPVCoordinates<DerivativeStructure> stationApproxUplink =
  200.                             offsetToInertialApproxUplink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(approxUplinkDateDS,
  201.                                                                                                                     zero, zero, zero));

  203.             final DerivativeStructure tauU = signalTimeOfFlight(stationApproxUplink, transitPV.getPosition(), transitPV.getDate());

  205.             final TimeStampedFieldPVCoordinates<DerivativeStructure> stationUplink =
  206.                             stationApproxUplink.shiftedBy(transitPV.getDate().durationFrom(approxUplinkDateDS).subtract(tauU));

  208.             final EstimatedMeasurement<RangeRate> evalOneWay2 =
  209.                             oneWayTheoreticalEvaluation(iteration, evaluation, false,
  210.                                                         stationUplink, transitPV, transitState, indices);

  212.             // combine uplink and downlink values
  213.             estimated = new EstimatedMeasurement<>(this, iteration, evaluation,
  214.                                                    evalOneWay1.getStates(),
  215.                                                    new TimeStampedPVCoordinates[] {
  216.                                                        evalOneWay2.getParticipants()[0],
  217.                                                        evalOneWay1.getParticipants()[0],
  218.                                                        evalOneWay1.getParticipants()[1]
  219.                                                    });
  220.             estimated.setEstimatedValue(0.5 * (evalOneWay1.getEstimatedValue()[0] + evalOneWay2.getEstimatedValue()[0]));

  222.             // combine uplink and downlink partial derivatives with respect to state
  223.             final double[][] sd1 = evalOneWay1.getStateDerivatives(0);
  224.             final double[][] sd2 = evalOneWay2.getStateDerivatives(0);
  225.             final double[][] sd = new double[sd1.length][sd1[0].length];
  226.             for (int i = 0; i < sd.length; ++i) {
  227.                 for (int j = 0; j < sd[0].length; ++j) {
  228.                     sd[i][j] = 0.5 * (sd1[i][j] + sd2[i][j]);
  229.                 }
  230.             }
  231.             estimated.setStateDerivatives(0, sd);

  233.             // combine uplink and downlink partial derivatives with respect to parameters
  234.             evalOneWay1.getDerivativesDrivers().forEach(driver -> {
  235.                 final double[] pd1 = evalOneWay1.getParameterDerivatives(driver);
  236.                 final double[] pd2 = evalOneWay2.getParameterDerivatives(driver);
  237.                 final double[] pd = new double[pd1.length];
  238.                 for (int i = 0; i < pd.length; ++i) {
  239.                     pd[i] = 0.5 * (pd1[i] + pd2[i]);
  240.                 }
  241.                 estimated.setParameterDerivatives(driver, pd);
  242.             });

  244.         } else {
  245.             estimated = evalOneWay1;
  246.         }

  248.         return estimated;

  250.     }

  252.     /** Evaluate measurement in one-way.
  253.      * @param iteration iteration number
  254.      * @param evaluation evaluations counter
  255.      * @param downlink indicator for downlink leg
  256.      * @param stationPV station coordinates when signal is at station
  257.      * @param transitPV spacecraft coordinates at onboard signal transit
  258.      * @param transitState orbital state at onboard signal transit
  259.      * @param indices indices of the estimated parameters in derivatives computations
  260.      * @return theoretical value
  261.      * @exception OrekitException if value cannot be computed
  262.      * @see #evaluate(SpacecraftStatet)
  263.      */
  264.     private EstimatedMeasurement<RangeRate> oneWayTheoreticalEvaluation(final int iteration, final int evaluation, final boolean downlink,
  265.                                                                         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationPV,
  266.                                                                         final TimeStampedFieldPVCoordinates<DerivativeStructure> transitPV,
  267.                                                                         final SpacecraftState transitState,
  268.                                                                         final Map<String, Integer> indices)
  269.         throws OrekitException {

  271.         // prepare the evaluation
  272.         final EstimatedMeasurement<RangeRate> estimated =
  273.                         new EstimatedMeasurement<RangeRate>(this, iteration, evaluation,
  274.                                                             new SpacecraftState[] {
  275.                                                                 transitState
  276.                                                             }, new TimeStampedPVCoordinates[] {
  277.                                                                 (downlink ? transitPV : stationPV).toTimeStampedPVCoordinates(),
  278.                                                                 (downlink ? stationPV : transitPV).toTimeStampedPVCoordinates()
  279.                                                             });

  281.         // range rate value
  282.         final FieldVector3D<DerivativeStructure> stationPosition  = stationPV.getPosition();
  283.         final FieldVector3D<DerivativeStructure> relativePosition = stationPosition.subtract(transitPV.getPosition());

  285.         final FieldVector3D<DerivativeStructure> stationVelocity  = stationPV.getVelocity();
  286.         final FieldVector3D<DerivativeStructure> relativeVelocity = stationVelocity.subtract(transitPV.getVelocity());

  288.         // radial direction
  289.         final FieldVector3D<DerivativeStructure> lineOfSight      = relativePosition.normalize();

  291.         // range rate
  292.         final DerivativeStructure rangeRate = FieldVector3D.dotProduct(relativeVelocity, lineOfSight);

  294.         estimated.setEstimatedValue(rangeRate.getValue());

  296.         // compute partial derivatives of (rr) with respect to spacecraft state Cartesian coordinates
  297.         final double[] derivatives = rangeRate.getAllDerivatives();
  298.         estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 1, 7));

  300.         // set partial derivatives with respect to parameters
  301.         // (beware element at index 0 is the value, not a derivative)
  302.         for (final ParameterDriver driver : getParametersDrivers()) {
  303.             final Integer index = indices.get(driver.getName());
  304.             if (index != null) {
  305.                 estimated.setParameterDerivatives(driver, derivatives[index + 1]);
  306.             }
  307.         }

  309.         return estimated;

  311.     }

  313. }
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