Merge pull request #55 from DLpadilla/altimetry

Altimetry

Author: AlexS12

src/pyfme/utils/altimetry.py

@@ -0,0 +1,65 @@
+"""
+Functions which transform geometric altitude into geopotential altitude, and
+vice versa.
+
+"""
+
+
+def geopotential2geometric(h):
+    """Geometric altiude above MSL (mean sea level)
+
+    This function transforms geopotential altitude into geometric altitude.
+
+    Parameters
+    ----------
+    h : float
+        Geopotential altitude above MSL (mean sea level) (m)
+    Returns
+    -------
+    z : float
+        Geometric altitude above MSL (mean sea level) (m)
+
+    See Also
+    --------
+    geopotential
+
+    References
+    ----------
+    .. [1] International Organization for Standardization, Standard Atmosphere,
+        ISO 2533:1975, 1975
+
+    """
+
+    Re = 6371000  # Mean radius Earth (m)
+    z = Re * h / (Re - h)
+    return z
+
+
+def geometric2geopotential(z):
+    """Geopotential altiude above MSL (mean sea level)
+
+    This function transforms geometric altitude into geopotential altitude.
+
+    Parameters
+    ----------
+    z : float
+        Geometric altitude above MSL (mean sea level) (m)
+    Returns
+    -------
+    h : float
+        Geopotential altitude above MSL (mean sea level) (m)
+
+    See Also
+    --------
+    geometric
+
+    References
+    ----------
+    .. [1] International Organization for Standardization, Standard Atmosphere,
+        ISO 2533:1975, 1975
+
+    """
+
+    Re = 6371000  # Mean radius Earth (m)
+    h = Re * z / (Re + z)
+    return h

src/pyfme/utils/tests/test_altimetry.py

@@ -0,0 +1,50 @@
+
+"""
+Tests of altimetry.
+"""
+
+from numpy.testing import (assert_almost_equal)
+import pytest
+
+from pyfme.utils.altimetry import (geopotential2geometric,
+                                   geometric2geopotential)
+
+
+def test1_geopotential2geometric():
+
+    h = 11000.0
+
+    z = geopotential2geometric(h)
+    expected_z = 11019.025157232705
+
+    assert_almost_equal(z, expected_z)
+
+
+def test2_geopotential2geometric():
+
+    h = 20000.0
+
+    z = geopotential2geometric(h)
+    expected_z = 20062.982207526373
+
+    assert_almost_equal(z, expected_z)
+
+
+def test1_geometric2geopotential():
+
+    z = 0.0
+
+    h = geometric2geopotential(z)
+    expected_h = 0.0
+
+    assert_almost_equal(h, expected_h)
+
+
+def test2_geometric2geopotential():
+
+    z = 86000.0
+
+    h = geometric2geopotential(z)
+    expected_h = 84854.57642868205
+
+    assert_almost_equal(h, expected_h)