All USCRN stations are equipped with a standard set of core sensors attached to a 10-foot (3-meter) mast. Off the shelf, commercially-available sensors are selected based on performance, durability, and cost. Many USCRN stations are equipped to observe relative humidity, soil moisture and soil temperature, and all have the capability to add supplementary sensors in the future.
The core parameters being measured are:
USCRN stations are equipped with three temperature sensors each mounted in a separate aspirated solar radiation shield. In general, an aspirated air temperature sensor is superior to one mounted in a passive radiation shield. Errors in a passive shield can be as large as several degrees Centigrade in calm wind and strong solar radiation/sunlight conditions.
All USCRN stations are equipped with heated precipitation gauges configured with three vibrating-wires to measure both liquid and solid precipitation, and a wetness sensor to improve upon the gauge's accuracy. Most USCRN stations are also equipped with a tipping bucket gauge.
Solar radiation (sunlight) is one of two variables needed to develop the relationship between air temperature measured at a USCRN station and air temperature measured at nearby historical stations. Solar radiation also can be used to assess the type of clouds during daytime and it is an important variable in agricultural and hydro-meteorological models. The USCRN contributes significantly to the development of a high quality U.S. solar radiation database.
Wind speed at the height of the temperature sensor is the second of two variables needed to develop the transfer function between temperature measured at a USCRN station and temperature measured at nearby or co-located historical stations.
These variables are transmitted hourly via satellite, and summary statistics are computed operationally at the National Climatic Data Center (NCDC).
The primary purpose of the USCRN network is to monitor air temperature and precipitation. In addition to air temperature and precipitation, each station measures ground surface (IR) temperature, solar radiation, wind speed, and several values that monitor the operating condition of the equipment. These secondary parameters contribute to improving the confidence in the observational measurements, and provide insight into the reliability and performance of the primary sensors. Each station transmits data once every hour to a GOES satellite; within a few moments of transmission the data are available on this web site. This page describes the details of this data stream.
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Primary Measurements: Surface Air Temperature Precipitation |
Secondary Measurements: IR Ground Surface Temperature Solar Radiation Wind Speed Miscellaneous |
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Surface Air Temperature
Each USCRN station has three thermometers which report independent temperature measurements each hour. These three observed temperature value are used to derive a single official USCRN temperature value for the hour. This single value is sometimes a median and sometimes an average of various combinations of the three observed values, depending on information about which equipment is functioning reliably. For the details of how this single value is computed, see the Official USCRN Temperature Algorithm. Each station transmits the three independent observed values; the computation of the official USCRN temperature value is done after these values arrive at NCDC. The discussion below describes the details of the three observed values. Each station has three Thermometrics platinum resistance thermometers, each of which is housed in its own Met One 076B 7308 aspirated solar shield. Each thermometer measures the temperature (in degrees Celsius) every 2 seconds. Every 5 minutes the station datalogger computes the average of these 2-second values, giving 12 5-minute averages for each thermometer: Tik = average of 2-second values for i-th 5-minute period in the hour, i=1,...,12. [k is the thermometer number (1, 2, or 3).] The station's hourly data stream contains the following 7 values for each thermometer (a total of 21 values):
In addition to the above thermometer values, the station also measures the speed of the fan in each aspirated shield. As the shield's fan rotates, a contact closes and generates a pulse twice per rotation. The datalogger counts these pulses every two seconds. Every hour these 2-second values are averaged to obtain an average number of pulses per second for the hour. The hourly data stream from the station thus include the following values (one value for each of the three sensors): FSk = average of 2-second pulse rates for the hour, in pulses per second, for shield number k = 1,2,3. Note that the speed of the fan, in revolutions per second, is half of FSk. For more details about the temperature sensor and
measurements, see the
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Precipitation
Each USCRN station measures precipitation with a Geonor T-200B precipitation gauge. This gauge produces several independent observed precipitation measurements each hour. These observed values are used to derive a single official USCRN precipitation value for the hour. For the details of how this single value is computed, see the Official USCRN Precipitation Algorithm. Each station transmits the observed values; the computation of the official USCRN precipitation value is done after these values arrive at NCDC. The discussion below describes the details of the observed values. The Geonor T-200B uses a collection bucket which is suspended by three vibrating wire strain gauges. Each wire, when excited with 12V DC, vibrates with a frequency relative to the weight in the collection bucket. The gauge is surrounded by a small wind/snow shield, and a controlled heater device is attached to the gauge to prevent ice buildup. The station datalogger measures the frequency of each vibrating wire and converts it to a gauge depth (in mm) each hour on the hour, at 15 minutes past the hour, at 30 minutes past the hour, and at 45 minutes past the hour. The hourly data stream contains the following values 12 for each wire k = 1,2,3 (a total of 36 values):
For more details on the operation of the Geonor precipitation gauge
and how these values are computed, see the
A Hydrological Services Tipping Bucket Rain Gauge Model TB-3 is installed at some sites for comparison purposes only. Its data are not quality controlled and are not considered official USCRN precipitation readings. |
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IR Ground Surface Temperature
An Apogee Instruments IRTS-P infrared temperature sensor measures the infrared ground surface temperature (in degrees Celsius) at each station. The datalogger samples the sensor every two seconds. Every five minutes these two-second samples are averaged to obtain 5-minute values. Each hour the station's data stream contains:
For more details about the IR Ground Surface Temperature sensor, see
the |
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Solar Radiation
A Kipp & Zonen SP Lite Pyranometer measures solar radiation (watts per meter squared, W/m2) at each station. The datalogger samples the sensor every two seconds. Every five minutes these two-second samples are averaged to obtain 5-minute values. Each hour the station's data stream contains:
For more details about the solar radiation sensor, see
the |
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Wind Speed
A Met One Model 014A anemometer measures wind speed (in meters per second) at each station. The datalogger samples the anemometer every two seconds. Every five minutes these two-second samples are averaged to obtain 5-minute values. Each hour the station's data stream contains:
For more details about the wind speed measurement, see
the |
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Miscellaneous
In addition to the above elemental observations, the hourly data stream from each station includes the following values:
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Data Stream Summary
In summary, the hourly data stream from each station contains the following values. (In the table below, you can click on a value to jump to the place in this page where it is described in more detail). |




