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3    * contributor license agreements.  See the NOTICE file distributed with
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5    * CS licenses this file to You under the Apache License, Version 2.0
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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  package org.orekit.estimation.measurements.modifiers;
18  
19  import java.util.Collections;
20  import java.util.List;
21  
22  import org.orekit.estimation.measurements.EstimatedMeasurementBase;
23  import org.orekit.estimation.measurements.EstimationModifier;
24  import org.orekit.estimation.measurements.RangeRate;
25  import org.orekit.propagation.SpacecraftState;
26  import org.orekit.utils.Constants;
27  import org.orekit.utils.ParameterDriver;
28  
29  /** Class modifying theoretical range-rate measurement with relativistic frequency deviation.
30   * <p>
31   * Relativistic clock correction is caused by the motion of the satellite as well as
32   * the change in the gravitational potential
33   * </p>
34   * @author Bryan Cazabonne
35   * @since 10.3
36   *
37   * @see "Teunissen, Peter, and Oliver Montenbruck, eds. Springer handbook of global navigation
38   * satellite systems. Chapter 19.2. Springer, 2017."
39   */
40  public class RelativisticClockRangeRateModifier extends AbstractRelativisticClockModifier implements EstimationModifier<RangeRate> {
41  
42      /** Gravitational constant. */
43      private final double gm;
44  
45      /** Simple constructor.
46       * @param gm gravitational constant for main body in signal path vicinity.
47       */
48      public RelativisticClockRangeRateModifier(final double gm) {
49          super();
50          this.gm = gm;
51      }
52  
53      /** {@inheritDoc} */
54      @Override
55      public List<ParameterDriver> getParametersDrivers() {
56          return Collections.emptyList();
57      }
58  
59      /** {@inheritDoc} */
60      @Override
61      public void modifyWithoutDerivatives(final EstimatedMeasurementBase<RangeRate> estimated) {
62          // Spacecraft state
63          final SpacecraftState state = estimated.getStates()[0];
64  
65          // Relativistic frequency deviation
66          final double factor = -gm * getScaleFactor();
67          final double dfRel = factor *
68                          (reciprocal(state.getA()) - reciprocal(state.getPosition().getNorm()));
69  
70          // Update estimated value taking into account the relativistic effect.
71          final double[] newValue = estimated.getEstimatedValue().clone();
72          newValue[0] = newValue[0] + dfRel * Constants.SPEED_OF_LIGHT;
73          estimated.modifyEstimatedValue(this, newValue);
74      }
75  
76      /** Returns the inverse of the given value.
77       * @param value value to inverse
78       * @return the inverse of the value
79       */
80      private static double reciprocal(final double value) {
81          return 1.0 / value;
82      }
83  
84  }