KlobucharIonoModel.java
- /* Copyright 2002-2022 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.models.earth.ionosphere;
- import java.util.Collections;
- import java.util.List;
- import org.hipparchus.Field;
- import org.hipparchus.CalculusFieldElement;
- import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
- import org.hipparchus.geometry.euclidean.threed.Vector3D;
- import org.hipparchus.util.FastMath;
- import org.hipparchus.util.FieldSinCos;
- import org.hipparchus.util.MathUtils;
- import org.hipparchus.util.SinCos;
- import org.orekit.annotation.DefaultDataContext;
- import org.orekit.bodies.FieldGeodeticPoint;
- import org.orekit.bodies.GeodeticPoint;
- import org.orekit.data.DataContext;
- import org.orekit.frames.TopocentricFrame;
- import org.orekit.propagation.FieldSpacecraftState;
- import org.orekit.propagation.SpacecraftState;
- import org.orekit.time.AbsoluteDate;
- import org.orekit.time.DateTimeComponents;
- import org.orekit.time.FieldAbsoluteDate;
- import org.orekit.time.TimeScale;
- import org.orekit.utils.Constants;
- import org.orekit.utils.ParameterDriver;
- /**
- * Klobuchar ionospheric delay model.
- * Klobuchar ionospheric delay model is designed as a GNSS correction model.
- * The parameters for the model are provided by the GPS satellites in their broadcast
- * messsage.
- * This model is based on the assumption the electron content is concentrated
- * in 350 km layer.
- *
- * The delay refers to L1 (1575.42 MHz).
- * If the delay is sought for L2 (1227.60 MHz), multiply the result by 1.65 (Klobuchar, 1996).
- * More generally, since ionospheric delay is inversely proportional to the square of the signal
- * frequency f, to adapt this model to other GNSS frequencies f, multiply by (L1 / f)^2.
- *
- * References:
- * ICD-GPS-200, Rev. C, (1997), pp. 125-128
- * Klobuchar, J.A., Ionospheric time-delay algorithm for single-frequency GPS users,
- * IEEE Transactions on Aerospace and Electronic Systems, Vol. 23, No. 3, May 1987
- * Klobuchar, J.A., "Ionospheric Effects on GPS", Global Positioning System: Theory and
- * Applications, 1996, pp.513-514, Parkinson, Spilker.
- *
- * @author Joris Olympio
- * @since 7.1
- *
- */
- public class KlobucharIonoModel implements IonosphericModel {
- /** Serializable UID. */
- private static final long serialVersionUID = 7277525837842061107L;
- /** The 4 coefficients of a cubic equation representing the amplitude of the vertical delay. Units are sec/semi-circle^(i-1) for the i-th coefficient, i=1, 2, 3, 4. */
- private final double[] alpha;
- /** The 4 coefficients of a cubic equation representing the period of the model. Units are sec/semi-circle^(i-1) for the i-th coefficient, i=1, 2, 3, 4. */
- private final double[] beta;
- /** GPS time scale. */
- private final TimeScale gps;
- /** Create a new Klobuchar ionospheric delay model, when a single frequency system is used.
- * This model accounts for at least 50 percent of RMS error due to ionospheric propagation effect (ICD-GPS-200)
- *
- * <p>This constructor uses the {@link DataContext#getDefault() default data context}.
- *
- * @param alpha coefficients of a cubic equation representing the amplitude of the vertical delay.
- * @param beta coefficients of a cubic equation representing the period of the model.
- * @see #KlobucharIonoModel(double[], double[], TimeScale)
- */
- @DefaultDataContext
- public KlobucharIonoModel(final double[] alpha, final double[] beta) {
- this(alpha, beta, DataContext.getDefault().getTimeScales().getGPS());
- }
- /**
- * Create a new Klobuchar ionospheric delay model, when a single frequency system is
- * used. This model accounts for at least 50 percent of RMS error due to ionospheric
- * propagation effect (ICD-GPS-200)
- *
- * @param alpha coefficients of a cubic equation representing the amplitude of the
- * vertical delay.
- * @param beta coefficients of a cubic equation representing the period of the
- * model.
- * @param gps GPS time scale.
- * @since 10.1
- */
- public KlobucharIonoModel(final double[] alpha,
- final double[] beta,
- final TimeScale gps) {
- this.alpha = alpha.clone();
- this.beta = beta.clone();
- this.gps = gps;
- }
- /**
- * Calculates the ionospheric path delay for the signal path from a ground
- * station to a satellite.
- * <p>
- * The path delay is computed for any elevation angle.
