Initial commit

ocbrdf/brdf_model_M02.py

@@ -0,0 +1,182 @@
+import numpy as np
+import xarray as xr
+
+from brdf_utils import ADF_OCP, solve_2nd_order_poly, drop_unused_coords
+
+''' Morel et al. (2002) BRDF 校正
+    包含 R gothic
+    f/Q 查找表，与 OLCI 业务处理器中的一致（参见 OLCI "OCP" ADF）
+    使用 OC4ME 叶绿素反演，进行两次迭代，未应用叶绿素差值收敛标准（1%）
+'''
+
+""" M02 系数的类 """
+
+
+class Coeffs():
+    def __init__(self, Rgoth, foq):
+        self.Rgoth = Rgoth
+        self.foq = foq
+
+
+""" Class for M02 BRDF model """
+class M02:
+    """ Initialise M02 model: BRDF LUT, coeffs, OC4ME parameters, water IOPs LUT
+        Note: bands are fixed and defined at class initilization, but could be initialized in init_pixels if needed
+    """
+
+    def __init__(self, bands, aot, wind, adf=None):
+        if adf is None:
+            adf = ADF_OCP
+
+        # Check required bands are existing, within a 25 nm threshold
+        self.bands = bands
+        threshold = 25.
+        bands_required = [442.5, 490, 510, 560]
+        bands_ref = bands.sel(bands=bands_required, method='nearest')
+        for band_ref, band_required in zip(bands_ref, bands_required):
+            assert abs(band_ref - band_required) < threshold, 'Band %d nm missing or too far' % band_ref
+        self.b442, self.b490, self.b510, self.b560 = bands_ref
+
+        # Read BRDF LUT and compute default coeffs
+        LUT_OCP = xr.open_dataset(adf % 'M02',engine='netcdf4')
+        self.LUT = xr.Dataset()
+
+        # Homogeneise naming convention with other methods... (PZA --> OZA transformation comes below...)
+        self.LUT['Rgoth'] = LUT_OCP.r_goth_LUT.rename({'PZA_r_goth':'theta_v_Rgoth',
+                                                       'wind_speeds_r_goth':'wind_Rgoth'})
+        self.LUT['foq'] = LUT_OCP.f_over_q_LUT.rename({'SZA_FOQ':'theta_s',
+                                                       'PZA_FOQ':'theta_v',
+                                                       'RAA_FOQ':'delta_phi',
+                                                       'wind_speeds_FOQ':'wind_foq',
+                                                       'tau_a_FOQ':'aot_foq',
+                                                       'log_chl_FOQ':'log_chl_foq'})
+
+        # f0 factor to convert Rrs to Irradiance Reflectance (R) --> in order to apply OC4ME
+        self.LUT['f0'] = LUT_OCP.f0_LUT
+
+        # Index of refraction
+        self.n_w = float(LUT_OCP.water_refraction_index.data)
+
+        # Remove trivial aot indexation
+        self.LUT['foq'] = self.LUT['foq'].squeeze()
+
+        # Interpolate for wind speed.
+        self.LUT['Rgoth'] = self.LUT['Rgoth'].interp(wind_Rgoth=np.clip(wind,0,16))
+        self.LUT['foq'  ] = self.LUT['foq'  ].interp(wind_foq  =np.clip(wind,0,10))
+
+        #
+        self.coeffs0 = self.interp_geometries(0., 0., 0.)
