RangeRate.java

  1. /* Copyright 2002-2025 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.Map;

  22. import org.hipparchus.analysis.differentiation.Gradient;
  23. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  24. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  25. import org.orekit.frames.FieldTransform;
  26. import org.orekit.frames.Transform;
  27. import org.orekit.propagation.SpacecraftState;
  28. import org.orekit.time.AbsoluteDate;
  29. import org.orekit.time.FieldAbsoluteDate;
  30. import org.orekit.utils.Constants;
  31. import org.orekit.utils.ParameterDriver;
  32. import org.orekit.utils.TimeSpanMap.Span;
  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 GroundReceiverMeasurement<RangeRate> {

  52.     /** Type of the measurement. */
  53.     public static final String MEASUREMENT_TYPE = "RangeRate";

  55.     /** Simple constructor.
  56.      * @param station ground station from which measurement is performed
  57.      * @param date date of the measurement
  58.      * @param rangeRate observed value, m/s
  59.      * @param sigma theoretical standard deviation
  60.      * @param baseWeight base weight
  61.      * @param twoway if true, this is a two-way measurement
  62.      * @param satellite satellite related to this measurement
  63.      * @since 9.3
  64.      */
  65.     public RangeRate(final GroundStation station, final AbsoluteDate date,
  66.                      final double rangeRate, final double sigma, final double baseWeight,
  67.                      final boolean twoway, final ObservableSatellite satellite) {
  68.         super(station, twoway, date, rangeRate, sigma, baseWeight, satellite);
  69.     }

  71.     /** {@inheritDoc} */
  72.     @Override
  73.     protected EstimatedMeasurementBase<RangeRate> theoreticalEvaluationWithoutDerivatives(final int iteration,
  74.                                                                                           final int evaluation,
  75.                                                                                           final SpacecraftState[] states) {

  77.         final GroundReceiverCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states[0]);
  78.         final TimeStampedPVCoordinates transitPV = common.getTransitPV();

  80.         // one-way (downlink) range-rate
  81.         final EstimatedMeasurementBase<RangeRate> evalOneWay1 =
  82.                         oneWayTheoreticalEvaluation(iteration, evaluation, true,
  83.                                                     common.getStationDownlink(),
  84.                                                     transitPV,
  85.                                                     common.getTransitState());
  86.         final EstimatedMeasurementBase<RangeRate> estimated;
  87.         if (isTwoWay()) {
  88.             // one-way (uplink) light time correction
  89.             final Transform offsetToInertialApproxUplink =
  90.                             getStation().getOffsetToInertial(common.getState().getFrame(),
  91.                                                              common.getStationDownlink().getDate().shiftedBy(-2 * common.getTauD()),
  92.                                                              false);
  93.             final AbsoluteDate approxUplinkDate = offsetToInertialApproxUplink.getDate();

  95.             final TimeStampedPVCoordinates stationApproxUplink =
  96.                             offsetToInertialApproxUplink.transformPVCoordinates(new TimeStampedPVCoordinates(approxUplinkDate,
  97.                                                                                                              Vector3D.ZERO, Vector3D.ZERO, Vector3D.ZERO));

  99.             final double tauU = signalTimeOfFlightAdjustableEmitter(stationApproxUplink, transitPV.getPosition(),
  100.                                                                     transitPV.getDate(), common.getState().getFrame());

  102.             final TimeStampedPVCoordinates stationUplink =
  103.                             stationApproxUplink.shiftedBy(transitPV.getDate().durationFrom(approxUplinkDate) - tauU);

  105.             final EstimatedMeasurementBase<RangeRate> evalOneWay2 =
  106.                             oneWayTheoreticalEvaluation(iteration, evaluation, false,
  107.                                                         stationUplink, transitPV, common.getTransitState());

  109.             // combine uplink and downlink values
  110.             estimated = new EstimatedMeasurementBase<>(this, iteration, evaluation,
  111.                                                        evalOneWay1.getStates(),
  112.                                                        new TimeStampedPVCoordinates[] {
  113.                                                            evalOneWay2.getParticipants()[0],
  114.                                                            evalOneWay1.getParticipants()[0],
  115.                                                            evalOneWay1.getParticipants()[1]
  116.                                                        });
  117.             estimated.setEstimatedValue(0.5 * (evalOneWay1.getEstimatedValue()[0] + evalOneWay2.getEstimatedValue()[0]));

  119.         } else {
  120.             estimated = evalOneWay1;
  121.         }

  123.         return estimated;

  125.     }

  127.     /** {@inheritDoc} */
  128.     @Override
  129.     protected EstimatedMeasurement<RangeRate> theoreticalEvaluation(final int iteration, final int evaluation,
  130.                                                                     final SpacecraftState[] states) {

  132.         final SpacecraftState state = states[0];

