OneWayGNSSPhase.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.gnss;

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

  23. import org.hipparchus.analysis.differentiation.Gradient;
  24. import org.orekit.estimation.measurements.AbstractMeasurement;
  25. import org.orekit.estimation.measurements.EstimatedMeasurement;
  26. import org.orekit.estimation.measurements.ObservableSatellite;
  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.PVCoordinatesProvider;
  32. import org.orekit.utils.ParameterDriver;
  33. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  34. import org.orekit.utils.TimeStampedPVCoordinates;

  36. /** One-way GNSS phase measurement.
  37.  * <p>
  38.  * This class can be used in precise orbit determination applications
  39.  * for modeling a phase measurement between a GNSS satellite (emitter)
  40.  * and a LEO satellite (receiver).
  41.  * <p>
  42.  * The one-way GNSS phase measurement assumes knowledge of the orbit and
  43.  * the clock offset of the emitting GNSS satellite. For instance, it is
  44.  * possible to use a SP3 file or a GNSS navigation message to recover
  45.  * the satellite's orbit and clock.
  46.  * <p>
  47.  * This class is very similar to {@link InterSatellitesPhase} measurement
  48.  * class. However, using the one-way GNSS phase measurement, the orbit and clock
  49.  * of the emitting GNSS satellite are <b>NOT</b> estimated simultaneously with
  50.  * LEO satellite coordinates.
  51.  *
  52.  * @author Bryan Cazabonne
  53.  * @since 10.3
  54.  */
  55. public class OneWayGNSSPhase extends AbstractMeasurement<OneWayGNSSPhase> {

  57.     /** Name for ambiguity driver. */
  58.     public static final String AMBIGUITY_NAME = "ambiguity";

  60.     /** Driver for ambiguity. */
  61.     private final ParameterDriver ambiguityDriver;

  63.     /** Emitting satellite. */
  64.     private final PVCoordinatesProvider remote;

  66.     /** Clock offset of the emitting satellite. */
  67.     private final double dtRemote;

  69.     /** Wavelength of the phase observed value [m]. */
  70.     private final double wavelength;

  72.     /** Simple constructor.
  73.      * @param remote provider for GNSS satellite which simply emits the signal
  74.      * @param dtRemote clock offset of the GNSS satellite, in seconds
  75.      * @param date date of the measurement
  76.      * @param phase observed value, in cycles
  77.      * @param wavelength phase observed value wavelength, in meters
  78.      * @param sigma theoretical standard deviation
  79.      * @param baseWeight base weight
  80.      * @param local satellite which receives the signal and perform the measurement
  81.      */
  82.     public OneWayGNSSPhase(final PVCoordinatesProvider remote,
  83.                            final double dtRemote,
  84.                            final AbsoluteDate date,
  85.                            final double phase, final double wavelength, final double sigma,
  86.                            final double baseWeight, final ObservableSatellite local) {
  87.         // Call super constructor
  88.         super(date, phase, sigma, baseWeight, Arrays.asList(local));

  90.         // Initialize phase ambiguity driver
  91.         ambiguityDriver = new ParameterDriver(AMBIGUITY_NAME, 0.0, 1.0,
  92.                                               Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  94.         // The local satellite clock offset affects the measurement
  95.         addParameterDriver(ambiguityDriver);
  96.         addParameterDriver(local.getClockOffsetDriver());

  98.         // Initialise fields
  99.         this.dtRemote   = dtRemote;
  100.         this.remote     = remote;
  101.         this.wavelength = wavelength;
  102.     }

  104.     /** Get the wavelength.
  105.      * @return wavelength (m)
  106.      */
  107.     public double getWavelength() {
  108.         return wavelength;
  109.     }

  111.     /** Get the driver for phase ambiguity.
  112.      * @return the driver for phase ambiguity
  113.      */
  114.     public ParameterDriver getAmbiguityDriver() {
  115.         return ambiguityDriver;
  116.     }

  118.     /** {@inheritDoc} */
  119.     @Override
  120.     protected EstimatedMeasurement<OneWayGNSSPhase> theoreticalEvaluation(final int iteration,
  121.                                                                           final int evaluation,
  122.                                                                           final SpacecraftState[] states) {

