Initial commit
This commit is contained in:
191
ocbrdf/brdf_model_L11.py
Normal file
191
ocbrdf/brdf_model_L11.py
Normal file
@ -0,0 +1,191 @@
|
||||
import numpy as np
|
||||
import xarray as xr
|
||||
|
||||
from brdf_utils import ADF_OCP, solve_2nd_order_poly, drop_unused_coords
|
||||
from Raman import Raman
|
||||
|
||||
|
||||
''' Lee et al. (2011) BRDF correction
|
||||
With QAA v6 inversion
|
||||
|
||||
'''
|
||||
|
||||
# Init Raman class
|
||||
Raman = Raman()
|
||||
|
||||
""" Class for L11 coefficients """
|
||||
class Coeffs():
|
||||
def __init__(self,Gw0,Gw1,Gp0,Gp1):
|
||||
self.Gw0 = Gw0
|
||||
self.Gw1 = Gw1
|
||||
self.Gp0 = Gp0
|
||||
self.Gp1 = Gp1
|
||||
|
||||
""" Class for L11 BRDF model """
|
||||
class L11:
|
||||
|
||||
""" Initialise L11 model: BRDF LUT, coeffs, QAA 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, adf=None):
|
||||
if adf is None:
|
||||
adf = ADF_OCP
|
||||
|
||||
# Check required bands are existing, within a 10 nm threshold
|
||||
self.bands = bands
|
||||
threshold = 10.
|
||||
bands_required = [442, 490, 560, 665]
|
||||
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.b560, self.b665 = bands_ref
|
||||
|
||||
# Read BRDF LUT and compute default coeffs
|
||||
LUT_OCP = xr.open_dataset(adf % 'L11',engine='netcdf4')
|
||||
self.LUT = xr.Dataset()
|
||||
self.LUT['Gw0'] = LUT_OCP.Gw0
|
||||
self.LUT['Gw1'] = LUT_OCP.Gw1
|
||||
self.LUT['Gp0'] = LUT_OCP.Gp0
|
||||
self.LUT['Gp1'] = LUT_OCP.Gp1
|
||||
|
||||
self.coeffs0 = self.interp(0.,0.,0.)
|
||||
self.coeffs = Coeffs(np.nan,np.nan,np.nan,np.nan)
|
||||
|
||||
# Read IOPs of pure water (store in LUT for further spectral interpolation)
|
||||
self.awLUT = LUT_OCP.aw.rename({'IOP_wl':'bands'})
|
||||
self.bbwLUT = LUT_OCP.bbw.rename({'IOP_wl':'bands'})
|
||||
|
||||
# Read QAA parameters
|
||||
self.a0G = LUT_OCP.a0G.values
|
||||
self.a0R = LUT_OCP.a0R.values
|
||||
self.gamma = LUT_OCP.gamma.values
|
||||
self.niter = LUT_OCP.niter.values
|
||||
|
||||
""" 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(theta_s, theta_v, delta_phi)
|
||||
|
||||
# Compute IOPs at current bands
|
||||
self.aw = self.awLUT.interp(bands = self.bands, kwargs={'fill_value':'extrapolate'})
|
||||
self.bbw = self.bbwLUT.interp(bands = self.bands, kwargs={'fill_value':'extrapolate'})
|
||||
|
||||
""" Interpolate coefficients """
|
||||
def interp(self, theta_s, theta_v, delta_phi):
|
||||
Gw0 = self.LUT.Gw0.interp(theta_s=theta_s,theta_v=theta_v,delta_phi=delta_phi)
|
||||
Gw1 = self.LUT.Gw1.interp(theta_s=theta_s,theta_v=theta_v,delta_phi=delta_phi)
|
||||
Gp0 = self.LUT.Gp0.interp(theta_s=theta_s,theta_v=theta_v,delta_phi=delta_phi)
|
||||
Gp1 = self.LUT.Gp1.interp(theta_s=theta_s,theta_v=theta_v,delta_phi=delta_phi)
|
||||
return Coeffs(Gw0,Gw1,Gp0,Gp1)
|
||||
|
||||
""" Compute remote-sensing reflectance, without Raman effect (vanish in the normalization factor) """
|
||||
def forward(self, ds, normalized=False):
|
||||
omega_b = ds['omega_b']
|
||||
eta_b = ds['eta_b']
|
||||
|
||||
if normalized:
|
||||
coeffs = self.coeffs0
|
||||
else:
|
||||
coeffs = self.coeffs
|
||||
mod_Rrs = (coeffs.Gw0+coeffs.Gw1*omega_b*eta_b)*omega_b*eta_b + (coeffs.Gp0+coeffs.Gp1*omega_b*(1-eta_b))*omega_b*(1-eta_b)
|
||||
|
||||
return mod_Rrs
|
||||
|
||||
""" Apply QAA to retrieve IOP (omega_b, eta_b) from Rrs """
|
||||
def backward(self, ds, iter_brdf):
|
||||
|
||||
Rrs = ds['nrrs']
|
||||
|
||||
# Select G coeff according to iteration
|
||||
if iter_brdf == 0:
|
||||
coeffs = self.coeffs
|
||||
else:
|
||||
coeffs = self.coeffs0
|
||||
|
||||
# Apply Raman correction
|
||||
Rrs = Raman.correct(Rrs)
