ModifiedSaastamoinenModel.java
/* Copyright 2011-2012 Space Applications Services
* Licensed to CS Communication & Systèmes (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.troposphere;
import java.util.Collections;
import java.util.List;
import java.util.regex.Pattern;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.Field;
import org.hipparchus.analysis.interpolation.BilinearInterpolatingFunction;
import org.hipparchus.analysis.interpolation.LinearInterpolator;
import org.hipparchus.analysis.polynomials.PolynomialSplineFunction;
import org.hipparchus.util.FastMath;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.bodies.FieldGeodeticPoint;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.data.DataContext;
import org.orekit.data.DataProvidersManager;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.models.earth.weather.ConstantPressureTemperatureHumidityProvider;
import org.orekit.models.earth.weather.FieldPressureTemperatureHumidity;
import org.orekit.models.earth.weather.HeightDependentPressureTemperatureHumidityConverter;
import org.orekit.models.earth.weather.PressureTemperatureHumidity;
import org.orekit.models.earth.weather.PressureTemperatureHumidityProvider;
import org.orekit.models.earth.weather.water.Wang1988;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.FieldTrackingCoordinates;
import org.orekit.utils.InterpolationTableLoader;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TrackingCoordinates;
/** The modified Saastamoinen model. Estimates the path delay imposed to
* electro-magnetic signals by the troposphere according to the formula:
* <pre>
* δ = 2.277e-3 / cos z * (P + (1255 / T + 0.05) * e - B * tan² z) + δR
* </pre>
* with the following input data provided to the model:
* <ul>
* <li>z: zenith angle</li>
* <li>P: atmospheric pressure</li>
* <li>T: temperature</li>
* <li>e: partial pressure of water vapour</li>
* <li>B, δR: correction terms</li>
* </ul>
* <p>
* The model supports custom δR correction terms to be read from a
* configuration file (saastamoinen-correction.txt) via the
* {@link DataProvidersManager}.
* </p>
* @author Thomas Neidhart
* @see "Guochang Xu, GPS - Theory, Algorithms and Applications, Springer, 2007"
* @since 12.1
*/
public class ModifiedSaastamoinenModel implements TroposphericModel {
/** Default file name for δR correction term table. */
public static final String DELTA_R_FILE_NAME = "^saastamoinen-correction\\.txt$";
/** Default lowest acceptable elevation angle [rad]. */
public static final double DEFAULT_LOW_ELEVATION_THRESHOLD = 0.05;
/** Provider for water pressure. */
public static final Wang1988 WATER = new Wang1988();
/** First pattern for δR correction term table. */
private static final Pattern FIRST_DELTA_R_PATTERN = Pattern.compile("^\\^");
/** Second pattern for δR correction term table. */
private static final Pattern SECOND_DELTA_R_PATTERN = Pattern.compile("\\$$");
/** Base delay coefficient. */
private static final double L0 = 2.277e-5;
/** Temperature numerator. */
private static final double T_NUM = 1255;
/** Wet offset. */
private static final double WET_OFFSET = 0.05;
/** X values for the B function. */
private static final double[] X_VALUES_FOR_B = {
0.0, 500.0, 1000.0, 1500.0, 2000.0, 2500.0, 3000.0, 4000.0, 5000.0
};
/** Y values for the B function.
* <p>
* The values have been scaled up by a factor 100.0 due to conversion from hPa to Pa.
* </p>
*/
private static final double[] Y_VALUES_FOR_B = {
115.6, 107.9, 100.6, 93.8, 87.4, 81.3, 75.7, 65.4, 56.3
};
/** Interpolation function for the B correction term. */
private static final PolynomialSplineFunction B_FUNCTION = new LinearInterpolator().interpolate(X_VALUES_FOR_B, Y_VALUES_FOR_B);
/** Interpolation function for the delta R correction term. */
private final BilinearInterpolatingFunction deltaRFunction;
/** Provider for atmospheric pressure, temperature and humidity at reference altitude. */
private final PressureTemperatureHumidityProvider pth0Provider;
/** Height dependent converter for pressure, temperature and humidity. */
private final HeightDependentPressureTemperatureHumidityConverter converter;
/** Lowest acceptable elevation angle [rad]. */
private double lowElevationThreshold;
/**
* Create a new Saastamoinen model for the troposphere using the given environmental
* conditions and table from the reference book.
*
* @param pth0Provider provider for atmospheric pressure, temperature and humidity at reference altitude
* @see #ModifiedSaastamoinenModel(PressureTemperatureHumidityProvider, String, DataProvidersManager)
*/
@DefaultDataContext
public ModifiedSaastamoinenModel(final PressureTemperatureHumidityProvider pth0Provider) {
this(pth0Provider, defaultDeltaR());
}
/** Create a new Saastamoinen model for the troposphere using the given
* environmental conditions. This constructor uses the {@link DataContext#getDefault()
* default data context} if {@code deltaRFileName != null}.