- * </p>
- * @param date current date
- * @param geo geodetic point of receiver/station
- * @param elevation elevation of the satellite in radians
- * @param azimuth azimuth of the satellite in radians
- * @param frequency frequency of the signal in Hz
- * @param parameters ionospheric model parameters
- * @return the path delay due to the ionosphere in m
- */
- public double pathDelay(final AbsoluteDate date, final GeodeticPoint geo,
- final double elevation, final double azimuth, final double frequency,
- final double[] parameters) {
- // Sine and cosine of the azimuth
- final SinCos sc = FastMath.sinCos(azimuth);
- // degrees to semicircles
- final double rad2semi = 1. / FastMath.PI;
- final double semi2rad = FastMath.PI;
- // Earth Centered angle
- final double psi = 0.0137 / (elevation / FastMath.PI + 0.11) - 0.022;
- // Subionospheric latitude: the latitude of the IPP (Ionospheric Pierce Point)
- // in [-0.416, 0.416], semicircle
- final double latIono = FastMath.min(
- FastMath.max(geo.getLatitude() * rad2semi + psi * sc.cos(), -0.416),
- 0.416);
- // Subionospheric longitude: the longitude of the IPP
- // in semicircle
- final double lonIono = geo.getLongitude() * rad2semi + (psi * sc.sin() / FastMath.cos(latIono * semi2rad));
- // Geomagnetic latitude, semicircle
- final double latGeom = latIono + 0.064 * FastMath.cos((lonIono - 1.617) * semi2rad);
- // day of week and tow (sec)
- // Note: Sunday=0, Monday=1, Tuesday=2, Wednesday=3, Thursday=4, Friday=5, Saturday=6
- final DateTimeComponents dtc = date.getComponents(gps);
- final int dofweek = dtc.getDate().getDayOfWeek();
- final double secday = dtc.getTime().getSecondsInLocalDay();
- final double tow = dofweek * 86400. + secday;
- final double t = 43200. * lonIono + tow;
- final double tsec = t - FastMath.floor(t / 86400.) * 86400; // Seconds of day
- // Slant factor, semicircle
- final double slantFactor = 1.0 + 16.0 * FastMath.pow(0.53 - elevation / FastMath.PI, 3);
- // Period of model, seconds
- final double period = FastMath.max(72000., beta[0] + (beta[1] + (beta[2] + beta[3] * latGeom) * latGeom) * latGeom);
- // Phase of the model, radians
- // (Max at 14.00 = 50400 sec local time)
- final double x = 2.0 * FastMath.PI * (tsec - 50400.0) / period;
- // Amplitude of the model, seconds
- final double amplitude = FastMath.max(0, alpha[0] + (alpha[1] + (alpha[2] + alpha[3] * latGeom) * latGeom) * latGeom);
- // Ionospheric correction (L1)
- double ionoTimeDelayL1 = slantFactor * (5. * 1e-9);
- if (FastMath.abs(x) < 1.570) {
- ionoTimeDelayL1 += slantFactor * (amplitude * (1.0 - FastMath.pow(x, 2) / 2.0 + FastMath.pow(x, 4) / 24.0));
- }
- // Ionospheric delay for the L1 frequency, in meters, with slant correction.
- final double ratio = FastMath.pow(1575.42e6 / frequency, 2);
- return ratio * Constants.SPEED_OF_LIGHT * ionoTimeDelayL1;
- }
- /** {@inheritDoc} */
- @Override
- public double pathDelay(final SpacecraftState state, final TopocentricFrame baseFrame,
- final double frequency, final double[] parameters) {
- // Elevation in radians
- final Vector3D position = state.getPVCoordinates(baseFrame).getPosition();
- final double elevation = position.getDelta();
- // Only consider measures above the horizon
- if (elevation > 0.0) {
- // Date
- final AbsoluteDate date = state.getDate();
- // Geodetic point
- final GeodeticPoint geo = baseFrame.getPoint();
- // Azimuth angle in radians
- double azimuth = FastMath.atan2(position.getX(), position.getY());
- if (azimuth < 0.) {
- azimuth += MathUtils.TWO_PI;
- }
- // Delay
- return pathDelay(date, geo, elevation, azimuth, frequency, parameters);
- }
- return 0.0;
- }
- /**
- * Calculates the ionospheric path delay for the signal path from a ground
- * station to a satellite.
- * <p>
- * The path delay is computed for any elevation angle.
