Operation
A small datalogger mounted on the mast of each station is connected to the electronic
sensors by wires. Once every minute, the datalogger takes a reading of each sensor
and records it. It continues for one hour, then averages the 60 readings for an
hourly average, or accumulates the 60 readings for an hourly total, and stores all
these in its memory. It continues collecting data in this manner throughout the
day (midnight to midnight). After 24 hours have elapsed, the datalogger then calculates
the daily averages and totals using the 24 hourly averages and totals and stores
them. The datalogger also determines the maximum and minimum temperatures and relative
humidities. These values are the highest and lowest of the one-minute readings during
the day.
After 12:00 midnight (Pacific Standard Time) the main CIMIS computer begins requesting
data from the stations (polling). This communication is done by telephone or internet.
Each station has its own telephone service and modem. Polling data continues through
the early morning hours and is finished for most stations by 4:00 a.m. Some stations
will not answer the phone call from the main computer during these early morning
hours due to phone connection problems.
Polling continues for these stations and is usually retrieved by 9:00 or 10:00 a.m.
The polling process repeats itself every 4 hours throughout the day to provide updated
hourly data.
After receiving the data, the CIMIS computer then performs three tasks:
1) Reference Evapotranspiration (ETo) is calculated,
2) The data is run through the quality control program and flags are placed appropriately
3) The data is stored in a database for retrieval by CIMIS users.
Once CIMIS weather station data has entered the database, it can be accessed by
Spatial CIMIS and combined with satellite data to provide Spatial CIMIS ETo. See
the Spatial Overview tab for more details.
Maintenance
Maintenance standards call for a CIMIS weather station maintenance visit every
3-4 weeks during the warmer months of the year. Visits decrease to about every five
or six weeks in the cooler months.
DWR maintained stations are visited by DWR staff out of DWR's Regional Offices.
Many other CIMIS stations are cooperatively maintained with help from local agencies
or individual people. All DWR maintained CIMIS weather stations are maintained according
to standards developed by DWR, including twice a year sensor calibration against
a set of standardized calibration sensors. Although our CIMIS stations not maintained
or owned by DWR are of high quality, DWR has limited control over the accuracy or
reliability of the weather data from them.
During the maintenance visit the station sensors are checked for operation and accuracy
and cleaned or replaced as required. Grass (fetch) in the field around and under
each station is mowed regularly to a height of about three inches. The grass is
irrigated and fertilized to keep it actively growing.
If you have any questions about station locations, siting environment, CIMIS data,
or possible cooperation for a new weather station, please call CIMIS Staff from one of our four DWR Regional Offices.