+        self.coeffs = Coeffs(np.nan, np.nan)
+
+        # Parameters for the OC4ME chl retrieval
+        self.OC4MEcoeff = LUT_OCP.log10_coeff_LUT.values
+        self.OC4MEepsilon = LUT_OCP.oc4me_epsilon
+        self.OC4MEchl0 = float(LUT_OCP.oc4me_chl0.values)
+        self.niter = LUT_OCP.oc4me_niter
+
+    """ Initialize pixel: coefficient at current geometry and water IOP at current bands """
+
+    def init_pixels(self, theta_s, theta_v, delta_phi):
+        self.coeffs = self.interp_geometries(theta_s, theta_v, delta_phi)
+
+    """ Interpolate coefficients """
+    def interp_geometries(self, theta_s, theta_v, delta_phi):
+        # Transform PZA to VZA (Snell's refraction Law)
+        theta_v = np.rad2deg(np.arcsin(np.sin(np.deg2rad(theta_v)) / self.n_w))
+        theta_v_Rgoth_0 = np.clip(theta_v,
+                                   float(np.min(self.LUT.theta_v_Rgoth)),
+                                   float(np.max(self.LUT.theta_v_Rgoth)))
+
+        theta_v_0 = np.clip(theta_v,
+                                   float(np.min(self.LUT.theta_v)),
+                                   float(np.max(self.LUT.theta_v)))
+
+        Rgoth = self.LUT.Rgoth.interp(theta_v_Rgoth=theta_v_Rgoth_0)
+        foq = self.LUT.foq.interp(theta_s=theta_s, theta_v=theta_v_0, delta_phi=delta_phi)
+
+        return Coeffs(Rgoth, foq)
+
+    """ Compute remote-sensing reflectance"""
+
+    def forward(self, ds, normalized=False):
+
+        if normalized:
+            coeffs = self.coeffs0
+        else:
+            coeffs = self.coeffs
+
+        wave_foq = np.clip(ds['bands'],
+                           float(np.min(coeffs.foq.wavelengths_FOQ)),
+                           float(np.max(coeffs.foq.wavelengths_FOQ)))
+
+        log10_chl_foq = np.clip(ds['log10_chl'],
+                           float(np.min(coeffs.foq.log_chl_foq)/np.log(10)),
+                           float(np.max(coeffs.foq.log_chl_foq)/np.log(10)))
+
+        # f/Q LUT indexed with ln(CHL), i.e. log_e(CHL)
+        log_chl_foq = log10_chl_foq * np.log(10)
+
+        forward_mod = coeffs.Rgoth * coeffs.foq.interp(wavelengths_FOQ=wave_foq).interp(log_chl_foq=log_chl_foq)
+
+        return forward_mod
+
+    """ Apply QAA to retrieve IOP (omega_b, eta_b) from Rrs """
+
+    def backward(self, ds, iter_brdf):
+
+        Rrs = ds['nrrs']
+
+        # Local renaming of bands
+        b442, b490, b510, b560 = self.b442, self.b490, self.b510, self.b560
+
+        # Convert to scalar if np.array of 1 value to avoid issues
+        try:
+            b442=b442.item()
+            b490=b490.item()
+            b510=b510.item()
+            b560=b560.item()
+        except:
+            pass
+
+        # Clip to f0 log10(CHL) values
+        log10_chl_f0 = np.clip(ds['log10_chl'],
+                           float(np.min(self.LUT['f0'].log_chl_f0)/np.log(10)),
+                           float(np.max(self.LUT['f0'].log_chl_f0)/np.log(10)))
+
+        # f/Q LUT indexed with ln(CHL), i.e. log_e(CHL)
+        log_chl_f0 = log10_chl_f0 * np.log(10)
+        f0_chl = self.LUT['f0'].interp(log_chl_f0=log_chl_f0)
+
+        fQ_chl = self.coeffs.foq.interp(log_chl_foq=log10_chl_f0)
+
+        # Drop unused coordinates to avoid ambiguities in indexation...
+        Rrs = drop_unused_coords(Rrs)
+        f0_chl = drop_unused_coords(f0_chl)
+        fQ_chl = drop_unused_coords(fQ_chl)
+
+        # Get Rrs at relevant bands for OC4ME and convert to Irradiance Reflectance (R)
+        R442 = np.pi * Rrs.sel(bands=b442) * f0_chl.sel(bands_f0=2.0) / fQ_chl.interp(wavelengths_FOQ=b442)
+        R490 = np.pi * Rrs.sel(bands=b490) * f0_chl.sel(bands_f0=3.0) / fQ_chl.interp(wavelengths_FOQ=b490)
+        R510 = np.pi * Rrs.sel(bands=b510) * f0_chl.sel(bands_f0=4.0) / fQ_chl.interp(wavelengths_FOQ=b510)
+        R560 = np.pi * Rrs.sel(bands=b560) * f0_chl.sel(bands_f0=5.0) / fQ_chl.interp(wavelengths_FOQ=b560)
+
+        R442 = drop_unused_coords(R442)
+        R490 = drop_unused_coords(R490)
+        R510 = drop_unused_coords(R510)
+        R560 = drop_unused_coords(R560)
+
+        # Compute the OC4ME "R"
+        # NB: Could be the case that R[442-560]<0,
+        #   then ds['log10_chl_OC4ME_Ratio'] will be NaN.
+        #   then ds['log10_chl'] will be NaN.
+        #   then forward_mod0/forward_mod (in brdf_prototype, ocbrdf/main.py) will be NaN.
+        #   then ds['C_BRDF'] = NaN.
+        #   In this case, C_BRDF will be set to 1 and C_BRDF_flag will be raised (see brdf_prototype, ocbrdf/main.py).
+        ds['log10_chl_OC4ME_Ratio'] = np.log10(np.max([R442, R490, R510], axis=0) / R560)
+
+        ds['log10_chl'] = 0 * ds['log10_chl_OC4ME_Ratio']
+        # Apply OC4ME 5-degree polynomial
+        for k, Ak in enumerate(self.OC4MEcoeff):
+            ds['log10_chl'] += Ak * (ds['log10_chl_OC4ME_Ratio'] ** k)
+
+        return ds