RangeRateTroposphericDelayModifier.java
/* Copyright 2002-2022 CS GROUP
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* 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
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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.Arrays;
import java.util.List;
import org.hipparchus.Field;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.analysis.differentiation.Gradient;
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.RangeRate;
import org.orekit.models.earth.troposphere.DiscreteTroposphericModel;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.Differentiation;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterFunction;
/** Class modifying theoretical range-rate measurements with tropospheric delay.
* The effect of tropospheric correction on the range-rate is directly computed
* through the computation of the tropospheric delay difference with respect to
* time.
*
* In general, for GNSS, VLBI, ... there is hardly any frequency dependence in the delay.
* For SLR techniques however, the frequency dependence is sensitive.
*
* @author Joris Olympio
* @since 8.0
*/
public class RangeRateTroposphericDelayModifier implements EstimationModifier<RangeRate> {
/** Tropospheric delay model. */
private final DiscreteTroposphericModel tropoModel;
/** Two-way measurement factor. */
private final double fTwoWay;
/** Constructor.
*
* @param model Tropospheric delay model appropriate for the current range-rate measurement method.
* @param tw Flag indicating whether the measurement is two-way.
*/
public RangeRateTroposphericDelayModifier(final DiscreteTroposphericModel model, final boolean tw) {
tropoModel = model;
if (tw) {
fTwoWay = 2.;
} else {
fTwoWay = 1.;
}
}
/** Compute the measurement error due to Troposphere.
* @param station station
* @param state spacecraft state
* @return the measurement error due to Troposphere
*/
public double rangeRateErrorTroposphericModel(final GroundStation station,
final SpacecraftState state) {
// The effect of tropospheric correction on the range rate is
// computed using finite differences.
final double dt = 10; // s
// spacecraft position and elevation as seen from the ground station
final Vector3D position = state.getPVCoordinates().getPosition();
// elevation
final double elevation1 = station.getBaseFrame().getElevation(position,
state.getFrame(),
state.getDate());
// only consider measures above the horizon
if (elevation1 > 0) {
// tropospheric delay in meters
final double d1 = tropoModel.pathDelay(elevation1, station.getBaseFrame().getPoint(), tropoModel.getParameters(), state.getDate());
// 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();
// elevation
final double elevation2 = station.getBaseFrame().getElevation(position2,
state2.getFrame(),
state2.getDate());
// tropospheric delay dt after
final double d2 = tropoModel.pathDelay(elevation2, station.getBaseFrame().getPoint(), tropoModel.getParameters(), state2.getDate());
return fTwoWay * (d2 - d1) / dt;
}
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
*/
public <T extends CalculusFieldElement<T>> T rangeRateErrorTroposphericModel(final GroundStation station,
final FieldSpacecraftState<T> state,
final T[] parameters) {
// Field
final Field<T> field = state.getDate().getField();
final T zero = field.getZero();
// The effect of tropospheric correction on the range rate is
// computed using finite differences.
final double dt = 10; // s
// spacecraft position and elevation as seen from the ground station
final FieldVector3D<T> position = state.getPVCoordinates().getPosition();
final T elevation1 = station.getBaseFrame().getElevation(position,
state.getFrame(),
state.getDate());
// only consider measures above the horizon
if (elevation1.getReal() > 0) {
// tropospheric delay in meters
final T d1 = tropoModel.pathDelay(elevation1, station.getBaseFrame().getPoint(field), parameters, state.getDate());
// propagate spacecraft state forward by dt
final FieldSpacecraftState<T> state2 = state.shiftedBy(dt);
// spacecraft position and elevation as seen from the ground station
final FieldVector3D<T> position2 = state2.getPVCoordinates().getPosition();
// elevation
final T elevation2 = station.getBaseFrame().getElevation(position2,
state2.getFrame(),
state2.getDate());
// tropospheric delay dt after
final T d2 = tropoModel.pathDelay(elevation2, station.getBaseFrame().getPoint(field), parameters, state2.getDate());
return (d2.subtract(d1)).divide(dt).multiply(fTwoWay);
}
return zero;
}
/** Compute the Jacobian of the delay term wrt state using
* automatic differentiation.
*
* @param derivatives tropospheric delay derivatives
*
* @return Jacobian of the delay wrt state
*/
private double[][] rangeRateErrorJacobianState(final double[] derivatives) {
final double[][] finiteDifferencesJacobian = new double[1][6];
System.arraycopy(derivatives, 0, finiteDifferencesJacobian[0], 0, 6);
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 rangeRateErrorParameterDerivative(final GroundStation station,
final ParameterDriver driver,
final SpacecraftState state) {
final ParameterFunction rangeError = new ParameterFunction() {
/** {@inheritDoc} */
@Override
public double value(final ParameterDriver parameterDriver) {
return rangeRateErrorTroposphericModel(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[] rangeRateErrorParameterDerivative(final double[] derivatives, final int freeStateParameters) {
// 0 ... freeStateParameters - 1 -> derivatives of the delay wrt state
// freeStateParameters ... n -> derivatives of the delay wrt tropospheric parameters
final int dim = derivatives.length - freeStateParameters;
final double[] rangeError = new double[dim];
for (int i = 0; i < dim; i++) {
rangeError[i] = derivatives[freeStateParameters + i];
}
return rangeError;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return tropoModel.getParametersDrivers();
}
/** {@inheritDoc} */
@Override
public void modify(final EstimatedMeasurement<RangeRate> estimated) {
final RangeRate 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 TroposphericGradientConverter converter =
new TroposphericGradientConverter(state, 6, new InertialProvider(state.getFrame()));
final FieldSpacecraftState<Gradient> gState = converter.getState(tropoModel);
final Gradient[] gParameters = converter.getParameters(gState, tropoModel);
final Gradient gDelay = rangeRateErrorTroposphericModel(station, gState, gParameters);
final double[] derivatives = gDelay.getGradient();
final double[][] djac = rangeRateErrorJacobianState(derivatives);
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 = rangeRateErrorParameterDerivative(derivatives, converter.getFreeStateParameters());
parameterDerivative += dDelaydP[index];
estimated.setParameterDerivatives(driver, parameterDerivative);
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 += rangeRateErrorParameterDerivative(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] + gDelay.getReal();
estimated.setEstimatedValue(newValue);
}
}