TidalDisplacement.java
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package org.orekit.models.earth.displacement;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.data.BodiesElements;
import org.orekit.data.PoissonSeries.CompiledSeries;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.IERSConventions;
import org.orekit.utils.PVCoordinatesProvider;
/**
* Modeling of displacement of reference points due to tidal effects.
* <p>
* This class implements displacement of reference point (i.e.
* {@link org.orekit.estimation.measurements.GroundStation ground stations})
* due to tidal effects, as per IERS conventions.
* </p>
* <p>
* Displacement can be computed with respect to either <em>conventional tide free</em>
* or <em>mean tide</em> coordinates. The difference between the two systems is
* about -12cm at poles and +6cm at equator. Selecting one system or the other
* depends on how the station coordinates have been computed (i.e. it depends
* whether the coordinates already include the permanent deformation or not).
* </p>
* <p>
* Instances of this class are guaranteed to be immutable
* </p>
* @see org.orekit.estimation.measurements.GroundStation
* @since 9.1
* @author Luc Maisonobe
*/
public class TidalDisplacement implements StationDisplacement {
/** Sun motion model. */
private final PVCoordinatesProvider sun;
/** Moon motion model. */
private final PVCoordinatesProvider moon;
/** Flag for permanent deformation. */
private final boolean removePermanentDeformation;
/** Ratio for degree 2 tide generated by Sun. */
private final double ratio2S;
/** Ratio for degree 3 tide generated by Sun. */
private final double ratio3S;
/** Ratio for degree 2 tide generated by Moon. */
private final double ratio2M;
/** Ratio for degree 3 tide generated by Moon. */
private final double ratio3M;
/** Displacement Shida number h⁽⁰⁾. */
private final double hSup0;
/** Displacement Shida number h⁽²⁾. */
private final double hSup2;
/** Displacement Shida number h₃. */
private final double h3;
/** Displacement Shida number hI diurnal. */
private final double hIDiurnal;
/** Displacement Shida number hI semi-diurnal. */
private final double hISemiDiurnal;
/** Displacement Love number l⁽⁰⁾. */
private final double lSup0;
/** Displacement Love number l⁽¹⁾ diurnal. */
private final double lSup1Diurnal;
/** Displacement Love number l⁽¹⁾ semi-diurnal. */
private final double lSup1SemiDiurnal;
/** Displacement Love number l⁽²⁾. */
private final double lSup2;
/** Displacement Love number l₃. */
private final double l3;
/** Displacement Love number lI diurnal. */
private final double lIDiurnal;
/** Displacement Love number lI semi-diurnal. */
private final double lISemiDiurnal;
/** Permanent deformation amplitude. */
private final double h0Permanent;
/** Function computing corrections in the frequency domain for diurnal tides.
* <ul>
* <li>f[0]: radial correction, longitude cosine part</li>
* <li>f[1]: radial correction, longitude sine part</li>
* <li>f[2]: North correction, longitude cosine part</li>
* <li>f[3]: North correction, longitude sine part</li>
* <li>f[4]: East correction, longitude cosine part</li>
* <li>f[5]: East correction, longitude sine part</li>
* </ul>
*/
private final CompiledSeries frequencyCorrectionDiurnal;
/** Function computing corrections in the frequency domain for zonal tides.
* <ul>
* <li>f[0]: radial correction</li>
* <li>f[1]: North correction, longitude cosine part</li>
* </ul>
*/
private final CompiledSeries frequencyCorrectionZonal;
/** Simple constructor.
