TDOATroposphericDelayModifier.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.hipparchus.Field;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
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.models.earth.troposphere.DiscreteTroposphericModel;
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 tropospheric delay.
* <p>
* The effect of tropospheric correction on the TDOA is a time delay computed
* directly from the difference in tropospheric delays for each downlink.
* </p><p>
* Tropospheric delay is not frequency dependent for signals up to 15 GHz.
* </p>
* @author Pascal Parraud
* @since 11.2
*/
public class TDOATroposphericDelayModifier implements EstimationModifier<TDOA> {
/** Tropospheric delay model. */
private final DiscreteTroposphericModel tropoModel;
/** Constructor.
*
* @param model tropospheric model appropriate for the current TDOA measurement method.
*/
public TDOATroposphericDelayModifier(final DiscreteTroposphericModel model) {
tropoModel = model;
}
/** Compute the measurement error due to Troposphere on a single downlink.
* @param station station
* @param state spacecraft state
* @return the measurement error due to Troposphere (s)
*/
private double timeErrorTroposphericModel(final GroundStation station, final SpacecraftState state) {
final Vector3D position = state.getPVCoordinates().getPosition();
// elevation
final double elevation = station.getBaseFrame().getElevation(position,
state.getFrame(),
state.getDate());
// only consider measurements above the horizon
if (elevation > 0) {
// Delay in meters
final double delay = tropoModel.pathDelay(elevation, station.getBaseFrame().getPoint(),
tropoModel.getParameters(), state.getDate());
// return delay in seconds
return delay / Constants.SPEED_OF_LIGHT;
}
return 0;
}
/** Compute the measurement error due to Troposphere on a single downlink.
* @param <T> type of the element
* @param station station
* @param state spacecraft state
* @param parameters tropospheric model parameters
* @return the measurement error due to Troposphere (s)
*/
private <T extends CalculusFieldElement<T>> T timeErrorTroposphericModel(final GroundStation station,
final FieldSpacecraftState<T> state,
final T[] parameters) {
// Field
final Field<T> field = state.getDate().getField();
final T zero = field.getZero();
// elevation
final FieldVector3D<T> pos = state.getPVCoordinates().getPosition();
final T elevation = station.getBaseFrame().getElevation(pos,
state.getFrame(),
state.getDate());
// only consider measurements above the horizon
if (elevation.getReal() > 0) {
// delay in meters
final T delay = tropoModel.pathDelay(elevation, station.getBaseFrame().getPoint(field),
parameters, state.getDate());
// return delay in seconds
return delay.divide(Constants.SPEED_OF_LIGHT);
}
return zero;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return tropoModel.getParametersDrivers();
}
/** {@inheritDoc} */
@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, tropoModel,
new ModifierGradientConverter(state, 6, new InertialProvider(state.getFrame())),
primeStation, secondStation,
this::timeErrorTroposphericModel,
this::timeErrorTroposphericModel);
}
}