TurnAroundRange.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.Constants;
  33. import org.orekit.utils.FieldPVCoordinates;
  34. import org.orekit.utils.PVCoordinates;
  35. import org.orekit.utils.ParameterDriver;
  36. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  37. import org.orekit.utils.TimeStampedPVCoordinates;

  39. /** Class modeling a turn-around range measurement using a master ground station and a slave ground station.
  40.  * <p>
  41.  * The measurement is considered to be a signal:
  42.  * - Emitted from the master ground station
  43.  * - Reflected on the spacecraft
  44.  * - Reflected on the slave ground station
  45.  * - Reflected on the spacecraft again
  46.  * - Received on the master ground station
  47.  * Its value is the elapsed time between emission and reception
  48.  * divided by 2c were c is the speed of light.
  49.  * The motion of the stations and the spacecraft
  50.  * during the signal flight time are taken into account.
  51.  * The date of the measurement corresponds to the
  52.  * reception on ground of the reflected signal.
  53.  * </p>
  54.  * @author Thierry Ceolin
  55.  * @author Luc Maisonobe
  56.  * @author Maxime Journot
  57.  *
  58.  * @since 9.0
  59.  */
  60. public class TurnAroundRange extends AbstractMeasurement<TurnAroundRange> {

  62.     /** Master ground station from which measurement is performed. */
  63.     private final GroundStation masterStation;

  65.     /** Slave ground station reflecting the signal. */
  66.     private final GroundStation slaveStation;

  68.     /** Simple constructor.
  69.      * <p>
  70.      * This constructor uses 0 as the index of the propagator related
  71.      * to this measurement, thus being well suited for mono-satellite
  72.      * orbit determination.
  73.      * </p>
  74.      * @param masterStation ground station from which measurement is performed
  75.      * @param slaveStation ground station reflecting the signal
  76.      * @param date date of the measurement
  77.      * @param turnAroundRange observed value
  78.      * @param sigma theoretical standard deviation
  79.      * @param baseWeight base weight
  80.      * @exception OrekitException if a {@link org.orekit.utils.ParameterDriver}
  81.      * name conflict occurs
  82.      */
  83.     public TurnAroundRange(final GroundStation masterStation, final GroundStation slaveStation,
  84.                            final AbsoluteDate date, final double turnAroundRange,
  85.                            final double sigma, final double baseWeight)
  86.         throws OrekitException {
  87.         this(masterStation, slaveStation, date, turnAroundRange, sigma, baseWeight, 0);
  88.     }

  90.     /** Simple constructor.
  91.      * @param masterStation ground station from which measurement is performed
  92.      * @param slaveStation ground station reflecting the signal
  93.      * @param date date of the measurement
  94.      * @param turnAroundRange observed value
  95.      * @param sigma theoretical standard deviation
  96.      * @param baseWeight base weight
  97.      * @param propagatorIndex index of the propagator related to this measurement
  98.      * @exception OrekitException if a {@link org.orekit.utils.ParameterDriver}
  99.      * name conflict occurs
  100.      * @since 9.0
  101.      */
  102.     public TurnAroundRange(final GroundStation masterStation, final GroundStation slaveStation,
  103.                            final AbsoluteDate date, final double turnAroundRange,
  104.                            final double sigma, final double baseWeight,
  105.                            final int propagatorIndex)
  106.         throws OrekitException {
  107.         super(date, turnAroundRange, sigma, baseWeight, Arrays.asList(propagatorIndex),
  108.               masterStation.getEastOffsetDriver(),
  109.               masterStation.getNorthOffsetDriver(),
  110.               masterStation.getZenithOffsetDriver(),
  111.               masterStation.getPrimeMeridianOffsetDriver(),
  112.               masterStation.getPrimeMeridianDriftDriver(),
  113.               masterStation.getPolarOffsetXDriver(),
  114.               masterStation.getPolarDriftXDriver(),
  115.               masterStation.getPolarOffsetYDriver(),
  116.               masterStation.getPolarDriftYDriver(),
  117.               slaveStation.getEastOffsetDriver(),
  118.               slaveStation.getNorthOffsetDriver(),
  119.               slaveStation.getZenithOffsetDriver(),
  120.               slaveStation.getPrimeMeridianOffsetDriver(),
  121.               slaveStation.getPrimeMeridianDriftDriver(),
  122.               slaveStation.getPolarOffsetXDriver(),
  123.               slaveStation.getPolarDriftXDriver(),
  124.               slaveStation.getPolarOffsetYDriver(),
  125.               slaveStation.getPolarDriftYDriver());
  126.         this.masterStation = masterStation;
  127.         this.slaveStation = slaveStation;
  128.     }