* @param rEarth Earth equatorial radius (from gravity field model)
* @param sunEarthSystemMassRatio Sun/(Earth + Moon) mass ratio
* (typically {@link org.orekit.utils.Constants#JPL_SSD_SUN_EARTH_PLUS_MOON_MASS_RATIO Constants.JPL_SSD_SUN_EARTH_PLUS_MOON_MASS_RATIO})
* @param earthMoonMassRatio Earth/Moon mass ratio
* (typically {@link org.orekit.utils.Constants#JPL_SSD_EARTH_MOON_MASS_RATIO Constants.JPL_SSD_EARTH_MOON_MASS_RATIO})
* @param sun Sun model
* @param moon Moon model
* @param conventions IERS conventions to use
* @param removePermanentDeformation if true, the station coordinates are
* considered <em>mean tide</em> and already include the permanent deformation, hence
* it should be removed from the displacement to avoid considering it twice;
* if false, the station coordinates are considered <em>conventional tide free</em>
* so the permanent deformation must be included in the displacement
* @see org.orekit.frames.FramesFactory#getITRF(IERSConventions, boolean)
* @see org.orekit.frames.FramesFactory#getEOPHistory(IERSConventions, boolean)
* @see org.orekit.utils.Constants#JPL_SSD_SUN_EARTH_PLUS_MOON_MASS_RATIO
* @see org.orekit.utils.Constants#JPL_SSD_EARTH_MOON_MASS_RATIO
*/
public TidalDisplacement(final double rEarth,
final double sunEarthSystemMassRatio,
final double earthMoonMassRatio,
final PVCoordinatesProvider sun, final PVCoordinatesProvider moon,
final IERSConventions conventions,
final boolean removePermanentDeformation) {
final double sunEarthMassRatio = sunEarthSystemMassRatio * (1 + 1 / earthMoonMassRatio);
final double moonEarthMassRatio = 1.0 / earthMoonMassRatio;
this.sun = sun;
this.moon = moon;
this.removePermanentDeformation = removePermanentDeformation;
final double r2 = rEarth * rEarth;
final double r4 = r2 * r2;
this.ratio2S = r4 * sunEarthMassRatio;
this.ratio3S = ratio2S * rEarth;
this.ratio2M = r4 * moonEarthMassRatio;
this.ratio3M = ratio2M * rEarth;
// Get the nominal values for the Love and Shiva numbers
final double[] hl = conventions.getNominalTidalDisplacement();
hSup0 = hl[ 0];
hSup2 = hl[ 1];
h3 = hl[ 2];
hIDiurnal = hl[ 3];
hISemiDiurnal = hl[ 4];
lSup0 = hl[ 5];
lSup1Diurnal = hl[ 6];
lSup1SemiDiurnal = hl[ 7];
lSup2 = hl[ 8];
l3 = hl[ 9];
lIDiurnal = hl[10];
lISemiDiurnal = hl[11];
h0Permanent = hl[12];
this.frequencyCorrectionDiurnal = conventions.getTidalDisplacementFrequencyCorrectionDiurnal();
this.frequencyCorrectionZonal = conventions.getTidalDisplacementFrequencyCorrectionZonal();
}
/** {@inheritDoc} */
@Override
public Vector3D displacement(final BodiesElements elements, final Frame earthFrame, final Vector3D referencePoint) {
final AbsoluteDate date = elements.getDate();
// preliminary computation (we hold everything in local variables so method is thread-safe)
final PointData pointData = new PointData(referencePoint);
final Vector3D sunPosition = sun.getPosition(date, earthFrame);
final BodyData sunData = new BodyData(sunPosition, ratio2S, ratio3S, pointData);
final Vector3D moonPosition = moon.getPosition(date, earthFrame);
final BodyData moonData = new BodyData(moonPosition, ratio2M, ratio3M, pointData);
// step 1 in IERS procedure: corrections in the time domain
Vector3D displacement = timeDomainCorrection(pointData, sunData, moonData);
// step 2 in IERS procedure: corrections in the frequency domain
displacement = displacement.add(frequencyDomainCorrection(elements, pointData));
if (removePermanentDeformation) {
// the station coordinates already include permanent deformation,
// so it should not be included in the displacement that will be
// added to these coordinates to avoid considering this deformation twice
// as step 1 did include permanent deformation, we remove it here
displacement = displacement.subtract(permanentDeformation(pointData));
}
return displacement;
}
/** Compute the corrections in the time domain (step 1 in IERS procedure).
