TDOAIonosphericDelayModifier.java
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* this work for additional information regarding copyright ownership.
* 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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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.estimation.measurements.modifiers;
import java.util.List;
import org.hipparchus.CalculusFieldElement;
import org.orekit.attitudes.InertialProvider;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.GroundStation;
import org.orekit.estimation.measurements.TDOA;
import org.orekit.frames.TopocentricFrame;
import org.orekit.models.earth.ionosphere.IonosphericModel;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.Constants;
import org.orekit.utils.ParameterDriver;
/** Class modifying theoretical TDOA measurements with ionospheric delay.
* <p>
* The effect of ionospheric correction on the TDOA is a time delay computed
* directly from the difference in ionospheric delays for each downlink.
* </p><p>
* The ionospheric delay depends on the frequency of the signal.
* </p>
* @author Pascal Parraud
* @since 11.2
*/
public class TDOAIonosphericDelayModifier implements EstimationModifier<TDOA> {
/** Ionospheric delay model. */
private final IonosphericModel ionoModel;
/** Frequency [Hz]. */
private final double frequency;
/** Constructor.
*
* @param model ionospheric model appropriate for the current TDOA measurement method
* @param freq frequency of the signal in Hz
*/
public TDOAIonosphericDelayModifier(final IonosphericModel model,
final double freq) {
ionoModel = model;
frequency = freq;
}
/** Compute the measurement error due to ionosphere on a single downlink.
* @param station station
* @param state spacecraft state
* @return the measurement error due to ionosphere (s)
*/
private double timeErrorIonosphericModel(final GroundStation station,
final SpacecraftState state) {
// base frame associated with the station
final TopocentricFrame baseFrame = station.getBaseFrame();
// delay in meters
final double delay = ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters());
// return delay in seconds
return delay / Constants.SPEED_OF_LIGHT;
}
/** Compute the measurement error due to ionosphere on a single downlink.
* @param <T> type of the elements
* @param station station
* @param state spacecraft state
* @param parameters ionospheric model parameters
* @return the measurement error due to ionosphere (s)
*/
private <T extends CalculusFieldElement<T>> T timeErrorIonosphericModel(final GroundStation station,
final FieldSpacecraftState<T> state,
final T[] parameters) {
// Base frame associated with the station
final TopocentricFrame baseFrame = station.getBaseFrame();
// Delay in meters
final T delay = ionoModel.pathDelay(state, baseFrame, frequency, parameters);
// return delay in seconds
return delay.divide(Constants.SPEED_OF_LIGHT);
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return ionoModel.getParametersDrivers();
}
@Override
public void modify(final EstimatedMeasurement<TDOA> estimated) {
final TDOA measurement = estimated.getObservedMeasurement();
final GroundStation primeStation = measurement.getPrimeStation();
final GroundStation secondStation = measurement.getSecondStation();
final SpacecraftState state = estimated.getStates()[0];
TDOAModifierUtil.modify(estimated, ionoModel,
new ModifierGradientConverter(state, 6, new InertialProvider(state.getFrame())),
primeStation, secondStation,
this::timeErrorIonosphericModel,
this::timeErrorIonosphericModel);
}
}