RangeRate.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;

  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.frames.FieldTransform;
  28. import org.orekit.propagation.SpacecraftState;
  29. import org.orekit.time.AbsoluteDate;
  30. import org.orekit.time.FieldAbsoluteDate;
  31. import org.orekit.utils.ParameterDriver;
  32. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  33. import org.orekit.utils.TimeStampedPVCoordinates;

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

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

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

  57.     /** Simple constructor.
  58.      * @param station ground station from which measurement is performed
  59.      * @param date date of the measurement
  60.      * @param rangeRate observed value, m/s
  61.      * @param sigma theoretical standard deviation
  62.      * @param baseWeight base weight
  63.      * @param twoway if true, this is a two-way measurement
  64.      * @param satellite satellite related to this measurement
  65.      * @since 9.3
  66.      */
  67.     public RangeRate(final GroundStation station, final AbsoluteDate date,
  68.                      final double rangeRate, final double sigma, final double baseWeight,
  69.                      final boolean twoway, final ObservableSatellite satellite) {
  70.         super(date, rangeRate, sigma, baseWeight, Arrays.asList(satellite));
  71.         addParameterDriver(station.getClockOffsetDriver());
  72.         addParameterDriver(station.getEastOffsetDriver());
  73.         addParameterDriver(station.getNorthOffsetDriver());
  74.         addParameterDriver(station.getZenithOffsetDriver());
  75.         addParameterDriver(station.getPrimeMeridianOffsetDriver());
  76.         addParameterDriver(station.getPrimeMeridianDriftDriver());
  77.         addParameterDriver(station.getPolarOffsetXDriver());
  78.         addParameterDriver(station.getPolarDriftXDriver());
  79.         addParameterDriver(station.getPolarOffsetYDriver());
  80.         addParameterDriver(station.getPolarDriftYDriver());
  81.         this.station = station;
  82.         this.twoway  = twoway;
  83.     }

  85.     /** Check if the instance represents a two-way measurement.
  86.      * @return true if the instance represents a two-way measurement
  87.      */
  88.     public boolean isTwoWay() {
  89.         return twoway;
  90.     }

  92.     /** Get the ground station from which measurement is performed.
  93.      * @return ground station from which measurement is performed
  94.      */
  95.     public GroundStation getStation() {
  96.         return station;
  97.     }

  99.     /** {@inheritDoc} */
  100.     @Override
  101.     protected EstimatedMeasurement<RangeRate> theoreticalEvaluation(final int iteration, final int evaluation,
  102.                                                                     final SpacecraftState[] states) {

  104.         final SpacecraftState state = states[0];

  106.         // Range-rate derivatives are computed with respect to spacecraft state in inertial frame
  107.         // and station position in station's offset frame
  108.         // -------
  109.         //
  110.         // Parameters:
  111.         //  - 0..2 - Position of the spacecraft in inertial frame
  112.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  113.         //  - 6..n - station parameters (clock offset, station offsets, pole, prime meridian...)
  114.         int nbParams = 6;
  115.         final Map<String, Integer> indices = new HashMap<>();
  116.         for (ParameterDriver driver : getParametersDrivers()) {
  117.             if (driver.isSelected()) {
  118.                 indices.put(driver.getName(), nbParams++);
  119.             }
  120.         }
  121.         final DSFactory factory = new DSFactory(nbParams, 1);
  122.         final Field<DerivativeStructure> field = factory.getDerivativeField();
  123.         final FieldVector3D<DerivativeStructure> zero = FieldVector3D.getZero(field);

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

  128.         // transform between station and inertial frame, expressed as a derivative structure
  129.         // The components of station's position in offset frame are the 3 last derivative parameters
  130.         final FieldTransform<DerivativeStructure> offsetToInertialDownlink =
  131.                         station.getOffsetToInertial(state.getFrame(), getDate(), factory, indices);
  132.         final FieldAbsoluteDate<DerivativeStructure> downlinkDateDS =
  133.                         offsetToInertialDownlink.getFieldDate();

  135.         // Station position in inertial frame at end of the downlink leg
  136.         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationDownlink =
  137.                         offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
  138.                                                                                                             zero, zero, zero));

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

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

  147.         // Transit state
  148.         final DerivativeStructure   delta        = downlinkDateDS.durationFrom(state.getDate());
  149.         final DerivativeStructure   deltaMTauD   = tauD.negate().add(delta);
  150.         final SpacecraftState       transitState = state.shiftedBy(deltaMTauD.getValue());

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

  155.         // one-way (downlink) range-rate
  156.         final EstimatedMeasurement<RangeRate> evalOneWay1 =
  157.                         oneWayTheoreticalEvaluation(iteration, evaluation, true,
  158.                                                     stationDownlink, transitPV, transitState, indices);
  159.         final EstimatedMeasurement<RangeRate> estimated;
  160.         if (twoway) {
  161.             // one-way (uplink) light time correction
  162.             final FieldTransform<DerivativeStructure> offsetToInertialApproxUplink =
  163.                             station.getOffsetToInertial(state.getFrame(),
  164.                                                         downlinkDateDS.shiftedBy(tauD.multiply(-2)), factory, indices);
  165.             final FieldAbsoluteDate<DerivativeStructure> approxUplinkDateDS =
  166.                             offsetToInertialApproxUplink.getFieldDate();