* @param pointData reference point data
* @param sunData Sun data
* @param moonData Moon data
* @return displacement of the reference point
*/
private Vector3D timeDomainCorrection(final PointData pointData,
final BodyData sunData, final BodyData moonData) {
final double h2 = hSup0 + hSup2 * pointData.f;
final double l2 = lSup0 + lSup2 * pointData.f;
// in-phase, degree 2 (equation 7.5 in IERS conventions 2010)
final double s2R = sunData.factor2 * 3.0 * l2 * sunData.dot;
final double s2r = sunData.factor2 * 0.5 * h2 * (3 * sunData.dot2 - 1) - s2R * sunData.dot;
final double m2R = moonData.factor2 * 3.0 * l2 * moonData.dot;
final double m2r = moonData.factor2 * 0.5 * h2 * (3 * moonData.dot2 - 1) - m2R * moonData.dot;
// in-phase, degree 3 (equation 7.6 in IERS conventions 2010)
final double s3R = sunData.factor3 * l3 * (7.5 * sunData.dot2 - 1.5);
final double s3r = sunData.factor3 * h3 * sunData.dot * (2.5 * sunData.dot2 - 1.5) - s3R * sunData.dot;
final double m3R = moonData.factor3 * l3 * (7.5 * moonData.dot2 - 1.5);
final double m3r = moonData.factor3 * h3 * moonData.dot * (2.5 * moonData.dot2 - 1.5) - m3R * moonData.dot;
// combine contributions along radial, Sun and Moon directions
final Vector3D inPhaseDisplacement = new Vector3D(s2r + m2r + s3r + m3r, pointData.radial,
(s2R + s3R) / sunData.r, sunData.position,
(m2R + m3R) / moonData.r, moonData.position);
// out-of-phase, degree 2, diurnal tides (equations 7.10a and 7.10b in IERS conventions 2010)
final double drOd = -0.75 * hIDiurnal * pointData.sin2Phi *
(sunData.factor2 * sunData.sin2Phi * sunData.sinDeltaLambda +
moonData.factor2 * moonData.sin2Phi * moonData.sinDeltaLambda);
final double dnOd = -1.5 * lIDiurnal * pointData.cos2Phi *
(sunData.factor2 * sunData.sin2Phi * sunData.sinDeltaLambda +
moonData.factor2 * moonData.sin2Phi * moonData.sinDeltaLambda);
final double deOd = -1.5 * lIDiurnal * pointData.sinPhi *
(sunData.factor2 * sunData.sin2Phi * sunData.cosDeltaLambda +
moonData.factor2 * moonData.sin2Phi * moonData.cosDeltaLambda);
// out-of-phase, degree 2, semi-diurnal tides (equation 7.11 in IERS conventions 2010)
final double drOsd = -0.75 * hISemiDiurnal * pointData.cosPhi2 *
(sunData.factor2 * sunData.cosPhi2 * sunData.sin2DeltaLambda +
moonData.factor2 * moonData.cosPhi2 * moonData.sin2DeltaLambda);
final double dnOsd = 0.75 * lISemiDiurnal * pointData.sin2Phi *
(sunData.factor2 * sunData.cosPhi2 * sunData.sin2DeltaLambda +
moonData.factor2 * moonData.cosPhi2 * moonData.sin2DeltaLambda);
final double deOsd = -1.5 * lISemiDiurnal * pointData.cosPhi *
(sunData.factor2 * sunData.cosPhi2 * sunData.cos2DeltaLambda +
moonData.factor2 * moonData.cosPhi2 * moonData.cos2DeltaLambda);
// latitude dependency, diurnal tides (equation 7.8 in IERS conventions 2010)
final double dnLd = -lSup1Diurnal * pointData.sinPhi2 *
(sunData.factor2 * sunData.p21 * sunData.cosDeltaLambda +
moonData.factor2 * moonData.p21 * moonData.cosDeltaLambda);
final double deLd = lSup1Diurnal * pointData.sinPhi * pointData.cos2Phi *
(sunData.factor2 * sunData.p21 * sunData.sinDeltaLambda +
moonData.factor2 * moonData.p21 * moonData.sinDeltaLambda);
// latitude dependency, semi-diurnal tides (equation 7.9 in IERS conventions 2010)
final double dnLsd = -0.25 * lSup1SemiDiurnal * pointData.sin2Phi *
(sunData.factor2 * sunData.p22 * sunData.cos2DeltaLambda +
moonData.factor2 * moonData.p22 * moonData.cos2DeltaLambda);
final double deLsd = -0.25 * lSup1SemiDiurnal * pointData.sin2Phi * pointData.sinPhi *
(sunData.factor2 * sunData.p22 * sunData.sin2DeltaLambda +
moonData.factor2 * moonData.p22 * moonData.sin2DeltaLambda);
// combine diurnal and semi-diurnal tides
final Vector3D outOfPhaseDisplacement = new Vector3D(drOd + drOsd, pointData.radial,
dnOd + dnOsd + dnLd + dnLsd, pointData.north,
deOd + deOsd + deLd + deLsd, pointData.east);
return inPhaseDisplacement.add(outOfPhaseDisplacement);
}
/** Compute the corrections in the frequency domain (step 2 in IERS procedure).
