1   /* Copyright 2002-2025 CS GROUP
2    * Licensed to CS GROUP (CS) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * CS licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
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,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.orekit.models.earth.atmosphere;
18  
19  import org.hipparchus.CalculusFieldElement;
20  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
21  import org.hipparchus.geometry.euclidean.threed.Vector3D;
22  import org.hipparchus.util.FastMath;
23  import org.orekit.bodies.BodyShape;
24  import org.orekit.bodies.FieldGeodeticPoint;
25  import org.orekit.bodies.GeodeticPoint;
26  import org.orekit.frames.Frame;
27  import org.orekit.time.AbsoluteDate;
28  import org.orekit.time.FieldAbsoluteDate;
29  
30  
31  /** Simple exponential atmospheric model.
32   * <p>This model represents a simple atmosphere with an exponential
33   * density and rigidly bound to the underlying rotating body.</p>
34   * @author Fabien Maussion
35   * @author Luc Maisonobe
36   */
37  public class SimpleExponentialAtmosphere implements Atmosphere {
38  
39      /** Earth shape model. */
40      private BodyShape    shape;
41  
42      /** Reference density. */
43      private double       rho0;
44  
45      /** Reference altitude. */
46      private double       h0;
47  
48      /** Reference altitude scale. */
49      private double       hscale;
50  
51      /** Create an exponential atmosphere.
52       * @param shape body shape model
53       * @param rho0 Density at the altitude h0
54       * @param h0 Altitude of reference (m)
55       * @param hscale Scale factor
56       */
57      public SimpleExponentialAtmosphere(final BodyShape shape, final double rho0,
58                                         final double h0, final double hscale) {
59          this.shape  = shape;
60          this.rho0   = rho0;
61          this.h0     = h0;
62          this.hscale = hscale;
63      }
64  
65      /** {@inheritDoc} */
66      public Frame getFrame() {
67          return shape.getBodyFrame();
68      }
69  
70      /** {@inheritDoc} */
71      public double getDensity(final AbsoluteDate date, final Vector3D position, final Frame frame) {
72          final GeodeticPoint gp = shape.transform(position, frame, date);
73          return rho0 * FastMath.exp((h0 - gp.getAltitude()) / hscale);
74      }
75  
76      @Override
77      public <T extends CalculusFieldElement<T>> T
78          getDensity(final FieldAbsoluteDate<T> date, final FieldVector3D<T> position,
79                     final Frame frame) {
80          final FieldGeodeticPoint<T> gp = shape.transform(position, frame, date);
81          return gp.getAltitude().subtract(h0).divide(-hscale).exp().multiply(rho0);
82      }
83  
84  }