*
* @param pth0Provider provider for atmospheric pressure, temperature and humidity at reference altitude
* @param deltaRFileName regular expression for filename containing δR
* correction term table (typically {@link #DELTA_R_FILE_NAME}), if null
* default values from the reference book are used
* @see #ModifiedSaastamoinenModel(PressureTemperatureHumidityProvider, String, DataProvidersManager)
*/
@DefaultDataContext
public ModifiedSaastamoinenModel(final PressureTemperatureHumidityProvider pth0Provider,
final String deltaRFileName) {
this(pth0Provider, deltaRFileName,
DataContext.getDefault().getDataProvidersManager());
}
/** Create a new Saastamoinen model for the troposphere using the given
* environmental conditions. This constructor allows the user to specify the source of
* of the δR file.
*
* @param pth0Provider provider for atmospheric pressure, temperature and humidity at reference altitude
* @param deltaRFileName regular expression for filename containing δR
* correction term table (typically {@link #DELTA_R_FILE_NAME}), if null
* default values from the reference book are used
* @param dataProvidersManager provides access to auxiliary data.
*/
public ModifiedSaastamoinenModel(final PressureTemperatureHumidityProvider pth0Provider,
final String deltaRFileName,
final DataProvidersManager dataProvidersManager) {
this(pth0Provider,
deltaRFileName == null ?
defaultDeltaR() :
loadDeltaR(deltaRFileName, dataProvidersManager));
}
/** Create a new Saastamoinen model.
*
* @param pth0Provider provider for atmospheric pressure, temperature and humidity at reference altitude
* @param deltaR δR correction term function
*/
private ModifiedSaastamoinenModel(final PressureTemperatureHumidityProvider pth0Provider,
final BilinearInterpolatingFunction deltaR) {
this.pth0Provider = pth0Provider;
this.converter = new HeightDependentPressureTemperatureHumidityConverter(WATER);
this.deltaRFunction = deltaR;
this.lowElevationThreshold = DEFAULT_LOW_ELEVATION_THRESHOLD;
}
/** Create a new Saastamoinen model using a standard atmosphere model.
*
* <ul>
* <li>altitude: 0m</li>
* <li>temperature: 18 degree Celsius</li>
* <li>pressure: 1013.25 mbar</li>
* <li>humidity: 50%</li>
* <li>@link {@link Wang1988 Wang 1988} model to compute water vapor pressure</li>
* </ul>
*
* @return a Saastamoinen model with standard environmental values
*/
@DefaultDataContext
public static ModifiedSaastamoinenModel getStandardModel() {
final double altitude = 0;
final double pressure = TroposphericModelUtils.HECTO_PASCAL.toSI(1013.25);
final double temperature = 273.15 + 18;
final double humidity = 0.5;
final PressureTemperatureHumidity pth = new PressureTemperatureHumidity(altitude,
pressure,
temperature,
WATER.waterVaporPressure(pressure,
temperature,
humidity),
Double.NaN,
Double.NaN);
final PressureTemperatureHumidityProvider pth0Provider = new ConstantPressureTemperatureHumidityProvider(pth);
return new ModifiedSaastamoinenModel(pth0Provider);
}
/** Get provider for atmospheric pressure, temperature and humidity at reference altitude.
* @return provider for atmospheric pressure, temperature and humidity at reference altitude
*/
public PressureTemperatureHumidityProvider getPth0Provider() {
return pth0Provider;
}
/** {@inheritDoc}
* <p>
* The Saastamoinen model is not defined for altitudes below 0.0. for continuity
* reasons, we use the value for h = 0 when altitude is negative.
* </p>
* <p>
* There are also numerical issues for elevation angles close to zero. For continuity reasons,
* elevations lower than a threshold will use the value obtained
* for the threshold itself.