- * </p>
- * @param <T> type of the elements
- * @param date current date
- * @param geo geodetic point of receiver/station
- * @param elevation elevation of the satellite in radians
- * @param azimuth azimuth of the satellite in radians
- * @param frequency frequency of the signal in Hz
- * @param parameters ionospheric model parameters
- * @return the path delay due to the ionosphere in m
- */
- public <T extends CalculusFieldElement<T>> T pathDelay(final FieldAbsoluteDate<T> date, final FieldGeodeticPoint<T> geo,
- final T elevation, final T azimuth, final double frequency,
- final T[] parameters) {
- // Sine and cosine of the azimuth
- final FieldSinCos<T> sc = FastMath.sinCos(azimuth);
- // Field
- final Field<T> field = date.getField();
- final T zero = field.getZero();
- final T one = field.getOne();
- // degrees to semicircles
- final T pi = one.getPi();
- final T rad2semi = pi.reciprocal();
- // Earth Centered angle
- final T psi = elevation.divide(pi).add(0.11).divide(0.0137).reciprocal().subtract(0.022);
- // Subionospheric latitude: the latitude of the IPP (Ionospheric Pierce Point)
- // in [-0.416, 0.416], semicircle
- final T latIono = FastMath.min(
- FastMath.max(geo.getLatitude().multiply(rad2semi).add(psi.multiply(sc.cos())), zero.subtract(0.416)),
- zero.add(0.416));
- // Subionospheric longitude: the longitude of the IPP
- // in semicircle
- final T lonIono = geo.getLongitude().multiply(rad2semi).add(psi.multiply(sc.sin()).divide(FastMath.cos(latIono.multiply(pi))));
- // Geomagnetic latitude, semicircle
- final T latGeom = latIono.add(FastMath.cos(lonIono.subtract(1.617).multiply(pi)).multiply(0.064));
- // day of week and tow (sec)
- // Note: Sunday=0, Monday=1, Tuesday=2, Wednesday=3, Thursday=4, Friday=5, Saturday=6
- final DateTimeComponents dtc = date.getComponents(gps);
- final int dofweek = dtc.getDate().getDayOfWeek();
- final double secday = dtc.getTime().getSecondsInLocalDay();
- final double tow = dofweek * 86400. + secday;
- final T t = lonIono.multiply(43200.).add(tow);
- final T tsec = t.subtract(FastMath.floor(t.divide(86400.)).multiply(86400.)); // Seconds of day
- // Slant factor, semicircle
- final T slantFactor = FastMath.pow(elevation.divide(pi).negate().add(0.53), 3).multiply(16.0).add(one);
- // Period of model, seconds
- final T period = FastMath.max(zero.add(72000.), latGeom.multiply(latGeom.multiply(latGeom.multiply(beta[3]).add(beta[2])).add(beta[1])).add(beta[0]));
- // Phase of the model, radians
- // (Max at 14.00 = 50400 sec local time)
- final T x = tsec.subtract(50400.0).multiply(pi.multiply(2.0)).divide(period);
- // Amplitude of the model, seconds
- final T amplitude = FastMath.max(zero, latGeom.multiply(latGeom.multiply(latGeom.multiply(alpha[3]).add(alpha[2])).add(alpha[1])).add(alpha[0]));
- // Ionospheric correction (L1)
- T ionoTimeDelayL1 = slantFactor.multiply(5. * 1e-9);
- if (FastMath.abs(x.getReal()) < 1.570) {
- ionoTimeDelayL1 = ionoTimeDelayL1.add(slantFactor.multiply(amplitude.multiply(one.subtract(FastMath.pow(x, 2).multiply(0.5)).add(FastMath.pow(x, 4).divide(24.0)))));
- }
- // Ionospheric delay for the L1 frequency, in meters, with slant correction.
- final double ratio = FastMath.pow(1575.42e6 / frequency, 2);
- return ionoTimeDelayL1.multiply(Constants.SPEED_OF_LIGHT).multiply(ratio);
- }
- /** {@inheritDoc} */
- @Override
- public <T extends CalculusFieldElement<T>> T pathDelay(final FieldSpacecraftState<T> state, final TopocentricFrame baseFrame,
- final double frequency, final T[] parameters) {
- // Elevation and azimuth in radians
- final FieldVector3D<T> position = state.getPVCoordinates(baseFrame).getPosition();
- final T elevation = position.getDelta();
- if (elevation.getReal() > 0.0) {
- // Date
- final FieldAbsoluteDate<T> date = state.getDate();
- // Geodetic point
- final FieldGeodeticPoint<T> geo = baseFrame.getPoint(date.getField());
- // Azimuth angle in radians
- T azimuth = FastMath.atan2(position.getX(), position.getY());
- if (azimuth.getReal() < 0.) {
- azimuth = azimuth.add(MathUtils.TWO_PI);
- }
- // Delay
- return pathDelay(date, geo, elevation, azimuth, frequency, parameters);
- }
- return elevation.getField().getZero();
- }
- @Override
- public List<ParameterDriver> getParametersDrivers() {
- return Collections.emptyList();
- }
- }