* @param elements elements affecting Earth orientation
* @param pointData reference point data
* @return displacement of the reference point
*/
private Vector3D frequencyDomainCorrection(final BodiesElements elements, final PointData pointData) {
// corrections due to diurnal tides
final double[] cD = frequencyCorrectionDiurnal.value(elements);
final double drD = pointData.sin2Phi * (cD[0] * pointData.cosLambda + cD[1] * pointData.sinLambda);
final double dnD = pointData.cos2Phi * (cD[2] * pointData.cosLambda + cD[3] * pointData.sinLambda);
final double deD = pointData.sinPhi * (cD[4] * pointData.cosLambda + cD[5] * pointData.sinLambda);
// corrections due to zonal long period tides
final double[] cZ = frequencyCorrectionZonal.value(elements);
final double drZ = (1.5 * pointData.sinPhi2 - 0.5) * cZ[0];
final double dnZ = pointData.sin2Phi * cZ[1];
return new Vector3D(drD + drZ, pointData.radial,
dnD + dnZ, pointData.north,
deD, pointData.east);
}
/** Compute the permanent part of the deformation.
* @param pointData reference point data
* @return displacement of the reference point
*/
private Vector3D permanentDeformation(final PointData pointData) {
final double h2 = hSup0 + hSup2 * pointData.f;
final double l2 = lSup0 + lSup2 * pointData.f;
// permanent deformation, which depend only on latitude
final double factor = FastMath.sqrt(1.25 / FastMath.PI);
final double dr = factor * h2 * h0Permanent * pointData.f;
final double dn = factor * 1.5 * l2 * h0Permanent * pointData.sin2Phi;
return new Vector3D(dr, pointData.radial,
dn, pointData.north);
}
/** Holder for various intermediate data related to reference point. */
private static class PointData {
/** Reference point position in {@link #getEarthFrame() Earth frame}. */
private final Vector3D position;
/** Distance to geocenter. */
private final double r;
/** Sine of geocentric latitude (NOT geodetic latitude). */
private final double sinPhi;
/** Cosine of geocentric latitude (NOT geodetic latitude). */
private final double cosPhi;
/** Square of the sine of the geocentric latitude (NOT geodetic latitude). */
private final double sinPhi2;
/** Square of the cosine of the geocentric latitude (NOT geodetic latitude). */
private final double cosPhi2;
/** Sine of twice the geocentric latitude (NOT geodetic latitude). */
private final double sin2Phi;
/** Cosine of twice the geocentric latitude (NOT geodetic latitude). */
private final double cos2Phi;
/** Sine of longitude. */
private final double sinLambda;
/** Cosine of longitude. */
private final double cosLambda;
/** Unit radial vector (NOT zenith as it starts from geocenter). */
private final Vector3D radial;
/** Unit vector in North direction. */
private final Vector3D north;
/** Unit vector in East direction. */
private final Vector3D east;
/** (3 sin²φ - 1) / 2 where φ is geoCENTRIC latitude of the reference point (NOT geodetic latitude). */
private final double f;
/** Simple constructor.
