AZMET Sensors

   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

     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 

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

     Precipitation  Sierra Misco       Tipping       Gage Top  +/-1mm
                    RG2501 Rain        Bucket With   At ~43 cm
                    Gage               Magnetic      Above 
                                       ReedSwitch    surface

                   Texas Electronics   Tipping       Gage Top  +/-1mm
                   Model # TE525       Bucket With   At ~43 cm
                   Rain Gage           Magnetic      Above 
                                       Reed Switch   surface

     Wind Speed     Met One Model      Anemometer    3.0 m     +/-1.5%
                    014A Wind Speed    Using Reed    Above          
                    Sensor             Switch        Surface

                    RM Young           Anemometer    3.0 m     +/-0.5 m/s
                    Wind Sentry        Generating    Above          
                    Model 03101-5      AC Voltage    Surface

     Wind Direct.   Met One Model      Wind Vane     3.0 m     +/-5 degrees
                    024A Wind Dir.     Attached to   Above 
                    Sensor             Potentiom.    Surface

                    RM Young           Wind Vane     3.0 m     +/-5 degrees
                    Wind Sentry        Attached to   Above          
                    Model 03301-5      Potentiom.    Surface