AngularTroposphericDelayModifier.java
/* Copyright 2002-2019 CS Systèmes d'Information
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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.models.earth.troposphere.DiscreteTroposphericModel;
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 tropospheric delay.
* The effect of tropospheric correction on the angular is computed
* through the computation of the tropospheric delay.The spacecraft state
* is shifted by the computed delay time and elevation and azimuth are computed
* again with the new spacecraft state.
*
* In general, for GNSS, VLBI, ... there is hardly any frequency dependence in the delay.
* For SLR techniques however, the frequency dependence is sensitive.
*
* @author Thierry Ceolin
* @since 8.0
*/
public class AngularTroposphericDelayModifier implements EstimationModifier<AngularAzEl> {
/** Tropospheric delay model. */
private final DiscreteTroposphericModel tropoModel;
/** Constructor.
*
* @param model Tropospheric delay model appropriate for the current angular measurement method.
*/
public AngularTroposphericDelayModifier(final DiscreteTroposphericModel model) {
tropoModel = model;
}
/** Get the station height above mean sea level.
*
* @param station ground station (or measuring station)
* @return the measuring station height above sea level, m
*/
private double getStationHeightAMSL(final GroundStation station) {
// FIXME heigth should be computed with respect to geoid WGS84+GUND = EGM2008 for example
final double height = station.getBaseFrame().getPoint().getAltitude();
return height;
}
/** Compute the measurement error due to Troposphere.
* @param station station
* @param state spacecraft state
* @return the measurement error due to Troposphere
*/
private double angularErrorTroposphericModel(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 measures above the horizon
if (elevation > 0.0) {
// altitude AMSL in meters
final double height = getStationHeightAMSL(station);
// delay in meters
final double delay = tropoModel.pathDelay(elevation, height, tropoModel.getParameters(), state.getDate());
// one-way measurement.
return delay;
}
return 0;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return tropoModel.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 = angularErrorTroposphericModel(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 measurement 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 tropospheric delay.
// Azimuth - elevation values
estimated.setEstimatedValue(azimuth, elevation);
}
}