* @param position reference point position in {@link #getEarthFrame() Earth frame}
*/
PointData(final Vector3D position) {
this.position = position;
final double x = position.getX();
final double y = position.getY();
final double z = position.getZ();
final double x2 = x * x;
final double y2 = y * y;
final double z2 = z * z;
// preliminary computation related to station position
final double rho2 = x2 + y2;
final double rho = FastMath.sqrt(rho2);
final double r2 = rho2 + z2;
r = FastMath.sqrt(r2);
sinPhi = z / r;
cosPhi = rho / r;
sinPhi2 = sinPhi * sinPhi;
cosPhi2 = cosPhi * cosPhi;
sin2Phi = 2 * sinPhi * cosPhi;
cos2Phi = cosPhi2 - sinPhi2;
if (rho == 0.0) {
// at pole
sinLambda = 0.0;
cosLambda = 1.0;
} else {
// regular point
sinLambda = y / rho;
cosLambda = x / rho;
}
radial = new Vector3D(x / r, y / r, sinPhi);
north = new Vector3D(-cosLambda * sinPhi, -sinLambda * sinPhi, cosPhi);
east = new Vector3D(-sinLambda, cosLambda, 0);
// (3 sin²φ - 1) / 2 where φ is geoCENTRIC latitude of the reference point (NOT geodetic latitude)
f = (z2 - 0.5 * rho2) / r2;
}
}
/** Holder for various intermediate data related to tide generating body. */
private static class BodyData {
/** Body position in Earth frame. */
private final Vector3D position;
/** Distance to geocenter. */
private final double r;
/** Dot product with reference point direction. */
private final double dot;
/** Squared dot product with reference point direction. */
private final double dot2;
/** Factor for degree 2 tide. */
private final double factor2;
/** Factor for degree 3 tide. */
private final double factor3;
/** Square of the cosine of the geocentric latitude (NOT geodetic latitude). */
private final double cosPhi2;
/** Sine of twice the geocentric latitude (NOT geodetic latitude). */
private final double sin2Phi;
/** Legendre function P₂¹. */
private final double p21;
/** Legendre function P₂². */
private final double p22;
/** Sine of the longitude difference with reference point. */
private final double sinDeltaLambda;
/** Cosine of the longitude difference with reference point. */
private final double cosDeltaLambda;
/** Sine of twice the longitude difference with reference point. */
private final double sin2DeltaLambda;
/** Cosine of twice the longitude difference with reference point. */
private final double cos2DeltaLambda;
/** Simple constructor.
* @param position body position in Earth frame
* @param ratio2 ratio for the degree 2 tide generated by this body
* @param ratio3 ratio for the degree 3 tide generated by this body
* @param pointData reference point data
*/
BodyData(final Vector3D position, final double ratio2, final double ratio3,
final PointData pointData) {
final double x = position.getX();
final double y = position.getY();
final double z = position.getZ();
final double x2 = x * x;
final double y2 = y * y;
final double z2 = z * z;
this.position = position;
final double r2 = x2 + y2 + z2;
r = FastMath.sqrt(r2);
dot = Vector3D.dotProduct(position, pointData.position) / (r * pointData.r);
dot2 = dot * dot;
factor2 = ratio2 / (r2 * r);
factor3 = ratio3 / (r2 * r2);
final double rho = FastMath.sqrt(x2 + y2);
final double sinPhi = z / r;
final double cosPhi = rho / r;
final double sinCos = sinPhi * cosPhi;
cosPhi2 = cosPhi * cosPhi;
sin2Phi = 2 * sinCos;
p21 = 3 * sinCos;
p22 = 3 * cosPhi2;
final double sinLambda = y / rho;
final double cosLambda = x / rho;
sinDeltaLambda = pointData.sinLambda * cosLambda - pointData.cosLambda * sinLambda;
cosDeltaLambda = pointData.cosLambda * cosLambda + pointData.sinLambda * sinLambda;
sin2DeltaLambda = 2 * sinDeltaLambda * cosDeltaLambda;
cos2DeltaLambda = cosDeltaLambda * cosDeltaLambda - sinDeltaLambda * sinDeltaLambda;
}
}
}