  130.     /** Get the master ground station from which measurement is performed.
  131.      * @return master ground station from which measurement is performed
  132.      */
  133.     public GroundStation getMasterStation() {
  134.         return masterStation;
  135.     }

  137.     /** Get the slave ground station reflecting the signal.
  138.      * @return slave ground station reflecting the signal
  139.      */
  140.     public GroundStation getSlaveStation() {
  141.         return slaveStation;
  142.     }

  144.     /** {@inheritDoc} */
  145.     @Override
  146.     protected EstimatedMeasurement<TurnAroundRange> theoreticalEvaluation(final int iteration, final int evaluation,
  147.                                                                           final SpacecraftState[] states)
  148.         throws OrekitException {

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

  152.         // Turn around range derivatives are computed with respect to:
  153.         // - Spacecraft state in inertial frame
  154.         // - Master station parameters
  155.         // - Slave station parameters
  156.         // --------------------------
  157.         //
  158.         //  - 0..2 - Position of the spacecraft in inertial frame
  159.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  160.         //  - 6..n - stations' parameters (stations' offsets, pole, prime meridian...)
  161.         int nbParams = 6;
  162.         final Map<String, Integer> indices = new HashMap<>();
  163.         for (ParameterDriver driver : getParametersDrivers()) {
  164.             // we have to check for duplicate keys because master and slave station share
  165.             // pole and prime meridian parameters names that must be considered
  166.             // as one set only (they are combined together by the estimation engine)
  167.             if (driver.isSelected() && !indices.containsKey(driver.getName())) {
  168.                 indices.put(driver.getName(), nbParams++);
  169.             }
  170.         }
  171.         final DSFactory                          factory = new DSFactory(nbParams, 1);
  172.         final Field<DerivativeStructure>         field   = factory.getDerivativeField();
  173.         final FieldVector3D<DerivativeStructure> zero    = FieldVector3D.getZero(field);

  175.         // Place the derivative structures in a time-stamped PV
  176.         final TimeStampedFieldPVCoordinates<DerivativeStructure> pvaDS = getCoordinates(state, 0, factory);

  178.         // The path of the signal is divided in two legs.
  179.         // Leg1: Emission from master station to satellite in masterTauU seconds
  180.         //     + Reflection from satellite to slave station in slaveTauD seconds
  181.         // Leg2: Reflection from slave station to satellite in slaveTauU seconds
  182.         //     + Reflection from satellite to master station in masterTaudD seconds
  183.         // The measurement is considered to be time stamped at reception on ground
  184.         // by the master station. All times are therefore computed as backward offsets
  185.         // with respect to this reception time.
  186.         //
  187.         // Two intermediate spacecraft states are defined:
  188.         //  - transitStateLeg2: State of the satellite when it bounced back the signal
  189.         //                      from slave station to master station during the 2nd leg
  190.         //  - transitStateLeg1: State of the satellite when it bounced back the signal
  191.         //                      from master station to slave station during the 1st leg

  193.         // Compute propagation time for the 2nd leg of the signal path
  194.         // --

  196.         // Time difference between t (date of the measurement) and t' (date tagged in spacecraft state)
  197.         // (if state has already been set up to pre-compensate propagation delay,
  198.         // we will have delta = masterTauD + slaveTauU)
  199.         final AbsoluteDate measurementDate = getDate();
  200.         final FieldAbsoluteDate<DerivativeStructure> measurementDateDS = new FieldAbsoluteDate<>(field, measurementDate);
  201.         final double delta = measurementDate.durationFrom(state.getDate());

