RangeTroposphericDelayModifier.java
/* Copyright 2002-2019 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.
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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.Arrays;
import java.util.List;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.analysis.differentiation.DerivativeStructure;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.GroundStation;
import org.orekit.estimation.measurements.Range;
import org.orekit.models.earth.DiscreteTroposphericModel;
import org.orekit.models.earth.TroposphericModel;
import org.orekit.orbits.OrbitType;
import org.orekit.orbits.PositionAngle;
import org.orekit.propagation.FieldSpacecraftState;
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 measurement with tropospheric delay.
* The effect of tropospheric correction on the range is directly computed
* through the computation of the tropospheric delay.
*
* In general, for GNSS, VLBI, ... there is hardly any frequency dependence in the delay.
* For SLR techniques however, the frequency dependence is sensitive.
*
* @author Maxime Journot
* @author Joris Olympio
* @since 8.0
*/
public class RangeTroposphericDelayModifier implements EstimationModifier<Range> {
/** Tropospheric delay model. */
private final DiscreteTroposphericModel tropoModel;
/** Constructor.
*
* @param model Tropospheric delay model appropriate for the current range measurement method.
*/
public RangeTroposphericDelayModifier(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;
}
/** Get the station height above mean sea level.
* @param <T> type of the elements
* @param field field of the elements
* @param station ground station (or measuring station)
* @return the measuring station height above sea level, m
*/
private <T extends RealFieldElement<T>> T getStationHeightAMSL(final Field<T> field, final GroundStation station) {
// FIXME heigth should be computed with respect to geoid WGS84+GUND = EGM2008 for example
final T height = station.getBaseFrame().getPoint(field).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 rangeErrorTroposphericModel(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) {
// altitude AMSL in meters
final double height = getStationHeightAMSL(station);
// delay in meters
final double delay = tropoModel.pathDelay(elevation, height, tropoModel.getParameters(), state.getDate());
return delay;
}
return 0;
}
/** Compute the measurement error due to Troposphere.
* @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
*/
private <T extends RealFieldElement<T>> T rangeErrorTroposphericModel(final GroundStation station,
final FieldSpacecraftState<T> state,
final T[] parameters) {
// Field
final Field<T> field = state.getDate().getField();
final T zero = field.getZero();
// satellite elevation
final FieldVector3D<T> position = state.getPVCoordinates().getPosition();
final T elevation = station.getBaseFrame().getElevation(position,
state.getFrame(),
state.getDate());
// only consider measures above the horizon
if (elevation.getReal() > 0) {
// altitude AMSL in meters
final T height = getStationHeightAMSL(field, station);
// delay in meters
final T delay = tropoModel.pathDelay(elevation, height, parameters, state.getDate());
return delay;
}
return zero;
}
/** Compute the Jacobian of the delay term wrt state using
* automatic differentiation.
*
* @param derivatives tropospheric delay derivatives
* @param freeStateParameters dimension of the state.
*
* @return Jacobian of the delay wrt state
*/
private double[][] rangeErrorJacobianState(final double[] derivatives, final int freeStateParameters) {
final double[][] finiteDifferencesJacobian = new double[1][6];
for (int i = 0; i < freeStateParameters; i++) {
// First element is the value of the delay
finiteDifferencesJacobian[0][i] = derivatives[i + 1];
}
return finiteDifferencesJacobian;
}
/** Compute the Jacobian of the delay term wrt state.
*
* @param station station
* @param refstate reference spacecraft state
*
* @return Jacobian of the delay wrt state
*/
private double[][] rangeErrorJacobianState(final GroundStation station, final SpacecraftState refstate) {
final double[][] finiteDifferencesJacobian =
Differentiation.differentiate(new StateFunction() {
public double[] value(final SpacecraftState state) {
// evaluate target's elevation with a changed target position
final double value = rangeErrorTroposphericModel(station, state);
return new double[] {value };
}
}, 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
* @return derivative of the delay wrt station offset parameter
*/
private double rangeErrorParameterDerivative(final GroundStation station,
final ParameterDriver driver,
final SpacecraftState state) {
final ParameterFunction rangeError = new ParameterFunction() {
/** {@inheritDoc} */
@Override
public double value(final ParameterDriver parameterDriver) {
return rangeErrorTroposphericModel(station, state);
}
};
final ParameterFunction rangeErrorDerivative =
Differentiation.differentiate(rangeError, 3, 10.0 * driver.getScale());
return rangeErrorDerivative.value(driver);
}
/** Compute the derivative of the delay term wrt parameters using
* automatic differentiation.
*
* @param derivatives tropospheric delay derivatives
* @param freeStateParameters dimension of the state.
* @return derivative of the delay wrt tropospheric model parameters
*/
private double[] rangeErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
// 0 -> value of the delay
// 1 ... freeStateParameters -> derivatives of the delay wrt state
// freeStateParameters + 1 ... n -> derivatives of the delay wrt tropospheric parameters
final int dim = derivatives.length - 1 - freeStateParameters;
final double[] rangeError = new double[dim];
for (int i = 0; i < dim; i++) {
rangeError[i] = derivatives[1 + freeStateParameters + i];
}
return rangeError;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return tropoModel.getParametersDrivers();
}
/** {@inheritDoc} */
@Override
public void modify(final EstimatedMeasurement<Range> estimated) {
final Range measurement = estimated.getObservedMeasurement();
final GroundStation station = measurement.getStation();
final SpacecraftState state = estimated.getStates()[0];
final double[] oldValue = estimated.getEstimatedValue();
// update estimated derivatives with Jacobian of the measure wrt state
final TroposphericDSConverter converter = new TroposphericDSConverter(state, 6, Propagator.DEFAULT_LAW);
final FieldSpacecraftState<DerivativeStructure> dsState = converter.getState(tropoModel);
final DerivativeStructure[] dsParameters = converter.getParameters(dsState, tropoModel);
final DerivativeStructure dsDelay = rangeErrorTroposphericModel(station, dsState, dsParameters);
final double[] derivatives = dsDelay.getAllDerivatives();
double[][] djac = new double[1][6];
// This implementation will disappear when the implementations of TroposphericModel
// will directly be implementations of DiscreteTroposphericModel
if (tropoModel instanceof TroposphericModel) {
djac = rangeErrorJacobianState(station, state);
} else {
djac = rangeErrorJacobianState(derivatives, converter.getFreeStateParameters());
}
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);
int index = 0;
for (final ParameterDriver driver : getParametersDrivers()) {
if (driver.isSelected()) {
// update estimated derivatives with derivative of the modification wrt tropospheric parameters
double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
final double[] dDelaydP = rangeErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
parameterDerivative += dDelaydP[index];
estimated.setParameterDerivatives(driver, parameterDerivative);
index = index + 1;
}
}
for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
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 += rangeErrorParameterDerivative(station, driver, state);
estimated.setParameterDerivatives(driver, parameterDerivative);
}
}
// update estimated value taking into account the tropospheric delay.
// The tropospheric delay is directly added to the range.
final double[] newValue = oldValue.clone();
newValue[0] = newValue[0] + dsDelay.getReal();
estimated.setEstimatedValue(newValue);
}
}