Each AZMET weather station is controlled by a Campbell Scientific Inc.
   datalogger. From 1987 to 1992, the datalogger sampled the sensors every
   60 seconds. From 1993 to present, the sampling rate is every 10 seconds.
   At the end of each hour, the datalogger processes and stores all the 
   sampled measurements for that hour.  Rain and solar measurements are 
   totalized.  Soil temps are point measurements taken on the hour, and
   all other readings are averaged from measurements during the hour.
   An AZMET hour starts at one second after the hour and goes to the top
   of the next hour. For example, the data listed for the 8:00 hour are
   measurements from 7:00:01 to 8:00:00.
   At midnight, the datalogger processes all the 10 second measurements,
   picks out the daily maximums and minimums, and calculates the daily
   averages, and totals.  An AZMET day begins one second after midnight.

   AZMET is on Arizona time; Mountain Standard Time.
   Arizona does not adjust clocks for daylight savings time.

   Below is a list of the sensors used at AZMET stations.
   Once a year, we replace all the Solar sensors and Wind Speed sensors
   with recalibrated sensors.  Humidity sensor chips are replaced twice
   a year.  Other sensors are carefully monitored and checked during
   each station visit.


     Measurement     Instrument Model  Sensor Type   Siting   Accuracy
     -----------     ----------------  -----------   ------   --------
     Air Temp.       Vaisala           Thermistor    1.5 m     +/-0.4C
     1992-Present    HMP35C, HMP45C    Fenwall       Above
                                       (UUT51J1)     Surface

     Air Temp.       Camp. Sci. Model  Thermistor    1.5 m     +/-0.2C
     1987-1995       207 Probe         Fenwall       Above
                                       (UUT51J1)     Surface


     Rel. Humidity   Vaisala           Vaisala       1.5 m     +/-2%RH
     1992-Present    HMP35C, HMP45C    Capacitive    Above
                                                     Surface

     Rel. Humidity   Camp. Sci. Model  Resistance    1.5 m     +/-5%RH
     1987-1995       207 Probe         Chip: Phys    Above
                                       Chem PCRC11   Surface



     Soil Temp.     Thermocouple       Type 1        5,10 cm   +/-0.2C
                                       Copper-       Depth
                                       constantan    Bare 
                                                     Surface

     Solar Radiat.  LiCor LI200        Silcon Cell   2.5m      +/-5%
                    Pyranometer        Pyranometer   Above
                                                     Surface

Licor LI200 Description