  134.         // Range-rate derivatives are computed with respect to spacecraft state in inertial frame
  135.         // and station position in station's offset frame
  136.         // -------
  137.         //
  138.         // Parameters:
  139.         //  - 0..2 - Position of the spacecraft in inertial frame
  140.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  141.         //  - 6..n - station parameters (clock offset, clock drift, station offsets, pole, prime meridian...)
  142.         final GroundReceiverCommonParametersWithDerivatives common = computeCommonParametersWithDerivatives(state);
  143.         final int nbParams = common.getTauD().getFreeParameters();
  144.         final TimeStampedFieldPVCoordinates<Gradient> transitPV = common.getTransitPV();

  146.         // one-way (downlink) range-rate
  147.         final EstimatedMeasurement<RangeRate> evalOneWay1 =
  148.                         oneWayTheoreticalEvaluation(iteration, evaluation, true,
  149.                                                     common.getStationDownlink(), transitPV,
  150.                                                     common.getTransitState(), common.getIndices(), nbParams);
  151.         final EstimatedMeasurement<RangeRate> estimated;
  152.         if (isTwoWay()) {
  153.             // one-way (uplink) light time correction
  154.             final FieldTransform<Gradient> offsetToInertialApproxUplink =
  155.                             getStation().getOffsetToInertial(state.getFrame(),
  156.                                                              common.getStationDownlink().getDate().shiftedBy(common.getTauD().multiply(-2)),
  157.                                                              nbParams, common.getIndices());
  158.             final FieldAbsoluteDate<Gradient> approxUplinkDateDS =
  159.                             offsetToInertialApproxUplink.getFieldDate();

  161.             final FieldVector3D<Gradient> zero = FieldVector3D.getZero(common.getTauD().getField());
  162.             final TimeStampedFieldPVCoordinates<Gradient> stationApproxUplink =
  163.                             offsetToInertialApproxUplink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(approxUplinkDateDS,
  164.                                                                                                                     zero, zero, zero));

  166.             final Gradient tauU = signalTimeOfFlightAdjustableEmitter(stationApproxUplink, transitPV.getPosition(), transitPV.getDate(),
  167.                                                                       state.getFrame());

  169.             final TimeStampedFieldPVCoordinates<Gradient> stationUplink =
  170.                             stationApproxUplink.shiftedBy(transitPV.getDate().durationFrom(approxUplinkDateDS).subtract(tauU));

  172.             final EstimatedMeasurement<RangeRate> evalOneWay2 =
  173.                             oneWayTheoreticalEvaluation(iteration, evaluation, false,
  174.                                                         stationUplink, transitPV, common.getTransitState(),
  175.                                                         common.getIndices(), nbParams);

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

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

  198.             // combine uplink and downlink partial derivatives with respect to parameters
  199.             evalOneWay1.getDerivativesDrivers().forEach(driver -> {
  200.                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  201.                     final double[] pd1 = evalOneWay1.getParameterDerivatives(driver, span.getStart());
  202.                     final double[] pd2 = evalOneWay2.getParameterDerivatives(driver, span.getStart());
  203.                     final double[] pd = new double[pd1.length];
  204.                     for (int i = 0; i < pd.length; ++i) {
  205.                         pd[i] = 0.5 * (pd1[i] + pd2[i]);
  206.                     }
  207.                     estimated.setParameterDerivatives(driver, span.getStart(), pd);
  208.                 }
  209.             });

  211.         } else {
  212.             estimated = evalOneWay1;
  213.         }

  215.         return estimated;

  217.     }

  219.     /** Evaluate measurement in one-way without derivatives.
  220.      * @param iteration iteration number
  221.      * @param evaluation evaluations counter
  222.      * @param downlink indicator for downlink leg
  223.      * @param stationPV station coordinates when signal is at station
  224.      * @param transitPV spacecraft coordinates at onboard signal transit
  225.      * @param transitState orbital state at onboard signal transit
  226.      * @return theoretical value
  227.      * @since 12.0
  228.      */
  229.     private EstimatedMeasurementBase<RangeRate> oneWayTheoreticalEvaluation(final int iteration, final int evaluation, final boolean downlink,
  230.                                                                             final TimeStampedPVCoordinates stationPV,
  231.                                                                             final TimeStampedPVCoordinates transitPV,
  232.                                                                             final SpacecraftState transitState) {

  234.         // prepare the evaluation
  235.         final EstimatedMeasurementBase<RangeRate> estimated =
  236.                         new EstimatedMeasurementBase<>(this, iteration, evaluation,
  237.                                                        new SpacecraftState[] {
  238.                                                            transitState
  239.                                                        }, new TimeStampedPVCoordinates[] {
  240.                                                            downlink ? transitPV : stationPV,
  241.                                                            downlink ? stationPV : transitPV
  242.                                                        });

  244.         // range rate value
  245.         final Vector3D stationPosition  = stationPV.getPosition();
  246.         final Vector3D relativePosition = stationPosition.subtract(transitPV.getPosition());

