Question on topics in weather.csv

[golfvert]

In the current weather.csv, I can see:

5 | ship-sub-hourly | Ship based weather observations with a reporting frequency < 1 hour |  
6 | fixed-marine-platforms-hourly | Hourly weather observations from fixed marine platforms, e.g. rigs and offshore platforms |  
7 | fixed-marine-platforms-sub-hourly | Weather observations from fixed marine platforms, e.g. rigs and offshore platforms, with a reporting frequency < 1 hour |  
8 | fixed-land-stations-sub-hourly | Weather observations from fixed land stations with a reporting frequency < 1 hour |  
9 | mobile-land-stations-sub-hourly | Weather observations from mobile land stations with a reporting frequency < 1 hour

What is the purpose of splitting hourly and sub-hourly ?

There is no fixed-land-stations-hourly for example. They are synop ?

[amilan17]

@david-i-berry