Network Maintenance The Department of Water Resources' (DWR) objective in operating the weather station network is to collect and disseminate high quality, accurate, and reliable irrigation management data to the public. To meet this objective, DWR is standardizing the operations and maintenance of the weather station network. All the weather stations in the CIMIS net- work are virtually identical, in that they all have the same equipment and sensors and operate similarly. All stations have their equipment and sensors mounted on a mast that is mounted on a tripod base. The sensors and their heights are as follows: Sensor Sensor Height Pyranometer (solar radiation) 2 meters Soil Temperature Sensor 15 centimeters below ground level Air Temperature Sensor 1.5 meters Humidity Sensor 1.5 meters Anemometer (wind speed) 2 meters Wind Vane (wind direction) 2 meters Precipitation Gauge 1 meter Operation A small datalogger (a small microprocessor) 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 data- loggers 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 (always Pacific Standard Time) a microcomputer located with the main CIMIS computer begins the interrogations of the stations. This communication is done using telephone lines. Each station has its own telephone service and modem. The microcomputer makes a phone connection with a datalogger and the data is dumped to the micro- computer. This continues through the early morning hours. The majority of the stations will be interrogated by 4:00 a.m. Some stations will not answer the phone call from the microcomputer during these early morning hours due to problems with the telephone lines themselves. Usually these stations will answer the telephone by 9:00 or 10:00 a.m. The collected data is transferred to the CIMIS computer. 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, and 3) the data is stored in a relational database for retrieval by CIMIS users. Maintenance All DWR maintained CIMIS weather stations are maintained according to standards developed by DWR. Those stations owned by DWR are maintained by DWR staff or with help from local agencies or people. Stations in the CIMIS network owned by others are maintained either by DWR or by the owners (in which case they may or may not be maintained to DWR's standards). DWR has no control over making sure the weather data from stations not maintained by DWR is accurate or reliable. Maintenance standards call for a 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. The main purpose of the maintenance visit is to check the sensors for accuracy and/or operation and to clean or replace sensors as required. The grass which is under each weather station site is mowed regularly to a height of about three inches. The grass is irrigated and fertilized to keep it actively growing. DWR maintained stations are visited by DWR staff out of DWR's District Offices. If you have any questions about station locations, siting environment, data or possible cooperation with a new weather station, please call one of our four DWR District Offices. All DWR maintained stations are calibrated for accuracy by DWR twice a year. Stations' sensors are compared against a set of standardized sensors used only for calibrations.