BistaticRange.java
- /* Copyright 2002-2023 Mark Rutten
- * Licensed to CS GROUP (CS) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * Mark Rutten licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- package org.orekit.estimation.measurements;
- import java.util.Arrays;
- import java.util.HashMap;
- import java.util.Map;
- import org.hipparchus.analysis.differentiation.Gradient;
- import org.hipparchus.analysis.differentiation.GradientField;
- import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
- import org.hipparchus.geometry.euclidean.threed.Vector3D;
- import org.orekit.frames.FieldTransform;
- import org.orekit.frames.Transform;
- import org.orekit.propagation.SpacecraftState;
- import org.orekit.time.AbsoluteDate;
- import org.orekit.time.FieldAbsoluteDate;
- import org.orekit.utils.Constants;
- import org.orekit.utils.ParameterDriver;
- import org.orekit.utils.TimeSpanMap.Span;
- import org.orekit.utils.TimeStampedFieldPVCoordinates;
- import org.orekit.utils.TimeStampedPVCoordinates;
- /**
- * Class modeling a bistatic range measurement using
- * an emitter ground station and a receiver ground station.
- * <p>
- * The measurement is considered to be a signal:
- * <ul>
- * <li>Emitted from the emitter ground station</li>
- * <li>Reflected on the spacecraft</li>
- * <li>Received on the receiver ground station</li>
- * </ul>
- * The date of the measurement corresponds to the reception on ground of the reflected signal.
- * <p>
- * The motion of the stations and the spacecraft during the signal flight time are taken into account.
- * </p>
- *
- * @author Mark Rutten
- * @since 11.2
- */
- public class BistaticRange extends GroundReceiverMeasurement<BistaticRange> {
- /** Type of the measurement. */
- public static final String MEASUREMENT_TYPE = "BistaticRange";
- /**
- * Ground station from which transmission is made.
- */
- private final GroundStation emitter;
- /**
- * Simple constructor.
- *
- * @param emitter ground station from which transmission is performed
- * @param receiver ground station from which measurement is performed
- * @param date date of the measurement
- * @param range observed value
- * @param sigma theoretical standard deviation
- * @param baseWeight base weight
- * @param satellite satellite related to this measurement
- * @since 11.2
- */
- public BistaticRange(final GroundStation emitter, final GroundStation receiver, final AbsoluteDate date,
- final double range, final double sigma, final double baseWeight,
- final ObservableSatellite satellite) {
- super(receiver, true, date, range, sigma, baseWeight, satellite);
- addParameterDriver(emitter.getClockOffsetDriver());
- addParameterDriver(emitter.getEastOffsetDriver());
- addParameterDriver(emitter.getNorthOffsetDriver());
- addParameterDriver(emitter.getZenithOffsetDriver());
- addParameterDriver(emitter.getPrimeMeridianOffsetDriver());
- addParameterDriver(emitter.getPrimeMeridianDriftDriver());
- addParameterDriver(emitter.getPolarOffsetXDriver());
- addParameterDriver(emitter.getPolarDriftXDriver());
- addParameterDriver(emitter.getPolarOffsetYDriver());
- addParameterDriver(emitter.getPolarDriftYDriver());
- this.emitter = emitter;
- }
- /** Get the emitter ground station.
- * @return emitter ground station
- */
- public GroundStation getEmitterStation() {
- return emitter;
- }
- /** Get the receiver ground station.