  124.         // Phase derivatives are computed with respect to spacecrafts states in inertial frame
  125.         // Parameters:
  126.         //  - 0..2  - Position of the receiver satellite in inertial frame
  127.         //  - 3..5  - Velocity of the receiver satellite in inertial frame
  128.         //  - 6..n  - Measurement parameters: ambiguity and clock offset
  129.         int nbEstimatedParamsPhase = 6;
  130.         final Map<String, Integer> parameterIndicesPhase = new HashMap<>();
  131.         for (ParameterDriver phaseMeasurementDriver : getParametersDrivers()) {
  132.             if (phaseMeasurementDriver.isSelected()) {
  133.                 parameterIndicesPhase.put(phaseMeasurementDriver.getName(), nbEstimatedParamsPhase++);
  134.             }
  135.         }

  137.         // Coordinates of both satellites
  138.         final SpacecraftState localState  = states[0];
  139.         final TimeStampedFieldPVCoordinates<Gradient> pvaLocal  = getCoordinates(localState, 0, nbEstimatedParamsPhase);
  140.         final TimeStampedPVCoordinates                pvaRemote = remote.getPVCoordinates(getDate(), localState.getFrame());

  142.         // Downlink delay
  143.         final Gradient dtLocal = getSatellites().get(0).getClockOffsetDriver().getValue(nbEstimatedParamsPhase, parameterIndicesPhase);
  144.         final FieldAbsoluteDate<Gradient> arrivalDate = new FieldAbsoluteDate<>(getDate(), dtLocal.negate());

  146.         final TimeStampedFieldPVCoordinates<Gradient> s1Downlink =
  147.                         pvaLocal.shiftedBy(arrivalDate.durationFrom(pvaLocal.getDate()));
  148.         final Gradient tauD = signalTimeOfFlight(new TimeStampedFieldPVCoordinates<>(pvaRemote.getDate(), dtLocal.getField().getOne(), pvaRemote),
  149.                                                  s1Downlink.getPosition(), arrivalDate);

  151.         // Transit state
  152.         final double   delta      = getDate().durationFrom(pvaRemote.getDate());
  153.         final Gradient deltaMTauD = tauD.negate().add(delta);

  155.         // prepare the evaluation
  156.         final EstimatedMeasurement<OneWayGNSSPhase> estimatedPhase =
  157.                         new EstimatedMeasurement<>(this, iteration, evaluation,
  158.                                                    new SpacecraftState[] {
  159.                                                        localState.shiftedBy(deltaMTauD.getValue())
  160.                                                    }, new TimeStampedPVCoordinates[] {
  161.                                                        pvaRemote.shiftedBy(delta - tauD.getValue()),
  162.                                                        localState.shiftedBy(delta).getPVCoordinates()
  163.                                                    });

  165.         // Phase value
  166.         final double   cOverLambda      = Constants.SPEED_OF_LIGHT / wavelength;
  167.         final Gradient ambiguity        = ambiguityDriver.getValue(nbEstimatedParamsPhase, parameterIndicesPhase);
  168.         final Gradient phase            = tauD.add(dtLocal).subtract(dtRemote).multiply(cOverLambda).add(ambiguity);
  169.         final double[] phaseDerivatives = phase.getGradient();

  171.         // Set value and state derivatives of the estimated measurement
  172.         estimatedPhase.setEstimatedValue(phase.getValue());
  173.         estimatedPhase.setStateDerivatives(0, Arrays.copyOfRange(phaseDerivatives, 0,  6));

  175.         // Set partial derivatives with respect to parameters
  176.         for (final ParameterDriver phaseMeasurementDriver : getParametersDrivers()) {
  177.             final Integer index = parameterIndicesPhase.get(phaseMeasurementDriver.getName());
  178.             if (index != null) {
  179.                 estimatedPhase.setParameterDerivatives(phaseMeasurementDriver, phaseDerivatives[index]);
  180.             }
  181.         }

  183.         // Return the estimated measurement
  184.         return estimatedPhase;

  186.     }

  188. }
Created with JaCoCo 0.8.6.202009150832