* </p>
* @see #getLowElevationThreshold()
* @see #setLowElevationThreshold(double)
*/
@Override
public TroposphericDelay pathDelay(final TrackingCoordinates trackingCoordinates,
final GeodeticPoint point,
final PressureTemperatureHumidity weather,
final double[] parameters, final AbsoluteDate date) {
// limit the height to model range
final double fixedHeight = FastMath.min(FastMath.max(point.getAltitude(), X_VALUES_FOR_B[0]),
X_VALUES_FOR_B[X_VALUES_FOR_B.length - 1]);
final PressureTemperatureHumidity pth = converter.convert(weather, fixedHeight);
// interpolate the b correction term
final double B = B_FUNCTION.value(fixedHeight);
// calculate the zenith angle from the elevation
final double z = FastMath.abs(0.5 * FastMath.PI -
FastMath.max(trackingCoordinates.getElevation(), lowElevationThreshold));
// get correction factor
final double deltaR = getDeltaR(fixedHeight, z);
// calculate the path delay in m
// beware since version 12.1 pressures are in Pa and not in hPa, hence the scaling has changed
final double invCos = 1.0 / FastMath.cos(z);
final double tan = FastMath.tan(z);
final double zh = L0 * pth.getPressure();
final double zw = L0 * (T_NUM / pth.getTemperature() + WET_OFFSET) * pth.getWaterVaporPressure();
final double sh = zh * invCos;
final double sw = (zw - L0 * B * tan * tan) * invCos + deltaR;
return new TroposphericDelay(zh, zw, sh, sw);
}
/** {@inheritDoc}
* <p>
* The Saastamoinen model is not defined for altitudes below 0.0. for continuity
* reasons, we use the value for h = 0 when altitude is negative.
* </p>
* <p>
* There are also numerical issues for elevation angles close to zero. For continuity reasons,
* elevations lower than a threshold will use the value obtained
* for the threshold itself.
* </p>
* @see #getLowElevationThreshold()
* @see #setLowElevationThreshold(double)
*/
@Override
public <T extends CalculusFieldElement<T>> FieldTroposphericDelay<T> pathDelay(final FieldTrackingCoordinates<T> trackingCoordinates,
final FieldGeodeticPoint<T> point,
final FieldPressureTemperatureHumidity<T> weather,
final T[] parameters, final FieldAbsoluteDate<T> date) {
// limit the height to model range
final T fixedHeight = FastMath.min(FastMath.max(point.getAltitude(), X_VALUES_FOR_B[0]),
X_VALUES_FOR_B[X_VALUES_FOR_B.length - 1]);
final FieldPressureTemperatureHumidity<T> pth = converter.convert(weather, fixedHeight);
final Field<T> field = date.getField();
final T zero = field.getZero();
// interpolate the b correction term
final T B = B_FUNCTION.value(fixedHeight);
// calculate the zenith angle from the elevation
final T z = FastMath.abs(FastMath.max(trackingCoordinates.getElevation(),
zero.newInstance(lowElevationThreshold)).negate().
add(zero.getPi().multiply(0.5)));
// get correction factor
final T deltaR = getDeltaR(fixedHeight, z, field);
// calculate the path delay in m
// beware since version 12.1 pressures are in Pa and not in hPa, hence the scaling has changed
final T invCos = FastMath.cos(z).reciprocal();
final T tan = FastMath.tan(z);
final T zh = pth.getPressure().multiply(L0);
final T zw = pth.getTemperature().reciprocal().multiply(T_NUM).add(WET_OFFSET).
multiply(pth.getWaterVaporPressure()).multiply(L0);
final T sh = zh.multiply(invCos);
final T sw = zw.subtract(B.multiply(tan).multiply(tan).multiply(L0)).multiply(invCos).add(deltaR);
return new FieldTroposphericDelay<>(zh, zw, sh, sw);
}
/** Calculates the delta R correction term using linear interpolation.
* @param height the height of the station in m
* @param zenith the zenith angle of the satellite
* @return the delta R correction term in m
*/
private double getDeltaR(final double height, final double zenith) {
// limit the height to a range of [0, 5000] m
final double h = FastMath.min(FastMath.max(0, height), 5000);
// limit the zenith angle to 90 degree
// Note: the function is symmetric for negative zenith angles
final double z = FastMath.min(Math.abs(zenith), 0.5 * FastMath.PI);
return deltaRFunction.value(h, z);
}
/** Calculates the delta R correction term using linear interpolation.
* @param <T> type of the elements
* @param height the height of the station in m
* @param zenith the zenith angle of the satellite
* @param field field used by default
* @return the delta R correction term in m
*/
private <T extends CalculusFieldElement<T>> T getDeltaR(final T height, final T zenith,
final Field<T> field) {
final T zero = field.getZero();
// limit the height to a range of [0, 5000] m
final T h = FastMath.min(FastMath.max(zero, height), zero.add(5000));
// limit the zenith angle to 90 degree
// Note: the function is symmetric for negative zenith angles
final T z = FastMath.min(zenith.abs(), zero.getPi().multiply(0.5));
return deltaRFunction.value(h, z);
}
/** Load δR function.
* @param deltaRFileName regular expression for filename containing δR
* correction term table
* @param dataProvidersManager provides access to auxiliary data.
