AngularIonosphericDelayModifier.java
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package org.orekit.estimation.measurements.modifiers;
import java.util.List;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.MathUtils;
import org.orekit.estimation.measurements.AngularAzEl;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.GroundStation;
import org.orekit.frames.Frame;
import org.orekit.frames.TopocentricFrame;
import org.orekit.models.earth.ionosphere.IonosphericModel;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.Constants;
import org.orekit.utils.ParameterDriver;
/** Class modifying theoretical angular measurement with ionospheric delay.
* The effect of ionospheric correction on the angular measurement is computed
* through the computation of the ionospheric delay. The spacecraft state
* is shifted by the computed delay time and elevation and azimuth are computed
* again with the new spacecraft state.
*
* The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
* For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
* <p>
* Since 10.0, state derivatives and ionospheric parameters derivates are computed
* using automatic differentiation.
* </p>
* @author Thierry Ceolin
* @since 8.0
*/
public class AngularIonosphericDelayModifier implements EstimationModifier<AngularAzEl> {
/** Ionospheric delay model. */
private final IonosphericModel ionoModel;
/** Frequency [Hz]. */
private final double frequency;
/** Constructor.
*
* @param model Ionospheric delay model appropriate for the current angular measurement method.
* @param freq frequency of the signal in Hz
*/
public AngularIonosphericDelayModifier(final IonosphericModel model,
final double freq) {
ionoModel = model;
frequency = freq;
}
/** Compute the measurement error due to ionosphere.
* @param station station
* @param state spacecraft state
* @return the measurement error due to ionosphere
*/
private double angularErrorIonosphericModel(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;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return ionoModel.getParametersDrivers();
}
@Override
public void modify(final EstimatedMeasurement<AngularAzEl> estimated) {
final AngularAzEl measure = estimated.getObservedMeasurement();
final GroundStation station = measure.getStation();
final SpacecraftState state = estimated.getStates()[0];
final double delay = angularErrorIonosphericModel(station, state);
// Delay is taken into account to shift the spacecraft position
final double dt = delay / Constants.SPEED_OF_LIGHT;
// Position of the spacecraft shifted of dt
final SpacecraftState transitState = state.shiftedBy(-dt);
// Update estimated value taking into account the ionospheric delay.
final AbsoluteDate date = transitState.getDate();
final Vector3D position = transitState.getPVCoordinates().getPosition();
final Frame inertial = transitState.getFrame();
// Elevation and azimuth in radians
final double elevation = station.getBaseFrame().getElevation(position, inertial, date);
final double baseAzimuth = station.getBaseFrame().getAzimuth(position, inertial, date);
final double twoPiWrap = MathUtils.normalizeAngle(baseAzimuth, measure.getObservedValue()[0]) - baseAzimuth;
final double azimuth = baseAzimuth + twoPiWrap;
// Update estimated value taking into account the ionospheric delay.
// Azimuth - elevation values
estimated.setEstimatedValue(azimuth, elevation);
}
}