The ARM Surface Meteorology Systems (MET) uses mainly conventional in situ sensors to obtain 1-minute statistics of surface wind speed, wind direction, air temperature, relative humidity, barometric pressure, and rain-rate. Additional sensors may be added to or removed from the base set of sensors depending upon the deployment location, climate regime, or programmatic needs. In addition, sensor types may change depending upon the climate regime of the deployment. These changes/additions are noted in the Deployment Locations and History section of the instrument handbook.
The Present Weather Detector was added to most MET systems at the Central Facilities and the Mobile Facilities in the past couple years. The Present Weather Detector (PWD) is an intelligent, multi-variable sensor for automatic weather observing systems (PWD User Guide, Attached). The PWD can measure the intensity and amount of both liquid and solid precipitation. A schematic of the PWD is shown in the PWD schematic, below. The PWD uses optical data along with data from the Vaisala Rain Sensor and the Temperature sensor to determine the precipitation intensity and type.
The MET was deployed on the MAGIC mobile deployment, but was known as the Marinemet (below, right) and had additional sensors installed.
For more information see MET.
The NSA metrics will normally have some flags tripped around the time it does the CMH daily self-check. The rest of the sites, albeit with some different variables, should be green for the most part. The TWP MET has an Optical Rain Gauge in addition to the normal Tipping Bucket Rain Gauge and Present Weather Detector. These additional instruments are still considered to be under the MET instrument.