AngularTroposphericDelayModifier.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.Collections;
- import java.util.List;
- import org.hipparchus.geometry.euclidean.threed.Vector3D;
- import org.hipparchus.util.MathUtils;
- import org.orekit.errors.OrekitException;
- 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.TroposphericModel;
- 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 TroposphericModel tropoModel;
- /** Constructor.
- *
- * @param model Tropospheric delay model appropriate for the current angular measurement method.
- */
- public AngularTroposphericDelayModifier(final TroposphericModel 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
- * @throws OrekitException if frames transformations cannot be computed
- */
- private double angularErrorTroposphericModel(final GroundStation station,
- final SpacecraftState state)
- throws OrekitException {
- //
- 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);
- // one-way measurement.
- return delay;
- }
- return 0;
- }
- /** {@inheritDoc} */
- @Override
- public List<ParameterDriver> getParametersDrivers() {
- return Collections.emptyList();
- }
- @Override
- public void modify(final EstimatedMeasurement<AngularAzEl> estimated)
- throws OrekitException {
- 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);
- }
- }