  168.             final TimeStampedFieldPVCoordinates<DerivativeStructure> stationApproxUplink =
  169.                             offsetToInertialApproxUplink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(approxUplinkDateDS,
  170.                                                                                                                     zero, zero, zero));

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

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

  177.             final EstimatedMeasurement<RangeRate> evalOneWay2 =
  178.                             oneWayTheoreticalEvaluation(iteration, evaluation, false,
  179.                                                         stationUplink, transitPV, transitState, indices);

  181.             // combine uplink and downlink values
  182.             estimated = new EstimatedMeasurement<>(this, iteration, evaluation,
  183.                                                    evalOneWay1.getStates(),
  184.                                                    new TimeStampedPVCoordinates[] {
  185.                                                        evalOneWay2.getParticipants()[0],
  186.                                                        evalOneWay1.getParticipants()[0],
  187.                                                        evalOneWay1.getParticipants()[1]
  188.                                                    });
  189.             estimated.setEstimatedValue(0.5 * (evalOneWay1.getEstimatedValue()[0] + evalOneWay2.getEstimatedValue()[0]));

  191.             // combine uplink and downlink partial derivatives with respect to state
  192.             final double[][] sd1 = evalOneWay1.getStateDerivatives(0);
  193.             final double[][] sd2 = evalOneWay2.getStateDerivatives(0);
  194.             final double[][] sd = new double[sd1.length][sd1[0].length];
  195.             for (int i = 0; i < sd.length; ++i) {
  196.                 for (int j = 0; j < sd[0].length; ++j) {
  197.                     sd[i][j] = 0.5 * (sd1[i][j] + sd2[i][j]);
  198.                 }
  199.             }
  200.             estimated.setStateDerivatives(0, sd);

  202.             // combine uplink and downlink partial derivatives with respect to parameters
  203.             evalOneWay1.getDerivativesDrivers().forEach(driver -> {
  204.                 final double[] pd1 = evalOneWay1.getParameterDerivatives(driver);
  205.                 final double[] pd2 = evalOneWay2.getParameterDerivatives(driver);
  206.                 final double[] pd = new double[pd1.length];
  207.                 for (int i = 0; i < pd.length; ++i) {
  208.                     pd[i] = 0.5 * (pd1[i] + pd2[i]);
  209.                 }
  210.                 estimated.setParameterDerivatives(driver, pd);
  211.             });

  213.         } else {
  214.             estimated = evalOneWay1;
  215.         }

  217.         return estimated;

  219.     }

  221.     /** Evaluate measurement in one-way.
  222.      * @param iteration iteration number
  223.      * @param evaluation evaluations counter
  224.      * @param downlink indicator for downlink leg
  225.      * @param stationPV station coordinates when signal is at station
  226.      * @param transitPV spacecraft coordinates at onboard signal transit
  227.      * @param transitState orbital state at onboard signal transit
  228.      * @param indices indices of the estimated parameters in derivatives computations
  229.      * @return theoretical value
  230.      * @see #evaluate(SpacecraftStatet)
  231.      */
  232.     private EstimatedMeasurement<RangeRate> oneWayTheoreticalEvaluation(final int iteration, final int evaluation, final boolean downlink,
  233.                                                                         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationPV,
  234.                                                                         final TimeStampedFieldPVCoordinates<DerivativeStructure> transitPV,
  235.                                                                         final SpacecraftState transitState,
  236.                                                                         final Map<String, Integer> indices) {

  238.         // prepare the evaluation
  239.         final EstimatedMeasurement<RangeRate> estimated =
  240.                         new EstimatedMeasurement<RangeRate>(this, iteration, evaluation,
  241.                                                             new SpacecraftState[] {
  242.                                                                 transitState
  243.                                                             }, new TimeStampedPVCoordinates[] {
  244.                                                                 (downlink ? transitPV : stationPV).toTimeStampedPVCoordinates(),
  245.                                                                 (downlink ? stationPV : transitPV).toTimeStampedPVCoordinates()
  246.                                                             });

  248.         // range rate value
  249.         final FieldVector3D<DerivativeStructure> stationPosition  = stationPV.getPosition();
  250.         final FieldVector3D<DerivativeStructure> relativePosition = stationPosition.subtract(transitPV.getPosition());

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

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

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

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

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

  267.         // set partial derivatives with respect to parameters
  268.         // (beware element at index 0 is the value, not a derivative)
  269.         for (final ParameterDriver driver : getParametersDrivers()) {
  270.             final Integer index = indices.get(driver.getName());
  271.             if (index != null) {
  272.                 estimated.setParameterDerivatives(driver, derivatives[index + 1]);
  273.             }
  274.         }

  276.         return estimated;

  278.     }

  280. }
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