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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,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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   * It works only with orbit-based states.
31   * <p>
32   * Relativistic clock correction is caused by the motion of the satellite as well as
33   * the change in the gravitational potential
34   * </p>
35   * @author Bryan Cazabonne
36   * @since 10.3
37   *
38   * @see "Teunissen, Peter, and Oliver Montenbruck, eds. Springer handbook of global navigation
39   * satellite systems. Chapter 19.2. Springer, 2017."
40   */
41  public class RelativisticClockRangeRateModifier extends AbstractRelativisticClockModifier implements EstimationModifier<RangeRate> {
42  
43      /** Gravitational constant. */
44      private final double gm;
45  
46      /** Simple constructor.
47       * @param gm gravitational constant for main body in signal path vicinity.
48       */
49      public RelativisticClockRangeRateModifier(final double gm) {
50          super();
51          this.gm = gm;
52      }
53  
54      /** {@inheritDoc} */
55      @Override
56      public List<ParameterDriver> getParametersDrivers() {
57          return Collections.emptyList();
58      }
59  
60      /** {@inheritDoc} */
61      @Override
62      public void modifyWithoutDerivatives(final EstimatedMeasurementBase<RangeRate> estimated) {
63          // Spacecraft state
64          final SpacecraftState state = estimated.getStates()[0];
65  
66          // Relativistic frequency deviation
67          final double factor = -gm * getScaleFactor();
68          final double dfRel = factor *
69                          (reciprocal(state.getOrbit().getA()) - reciprocal(state.getPosition().getNorm()));
70  
71          // Update estimated value taking into account the relativistic effect.
72          final double[] newValue = estimated.getEstimatedValue().clone();
73          newValue[0] = newValue[0] + dfRel * Constants.SPEED_OF_LIGHT;
74          estimated.modifyEstimatedValue(this, newValue);
75      }
76  
77      /** Returns the inverse of the given value.
78       * @param value value to inverse
79       * @return the inverse of the value
80       */
81      private static double reciprocal(final double value) {
82          return 1.0 / value;
83      }
84  
85  }