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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
10   *
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.List;
20  
21  import org.hipparchus.CalculusFieldElement;
22  import org.orekit.estimation.measurements.GroundStation;
23  import org.orekit.frames.TopocentricFrame;
24  import org.orekit.models.earth.ionosphere.IonosphericModel;
25  import org.orekit.propagation.FieldSpacecraftState;
26  import org.orekit.propagation.SpacecraftState;
27  import org.orekit.utils.ParameterDriver;
28  
29  /** Base class modifying theoretical range-rate measurement with ionospheric delay.
30   * The effect of ionospheric correction on the range-rate is directly computed
31   * through the computation of the ionospheric delay difference with respect to
32   * time.
33   *
34   * The ionospheric delay depends on the frequency of the signal (GNSS, VLBI, ...).
35   * For optical measurements (e.g. SLR), the ray is not affected by ionosphere charged particles.
36   * <p>
37   * Since 10.0, state derivatives and ionospheric parameters derivates are computed
38   * using automatic differentiation.
39   * </p>
40   * @author Joris Olympio
41   * @since 11.2
42   */
43  public abstract class BaseRangeRateIonosphericDelayModifier {
44  
45      /** Ionospheric delay model. */
46      private final IonosphericModel ionoModel;
47  
48      /** Frequency [Hz]. */
49      private final double frequency;
50  
51      /** Constructor.
52       *
53       * @param model Ionospheric delay model appropriate for the current range-rate measurement method.
54       * @param freq frequency of the signal in Hz
55       */
56      protected BaseRangeRateIonosphericDelayModifier(final IonosphericModel model, final double freq) {
57          this.ionoModel = model;
58          this.frequency = freq;
59      }
60  
61      /** Get the ionospheric delay model.
62       * @return ionospheric delay model
63       */
64      protected IonosphericModel getIonoModel() {
65          return ionoModel;
66      }
67  
68      /** Compute the measurement error due to Ionosphere.
69       * @param station station
70       * @param state spacecraft state
71       * @return the measurement error due to Ionosphere
72       */
73      protected double rangeRateErrorIonosphericModel(final GroundStation station, final SpacecraftState state) {
74          final double dt = 10; // s
75          // Base frame associated with the station
76          final TopocentricFrame baseFrame = station.getBaseFrame();
77          // delay in meters
78          final double delay1 = ionoModel.pathDelay(state, baseFrame, frequency, ionoModel.getParameters(state.getDate()));
79          // propagate spacecraft state forward by dt
80          final SpacecraftState state2 = state.shiftedBy(dt);
81          // ionospheric delay dt after in meters
82          final double delay2 = ionoModel.pathDelay(state2, baseFrame, frequency, ionoModel.getParameters(state.getDate()));
83          // delay in meters
84          return (delay2 - delay1) / dt;
85      }
86  
87      /** Compute the measurement error due to Ionosphere.
88       * @param <T> type of the elements
89       * @param station station
90       * @param state spacecraft state
91       * @param parameters ionospheric model parameters
92       * @return the measurement error due to Ionosphere
93       */
94      protected <T extends CalculusFieldElement<T>> T rangeRateErrorIonosphericModel(final GroundStation station,
95                                                                                     final FieldSpacecraftState<T> state,
96                                                                                     final T[] parameters) {
97          final double dt = 10; // s
98          // Base frame associated with the station
99          final TopocentricFrame baseFrame = station.getBaseFrame();
100         // delay in meters
101         final T delay1 = ionoModel.pathDelay(state, baseFrame, frequency, parameters);
102         // propagate spacecraft state forward by dt
103         final FieldSpacecraftState<T> state2 = state.shiftedBy(dt);
104         // ionospheric delay dt after in meters
105         final T delay2 = ionoModel.pathDelay(state2, baseFrame, frequency, parameters);
106         // delay in meters
107         return delay2.subtract(delay1).divide(dt);
108     }
109 
110     /** Get the drivers for this modifier parameters.
111      * @return drivers for this modifier parameters
112      */
113     public List<ParameterDriver> getParametersDrivers() {
114         return ionoModel.getParametersDrivers();
115     }
116 
117 }