* @return δR function
*/
private static BilinearInterpolatingFunction loadDeltaR(
final String deltaRFileName,
final DataProvidersManager dataProvidersManager) {
// read the δR interpolation function from the config file
final InterpolationTableLoader loader = new InterpolationTableLoader();
dataProvidersManager.feed(deltaRFileName, loader);
if (!loader.stillAcceptsData()) {
final double[] elevations = loader.getOrdinateGrid();
for (int i = 0; i < elevations.length; ++i) {
elevations[i] = FastMath.toRadians(elevations[i]);
}
return new BilinearInterpolatingFunction(loader.getAbscissaGrid(), elevations,
loader.getValuesSamples());
}
throw new OrekitException(OrekitMessages.UNABLE_TO_FIND_FILE,
SECOND_DELTA_R_PATTERN.
matcher(FIRST_DELTA_R_PATTERN.matcher(deltaRFileName).replaceAll("")).
replaceAll(""));
}
/** Create the default δR function.
* @return δR function
*/
private static BilinearInterpolatingFunction defaultDeltaR() {
// the correction table in the referenced book only contains values for an angle of 60 - 80
// degree, thus for 0 degree, the correction term is assumed to be 0, for degrees > 80 it
// is assumed to be the same value as for 80.
// the height in m
final double[] xValForR = {
0, 500, 1000, 1500, 2000, 3000, 4000, 5000
};
// the zenith angle
final double[] yValForR = {
FastMath.toRadians( 0.00), FastMath.toRadians(60.00), FastMath.toRadians(66.00), FastMath.toRadians(70.00),
FastMath.toRadians(73.00), FastMath.toRadians(75.00), FastMath.toRadians(76.00), FastMath.toRadians(77.00),
FastMath.toRadians(78.00), FastMath.toRadians(78.50), FastMath.toRadians(79.00), FastMath.toRadians(79.50),
FastMath.toRadians(79.75), FastMath.toRadians(80.00), FastMath.toRadians(90.00)
};
final double[][] fval = new double[][] {
{
0.000, 0.003, 0.006, 0.012, 0.020, 0.031, 0.039, 0.050, 0.065, 0.075, 0.087, 0.102, 0.111, 0.121, 0.121
}, {
0.000, 0.003, 0.006, 0.011, 0.018, 0.028, 0.035, 0.045, 0.059, 0.068, 0.079, 0.093, 0.101, 0.110, 0.110
}, {
0.000, 0.002, 0.005, 0.010, 0.017, 0.025, 0.032, 0.041, 0.054, 0.062, 0.072, 0.085, 0.092, 0.100, 0.100
}, {
0.000, 0.002, 0.005, 0.009, 0.015, 0.023, 0.029, 0.037, 0.049, 0.056, 0.065, 0.077, 0.083, 0.091, 0.091
}, {
0.000, 0.002, 0.004, 0.008, 0.013, 0.021, 0.026, 0.033, 0.044, 0.051, 0.059, 0.070, 0.076, 0.083, 0.083
}, {
0.000, 0.002, 0.003, 0.006, 0.011, 0.017, 0.021, 0.027, 0.036, 0.042, 0.049, 0.058, 0.063, 0.068, 0.068
}, {
0.000, 0.001, 0.003, 0.005, 0.009, 0.014, 0.017, 0.022, 0.030, 0.034, 0.040, 0.047, 0.052, 0.056, 0.056
}, {
0.000, 0.001, 0.002, 0.004, 0.007, 0.011, 0.014, 0.018, 0.024, 0.028, 0.033, 0.039, 0.043, 0.047, 0.047
}
};
// the actual delta R is interpolated using a a bilinear interpolator
return new BilinearInterpolatingFunction(xValForR, yValForR, fval);
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.emptyList();
}
/** Get the low elevation threshold value for path delay computation.
* @return low elevation threshold, in rad.
* @see #pathDelay(TrackingCoordinates, GeodeticPoint, PressureTemperatureHumidity, double[], AbsoluteDate)
* @see #pathDelay(FieldTrackingCoordinates, FieldGeodeticPoint, FieldPressureTemperatureHumidity, CalculusFieldElement[], FieldAbsoluteDate)
* @since 10.2
*/
public double getLowElevationThreshold() {
return lowElevationThreshold;
}
/** Set the low elevation threshold value for path delay computation.
* @param lowElevationThreshold The new value for the threshold [rad]
* @see #pathDelay(TrackingCoordinates, GeodeticPoint, PressureTemperatureHumidity, double[], AbsoluteDate)
* @see #pathDelay(FieldTrackingCoordinates, FieldGeodeticPoint, FieldPressureTemperatureHumidity, CalculusFieldElement[], FieldAbsoluteDate)
* @since 10.2
*/
public void setLowElevationThreshold(final double lowElevationThreshold) {
this.lowElevationThreshold = lowElevationThreshold;
}
}