Merge pull request #800 from wroberts4/master

Fix 'virr_l1b' reader when slope attribute is 0

satpy/readers/virr_l1b.py

@@ -76,27 +76,29 @@ def get_dataset(self, dataset_id, ds_info):
             data = data.where((data >= self[file_key + '/attr/valid_range'][0]) &
                               (data <= self[file_key + '/attr/valid_range'][1]))
             if 'E' in dataset_id.name:
-                slope = self[self.l1b_prefix + 'Emissive_Radiance_Scales'].data[:, band_index][:, np.newaxis]
+                slope = self._correct_slope(self[self.l1b_prefix + 'Emissive_Radiance_Scales'].
+                                            data[:, band_index][:, np.newaxis])
                 intercept = self[self.l1b_prefix + 'Emissive_Radiance_Offsets'].data[:, band_index][:, np.newaxis]
                 # Converts cm^-1 (wavenumbers) and (mW/m^2)/(str/cm^-1) (radiance data)
                 # to SI units m^-1, mW*m^-3*str^-1.
                 wave_number = self['/attr/' + self.wave_number][band_index] * 100
-                bt_data = rad2temp(wave_number,
-                                   (data.data * slope + intercept) * 1e-5)
+                bt_data = rad2temp(wave_number, (data.data * slope + intercept) * 1e-5)
                 if isinstance(bt_data, np.ndarray):
                     # old versions of pyspectral produce numpy arrays
                     data.data = da.from_array(bt_data, chunks=data.data.chunks)
                 else:
                     # new versions of pyspectral can do dask arrays
                     data.data = bt_data
             elif 'R' in dataset_id.name:
-                slope = self['/attr/RefSB_Cal_Coefficients'][0::2]
+                slope = self._correct_slope(self['/attr/RefSB_Cal_Coefficients'][0::2])
                 intercept = self['/attr/RefSB_Cal_Coefficients'][1::2]
                 data = data * slope[band_index] + intercept[band_index]
         else:
+            slope = self._correct_slope(self[file_key + '/attr/Slope'])
+            intercept = self[file_key + '/attr/Intercept']
             data = data.where((data >= self[file_key + '/attr/valid_range'][0]) &
                               (data <= self[file_key + '/attr/valid_range'][1]))
-            data = self[file_key + '/attr/Intercept'] + self[file_key + '/attr/Slope'] * data
+            data = data * slope + intercept
         new_dims = {old: new for old, new in zip(data.dims, ('y', 'x'))}
         data = data.rename(new_dims)
         data.attrs.update({'platform_name': self['/attr/Satellite Name'],
@@ -111,6 +113,10 @@ def get_dataset(self, dataset_id, ds_info):
             data.attrs.update({'units': '1'})
         return data
 
+    def _correct_slope(self, slope):
+        # 0 slope is invalid. Note: slope can be a scalar or array.
+        return da.where(slope == 0, 1, slope)
+
     @property
     def start_time(self):
         start_time = self['/attr/Observing Beginning Date'] + 'T' + self['/attr/Observing Beginning Time'] + 'Z'

satpy/tests/reader_tests/test_virr_l1b.py

@@ -124,10 +124,12 @@ def _fy3_helper(self, platform_name, reader, Emissive_units):
                        'E1': 496.542155, 'E2': 297.444511, 'E3': 288.956557, 'solar_zenith_angle': .1,
                        'satellite_zenith_angle': .1, 'solar_azimuth_angle': .1, 'satellite_azimuth_angle': .1,
                        'longitude': 10}
-        datasets = reader.load([band for band, val in band_values.items()])
+        datasets = reader.load([band for band in band_values])
         for dataset in datasets:
+            # Object returned by get_dataset.
             ds = datasets[dataset.name]
             attributes = ds.attrs
+            self.assertTrue(isinstance(ds.data, da.Array))
             self.assertEqual('VIRR', attributes['sensor'])
             self.assertEqual(platform_name, attributes['platform_name'])
             self.assertEqual(datetime.datetime(2018, 12, 25, 21, 41, 47, 90000), attributes['start_time'])
@@ -166,7 +168,7 @@ def test_fy3b_file(self):
         self.assertTrue(FY3B_reader.file_handlers)
         self._fy3_helper('FY3B', FY3B_reader, 'milliWstts/m^2/cm^(-1)/steradian')
 
-    def test_FY3C_file(self):
+    def test_fy3c_file(self):
         from satpy.readers import load_reader
         FY3C_reader = load_reader(self.reader_configs)
         FY3C_files = FY3C_reader.select_files_from_pathnames(['tf2018359143912.FY3C-L_VIRRX_GEOXX.HDF',