RangeRate.java
/* Copyright 2002-2024 CS GROUP
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* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.estimation.measurements;
import java.util.Arrays;
import java.util.Map;
import org.hipparchus.analysis.differentiation.Gradient;
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 one-way or two-way range rate measurement between two vehicles.
* One-way range rate (or Doppler) measurements generally apply to specific satellites
* (e.g. GNSS, DORIS), where a signal is transmitted from a satellite to a
* measuring station.
* Two-way range rate measurements are applicable to any system. The signal is
* transmitted to the (non-spinning) satellite and returned by a transponder
* (or reflected back)to the same measuring station.
* The Doppler measurement can be obtained by multiplying the velocity by (fe/c), where
* fe is the emission frequency.
*
* @author Thierry Ceolin
* @author Joris Olympio
* @since 8.0
*/
public class RangeRate extends GroundReceiverMeasurement<RangeRate> {
/** Type of the measurement. */
public static final String MEASUREMENT_TYPE = "RangeRate";
/** Simple constructor.
* @param station ground station from which measurement is performed
* @param date date of the measurement
* @param rangeRate observed value, m/s
* @param sigma theoretical standard deviation
* @param baseWeight base weight
* @param twoway if true, this is a two-way measurement
* @param satellite satellite related to this measurement
* @since 9.3
*/
public RangeRate(final GroundStation station, final AbsoluteDate date,
final double rangeRate, final double sigma, final double baseWeight,
final boolean twoway, final ObservableSatellite satellite) {
super(station, twoway, date, rangeRate, sigma, baseWeight, satellite);
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<RangeRate> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final GroundReceiverCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states[0]);
final TimeStampedPVCoordinates transitPV = common.getTransitPV();
// one-way (downlink) range-rate
final EstimatedMeasurementBase<RangeRate> evalOneWay1 =
oneWayTheoreticalEvaluation(iteration, evaluation, true,
common.getStationDownlink(),
transitPV,
common.getTransitState());
final EstimatedMeasurementBase<RangeRate> estimated;
if (isTwoWay()) {
// one-way (uplink) light time correction
final Transform offsetToInertialApproxUplink =
getStation().getOffsetToInertial(common.getState().getFrame(),
common.getStationDownlink().getDate().shiftedBy(-2 * common.getTauD()),
false);
final AbsoluteDate approxUplinkDate = offsetToInertialApproxUplink.getDate();
final TimeStampedPVCoordinates stationApproxUplink =
offsetToInertialApproxUplink.transformPVCoordinates(new TimeStampedPVCoordinates(approxUplinkDate,
Vector3D.ZERO, Vector3D.ZERO, Vector3D.ZERO));
final double tauU = signalTimeOfFlight(stationApproxUplink, transitPV.getPosition(),
transitPV.getDate(), common.getState().getFrame());
final TimeStampedPVCoordinates stationUplink =
stationApproxUplink.shiftedBy(transitPV.getDate().durationFrom(approxUplinkDate) - tauU);
final EstimatedMeasurementBase<RangeRate> evalOneWay2 =
oneWayTheoreticalEvaluation(iteration, evaluation, false,
stationUplink, transitPV, common.getTransitState());
// combine uplink and downlink values
estimated = new EstimatedMeasurementBase<>(this, iteration, evaluation,
evalOneWay1.getStates(),
new TimeStampedPVCoordinates[] {
evalOneWay2.getParticipants()[0],
evalOneWay1.getParticipants()[0],
evalOneWay1.getParticipants()[1]
});
estimated.setEstimatedValue(0.5 * (evalOneWay1.getEstimatedValue()[0] + evalOneWay2.getEstimatedValue()[0]));
} else {
estimated = evalOneWay1;
}
return estimated;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<RangeRate> theoreticalEvaluation(final int iteration, final int evaluation,
final SpacecraftState[] states) {
final SpacecraftState state = states[0];
// Range-rate derivatives are computed with respect to spacecraft state in inertial frame
// and station position in station's offset frame
// -------
//
// Parameters:
// - 0..2 - Position of the spacecraft in inertial frame
// - 3..5 - Velocity of the spacecraft in inertial frame
// - 6..n - station parameters (clock offset, clock drift, station offsets, pole, prime meridian...)
