AbstractRelativisticJ2ClockModifier.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 org.hipparchus.util.FastMath;
- import org.orekit.estimation.measurements.EstimatedMeasurementBase;
- import org.orekit.frames.Frame;
- import org.orekit.orbits.KeplerianOrbit;
- import org.orekit.propagation.SpacecraftState;
- import org.orekit.utils.Constants;
- import org.orekit.utils.TimeStampedPVCoordinates;
- /**
- * Class modifying theoretical measurements with relativistic J2 clock correction.
- * <p>
- * Relativistic clock correction of the effects caused by the oblateness of Earth on
- * the gravity potential.
- * </p>
- * <p>
- * The time delay caused by this effect is computed based on the orbital parameters of the
- * emitter's orbit.
- * </p>
- *
- * @author Louis Aucouturier
- * @since 11.2
- *
- * @see "Teunissen, Peter, and Oliver Montenbruck, eds. Springer handbook of global navigation
- * satellite systems. Chapter 19.2. Equation 19.18 Springer, 2017."
- */
- public class AbstractRelativisticJ2ClockModifier {
- /**
- * Relativistic J2 effect constant.
- */
- private final double cJ2;
- /** Central attraction coefficient. */
- private final double gm;
- /**
- * Constructor for the Relativistic J2 Clock modifier.
- * @param gm Earth gravitational constant (mu) in m³/s².
- * @param c20 Earth un-normalized second zonal coefficient (Signed J2 constant, is negative) (Typical value -1.0826e-3).
- * @param equatorialRadius Earth equatorial radius in m.
- */
- public AbstractRelativisticJ2ClockModifier(final double gm,
- final double c20,
- final double equatorialRadius) {
- this.cJ2 = 1.5 * c20 * equatorialRadius * equatorialRadius /
- (Constants.SPEED_OF_LIGHT * Constants.SPEED_OF_LIGHT);
- this.gm = gm;
- }
- /**
- * Computes the relativistic J2 clock time delay correction.
- *
- * @param estimated EstimatedMeasurements on which to calculate the correction
- * @return dt_relJ2clk Time delay due to the relativistic J2 clock effect in seconds
- */
- protected double relativisticJ2Correction(final EstimatedMeasurementBase<?> estimated) {
- // Extracting the state of the receiver to determine the frame and mu
- /**
- * The satellite states are stored at the creation of the estimated measurements
- * and can contain up to 2 elements. In most cases, only the receiver's state and
- * therefore frame is stored, with the emitter's frame corresponding to the receiver's.
- * Still, in the InterSatellites case, the states of the 2 spacecrafts are stored,
- * and can contain different frames. This case is treated by looking at the length
- * of SpacecraftState stored in the Estimated Measurements, with the only length 2
- * case is the InterSatellites case.
- */
- final SpacecraftState[] states = estimated.getStates();
- final SpacecraftState state = (states.length < 2) ? states[0] : states[1];
- final Frame remoteFrame = state.getFrame();
- // Getting Participants to extract the remote PV
- final TimeStampedPVCoordinates[] pvs = estimated.getParticipants();
- // Checking if the correction is applied on a two-way GNSS problem
- // In that case the emitter is at index 1, else index 0
- final TimeStampedPVCoordinates pvRemote = (pvs.length < 3) ? pvs[0] : pvs[1];
- // Define a Keplerian orbit to extract the orbital parameters needed to compute the correction
- final KeplerianOrbit remoteOrbit = new KeplerianOrbit(pvRemote, remoteFrame, gm);
- final double orbitInclination = remoteOrbit.getI();
- // u = perigee argument + true anomaly
- final double orbitU = remoteOrbit.getTrueAnomaly() + remoteOrbit.getPerigeeArgument();
- final double n = remoteOrbit.getKeplerianMeanMotion();
- // Returning the value of the time delay
- return cJ2 * n * FastMath.sin(2 * orbitU) * FastMath.sin(orbitInclination) * FastMath.sin(orbitInclination);
- }
- }