#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Copyright (c) 2020 Satpy developers
#
# This file is part of satpy.
#
# satpy is free software: you can redistribute it and/or modify it under the
# terms of the GNU General Public License as published by the Free Software
# Foundation, either version 3 of the License, or (at your option) any later
# version.
#
# satpy is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# satpy. If not, see <http://www.gnu.org/licenses/>.
"""Classes related to the CREFL (corrected reflectance) modifier."""
import logging
import warnings
import numpy as np
from satpy.aux_download import DataDownloadMixin, retrieve
from satpy.modifiers import ModifierBase
from satpy.modifiers.angles import get_angles
LOG = logging.getLogger(__name__)
[docs]
class ReflectanceCorrector(ModifierBase, DataDownloadMixin):
"""Corrected Reflectance (crefl) modifier.
Uses a python rewrite of the C CREFL code written for VIIRS and MODIS.
"""
def __init__(self, *args, dem_filename=None, dem_sds="averaged elevation", # noqa: D417
url=None, known_hash=None, **kwargs):
"""Initialize the compositor with values from the user or from the configuration file.
If `dem_filename` can't be found or opened then correction is done
assuming TOA or sealevel options.
Args:
dem_filename (str): DEPRECATED
url (str): URL or local path to the Digital Elevation Model (DEM)
HDF4 file. If unset (None or empty string), then elevation
is assumed to be 0 everywhere.
known_hash (str): Optional SHA256 checksum to verify the download
of ``url``.
dem_sds (str): Name of the variable in the elevation file to load.
"""
if dem_filename is not None:
warnings.warn(
"'dem_filename' for 'ReflectanceCorrector' is "
"deprecated. Use 'url' instead.",
DeprecationWarning,
stacklevel=2
)
super(ReflectanceCorrector, self).__init__(*args, **kwargs)
self.dem_sds = dem_sds
self.url = url
self.known_hash = known_hash
self.dem_cache_key = self._get_registered_dem_cache_key()
[docs]
def _get_registered_dem_cache_key(self):
if not self.url:
return
reg_files = self.register_data_files([{
"url": self.url, "known_hash": self.known_hash}
])
return reg_files[0]
def __call__(self, datasets, optional_datasets, **info):
"""Create modified DataArray object by applying the crefl algorithm."""
refl_data, angles = self._extract_angle_data_arrays(datasets, optional_datasets)
results = self._call_crefl(refl_data, angles)
info.update(refl_data.attrs)
info["rayleigh_corrected"] = True
results.attrs = info
self.apply_modifier_info(refl_data, results)
return results
[docs]
def _call_crefl(self, refl_data, angles):
from satpy.modifiers._crefl_utils import run_crefl
avg_elevation = self._get_average_elevation()
results = run_crefl(refl_data,
*angles,
avg_elevation=avg_elevation,
)
return results
[docs]
def _get_average_elevation(self):
if self.dem_cache_key is None:
return
LOG.debug("Loading CREFL averaged elevation information from: %s",
self.dem_cache_key)
local_filename = retrieve(self.dem_cache_key)
avg_elevation = self._read_var_from_hdf4_file(local_filename, self.dem_sds).astype(np.float64)
if isinstance(avg_elevation, np.ma.MaskedArray):
avg_elevation = avg_elevation.filled(np.nan)
return avg_elevation
[docs]
@staticmethod
def _read_var_from_hdf4_file(local_filename, var_name):
try:
return ReflectanceCorrector._read_var_from_hdf4_file_pyhdf(local_filename, var_name)
except (ImportError, OSError):
return ReflectanceCorrector._read_var_from_hdf4_file_netcdf4(local_filename, var_name)
[docs]
@staticmethod
def _read_var_from_hdf4_file_netcdf4(local_filename, var_name):
from netCDF4 import Dataset as NCDataset
# HDF4 file, NetCDF library needs to be compiled with HDF4 support
nc = NCDataset(local_filename, "r")
# average elevation is stored as a 16-bit signed integer but with
# scale factor 1 and offset 0, convert it to float here
return nc.variables[var_name][:]
[docs]
@staticmethod
def _read_var_from_hdf4_file_pyhdf(local_filename, var_name):
from pyhdf.SD import SD, SDC
f = SD(local_filename, SDC.READ)
var = f.select(var_name)
data = var[:]
fill = ReflectanceCorrector._read_fill_value_from_hdf4(var, data.dtype)
return np.ma.MaskedArray(data, data == fill)
[docs]
@staticmethod
def _read_fill_value_from_hdf4(var, dtype):
from pyhdf.error import HDF4Error
try:
return var.getfillvalue()
except HDF4Error:
return np.iinfo(dtype).min