Add limb_correction keyword argument to MiRS reader

satpy/readers/mirs.py

@@ -190,13 +190,28 @@ def limb_correct_atms_bt(bt_data, surf_type_mask, coeff_fns, ds_info):
 
 
 class MiRSL2ncHandler(BaseFileHandler):
-    """MiRS handler for NetCDF4 files using xarray."""
+    """MiRS handler for NetCDF4 files using xarray.
 
-    def __init__(self, filename, filename_info, filetype_info):
+    The MiRS retrieval algorithm runs on multiple
+    sensors.  For the ATMS sensors, a limb correction
+    is applied by default.  In order to change that
+    behavior, use the keyword argument ``limb_correction=False``::
+
+
+        from satpy import Scene, find_files_and_readers
+
+        filenames = find_files_and_readers(base_dir, reader="mirs")
+        scene = Scene(filenames, reader_kwargs={'limb_correction': False})
+
+    """
+
+    def __init__(self, filename, filename_info, filetype_info,
+                 limb_correction=True):
         """Init method."""
         super(MiRSL2ncHandler, self).__init__(filename,
                                               filename_info,
-                                              filetype_info)
+                                              filetype_info,
+                                              )
 
         self.nc = xr.open_dataset(self.filename,
                                   decode_cf=True,
@@ -212,6 +227,7 @@ def __init__(self, filename, filename_info, filetype_info):
 
         self.platform_name = self._get_platform_name
         self.sensor = self._get_sensor
+        self.limb_correction = limb_correction
 
     @property
     def platform_shortname(self):
@@ -346,15 +362,15 @@ def get_dataset(self, ds_id, ds_info):
             data = self['BT']
             data = data.rename(new_name_or_name_dict=ds_info["name"])
 
-            if self.sensor.lower() != "atms":
-                LOG.info("Limb Correction will not be applied to non-ATMS BTs")
-                data = data[:, :, idx]
-            else:
+            if self.sensor.lower() == "atms" and self.limb_correction:
                 sfc_type_mask = self['Sfc_type']
                 data = limb_correct_atms_bt(data, sfc_type_mask,
                                             self._get_coeff_filenames,
                                             ds_info)
                 self.nc = self.nc.merge(data)
+            else:
+                LOG.info("No Limb Correction applied.")
+                data = data[:, :, idx]
         else:
             data = self[ds_id['name']]
 

satpy/tests/reader_tests/test_mirs.py

@@ -27,6 +27,7 @@
 
 AWIPS_FILE = "IMG_SX.M2.D17037.S1601.E1607.B0000001.WE.HR.ORB.nc"
 NPP_MIRS_L2_SWATH = "NPR-MIRS-IMG_v11r6_npp_s201702061601000_e201702061607000_c202012201658410.nc"
+N20_MIRS_L2_SWATH = "NPR-MIRS-IMG_v11r4_n20_s201702061601000_e201702061607000_c202012201658410.nc"
 OTHER_MIRS_L2_SWATH = "NPR-MIRS-IMG_v11r4_gpm_s201702061601000_e201702061607000_c202010080001310.nc"
 
 EXAMPLE_FILES = [AWIPS_FILE, NPP_MIRS_L2_SWATH, OTHER_MIRS_L2_SWATH]
@@ -82,7 +83,7 @@ def fake_coeff_from_fn(fn):
     return coeff_str
 
 
-def _get_datasets_with_attributes():
+def _get_datasets_with_attributes(**kwargs):
     """Represent files with two resolution of variables in them (ex. OCEAN)."""
     bt = xr.DataArray(np.linspace(1830, 3930, N_SCANLINE * N_FOV * N_CHANNEL).
                       reshape(N_SCANLINE, N_FOV, N_CHANNEL),
@@ -91,7 +92,8 @@ def _get_datasets_with_attributes():
                              'coordinates': "Longitude Latitude Freq",
                              'scale_factor': 0.01,
                              '_FillValue': -999,
-                             'valid_range': [0, 50000]})
+                             'valid_range': [0, 50000]},
+                      dims=('Scanline', 'Field_of_view', 'Channel'))
     rr = xr.DataArray(np.random.randint(100, 500, size=(N_SCANLINE, N_FOV)),
                       attrs={'long_name': "Rain Rate (mm/hr)",
                              'units': "mm/hr",
@@ -259,6 +261,7 @@ def _check_attrs(data_arr, platform_name):
         [
             ([AWIPS_FILE], TEST_VARS, "metop-a"),
             ([NPP_MIRS_L2_SWATH], TEST_VARS, "npp"),
+            ([N20_MIRS_L2_SWATH], TEST_VARS, "noaa-20"),
             ([OTHER_MIRS_L2_SWATH], TEST_VARS, "gpm"),
         ]
     )
@@ -275,8 +278,40 @@ def test_basic_load(self, filenames, loadable_ids, platform_name):
                 fd.side_effect = fake_coeff_from_fn
                 loaded_data_arrs = r.load(loadable_ids)
             assert loaded_data_arrs
+
             for data_id, data_arr in loaded_data_arrs.items():
                 if data_id['name'] not in ['latitude', 'longitude']:
                     self._check_area(data_arr)
                 self._check_fill(data_arr)
                 self._check_attrs(data_arr, platform_name)
+
+                if data_arr.attrs['sensor'] == 'atms':
+                    fd.assert_called()
+                else:
+                    fd.assert_not_called()
+
+    @pytest.mark.parametrize(
+        ("filenames", "loadable_ids"),
+        [
+            ([AWIPS_FILE], TEST_VARS),
+            ([NPP_MIRS_L2_SWATH], TEST_VARS),
+            ([N20_MIRS_L2_SWATH], TEST_VARS),
+            ([OTHER_MIRS_L2_SWATH], TEST_VARS),
+        ]
+    )
+    def test_kwarg_load(self, filenames, loadable_ids):
+        """Test the limb_correction kwarg when filehandler is loaded."""
+        from satpy.readers import load_reader
+        with mock.patch('satpy.readers.mirs.xr.open_dataset') as od:
+            od.side_effect = fake_open_dataset
+            r = load_reader(self.reader_configs)
+            loadables = r.select_files_from_pathnames(filenames)
+            r.create_filehandlers(loadables, fh_kwargs={"limb_correction": False})
+
+            with mock.patch('satpy.readers.mirs.read_atms_coeff_to_string') as \
+                    fd, mock.patch('satpy.readers.mirs.retrieve'):
+                fd.side_effect = fake_coeff_from_fn
+                loaded_data_arrs = r.load(loadable_ids)
+            assert loaded_data_arrs
+
+            fd.assert_not_called()