RangeRateIonosphericDelayModifier.java
/* Copyright 2002-2018 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.estimation.measurements.modifiers;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitExceptionWrapper;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.GroundStation;
import org.orekit.estimation.measurements.RangeRate;
import org.orekit.models.earth.IonosphericModel;
import org.orekit.orbits.OrbitType;
import org.orekit.orbits.PositionAngle;
import org.orekit.propagation.Propagator;
import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.Differentiation;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterFunction;
import org.orekit.utils.StateFunction;
/** Class modifying theoretical range-rate measurement with ionospheric delay.
* The effect of ionospheric correction on the range-rate is directly computed
* through the computation of the ionospheric delay difference with respect to
* time.
*
* 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.
*
* @author Joris Olympio
* @since 8.0
*/
public class RangeRateIonosphericDelayModifier implements EstimationModifier<RangeRate> {
/** Ionospheric delay model. */
private final IonosphericModel ionoModel;
/** Coefficient for measurment configuration (one-way, two-way). */
private final double fTwoWay;
/** Constructor.
*
* @param model Ionospheric delay model appropriate for the current range-rate measurement method.
* @param twoWay Flag indicating whether the measurement is two-way.
*/
public RangeRateIonosphericDelayModifier(final IonosphericModel model, final boolean twoWay) {
ionoModel = model;
if (twoWay) {
fTwoWay = 2.;
} else {
fTwoWay = 1.;
}
}
/** Compute the measurement error due to Ionosphere.
* @param station station
* @param state spacecraft state
* @return the measurement error due to Ionosphere
* @throws OrekitException if frames transformations cannot be computed
*/
private double rangeRateErrorIonosphericModel(final GroundStation station, final SpacecraftState state)
throws OrekitException {
// The effect of ionospheric correction on the range rate is
// computed using finite differences.
final double dt = 10; // s
//
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) {
// compute azimuth
final double azimuth = station.getBaseFrame().getAzimuth(position,
state.getFrame(),
state.getDate());
// delay in meters
final double delay1 = ionoModel.pathDelay(state.getDate(),
station.getBaseFrame().getPoint(),
elevation,
azimuth);
// propagate spacecraft state forward by dt
final SpacecraftState state2 = state.shiftedBy(dt);
// spacecraft position and elevation as seen from the ground station
final Vector3D position2 = state2.getPVCoordinates().getPosition();
final double elevation2 = station.getBaseFrame().getElevation(position2,
state2.getFrame(),
state2.getDate());
// compute azimuth in degrees
final double azimuth2 = station.getBaseFrame().getAzimuth(position2,
state2.getFrame(),
state2.getDate());
// ionospheric delay dt after in meters
final double delay2 = ionoModel.pathDelay(state2.getDate(),
station.getBaseFrame().getPoint(),
elevation2,
azimuth2);
// delay in meters
return fTwoWay * (delay2 - delay1) / dt;
}
return 0;
}
/** Compute the Jacobian of the delay term wrt state.
*
* @param station station
* @param refstate reference spacecraft state
*
* @return Jacobian of the delay wrt state
* @throws OrekitException if frames transformations cannot be computed
*/
private double[][] rangeErrorJacobianState(final GroundStation station,
final SpacecraftState refstate)
throws OrekitException {
final double[][] finiteDifferencesJacobian =
Differentiation.differentiate(new StateFunction() {
public double[] value(final SpacecraftState state) throws OrekitException {
try {
// evaluate target's elevation with a changed target position
final double value = rangeRateErrorIonosphericModel(station, state);
return new double[] {value };
} catch (OrekitException oe) {
throw new OrekitExceptionWrapper(oe);
}
}
}, 1, Propagator.DEFAULT_LAW, OrbitType.CARTESIAN,
PositionAngle.TRUE, 15.0, 3).value(refstate);
return finiteDifferencesJacobian;
}
/** Compute the derivative of the delay term wrt parameters.
*
* @param station ground station
* @param driver driver for the station offset parameter
* @param state spacecraft state
* @param delay current ionospheric delay
* @return derivative of the delay wrt station offset parameter
* @throws OrekitException if frames transformations cannot be computed
*/
private double rangeRateErrorParameterDerivative(final GroundStation station,
final ParameterDriver driver,
final SpacecraftState state,
final double delay)
throws OrekitException {
final ParameterFunction rangeError = new ParameterFunction() {
/** {@inheritDoc} */
@Override
public double value(final ParameterDriver parameterDriver) throws OrekitException {
return rangeRateErrorIonosphericModel(station, state);
}
};
final ParameterFunction rangeErrorDerivative =
Differentiation.differentiate(rangeError, driver, 3, 10.0);
return rangeErrorDerivative.value(driver);
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.emptyList();
}
/** {@inheritDoc} */
@Override
public void modify(final EstimatedMeasurement<RangeRate> estimated)
throws OrekitException {
final RangeRate measurement = estimated.getObservedMeasurement();
final GroundStation station = measurement.getStation();
final SpacecraftState state = estimated.getStates()[0];
final double[] oldValue = estimated.getEstimatedValue();
final double delay = rangeRateErrorIonosphericModel(station, state);
// update estimated value taking into account the ionospheric delay.
// The ionospheric delay is directly added to the range.
final double[] newValue = oldValue.clone();
newValue[0] = newValue[0] + delay;
estimated.setEstimatedValue(newValue);
// update estimated derivatives with Jacobian of the measure wrt state
final double[][] djac = rangeErrorJacobianState(station,
state);
final double[][] stateDerivatives = estimated.getStateDerivatives(0);
for (int irow = 0; irow < stateDerivatives.length; ++irow) {
for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
stateDerivatives[irow][jcol] += djac[irow][jcol];
}
}
estimated.setStateDerivatives(0, stateDerivatives);
for (final ParameterDriver driver : Arrays.asList(station.getEastOffsetDriver(),
station.getNorthOffsetDriver(),
station.getZenithOffsetDriver())) {
if (driver.isSelected()) {
// update estimated derivatives with derivative of the modification wrt station parameters
double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
parameterDerivative += rangeRateErrorParameterDerivative(station, driver, state, delay);
estimated.setParameterDerivatives(driver, parameterDerivative);
}
}
}
}