Increase accuracy by using ns

satpy/readers/viirs_vgac_l1c_nc.py

@@ -85,8 +85,8 @@ def extract_time_data(self, data, nc):
                                                          "days since %d/%m/%YT%H:%M:%S"))
         delta_part_of_day, delta_full_days = np.modf(nc["proj_time0"].values)
         delta_full_days = np.timedelta64(int(delta_full_days), "D")
-        delta_part_of_day = delta_part_of_day * np.timedelta64(1, "D").astype("timedelta64[us]")
-        delta_hours = data.values * np.timedelta64(1, "h").astype("timedelta64[us]")
+        delta_part_of_day = delta_part_of_day * np.timedelta64(1, "D").astype("timedelta64[ns]")
+        delta_hours = data.values * np.timedelta64(1, "h").astype("timedelta64[ns]")
         time_data = xr.DataArray(reference_time + delta_full_days + delta_part_of_day + delta_hours,
                                  coords=data.coords, attrs={"long_name": "Scanline time"})
         self._start_time = self.dt64_to_datetime(time_data[0].values)

satpy/tests/reader_tests/test_viirs_vgac_l1c_nc.py

@@ -98,8 +98,10 @@ def test_read_vgac(self, nc_filename):
         diff_s = (scn_["scanline_timestamps"][0] - np.datetime64("2023-03-28T09:08:07")
                   - np.timedelta64(123, "ms"))
         diff_e = np.datetime64("2023-03-28T10:11:12") - scn_["scanline_timestamps"][-1]
-        assert (np.abs(diff_e) < np.timedelta64(5000, "ns"))
-        assert (np.abs(diff_s) < np.timedelta64(5000, "ns"))
+        assert (diff_e < np.timedelta64(5000, "ns"))
+        assert (diff_s < np.timedelta64(5000, "ns"))
+        assert (diff_e > np.timedelta64(-5000, "ns"))
+        assert (diff_s > np.timedelta64(-5000, "ns"))
         assert (scn_["M05"][0, 0] == 100)
         assert (scn_["M15"][0, 0] == 400)
         assert scn_.start_time == datetime.datetime(year=2023, month=3, day=28,