added short description

mlair/plotting/preprocessing_plotting.py

@@ -442,6 +442,19 @@ class PlotAvailabilityHistogram(AbstractPlotClass):
 
 
 class PlotPeriodogram(AbstractPlotClass):
+    """
+    Create Lomb-Scargle periodogram in raw input and target data. The Lomb-Scargle version can deal with missing values.
+
+    This plot routine is creating the following plots:
+
+    * "raw": data is not aggregated, 1 graph per variable
+    * "": single data lines are aggregated, 1 graph per variable
+    * "total": data is aggregated on all variables, single graph
+
+    If data consists on different sampling rates, a separate plot is create for each sampling.
+
+    To work properly, the data handler must have the attribute `.id_class._data`.
+    """
 
     def __init__(self, generator: Dict[str, DataCollection], plot_folder: str = ".", plot_name="periodogram",
                  variables_dim="variables", time_dim="datetime", sampling="daily"):