|
||||
|
||||
# Local renaming of bands
|
||||
b442, b490, b560, b665 = self.b442, self.b490, self.b560, self.b665
|
||||
|
||||
# Apply upper and lower limits to Rrs(665) #TODO check if not finite or missing?
|
||||
Rrs442 = Rrs.sel(bands=b442)
|
||||
Rrs490 = Rrs.sel(bands=b490)
|
||||
Rrs560 = Rrs.sel(bands=b560)
|
||||
Rrs665 = Rrs.sel(bands=b665)
|
||||
mask= ((Rrs665 > 20*np.power(Rrs560,1.5)) | (Rrs665 < 0.9*np.power(Rrs560, 1.7)))
|
||||
if np.any(mask):
|
||||
Rrs665_ = 1.27*np.power(Rrs560, 1.47) + 0.00018*np.power(Rrs490/Rrs560,-3.19)
|
||||
# Redefine Rrs665 and Rrs[bands=b665] (both important for computations below)
|
||||
Rrs665 = xr.where(mask, Rrs665_, Rrs665)
|
||||
Rrs.loc[dict(bands=b665)] = Rrs665
|
||||
|
||||
# Calculate rrs below water for absorption computation
|
||||
rrs = Rrs / (0.52 + 1.7*Rrs)
|
||||
|
||||
# Define reference band band0 according to Rrs at 665 nm
|
||||
# and compute total absorption
|
||||
mask = Rrs.sel(bands=b665) < 0.0015
|
||||
band0 = xr.where(mask, b560, b665)
|
||||
aw0 = xr.where(mask, self.aw.sel(bands=b560), self.aw.sel(bands=b665))
|
||||
bbw0 = xr.where(mask, self.bbw.sel(bands=b560), self.bbw.sel(bands=b665))
|
||||
Rrs0 = xr.where(mask, Rrs.sel(bands=b560), Rrs.sel(bands=b665))
|
||||
# Compute a0 when band0 = b560
|
||||
rrs442 = rrs.sel(bands=b442)
|
||||
rrs490 = rrs.sel(bands=b490)
|
||||
rrs560 = rrs.sel(bands=b560)
|
||||
rrs665 = rrs.sel(bands=b665)
|
||||
chi = np.log10((rrs442 + rrs490) / (rrs560 + 5.0 * rrs665*rrs665 / rrs490))
|
||||
poly = np.polynomial.polynomial.polyval(chi, self.a0G)
|
||||
a0_560 = aw0 + np.power(10., poly)
|
||||
# Compute a0 when band0 = b665
|
||||
a0_665 = aw0 + self.a0R[0] * np.power(Rrs665 / (Rrs442 + Rrs490), self.a0R[1])
|
||||
# Compute a0 for all pixels
|
||||
a0 = xr.where(mask, a0_560, a0_665)
|
||||
|
||||
# Compute bbp at band0 by 2nd order polynomial inversion
|
||||
k0 = a0 + bbw0
|
||||
cA = coeffs.Gp0 + coeffs.Gp1 - Rrs0
|
||||
cB = coeffs.Gw0 * bbw0 + (coeffs.Gp0 -2*Rrs0) *k0
|
||||
cC = (coeffs.Gw0 * bbw0 - Rrs0 * k0) * k0 + coeffs.Gw1 * bbw0 * bbw0
|
||||
bbp0 = solve_2nd_order_poly(cA, cB, cC)
|
||||
|
||||
# Assume bbp0 = 0 if solve_2nd_order_poly fails to retrieve non-negative numbers
|
||||
# In this case activate bbp0_fail flag (which in turn activates QAA_fail)
|
||||
bbp0_fail = (bbp0 < 0) | (np.isinf(bbp0)) | (np.isnan(bbp0))
|
||||
bbp0 = xr.where(bbp0_fail, 0, bbp0)
|
||||
|
||||
# Compute bbp slope and extrapolate at all bands
|
||||
gamma = self.gamma[0] * (1.0 - self.gamma[1] * np.exp(-self.gamma[2] * (rrs442 / rrs560)))
|
||||
bbp = bbp0 * np.power(band0 / self.bands, gamma)
|
||||
|
||||
# Compute total bb
|
||||
bb = self.bbw + bbp
|
||||
|
||||
# Compute quasi-diffuse attenuation coefficient k at each band
|
||||
# by 2nd order polynomial inversion
|
||||
cA = Rrs
|
||||
cB = - (coeffs.Gw0 * self.bbw + coeffs.Gp0 * bbp)
|
||||
cC = - (coeffs.Gw1 * self.bbw *self.bbw + coeffs.Gp1 * bbp * bbp)
|
||||
k = solve_2nd_order_poly(cA, cB, cC)
|
||||
|
||||
# If k is not a positive value, then
|
||||
# i) k --> bbw + aw
|
||||
# ii) k_fail flag is activated
|
||||
k_fail = (k <= 0) | (np.isinf(k)) | (np.isnan(k))
|
||||
k = xr.where(k_fail, self.aw + self.bbw, k)
|
||||
|
||||
# Drop unused coords to avoid issues
|
||||
bb = drop_unused_coords(bb)
|
||||
k = drop_unused_coords(k)
|
||||
k_fail = drop_unused_coords(k_fail)
|
||||
bbp0_fail = drop_unused_coords(bbp0_fail)
|
||||
|
||||
# Set QAA_fail is either bbp0_fail or k_fail are activated
|
||||
ds['QAA_fail'] = (bbp0_fail) | (k_fail)
|
||||
|
||||
# Compute final IOPs
|
||||
ds['omega_b'] = bb / k
|
||||
ds['eta_b'] = self.bbw / bb
|
||||
|
||||
return ds
|
||||
|
||||
Reference in New Issue
Block a user