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