Handle OB.DAAC files, which do not have time variables (#296)

Co-authored-by: aynur <[email protected]>

podaac/subsetter/subset.py

@@ -560,6 +560,10 @@ def compute_time_variable_name(dataset: xr.Dataset, lat_var: xr.Variable, total_
         if var_name not in total_time_vars and 'time' in var_name_time.lower() and dataset[var_name].squeeze().dims[0] in lat_var.squeeze().dims:
             return var_name
 
+    # OB.DAAC data does not have a time variable. Returning the following field of a composite time value to avoid exceptions.
+    if '__scan_line_attributes__day' in dataset.data_vars:
+        return '__scan_line_attributes__day'
+
     raise ValueError('Unable to determine time variable')