final GroundReceiverCommonParametersWithDerivatives common = computeCommonParametersWithDerivatives(state);
final int nbParams = common.getTauD().getFreeParameters();
final TimeStampedFieldPVCoordinates<Gradient> transitPV = common.getTransitPV();
// one-way (downlink) range-rate
final EstimatedMeasurement<RangeRate> evalOneWay1 =
oneWayTheoreticalEvaluation(iteration, evaluation, true,
common.getStationDownlink(), transitPV,
common.getTransitState(), common.getIndices(), nbParams);
final EstimatedMeasurement<RangeRate> estimated;
if (isTwoWay()) {
// one-way (uplink) light time correction
final FieldTransform<Gradient> offsetToInertialApproxUplink =
getStation().getOffsetToInertial(state.getFrame(),
common.getStationDownlink().getDate().shiftedBy(common.getTauD().multiply(-2)),
nbParams, common.getIndices());
final FieldAbsoluteDate<Gradient> approxUplinkDateDS =
offsetToInertialApproxUplink.getFieldDate();
final FieldVector3D<Gradient> zero = FieldVector3D.getZero(common.getTauD().getField());
final TimeStampedFieldPVCoordinates<Gradient> stationApproxUplink =
offsetToInertialApproxUplink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(approxUplinkDateDS,
zero, zero, zero));
final Gradient tauU = signalTimeOfFlight(stationApproxUplink, transitPV.getPosition(), transitPV.getDate(),
state.getFrame());
final TimeStampedFieldPVCoordinates<Gradient> stationUplink =
stationApproxUplink.shiftedBy(transitPV.getDate().durationFrom(approxUplinkDateDS).subtract(tauU));
final EstimatedMeasurement<RangeRate> evalOneWay2 =
oneWayTheoreticalEvaluation(iteration, evaluation, false,
stationUplink, transitPV, common.getTransitState(),
common.getIndices(), nbParams);
// combine uplink and downlink values
estimated = new EstimatedMeasurement<>(this, iteration, evaluation,
evalOneWay1.getStates(),
new TimeStampedPVCoordinates[] {
evalOneWay2.getParticipants()[0],
evalOneWay1.getParticipants()[0],
evalOneWay1.getParticipants()[1]
});
estimated.setEstimatedValue(0.5 * (evalOneWay1.getEstimatedValue()[0] + evalOneWay2.getEstimatedValue()[0]));
// combine uplink and downlink partial derivatives with respect to state
final double[][] sd1 = evalOneWay1.getStateDerivatives(0);
final double[][] sd2 = evalOneWay2.getStateDerivatives(0);
final double[][] sd = new double[sd1.length][sd1[0].length];
for (int i = 0; i < sd.length; ++i) {
for (int j = 0; j < sd[0].length; ++j) {
sd[i][j] = 0.5 * (sd1[i][j] + sd2[i][j]);
}
}
estimated.setStateDerivatives(0, sd);
// combine uplink and downlink partial derivatives with respect to parameters
evalOneWay1.getDerivativesDrivers().forEach(driver -> {
for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
final double[] pd1 = evalOneWay1.getParameterDerivatives(driver, span.getStart());
final double[] pd2 = evalOneWay2.getParameterDerivatives(driver, span.getStart());
final double[] pd = new double[pd1.length];
for (int i = 0; i < pd.length; ++i) {
pd[i] = 0.5 * (pd1[i] + pd2[i]);
}
estimated.setParameterDerivatives(driver, span.getStart(), pd);
}
});
} else {
estimated = evalOneWay1;
}
return estimated;
}
/** Evaluate measurement in one-way without derivatives.