  248.         final Vector3D stationVelocity  = stationPV.getVelocity();
  249.         final Vector3D relativeVelocity = stationVelocity.subtract(transitPV.getVelocity());

  251.         // radial direction
  252.         final Vector3D lineOfSight      = relativePosition.normalize();

  254.         // line of sight velocity
  255.         final double lineOfSightVelocity = Vector3D.dotProduct(relativeVelocity, lineOfSight);

  257.         // range rate
  258.         double rangeRate = lineOfSightVelocity;

  260.         if (!isTwoWay()) {
  261.             // clock drifts, taken in account only in case of one way
  262.             final ObservableSatellite satellite    = getSatellites().get(0);
  263.             final double              dtsDot       = satellite.getClockDriftDriver().getValue(transitState.getDate());
  264.             final double              dtgDot       = getStation().getClockDriftDriver().getValue(stationPV.getDate());

  266.             final double clockDriftBiais = (dtgDot - dtsDot) * Constants.SPEED_OF_LIGHT;

  268.             rangeRate = rangeRate + clockDriftBiais;
  269.         }

  271.         estimated.setEstimatedValue(rangeRate);

  273.         return estimated;

  275.     }

  277.     /** Evaluate measurement in one-way.
  278.      * @param iteration iteration number
  279.      * @param evaluation evaluations counter
  280.      * @param downlink indicator for downlink leg
  281.      * @param stationPV station coordinates when signal is at station
  282.      * @param transitPV spacecraft coordinates at onboard signal transit
  283.      * @param transitState orbital state at onboard signal transit
  284.      * @param indices indices of the estimated parameters in derivatives computations
  285.      * @param nbParams the number of estimated parameters in derivative computations
  286.      * @return theoretical value
  287.      */
  288.     private EstimatedMeasurement<RangeRate> oneWayTheoreticalEvaluation(final int iteration, final int evaluation, final boolean downlink,
  289.                                                                         final TimeStampedFieldPVCoordinates<Gradient> stationPV,
  290.                                                                         final TimeStampedFieldPVCoordinates<Gradient> transitPV,
  291.                                                                         final SpacecraftState transitState,
  292.                                                                         final Map<String, Integer> indices,
  293.                                                                         final int nbParams) {

  295.         // prepare the evaluation
  296.         final EstimatedMeasurement<RangeRate> estimated =
  297.                         new EstimatedMeasurement<>(this, iteration, evaluation,
  298.                                                    new SpacecraftState[] {
  299.                                                        transitState
  300.                                                    }, new TimeStampedPVCoordinates[] {
  301.                                                        (downlink ? transitPV : stationPV).toTimeStampedPVCoordinates(),
  302.                                                        (downlink ? stationPV : transitPV).toTimeStampedPVCoordinates()
  303.                                                    });

  305.         // range rate value
  306.         final FieldVector3D<Gradient> stationPosition  = stationPV.getPosition();
  307.         final FieldVector3D<Gradient> relativePosition = stationPosition.subtract(transitPV.getPosition());

  309.         final FieldVector3D<Gradient> stationVelocity  = stationPV.getVelocity();
  310.         final FieldVector3D<Gradient> relativeVelocity = stationVelocity.subtract(transitPV.getVelocity());

  312.         // radial direction
  313.         final FieldVector3D<Gradient> lineOfSight      = relativePosition.normalize();

  315.         // line of sight velocity
  316.         final Gradient lineOfSightVelocity = FieldVector3D.dotProduct(relativeVelocity, lineOfSight);

  318.         // range rate
  319.         Gradient rangeRate = lineOfSightVelocity;

  321.         if (!isTwoWay()) {
  322.             // clock drifts, taken in account only in case of one way
  323.             final ObservableSatellite satellite    = getSatellites().get(0);
  324.             final Gradient            dtsDot       = satellite.getClockDriftDriver().getValue(nbParams, indices, transitState.getDate());
  325.             final Gradient            dtgDot       = getStation().getClockDriftDriver().getValue(nbParams, indices, stationPV.getDate().toAbsoluteDate());

  327.             final Gradient clockDriftBiais = dtgDot.subtract(dtsDot).multiply(Constants.SPEED_OF_LIGHT);

  329.             rangeRate = rangeRate.add(clockDriftBiais);
  330.         }

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

  334.         // compute first order derivatives of (rr) with respect to spacecraft state Cartesian coordinates
  335.         final double[] derivatives = rangeRate.getGradient();
  336.         estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));

  338.         // Set first order derivatives with respect to parameters
  339.         for (final ParameterDriver driver : getParametersDrivers()) {
  340.             for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  341.                 final Integer index = indices.get(span.getData());
  342.                 if (index != null) {
  343.                     estimated.setParameterDerivatives(driver, span.getStart(), derivatives[index]);
  344.                 }
  345.             }
  346.         }

  348.         return estimated;

  350.     }

  352. }
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