- * @return receiver ground station
- */
- public GroundStation getReceiverStation() {
- return getStation();
- }
- /**
- * {@inheritDoc}
- */
- @Override
- protected EstimatedMeasurementBase<BistaticRange> theoreticalEvaluationWithoutDerivatives(final int iteration,
- final int evaluation,
- final SpacecraftState[] states) {
- final SpacecraftState state = states[0];
- // Coordinates of the spacecraft
- final TimeStampedPVCoordinates pva = state.getPVCoordinates();
- // transform between station and inertial frame, expressed as a gradient
- // The components of station's position in offset frame are the 3 last derivative parameters
- final Transform offsetToInertialRx = getReceiverStation().getOffsetToInertial(state.getFrame(), getDate(), false);
- final AbsoluteDate downlinkDate = offsetToInertialRx.getDate();
- // Station position in inertial frame at end of the downlink leg
- final TimeStampedPVCoordinates stationReceiver =
- offsetToInertialRx.transformPVCoordinates(new TimeStampedPVCoordinates(downlinkDate,
- Vector3D.ZERO, Vector3D.ZERO, Vector3D.ZERO));
- // Compute propagation times
- // (if state has already been set up to pre-compensate propagation delay,
- // we will have delta == tauD and transitState will be the same as state)
- // Downlink delay
- final double tauD = signalTimeOfFlight(pva, stationReceiver.getPosition(), downlinkDate);
- // Transit state & Transit state (re)computed with gradients
- final double delta = downlinkDate.durationFrom(state.getDate());
- final double deltaMTauD = delta - tauD;
- final SpacecraftState transitState = state.shiftedBy(deltaMTauD);
- final TimeStampedPVCoordinates transitStateDS = pva.shiftedBy(deltaMTauD);
- // transform between secondary station topocentric frame (east-north-zenith) and inertial frame expressed as gradients
- // The components of secondary station's position in offset frame are the 3 last derivative parameters
- final AbsoluteDate transitDate = downlinkDate.shiftedBy(-tauD);
- final Transform offsetToInertialTxApprox = getEmitterStation().getOffsetToInertial(state.getFrame(), transitDate, true);
- // Secondary station PV in inertial frame at transit time
- final TimeStampedPVCoordinates transmitApprox =
- offsetToInertialTxApprox.transformPVCoordinates(new TimeStampedPVCoordinates(transitDate,
- Vector3D.ZERO, Vector3D.ZERO, Vector3D.ZERO));
- // Uplink time of flight from secondary station to transit state of leg2
- final double tauU = signalTimeOfFlight(transmitApprox, transitStateDS.getPosition(), transitStateDS.getDate());
- // Total time of flight
- final double tauTotal = tauU - deltaMTauD;
- // Absolute date of transmission
- final AbsoluteDate transmitDate = downlinkDate.shiftedBy(tauTotal);
- final Transform transmitToInert = emitter.getOffsetToInertial(state.getFrame(), transmitDate, true);
- // Secondary station PV in inertial frame at rebound date on secondary station
- final TimeStampedPVCoordinates stationTransmitter =
- transmitToInert.transformPVCoordinates(new TimeStampedPVCoordinates(transmitDate,
- Vector3D.ZERO, Vector3D.ZERO, Vector3D.ZERO));
- // Prepare the evaluation
- final EstimatedMeasurementBase<BistaticRange> estimated =
- new EstimatedMeasurementBase<>(this,
- iteration, evaluation,
- new SpacecraftState[] {
- transitState
- },
- new TimeStampedPVCoordinates[] {
- stationReceiver,
- transitStateDS,
- stationTransmitter
- });
- // Range value
- final double tau = tauD + tauU;
- final double range = tau * Constants.SPEED_OF_LIGHT;
- estimated.setEstimatedValue(range);
- return estimated;
- }
- /**
- * {@inheritDoc}
- */
- @Override
- protected EstimatedMeasurement<BistaticRange> theoreticalEvaluation(final int iteration,
- final int evaluation,
- final SpacecraftState[] states) {
- final SpacecraftState state = states[0];
- // Range derivatives are computed with respect to spacecraft state in inertial frame
- // and station parameters
- // ----------------------
- //
- // Parameters:
- // - 0..2 - Position of the spacecraft in inertial frame
- // - 3..5 - Velocity of the spacecraft in inertial frame
- // - 6..n - measurements parameters (clock offset, station offsets, pole, prime meridian, sat clock offset...)