* @param iteration iteration number
* @param evaluation evaluations counter
* @param downlink indicator for downlink leg
* @param stationPV station coordinates when signal is at station
* @param transitPV spacecraft coordinates at onboard signal transit
* @param transitState orbital state at onboard signal transit
* @return theoretical value
* @since 12.0
*/
private EstimatedMeasurementBase<RangeRate> oneWayTheoreticalEvaluation(final int iteration, final int evaluation, final boolean downlink,
final TimeStampedPVCoordinates stationPV,
final TimeStampedPVCoordinates transitPV,
final SpacecraftState transitState) {
// prepare the evaluation
final EstimatedMeasurementBase<RangeRate> estimated =
new EstimatedMeasurementBase<>(this, iteration, evaluation,
new SpacecraftState[] {
transitState
}, new TimeStampedPVCoordinates[] {
downlink ? transitPV : stationPV,
downlink ? stationPV : transitPV
});
// range rate value
final Vector3D stationPosition = stationPV.getPosition();
final Vector3D relativePosition = stationPosition.subtract(transitPV.getPosition());
final Vector3D stationVelocity = stationPV.getVelocity();
final Vector3D relativeVelocity = stationVelocity.subtract(transitPV.getVelocity());
// radial direction
final Vector3D lineOfSight = relativePosition.normalize();
// line of sight velocity
final double lineOfSightVelocity = Vector3D.dotProduct(relativeVelocity, lineOfSight);
// range rate
double rangeRate = lineOfSightVelocity;
if (!isTwoWay()) {
// clock drifts, taken in account only in case of one way
final ObservableSatellite satellite = getSatellites().get(0);
final double dtsDot = satellite.getClockDriftDriver().getValue(transitState.getDate());
final double dtgDot = getStation().getClockDriftDriver().getValue(stationPV.getDate());
final double clockDriftBiais = (dtgDot - dtsDot) * Constants.SPEED_OF_LIGHT;
rangeRate = rangeRate + clockDriftBiais;
}
estimated.setEstimatedValue(rangeRate);
return estimated;
}
/** Evaluate measurement in one-way.
* @param iteration iteration number
* @param evaluation evaluations counter
* @param downlink indicator for downlink leg
* @param stationPV station coordinates when signal is at station
* @param transitPV spacecraft coordinates at onboard signal transit
* @param transitState orbital state at onboard signal transit
* @param indices indices of the estimated parameters in derivatives computations
* @param nbParams the number of estimated parameters in derivative computations
* @return theoretical value
*/
private EstimatedMeasurement<RangeRate> oneWayTheoreticalEvaluation(final int iteration, final int evaluation, final boolean downlink,
final TimeStampedFieldPVCoordinates<Gradient> stationPV,
final TimeStampedFieldPVCoordinates<Gradient> transitPV,
final SpacecraftState transitState,
final Map<String, Integer> indices,
final int nbParams) {
// prepare the evaluation
final EstimatedMeasurement<RangeRate> estimated =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] {
transitState
}, new TimeStampedPVCoordinates[] {
(downlink ? transitPV : stationPV).toTimeStampedPVCoordinates(),
(downlink ? stationPV : transitPV).toTimeStampedPVCoordinates()
});
// range rate value
final FieldVector3D<Gradient> stationPosition = stationPV.getPosition();
final FieldVector3D<Gradient> relativePosition = stationPosition.subtract(transitPV.getPosition());
final FieldVector3D<Gradient> stationVelocity = stationPV.getVelocity();
final FieldVector3D<Gradient> relativeVelocity = stationVelocity.subtract(transitPV.getVelocity());
// radial direction
final FieldVector3D<Gradient> lineOfSight = relativePosition.normalize();
// line of sight velocity
final Gradient lineOfSightVelocity = FieldVector3D.dotProduct(relativeVelocity, lineOfSight);
// range rate
Gradient rangeRate = lineOfSightVelocity;
if (!isTwoWay()) {
// clock drifts, taken in account only in case of one way
final ObservableSatellite satellite = getSatellites().get(0);
final Gradient dtsDot = satellite.getClockDriftDriver().getValue(nbParams, indices, transitState.getDate());
final Gradient dtgDot = getStation().getClockDriftDriver().getValue(nbParams, indices, stationPV.getDate().toAbsoluteDate());
final Gradient clockDriftBiais = dtgDot.subtract(dtsDot).multiply(Constants.SPEED_OF_LIGHT);
rangeRate = rangeRate.add(clockDriftBiais);
}
estimated.setEstimatedValue(rangeRate.getValue());
// compute first order derivatives of (rr) with respect to spacecraft state Cartesian coordinates
final double[] derivatives = rangeRate.getGradient();
estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
// Set first order derivatives with respect to parameters
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;
}
}