#208 Merge pull request from deshima-dev/issue150

Add signal spike removal

decode/qlook.py

@@ -364,8 +364,10 @@ def pswsc(
             frequency_units=frequency_units,
         )
 
+        da_despiked = despike(da)
+
         # make spectrum
-        da_scan = select.by(da, "state", ["ON", "OFF"])
+        da_scan = select.by(da_despiked, "state", ["ON", "OFF"])
         da_sub = da_scan.groupby("scan").map(subtract_per_scan)
         spec = da_sub.mean("scan")
 
@@ -379,7 +381,7 @@ def pswsc(
         fig, axes = plt.subplots(1, 2, figsize=DEFAULT_FIGSIZE)
 
         ax = axes[0]  # type: ignore
-        plot.data(da.scan, ax=ax)
+        plot.data(da_despiked.scan, ax=ax)
 
         ax = axes[1]  # type: ignore
         plot.data(spec, x="frequency", s=5, hue=None, ax=ax)
@@ -1094,6 +1096,21 @@ def _scan(
         return save_qlook(fig, file, overwrite=overwrite, **options)
 
 
+def despike(dems: xr.DataArray, /) -> xr.DataArray:
+    is_spike = (
+        xr.zeros_like(dems.time, bool)
+        .reset_coords(drop=True)
+        .groupby(utils.phaseof(dems.beam))
+        .map(flag_spike)
+    )
+    return dems.where(~is_spike, drop=True)
+
+
+def flag_spike(index: xr.DataArray, /) -> xr.DataArray:
+    index[:1] = index[-1:] = True
+    return index
+
+
 def mean_in_time(dems: xr.DataArray) -> xr.DataArray:
     """Similar to DataArray.mean but keeps middle time."""
     middle = dems[len(dems) // 2 : len(dems) // 2 + 1]