- int nbParams = 6;
- final Map<String, Integer> indices = new HashMap<>();
- for (ParameterDriver driver : getParametersDrivers()) {
- if (driver.isSelected()) {
- for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
- if (!indices.containsKey(span.getData())) {
- indices.put(span.getData(), nbParams++);
- }
- }
- }
- }
- final FieldVector3D<Gradient> zero = FieldVector3D.getZero(GradientField.getField(nbParams));
- // Coordinates of the spacecraft expressed as a gradient
- final TimeStampedFieldPVCoordinates<Gradient> pvaDS = getCoordinates(state, 0, nbParams);
- // transform between station and inertial frame, expressed as a gradient
- // The components of station's position in offset frame are the 3 last derivative parameters
- final FieldTransform<Gradient> offsetToInertialRx =
- getReceiverStation().getOffsetToInertial(state.getFrame(), getDate(), nbParams, indices);
- final FieldAbsoluteDate<Gradient> downlinkDateDS = offsetToInertialRx.getFieldDate();
- // Station position in inertial frame at end of the downlink leg
- final TimeStampedFieldPVCoordinates<Gradient> stationReceiver =
- offsetToInertialRx.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
- zero, zero, zero));
- // Compute propagation times
- // (if state has already been set up to pre-compensate propagation delay,
- // we will have delta == tauD and transitState will be the same as state)
- // Downlink delay
- final Gradient tauD = signalTimeOfFlight(pvaDS, stationReceiver.getPosition(), downlinkDateDS);
- // Transit state & Transit state (re)computed with gradients
- final Gradient delta = downlinkDateDS.durationFrom(state.getDate());
- final Gradient deltaMTauD = tauD.negate().add(delta);
- final SpacecraftState transitState = state.shiftedBy(deltaMTauD.getValue());
- final TimeStampedFieldPVCoordinates<Gradient> transitStateDS = pvaDS.shiftedBy(deltaMTauD);
- // transform between secondary station topocentric frame (east-north-zenith) and inertial frame expressed as gradients
- // The components of secondary station's position in offset frame are the 3 last derivative parameters
- final FieldAbsoluteDate<Gradient> transitDate = downlinkDateDS.shiftedBy(tauD.negate());
- final FieldTransform<Gradient> offsetToInertialTxApprox =
- getEmitterStation().getOffsetToInertial(state.getFrame(), transitDate, nbParams, indices);
- // Secondary station PV in inertial frame at transit time
- final TimeStampedFieldPVCoordinates<Gradient> transmitApprox =
- offsetToInertialTxApprox.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(transitDate,
- zero, zero, zero));
- // Uplink time of flight from secondary station to transit state of leg2
- final Gradient tauU = signalTimeOfFlight(transmitApprox, transitStateDS.getPosition(), transitStateDS.getDate());
- // Total time of flight
- final Gradient tauTotal = deltaMTauD.negate().add(tauU);
- // Absolute date of transmission
- final FieldAbsoluteDate<Gradient> transmitDateDS = downlinkDateDS.shiftedBy(tauTotal);
- final FieldTransform<Gradient> transmitToInert =
- emitter.getOffsetToInertial(state.getFrame(), transmitDateDS, nbParams, indices);
- // Secondary station PV in inertial frame at rebound date on secondary station
- final TimeStampedFieldPVCoordinates<Gradient> stationTransmitter =
- transmitToInert.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(transmitDateDS,
- zero, zero, zero));
- // Prepare the evaluation
- final EstimatedMeasurement<BistaticRange> estimated = new EstimatedMeasurement<>(this,
- iteration, evaluation,
- new SpacecraftState[] {
- transitState
- },
- new TimeStampedPVCoordinates[] {
- stationReceiver.toTimeStampedPVCoordinates(),
- transitStateDS.toTimeStampedPVCoordinates(),
- stationTransmitter.toTimeStampedPVCoordinates()
- });
- // Range value
- final Gradient tau = tauD.add(tauU);
- final Gradient range = tau.multiply(Constants.SPEED_OF_LIGHT);
- estimated.setEstimatedValue(range.getValue());
- // Range partial derivatives with respect to state
- final double[] derivatives = range.getGradient();
- estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
- // set partial derivatives with respect to parameters
- // (beware element at index 0 is the value, not a derivative)
- for (final ParameterDriver driver : getParametersDrivers()) {
- for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
- final Integer index = indices.get(span.getData());
- if (index != null) {
- estimated.setParameterDerivatives(driver, span.getStart(), derivatives[index]);
- }
- }
- }
- return estimated;
- }
- }