  203.         // transform between master station topocentric frame (east-north-zenith) and inertial frame expressed as DerivativeStructures
  204.         final FieldTransform<DerivativeStructure> masterToInert =
  205.                         masterStation.getOffsetToInertial(state.getFrame(), measurementDateDS, factory, indices);

  207.         // Master station PV in inertial frame at measurement date
  208.         final TimeStampedFieldPVCoordinates<DerivativeStructure> masterArrival =
  209.                         masterToInert.transformPVCoordinates(new TimeStampedPVCoordinates(measurementDate,
  210.                                                                                           PVCoordinates.ZERO));

  212.         // Compute propagation times
  213.         final DerivativeStructure masterTauD = signalTimeOfFlight(pvaDS, masterArrival.getPosition(), measurementDateDS);

  215.         // Elapsed time between state date t' and signal arrival to the transit state of the 2nd leg
  216.         final DerivativeStructure dtLeg2 = masterTauD.negate().add(delta);

  218.         // Transit state where the satellite reflected the signal from slave to master station
  219.         final SpacecraftState transitStateLeg2 = state.shiftedBy(dtLeg2.getValue());

  221.         // Transit state pv of leg2 (re)computed with derivative structures
  222.         final TimeStampedFieldPVCoordinates<DerivativeStructure> transitStateLeg2PV = pvaDS.shiftedBy(dtLeg2);

  224.         // transform between slave station topocentric frame (east-north-zenith) and inertial frame expressed as DerivativeStructures
  225.         // The components of slave station's position in offset frame are the 3 last derivative parameters
  226.         final FieldAbsoluteDate<DerivativeStructure> approxReboundDate = measurementDateDS.shiftedBy(-delta);
  227.         final FieldTransform<DerivativeStructure> slaveToInertApprox =
  228.                         slaveStation.getOffsetToInertial(state.getFrame(), approxReboundDate, factory, indices);

  230.         // Slave station PV in inertial frame at approximate rebound date on slave station
  231.         final TimeStampedFieldPVCoordinates<DerivativeStructure> QSlaveApprox =
  232.                         slaveToInertApprox.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(approxReboundDate,
  233.                                                                                                       zero, zero, zero));

  235.         // Uplink time of flight from slave station to transit state of leg2
  236.         final DerivativeStructure slaveTauU = signalTimeOfFlight(QSlaveApprox,
  237.                                                                  transitStateLeg2PV.getPosition(),
  238.                                                                  transitStateLeg2PV.getDate());

  240.         // Total time of flight for leg 2
  241.         final DerivativeStructure tauLeg2 = masterTauD.add(slaveTauU);

  243.         // Compute propagation time for the 1st leg of the signal path
  244.         // --

  246.         // Absolute date of rebound of the signal to slave station
  247.         final FieldAbsoluteDate<DerivativeStructure> reboundDateDS = measurementDateDS.shiftedBy(tauLeg2.negate());
  248.         final FieldTransform<DerivativeStructure> slaveToInert =
  249.                         slaveStation.getOffsetToInertial(state.getFrame(), reboundDateDS, factory, indices);

  251.         // Slave station PV in inertial frame at rebound date on slave station
  252.         final TimeStampedFieldPVCoordinates<DerivativeStructure> slaveRebound =
  253.                         slaveToInert.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(reboundDateDS,
  254.                                                                                                 FieldPVCoordinates.getZero(field)));

  256.         // Downlink time of flight from transitStateLeg1 to slave station at rebound date
  257.         final DerivativeStructure slaveTauD = signalTimeOfFlight(transitStateLeg2PV,
  258.                                                                  slaveRebound.getPosition(),
  259.                                                                  reboundDateDS);


  262.         // Elapsed time between state date t' and signal arrival to the transit state of the 1st leg
  263.         final DerivativeStructure dtLeg1 = dtLeg2.subtract(slaveTauU).subtract(slaveTauD);

  265.         // Transit state pv of leg2 (re)computed with derivative structures
  266.         final TimeStampedFieldPVCoordinates<DerivativeStructure> transitStateLeg1PV = pvaDS.shiftedBy(dtLeg1);

