#30 pep8 and docs cmod5n code

nansencenter · Feb 5, 2018 · e116abf · e116abf
1 parent 1a70051
commit e116abf
Showing 1 changed file with 32 additions and 27 deletions.
diff --git a/openwind/cmod5n.py b/openwind/cmod5n.py
@@ -1,7 +1,14 @@
-from numpy import cos, exp, tanh
+from numpy import cos, exp, tanh, ones, array
 import warnings
 # Ignore overflow errors for wind calculations over land
-warnings.simplefilter("ignore", RuntimeWarning) 
+warnings.simplefilter("ignore", RuntimeWarning)
+
+# CMOD5.N model coefficients
+# https://www.ecmwf.int/en/elibrary/9873-cmod5n-c-band-geophysical-model-function-equivalent-neutral-wind
+# NB: 0 added as first element below, to avoid switching from 1-indexing to 0-indexing
+C = [0, -0.6878, -0.7957, 0.3380, -0.1728, 0.0000, 0.0040, 0.1103, 0.0159, 6.7329, 2.7713,
+     -2.2885, 0.4971, -0.7250, 0.0450, 0.0066, 0.3222, 0.0120, 22.7000, 2.0813, 3.0000,
+     8.3659, -3.3428, 1.3236, 6.2437, 2.3893, 0.3249, 4.1590, 1.6930]
 
 
 def cmod5n_forward(v, phi, theta):
@@ -15,8 +22,15 @@ def cmod5n_forward(v, phi, theta):
             2D array with incidence angles in [deg]
 
     Returns:
-        cmod_n:
-            Normalized backscatter (linear)
+        cmod_n: float, numpy.array
+            2D array with normalized backscatter (linear)
+
+    The CMOD5 Model Formulation and Coefficients were published in:
+    H. Hersbach, A. Stoffelen, and S. de Haan. 2007. An improved C-band scatterometer ocean
+    geophysical model function: CMOD5. Journal of Geophysical Research, Vol. 112, C03006,
+    doi:10.1029/2006JC003743
+
+    Access: http://onlinelibrary.wiley.com/doi/10.1029/2006JC003743/full
 
     A. STOFFELEN              MAY  1991 ECMWF  CMOD4
     A. STOFFELEN, S. DE HAAN  DEC  2001 KNMI   CMOD5 PROTOTYPE
@@ -30,32 +44,26 @@ def cmod5n_forward(v, phi, theta):
     THETM = 40.
     THETHR = 25.
     ZPOW = 1.6
-
-    # NB: 0 added as first element below, to avoid switching from 1-indexing to 0-indexing
-    C = [0, -0.6878, -0.7957,  0.3380, -0.1728, 0.0000,  0.0040, 0.1103, 0.0159, 6.7329,  2.7713,
-         -2.2885, 0.4971, -0.7250, 0.0450,  0.0066,  0.3222,  0.0120, 22.7000, 2.0813,  3.0000,
-         8.3659,  -3.3428,  1.3236,  6.2437,  2.3893, 0.3249,  4.1590, 1.6930]
 
     Y0 = C[19]
     PN = C[20]
-    A = C[19] - (C[19] - 1) / C[20]
 
+    A = C[19] - (C[19] - 1) / C[20]
     B = 1. / (C[20] * (C[19] - 1.) ** (3-1))
 
     # ANGLES
     FI = phi/DTOR
     CSFI = cos(FI)
-    CS2FI = 2.00 * CSFI * CSFI - 1.00
+    CS2FI = 2.0 * CSFI * CSFI - 1.0
 
     X = (theta - THETM) / THETHR
-    XX = X * X
 
     # B0: FUNCTION OF WIND SPEED AND INCIDENCE ANGLE
-    A0 = C[1] + C[2] * X + C[3] * XX + C[4] * X * XX
+    A0 = C[1] + C[2] * X + C[3] * (X ** 2) + C[4] * (X ** 3)
     A1 = C[5] + C[6] * X
     A2 = C[7] + C[8] * X
 
-    GAM = C[9] + C[10] * X + C[11] * XX
+    GAM = C[9] + C[10] * X + C[11] * (X ** 2)
     S0 = C[12] + C[13] * X
 
     # V is missing! Using V=v as substitute, this is apparently correct
@@ -67,7 +75,6 @@ def cmod5n_forward(v, phi, theta):
     A3 = 1. / (1. + exp(-S_vec))
     SlS0 = (S < S0)
     A3[SlS0] = A3[SlS0] * (S[SlS0] / S0[SlS0]) ** (S0[SlS0] * (1. - A3[SlS0]))
-    #A3=A3*(S/S0)**( S0*(1.- A3))
     B0 = (A3 ** GAM) * 10. ** (A0 + A1 * V)
 
     # B1: FUNCTION OF WIND SPEED AND INCIDENCE ANGLE
@@ -76,8 +83,8 @@ def cmod5n_forward(v, phi, theta):
     B1 = B1 / (exp(0.34 * (V - C[18])) + 1.)
 
     # B2: FUNCTION OF WIND SPEED AND INCIDENCE ANGLE
-    V0 = C[21] + C[22] * X + C[23] * XX
-    D1 = C[24] + C[25] * X + C[26] * XX
+    V0 = C[21] + C[22] * X + C[23] * (X ** 2)
+    D1 = C[24] + C[25] * X + C[26] * (X ** 2)
     D2 = C[27] + C[28] * X
 
     V2 = (V / V0 + 1.)
@@ -86,9 +93,9 @@ def cmod5n_forward(v, phi, theta):
     B2 = (-D1 + D2 * V2) * exp(-V2)
 
     # CMOD5_N: COMBINE THE THREE FOURIER TERMS
-    CMOD5_N = B0 * (1.0 + B1 * CSFI + B2 * CS2FI) ** ZPOW
+    cmod5_n = B0 * (1.0 + B1 * CSFI + B2 * CS2FI) ** ZPOW
 
-    return CMOD5_N
+    return cmod5_n
 
 
 def cmod5n_inverse(sigma0_obs, phi, incidence, iterations=10):
@@ -110,19 +117,17 @@ def cmod5n_inverse(sigma0_obs, phi, incidence, iterations=10):
             2D array with wind speeds at 10 m, neutral stratification
     """
 
-    from numpy import ones, array
-
     # First guess wind speed
-    V = array([10.])*ones(sigma0_obs.shape)
+    v = array([10.]) * ones(sigma0_obs.shape)
     step = 10.
 
     # Iterating until error is smaller than threshold
     for iterno in range(1, iterations):
         #print iterno
-        sigma0_calc = cmod5n_forward(V, phi, incidence)
-        ind = sigma0_calc-sigma0_obs > 0
-        V = V + step
-        V[ind] = V[ind] - 2 * step
+        sigma0_calc = cmod5n_forward(v, phi, incidence)
+        ind = sigma0_calc - sigma0_obs > 0
+        v = v + step
+        v[ind] = v[ind] - 2 * step
         step = step / 2
 
-    return V
+    return v