Understanding set_1, set_1d, set_2, etc.

[simondgreenhill]

I'm trying to understand Synoptic's variable naming convention. What do the suffixes to various variables (e.g. air_temp_set_1, air_temp_set_1d, air_temp_set2, etc.) mean? I know SynopticPy automatically strips the _set_1 suffix with some special handling if both _set_1 and _set_1d are present. From a limited number of examples I've looked at, I've only ever encountered data ending in _1 (i.e., no set_2, set_3, etc.). Should I pay attention to these suffixes? When might they matter?

[blaylockbk]

Good question.

Some stations have multiple sensors measuring the same things, like wind at 2 meters and wind at 10 meters. The Synoptic API returns both report as and uses wind_speed_set_1 and wind_speed_set_2 to distiguish between the two measurements. Usually you would have to have some insider knowledge about the station to know which is which (or it might be in the metadata if you're lucky). Most stations won't have multiple sensors.

The d in _set_1d means it is a derived variable. For example, if a station does not report Relative Humidity, but it reports temperature and dew point, if you request RH from the API, then Synoptic will derive RH from temperature and dew point. In other words, when you see the "_set_1d", it means the station does not directly measure that quantity, but it was derived from other measurments. I believe there is some metadata in the raw json that tells you what variables were used to create the derived quantity and I think it lists the "method" in the Syntopic API documentation. It's been awhile since I looked at that.

[simondgreenhill]

Awesome, thank you for the detailed and clear reply!