Add a reader for FY-4A LMI level 2 data

satpy/etc/readers/lmi_l2.yaml

@@ -0,0 +1,27 @@
+# References:
+#  - L2 Data of FY4A Lightning Mapping Imager
+#  - http://fy4.nsmc.org.cn/data/en/data/realtime.html
+
+reader:
+  name: lmi_l2
+  description: Lightning Mapping Imager Dataset reader
+  reader: !!python/name:satpy.readers.yaml_reader.FileYAMLReader
+  sensors: [lmi]
+
+file_types:
+  lmi:
+    file_reader: !!python/name:satpy.readers.lmi_l2.LMIL2FileHandler
+    file_patterns: ['{platform_id:4s}-_{instrument:3s}---_N_{observation_type:s}_{longitude:5s}_L2-_LMI{product:s}_SING_NUL_{start_time:%Y%m%d%H%M%S}_{end_time:%Y%m%d%H%M%S}_{resolution:s}_N{subtask_num:s}V{version:s}.NC']
+
+datasets:
+  LAT:
+    name: LAT
+    file_type: lmi
+    standard_name: latitude
+    units: degree_north
+
+  LON:
+    name: LON
+    file_type: lmi
+    standard_name: longitude
+    units: degree_east

satpy/readers/lmi_l2.py

@@ -0,0 +1,154 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+# Copyright (c) 2019 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/>.
+"""Lightning Mapping Imager Dataset reader
+
+The files read by this reader are described in:
+
+    http://fy4.nsmc.org.cn/data/en/data/realtime.html
+
+"""
+
+import numpy as np
+from satpy.readers.netcdf_utils import NetCDF4FileHandler, netCDF4
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class LMIL2FileHandler(NetCDF4FileHandler):
+    """File handler for LMI L2 netCDF files."""
+
+    @property
+    def start_time(self):
+        return self.filename_info['start_time']
+
+    @property
+    def end_time(self):
+        return self.filename_info['end_time']
+
+    @property
+    def platform_shortname(self):
+        return self.filename_info['platform_id']
+
+    @property
+    def sensor(self):
+        return self.filename_info['instrument'].lower()
+
+    def available_datasets(self, configured_datasets=None):
+        """Automatically determine datasets provided by this file."""
+        logger.debug("Available_datasets begin...")
+
+        handled_variables = set()
+
+        # update previously configured datasets
+        logger.debug("Starting previously configured variables loop...")
+        for is_avail, ds_info in (configured_datasets or []):
+            if ds_info['name'] == 'LAT':
+                lat_shape = self[ds_info['name']+'/shape']
+
+            # some other file handler knows how to load this
+            if is_avail is not None:
+                yield is_avail, ds_info
+
+            var_name = ds_info.get('file_key', ds_info['name'])
+            matches = self.file_type_matches(ds_info['file_type'])
+            # we can confidently say that we can provide this dataset and can
+            # provide more info
+            if matches and var_name in self:
+                logger.debug("Handling previously configured variable: %s",
+                             var_name)
+                # Because assembled variables and bounds use the same file_key,
+                # we need to omit file_key once.
+                handled_variables.add(var_name)
+                new_info = ds_info.copy()  # don't mess up the above yielded
+                yield True, new_info
+            elif is_avail is None:
+                # if we didn't know how to handle this dataset
+                # and no one else did,
+                # then we should keep it going down the chain.
+                yield is_avail, ds_info
+
+        # Iterate over dataset contents
+        for var_name, val in self.file_content.items():
+            # Only evaluate variables
+            if isinstance(val, netCDF4.Variable):
+                logger.debug("Evaluating new variable: %s", var_name)
+                var_shape = self[var_name + "/shape"]
+                logger.debug("Dims:{}".format(var_shape))
+                if (lat_shape == var_shape):
+                    logger.debug("Found valid additional dataset: %s",
+                                 var_name)
+
+                    # Skip anything we have already configured
+                    if (var_name in handled_variables):
+                        logger.debug("Already handled, skipping: %s", var_name)
+                        continue
+                    handled_variables.add(var_name)
+                    logger.debug("Using short name of: %s", var_name)
+
+                    # Create new ds_info object
+                    new_info = {
+                        'name': var_name,
+                        'file_key': var_name,
+                        'coordinates': ['LON', 'LAT'],
+                        'file_type': self.filetype_info['file_type'],
+                        'resolution': self.filename_info['resolution'].lower()
+                    }
+                    yield True, new_info
+
+    def get_metadata(self, data, ds_info):
+        """Get metadata."""
+        metadata = {}
+        metadata.update(data.attrs)
+        units = data.attrs['units']
+        # fix the wrong unit "uJ/m*m/ster"
+        if not units.isascii():
+            metadata['units'] = b'\xc2\xb5J/m*m/ster'
+        metadata.update(ds_info)
+        metadata.update({
+            'platform_shortname': self.filename_info['platform_id'],
+            'sensor': self.filename_info['instrument'].lower(),
+            'start_time': self.start_time,
+            'end_time': self.end_time,
+        })
+
+        return metadata
+
+    def get_dataset(self, ds_id, ds_info):
+        """Load a dataset."""
+        logger.debug("Getting data for: %s", ds_id.name)
+        file_key = ds_info.get('file_key', ds_id.name)
+        data = self[file_key]
+        data.attrs = self.get_metadata(data, ds_info)
+        # rename coords
+        data = data.rename({'x': 'y'})
+        # assign 'y' coords which is useful for multiscene,
+        # although the units isn't meters
+        len_data = data.coords['y'].shape[0]
+        data.coords['y'] = np.arange(len_data)
+        # check fill value
+        fill = data.attrs.pop('FillValue')
+        data = data.where(data != fill)
+        # remove attributes that could be confusing later
+        data.attrs.pop('ancillary_variables', None)
+        data.attrs.pop('Description', None)
+        # select valid data
+        data = data.where((data >= min(data.attrs['valid_range'])) &
+                          (data <= max(data.attrs['valid_range'])))
+
+        return data