EstimatedTroposphericModel.java
/* Copyright 2002-2019 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
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*
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package org.orekit.models.earth.troposphere;
import java.util.Collections;
import java.util.List;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathArrays;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.ParameterDriver;
/** An estimated tropospheric model. The tropospheric delay is computed according to the formula:
* <p>
* δ = δ<sub>h</sub> * m<sub>h</sub> + (δ<sub>t</sub> - δ<sub>h</sub>) * m<sub>w</sub>
* <p>
* With:
* <ul>
* <li>δ<sub>h</sub>: Tropospheric zenith hydro-static delay.</li>
* <li>δ<sub>t</sub>: Tropospheric total zenith delay.</li>
* <li>m<sub>h</sub>: Hydro-static mapping function.</li>
* <li>m<sub>w</sub>: Wet mapping function.</li>
* </ul>
* <p>
* The mapping functions m<sub>h</sub>(e) and m<sub>w</sub>(e) are
* computed thanks to a {@link #model} initialized by the user.
* The user has the possiblility to use several mapping function models for the computations:
* the {@link GlobalMappingFunctionModel Global Mapping Function}, or
* the {@link NiellMappingFunctionModel Niell Mapping Function}
* </p> <p>
* The tropospheric zenith delay δ<sub>h</sub> is computed empirically with a {@link SaastamoinenModel}
* while the tropospheric total zenith delay δ<sub>t</sub> is estimated as a {@link ParameterDriver}
*/
public class EstimatedTroposphericModel implements DiscreteTroposphericModel {
/** Name of the parameter of this model: the total zenith delay. */
public static final String TOTAL_ZENITH_DELAY = "total zenith delay";
/** Mapping Function model. */
private final MappingFunction model;
/** Driver for the tropospheric zenith total delay.*/
private final ParameterDriver totalZenithDelay;
/** The temperature at the station [K]. */
private double t0;
/** The atmospheric pressure [mbar]. */
private double p0;
/** Build a new instance using the given environmental conditions.
* @param t0 the temperature at the station [K]
* @param p0 the atmospheric pressure at the station [mbar]
* @param model mapping function model (NMF or GMF).
* @param totalDelay initial value for the tropospheric zenith total delay [m]
*/
public EstimatedTroposphericModel(final double t0, final double p0,
final MappingFunction model, final double totalDelay) {
totalZenithDelay = new ParameterDriver(EstimatedTroposphericModel.TOTAL_ZENITH_DELAY,
totalDelay, FastMath.scalb(1.0, 0), 0.0, Double.POSITIVE_INFINITY);
this.t0 = t0;
this.p0 = p0;
this.model = model;
}
/** Build a new instance using a standard atmosphere model.
* <ul>
* <li>temperature: 18 degree Celsius
* <li>pressure: 1013.25 mbar
* </ul>
* @param model mapping function model (NMF or GMF).
* @param totalDelay initial value for the tropospheric zenith total delay [m]
*/
public EstimatedTroposphericModel(final MappingFunction model, final double totalDelay) {
this(273.15 + 18.0, 1013.25, model, totalDelay);
}
@Override
public double[] mappingFactors(final double elevation, final double height,
final double[] parameters, final AbsoluteDate date) {
return model.mappingFactors(elevation, height, parameters, date);
}
@Override
public <T extends RealFieldElement<T>> T[] mappingFactors(final T elevation, final T height,
final T[] parameters, final FieldAbsoluteDate<T> date) {
return model.mappingFactors(elevation, height, parameters, date);
}
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.singletonList(totalZenithDelay);
}
@Override
public double pathDelay(final double elevation, final double height,
final double[] parameters, final AbsoluteDate date) {
// Mapping functions
final double[] mf = mappingFactors(elevation, height, parameters, date);
// Zenith delays
final double[] delays = computeZenithDelay(height, parameters, date);
// Total delay
return mf[0] * delays[0] + mf[1] * (delays[1] - delays[0]);
}
@Override
public <T extends RealFieldElement<T>> T pathDelay(final T elevation, final T height,
final T[] parameters, final FieldAbsoluteDate<T> date) {
// Mapping functions
final T[] mf = mappingFactors(elevation, height, parameters, date);
// Zenith delays
final T[] delays = computeZenithDelay(height, parameters, date);
// Total delay
return mf[0].multiply(delays[0]).add(mf[1].multiply(delays[1].subtract(delays[0])));
}
/** This method allows the computation of the zenith hydrostatic and zenith total delays.
* The resulting element is an array having the following form:
* <ul>
* <li>double[0] = D<sub>hz</sub> → zenith hydrostatic delay
* <li>double[1] = D<sub>tz</sub> → zenith total delay
* </ul>
* <p>
* The user have to be careful because the others tropospheric models in Orekit
* compute the zenith wet delay instead of the total zenith delay.
* </p>
* @param height the height of the station in m above sea level.
* @param parameters tropospheric model parameters.
* @param date current date
* @return a two components array containing the zenith hydrostatic and wet delays.
*/
public double[] computeZenithDelay(final double height, final double[] parameters,
final AbsoluteDate date) {
// Use an empirical model for tropospheric zenith hydro-static delay : Saastamoinen model
final SaastamoinenModel saastamoinen = new SaastamoinenModel(t0, p0, 0.0, (String) null);
// elevation = pi/2 because we compute the delay in the zenith direction
final double zhd = saastamoinen.pathDelay(0.5 * FastMath.PI, height, parameters, date);
final double ztd = parameters[0];
return new double[] {
zhd,
ztd
};
}
/** This method allows the computation of the zenith hydrostatic and zenith total delays.
* The resulting element is an array having the following form:
* <ul>
* <li>double[0] = D<sub>hz</sub> → zenith hydrostatic delay
* <li>double[1] = D<sub>tz</sub> → zenith total delay
* </ul>
* <p>
* The user have to be careful because the others tropospheric models in Orekit
* compute the zenith wet delay instead of the total zenith delay.
* </p>
* @param <T> type of the elements
* @param height the height of the station in m above sea level.
* @param parameters tropospheric model parameters.
* @param date current date
* @return a two components array containing the zenith hydrostatic and wet delays.
*/
public <T extends RealFieldElement<T>> T[] computeZenithDelay(final T height, final T[] parameters,
final FieldAbsoluteDate<T> date) {
// Field
final Field<T> field = date.getField();
final T zero = field.getZero();
// Use an empirical model for tropospheric zenith hydro-static delay : Saastamoinen model
final SaastamoinenModel saastamoinen = new SaastamoinenModel(t0, p0, 0.0, (String) null);
// elevation = pi/2 because we compute the delay in the zenith direction
final T zhd = saastamoinen.pathDelay(zero.add(0.5 * FastMath.PI), height, parameters, date);
final T ztd = parameters[0];
final T[] delays = MathArrays.buildArray(field, 2);
delays[0] = zhd;
delays[1] = ztd;
return delays;
}
}