  268.         // transform between master station topocentric frame (east-north-zenith) and inertial frame expressed as DerivativeStructures
  269.         // The components of master station's position in offset frame are the 3 third derivative parameters
  270.         final FieldAbsoluteDate<DerivativeStructure> approxEmissionDate =
  271.                         measurementDateDS.shiftedBy(-2 * (slaveTauU.getValue() + masterTauD.getValue()));
  272.         final FieldTransform<DerivativeStructure> masterToInertApprox =
  273.                         masterStation.getOffsetToInertial(state.getFrame(), approxEmissionDate, factory, indices);

  275.         // Master station PV in inertial frame at approximate emission date
  276.         final TimeStampedFieldPVCoordinates<DerivativeStructure> QMasterApprox =
  277.                         masterToInertApprox.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(approxEmissionDate,
  278.                                                                                                        zero, zero, zero));

  280.         // Uplink time of flight from master station to transit state of leg1
  281.         final DerivativeStructure masterTauU = signalTimeOfFlight(QMasterApprox,
  282.                                                                   transitStateLeg1PV.getPosition(),
  283.                                                                   transitStateLeg1PV.getDate());

  285.         // Master station PV in inertial frame at exact emission date
  286.         final AbsoluteDate emissionDate = transitStateLeg1PV.getDate().toAbsoluteDate().shiftedBy(-masterTauU.getValue());
  287.         final TimeStampedPVCoordinates masterDeparture =
  288.                         masterToInertApprox.shiftedBy(emissionDate.durationFrom(masterToInertApprox.getDate())).
  289.                         transformPVCoordinates(new TimeStampedPVCoordinates(emissionDate, PVCoordinates.ZERO)).
  290.                         toTimeStampedPVCoordinates();

  292.         // Total time of flight for leg 1
  293.         final DerivativeStructure tauLeg1 = slaveTauD.add(masterTauU);


  296.         // --
  297.         // Evaluate the turn-around range value and its derivatives
  298.         // --------------------------------------------------------

  300.         // The state we use to define the estimated measurement is a middle ground between the two transit states
  301.         // This is done to avoid calling "SpacecraftState.shiftedBy" function on long duration
  302.         // Thus we define the state at the date t" = date of rebound of the signal at the slave station
  303.         // Or t" = t -masterTauD -slaveTauU
  304.         // The iterative process in the estimation ensures that, after several iterations, the date stamped in the
  305.         // state S in input of this function will be close to t"
  306.         // Therefore we will shift state S by:
  307.         //  - +slaveTauU to get transitStateLeg2
  308.         //  - -slaveTauD to get transitStateLeg1
  309.         final EstimatedMeasurement<TurnAroundRange> estimated =
  310.                         new EstimatedMeasurement<>(this, iteration, evaluation,
  311.                                                    new SpacecraftState[] {
  312.                                                        transitStateLeg2.shiftedBy(-slaveTauU.getValue())
  313.                                                    },
  314.                                                    new TimeStampedPVCoordinates[] {
  315.                                                        masterDeparture,
  316.                                                        transitStateLeg1PV.toTimeStampedPVCoordinates(),
  317.                                                        slaveRebound.toTimeStampedPVCoordinates(),
  318.                                                        transitStateLeg2.getPVCoordinates(),
  319.                                                        masterArrival.toTimeStampedPVCoordinates()
  320.                                                    });

  322.         // Turn-around range value = Total time of flight for the 2 legs divided by 2 and multiplied by c
  323.         final double cOver2 = 0.5 * Constants.SPEED_OF_LIGHT;
  324.         final DerivativeStructure turnAroundRange = (tauLeg2.add(tauLeg1)).multiply(cOver2);
  325.         estimated.setEstimatedValue(turnAroundRange.getValue());

  327.         // Turn-around range partial derivatives with respect to state
  328.         final double[] derivatives = turnAroundRange.getAllDerivatives();
  329.         estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 1, 7));

  331.         // set partial derivatives with respect to parameters
  332.         // (beware element at index 0 is the value, not a derivative)
  333.         for (final ParameterDriver driver : getParametersDrivers()) {
  334.             final Integer index = indices.get(driver.getName());
  335.             if (index != null) {
  336.                 estimated.setParameterDerivatives(driver, derivatives[index + 1]);
  337.             }
  338.         }

  340.         return estimated;

  342.     }

  344. }
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