AngularIonosphericDelayModifier.java
- /* Copyright 2002-2024 CS GROUP
- * Licensed to CS GROUP (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.List;
- import org.hipparchus.geometry.euclidean.threed.Vector3D;
- import org.hipparchus.util.MathUtils;
- import org.orekit.estimation.measurements.AngularAzEl;
- import org.orekit.estimation.measurements.EstimatedMeasurementBase;
- 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;
- import org.orekit.utils.TrackingCoordinates;
- /** Class modifying theoretical angular measurement with ionospheric delay.
- * <p>
- * 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.
- * </p>
- * <p>
- * 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>
- * <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
- return ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters(state.getDate()));
- }
- /** {@inheritDoc} */
- @Override
- public List<ParameterDriver> getParametersDrivers() {
- return ionoModel.getParametersDrivers();
- }
- @Override
- public void modifyWithoutDerivatives(final EstimatedMeasurementBase<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.getPosition();
- final Frame inertial = transitState.getFrame();
- // Elevation and azimuth in radians
- final TrackingCoordinates tc = station.getBaseFrame().getTrackingCoordinates(position, inertial, date);
- final double twoPiWrap = MathUtils.normalizeAngle(tc.getAzimuth(), measure.getObservedValue()[0]) - tc.getAzimuth();
- final double azimuth = tc.getAzimuth() + twoPiWrap;
- // Update estimated value taking into account the ionospheric delay.
- // Azimuth - elevation values
- estimated.modifyEstimatedValue(this, azimuth, tc.getElevation());
- }
- }