add an extended version of iem. Still siplier than AIEM but better th…

…an IEM Fung 92

smrt/interface/iem_fung92_brogioni10.py

@@ -0,0 +1,38 @@
+
+
+"""
+Implement the interface boundary condition under IEM formulation provided by Fung et al. 1992. in IEEE TGRS 
+with an extended domain of validity (for large roughness or correlation length) by switching the Fresnel 
+coefficients according to Briogoni et al. 2010, IJRS. A better but more complex approach is given by Wu et al. 2003 (to be implemented)
+
+
+Use of this code requires special attention
+
+"""
+
+import numpy as np
+
+from smrt.core.fresnel import fresnel_coefficients
+from smrt.interface.iem_fung92 import IEM_Fung92
+from smrt.core.error import SMRTError
+
+
+class IEM_Fung92_Briogoni10(IEM_Fung92):
+    """A moderate rough surface model with backscatter, specular reflection and transmission only. Use with care!
+
+"""
+
+    def check_validity(self, ks, kl, eps_r):
+
+        # check validity
+        if ks > 3:
+            raise SMRTError("Warning, roughness_rms is too high for the given wavelength. Limit is ks < 3. Here ks=%g" % ks)
+
+    def fresnel_coefficients(self, eps_1, eps_2, mu_i, ks, kl):
+        """calculate the fresnel coefficients at the angle mu_i or 0° depending on ks*kl. The transition is abrupt."""
+
+        if ks * kl > np.sqrt(eps_2 / eps_1):
+            Rv, Rh, _ = fresnel_coefficients(eps_1, eps_2, 1)
+        else:
+            Rv, Rh, _ = fresnel_coefficients(eps_1, eps_2, mu_i)
+        return Rv, Rh

smrt/interface/test_iem_fung92_brogioni10.py

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+
+import numpy as np
+from smrt.interface.iem_fung92_brogioni10 import IEM_Fung92_Briogoni10
+from smrt.interface.iem_fung92 import IEM_Fung92
+from smrt.utils import dB
+
+def test_iem_fung92_biogoni10_continuty():
+
+    eps_r = 3 + 0.1j
+
+    iem_fung = IEM_Fung92(roughness_rms=0.429e-2, corr_length=3e-2)
+    iem_fung_brogioni = IEM_Fung92_Briogoni10(roughness_rms=0.429e-2, corr_length=3e-2)
+
+    frequency = 2.2e9
+
+    mu = np.cos(np.deg2rad([30, 50, 60]))
+
+    R = iem_fung.diffuse_reflection_matrix(frequency, 1, eps_r, mu, mu, np.pi, 2, debug=True)
+
+    R2 = iem_fung_brogioni.diffuse_reflection_matrix(frequency, 1, eps_r, mu, mu, np.pi, 2, debug=True)
+
+    sigma_vv = dB(4*np.pi * mu * R[0])
+    sigma_hh = dB(4*np.pi * mu * R[1])
+
+    sigma_vv2 = dB(4*np.pi * mu * R2[0])
+    sigma_hh2 = dB(4*np.pi * mu * R2[1])
+
+    assert np.allclose(sigma_vv, sigma_vv2)
+    assert np.allclose(sigma_hh, sigma_hh2)
+
+
+
+def test_iem_fung92_brogioni10():
+
+    eps_r = 3 + 0.1j
+
+    iem_fung = IEM_Fung92_Briogoni10(roughness_rms=0.429e-2, corr_length=30e-2)
+
+    frequency = 2.2e9
+
+    mu = np.cos(np.deg2rad([30, 50, 60]))
+
+    R = iem_fung.diffuse_reflection_matrix(frequency, 1, eps_r, mu, mu, np.pi, 2, debug=True)
+    sigma_vv = dB(4*np.pi * mu * R[0])
+    sigma_hh = dB(4*np.pi * mu * R[1])
+
+    print(sigma_vv)
+    print(sigma_hh)
+
+    assert np.all(np.abs(sigma_vv - [-25.8475821, -28.09794986, -27.1320767 ]) < 1e-2)
+    assert np.all(np.abs(sigma_hh - [-31.30415086, -40.67474292, -29.06341978]) < 1e-2)

smrt/substrate/iem_fung92_brogioni10.py

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+# coding: utf-8
+
+
+"""
+Implement the flat interface boundary for the bottom layer (substrate). The reflection and transmission
+are computed using the Fresnel coefficients. This model does not take any specific parameter.
+
+"""
+
+# local import
+from smrt.interface.iem_fung92_brogioni10 import IEM_Fung92_Briogoni10 as iIEM_Fung92_Briogoni10
+from smrt.core.interface import substrate_from_interface
+
+# autogenerate from interface.Flat
+@substrate_from_interface(iIEM_Fung92_Briogoni10)
+class IEM_Fung92_Briogoni10:
+    pass