PhaseCentersInterSatellitesBaseModifier.java
/* Copyright 2002-2024 Thales Alenia Space
* Licensed to CS GROUP (CS) under one or more
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* CS licenses this file to You under the Apache License, Version 2.0
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* http://www.apache.org/licenses/LICENSE-2.0
*
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package org.orekit.estimation.measurements.modifiers;
import org.orekit.estimation.measurements.AbstractMeasurement;
import org.orekit.estimation.measurements.EstimatedMeasurementBase;
import org.orekit.estimation.measurements.InterSatellitesRange;
import org.orekit.frames.StaticTransform;
import org.orekit.gnss.antenna.FrequencyPattern;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.TimeStampedPVCoordinates;
/** On-board antenna offset effect on inter-satellites phase measurements.
* @param <T> type of the measurement
* @author Luc Maisonobe
* @since 12.1
*/
public class PhaseCentersInterSatellitesBaseModifier<T extends AbstractMeasurement<T>> {
/** Uplink offset model. */
private final PhaseCentersOffsetComputer uplink;
/** Downlink offset model. */
private final PhaseCentersOffsetComputer downlink;
/** Simple constructor.
* @param pattern1 pattern for satellite 1
* (i.e. the satellite which receives the signal and performs the measurement)
* @param pattern2 pattern for satellite 2
* (i.e. the satellite which simply emits the signal in the one-way
* case, or reflects the signal in the two-way case)
*/
public PhaseCentersInterSatellitesBaseModifier(final FrequencyPattern pattern1,
final FrequencyPattern pattern2) {
this.uplink = new PhaseCentersOffsetComputer(pattern1, pattern2);
this.downlink = new PhaseCentersOffsetComputer(pattern2, pattern1);
}
/** Compute distance modification for one way measurement.
* @param estimated estimated measurement to modify
* @return distance modification to add to raw measurement
*/
public double oneWayDistanceModification(final EstimatedMeasurementBase<T> estimated) {
// The participants are satellite 2 at emission, satellite 1 at reception
final TimeStampedPVCoordinates[] participants = estimated.getParticipants();
final AbsoluteDate emissionDate = participants[0].getDate();
final AbsoluteDate receptionDate = participants[1].getDate();
// transforms from spacecraft to inertial frame at emission/reception dates
final SpacecraftState localState = estimated.getStates()[0];
final SpacecraftState receptionState = localState.shiftedBy(receptionDate.durationFrom(localState.getDate()));
final StaticTransform receptionSpacecraftToInert = receptionState.toStaticTransform().getInverse();
final SpacecraftState remoteState = estimated.getStates()[1];
final SpacecraftState emissionState = remoteState.shiftedBy(emissionDate.durationFrom(remoteState.getDate()));
final StaticTransform emissionSpacecraftToInert = emissionState.toStaticTransform().getInverse();
// compute offset due to phase centers
return downlink.offset(emissionSpacecraftToInert, receptionSpacecraftToInert);
}
/** Compute distance modification for two way measurement.
* @param estimated estimated measurement to modify
* @return distance modification to add to raw measurement
*/
public double twoWayDistanceModification(final EstimatedMeasurementBase<InterSatellitesRange> estimated) {
// the participants are satellite 1 at emission, satellite 2 at transit, satellite 1 at reception
final TimeStampedPVCoordinates[] participants = estimated.getParticipants();
final AbsoluteDate emissionDate = participants[0].getDate();
final AbsoluteDate transitDate = participants[1].getDate();
final AbsoluteDate receptionDate = participants[2].getDate();
// transforms from spacecraft to inertial frame at emission/reception dates
final SpacecraftState refState1 = estimated.getStates()[0];
final SpacecraftState receptionState = refState1.shiftedBy(receptionDate.durationFrom(refState1.getDate()));
final StaticTransform receptionSpacecraftToInert = receptionState.toStaticTransform().getInverse();
final SpacecraftState refState2 = estimated.getStates()[1];
final SpacecraftState transitState = refState2.shiftedBy(transitDate.durationFrom(refState2.getDate()));
final StaticTransform transitSpacecraftToInert = transitState.toStaticTransform().getInverse();
final SpacecraftState emissionState = refState1.shiftedBy(emissionDate.durationFrom(refState1.getDate()));
final StaticTransform emissionSpacecraftToInert = emissionState.toStaticTransform().getInverse();
// compute offsets due to phase centers
final double uplinkOffset = uplink.offset(emissionSpacecraftToInert, transitSpacecraftToInert);
final double downlinkOffset = downlink.offset(transitSpacecraftToInert, receptionSpacecraftToInert);
return 0.5 * (uplinkOffset + downlinkOffset);
}
}