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9    *   http://www.apache.org/licenses/LICENSE-2.0
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11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
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14   * See the License for the specific language governing permissions and
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17  
18  package org.orekit.estimation.measurements.modifiers;
19  
20  import java.util.Collections;
21  import java.util.List;
22  
23  import org.orekit.estimation.measurements.EstimatedMeasurementBase;
24  import org.orekit.estimation.measurements.EstimationModifier;
25  import org.orekit.estimation.measurements.gnss.InterSatellitesPhase;
26  import org.orekit.utils.Constants;
27  import org.orekit.utils.ParameterDriver;
28  
29  /**
30   * Class modifying theoretical inter-satellites phase measurements with relativistic J2 clock correction.
31   * <p>
32   * Relativistic clock correction of the effects caused by the oblateness of Earth on
33   * the gravity potential.
34   * </p>
35   * <p>
36   * The time delay caused by this effect is computed based on the orbital parameters of the
37   * emitter's orbit.
38   * </p>
39   *
40   * @author Louis Aucouturier
41   * @since 11.2
42   *
43   * @see "Teunissen, Peter, and Oliver Montenbruck, eds. Springer handbook of global navigation
44   * satellite systems. Chapter 19.2. Equation 19.18 Springer, 2017."
45   */
46  public class RelativisticJ2ClockInterSatellitesPhaseModifier extends AbstractRelativisticJ2ClockModifier implements EstimationModifier<InterSatellitesPhase> {
47  
48      /**
49       * Modifier constructor.
50       * @param gm Earth gravitational constant (mu) in m³/s².
51       * @param c20 Earth un-normalized second zonal coefficient (Signed J2 constant, is negative) (Typical value -1.0826e-3).
52       * @param equatorialRadius Earth equatorial radius in m.
53       */
54      public RelativisticJ2ClockInterSatellitesPhaseModifier(final double gm,
55                                                             final double c20,
56                                                             final double equatorialRadius) {
57          super(gm, c20, equatorialRadius);
58      }
59  
60  
61      /** {@inheritDoc} */
62      @Override
63      public List<ParameterDriver> getParametersDrivers() {
64          return Collections.emptyList();
65      }
66  
67      /** {@inheritDoc} */
68      @Override
69      public void modifyWithoutDerivatives(final EstimatedMeasurementBase<InterSatellitesPhase> estimated) {
70          // Relativistic clock correction
71          final double dtJ2 = relativisticJ2Correction(estimated);
72  
73          // Wavelength
74          final double wavelength = estimated.getObservedMeasurement().getWavelength();
75  
76          // Update estimated value taking into account the relativistic effect.
77          final double   cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
78          final double[] newValue = estimated.getEstimatedValue().clone();
79          newValue[0] = newValue[0] - dtJ2 * cOverLambda;
80          estimated.modifyEstimatedValue(this, newValue);
81      }
82  
83  }