minor changes for CF1.8 compliance

Author: leric2

mwr_raw2l1/config/L1_format.yaml

@@ -35,7 +35,8 @@ variables:
     _FillValue: null
     optional: False
     attributes:
-      long_name: Time interval endpoints
+      long_name: Start and end time (UTC) of the measurement
+      units: seconds since 1970-01-01 00:00:00
 
   lat:
     name: station_latitude
@@ -72,6 +73,7 @@ variables:
       long_name: Altitude above mean sea level of measurement station
       standard_name: altitude
       units: m
+      positive: up
 
   frequency:
     name: frequency
@@ -458,7 +460,7 @@ attributes:
   license: Closed-Use Non-Commercial General Licence 1.0 (CUNCGL)
   network_name: E-PROFILE
   campaign_name: ''
-  comment: ''
+  comment: ' '
   source: Ground Based Remote Sensing
   dependencies: None
   # history is directly set in NetCDF writer