CRN logo CRN logo
What Is Measured

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:

Air Temperature

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.

Precipitation

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

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

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).

Measured Elements

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.

Primary Measurements:
    Surface Air Temperature
    Precipitation

Data Stream Summary

Secondary Measurements:
    IR Ground Surface Temperature
    Solar Radiation
    Wind Speed
    Miscellaneous

Top 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):

  1. Tkavg = average (°C) of Tk1, ..., Tk12
  2. Tkstdev = standard deviation of Tk1, ..., Tk12
  3. Tkmin = minimum (°C) of Tk1, ..., Tk12
  4. Tkmintime = time at which the above minimum occurred
  5. Tkmax = maximum (°C) of Tk1, ..., Tk12
  6. Tkmaxtime = time at which the above maximum occurred
  7. Tk12 (°C)

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 doc documentAir Temperature Sensor Summary. For more details about the aspirated shield, see the doc documentAspirated Shield Summary.

 
Top 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):

  1. Pk1 = precipitation (mm) for 1st 15 minutes of the hour
  2. Pk2 = precipitation (mm) for 2nd 15 minutes of the hour
  3. Pk3 = precipitation (mm) for 3rd 15 minutes of the hour
  4. Pk4 = precipitation (mm) for 4th 15 minutes of the hour
  5. Pktot = precipitation total (mm) for hour
  6. Dk4 = gauge depth (mm) at end of 1st 15 minutes of the hour
  7. Dk4 = gauge depth (mm) at end of 2nd 15 minutes of the hour
  8. Dk4 = gauge depth (mm) at end of 3rd 15 minutes of the hour
  9. Dk4 = gauge depth (mm) at end of 4th 15 minutes of the hour
  10. Fkavg = average wire frequency for the hour
  11. Fkmin = minimum wire frequency for the hour
  12. Fkmax = maximum wire frequency for the hour

For more details on the operation of the Geonor precipitation gauge and how these values are computed, see the doc documentPrecipitation Gauge Summary.

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.

 
Top 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:

  1. IRavg = average (°C) of the 12 5-minute values for the hour
  2. IRstdev = standard deviation of the 12 5-minute values for the hour

For more details about the IR Ground Surface Temperature sensor, see the doc documentsummary.

 
Top 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:

  1. SRavg = average (W/m2) of the 12 5-minute values for the hour
  2. SRstdev = standard deviation of the 12 5-minute values for the hour

For more details about the solar radiation sensor, see the doc documentsummary.

 
Top 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:

  1. WSavg = average (meters/sec) of the 12 5-minute values for the hour
  2. WSstdev = standard deviation of the 12 5-minute values for the hour

For more details about the wind speed measurement, see the doc documentsummary.

 
Top Miscellaneous

In addition to the above elemental observations, the hourly data stream from each station includes the following values:

  1. FGBV = Battery voltage for fan and GOES transmitter battery
  2. FGBVfull = Battery voltage for fan and GOES transmitter battery under full load
  3. DLBV = Battery voltage for datalogger
  4. DLDO = Number of minutes in this hour that the datalogger door was open
 
Top 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).

Value Description Units
T1avg Average for air temp sensor #1 °C
T1stdev Standard deviation for air temp sensor #1  
T1min Minimum for air temp sensor #1 °C
T1mintime Time of minimum for air temp sensor #1 minutes
T1max Maximum for air temp sensor #1 °C
T1maxtime Time of maximum for air temp sensor #1 minutes
T112 Temp for last 5 minutes of hour for air temp sensor #1 °C
T2avg Average for air temp sensor #2 °C
T2stdev Standard deviation for air temp sensor #2  
T2min Minimum for air temp sensor #2 °C
T2mintime Time of minimum for air temp sensor #2 minutes
T2max Maximum for air temp sensor #2 °C
T2maxtime Time of maximum for air temp sensor #2 minutes
T212 Temp for last 5 minutes of hour for air temp sensor #2 °C
T3avg Average for air temp sensor #3 °C
T3stdev Standard deviation for air temp sensor #3  
T3min Minimum for air temp sensor #3 °C
T3mintime Time of minimum for air temp sensor #3 minutes
T3max Maximum for air temp sensor #3 °C
T3maxtime Time of maximum for air temp sensor #3 minutes
T312 Temp for last 5 minutes of hour for air temp sensor #3 °C
FS1 Average fan speed for aspirated shield #1 pulses/sec
FS2 Average fan speed for aspirated shield #2 pulses/sec
FS3 Average fan speed for aspirated shield #3 pulses/sec
P11 Precip for 1st 15 minutes of hour for vibrating wire #1 mm
P12 Precip for 2nd 15 minutes of hour for vibrating wire #1 mm
P13 Precip for 3rd 15 minutes of hour for vibrating wire #1 mm
P14 Precip for 4th 15 minutes of hour for vibrating wire #1 mm
P1tot Precip hourly total for vibrating wire #1 mm
D14 Gauge depth at end of 1st 15 minutes of hour for vibrating wire #1 mm
D14 Gauge depth at end of 2nd 15 minutes of hour for vibrating wire #1 mm
D14 Gauge depth at end of 3rd 15 minutes of hour for vibrating wire #1 mm
D14 Gauge depth at end of 4th 15 minutes of hour for vibrating wire #1 mm
F1avg Average frequency for vibrating wire #1 for hour Hz
F1min Minimum frequency for vibrating wire #1 for hour Hz
F1max Maximum frequency for vibrating wire #1 for hour Hz
P21 Precip for 1st 15 minutes of hour for vibrating wire #2 mm
P22 Precip for 2nd 15 minutes of hour for vibrating wire #2 mm
P23 Precip for 3rd 15 minutes of hour for vibrating wire #2 mm
P24 Precip for 4th 15 minutes of hour for vibrating wire #2 mm
P2tot Precip hourly total for vibrating wire #2 mm
D24 Gauge depth at end of 1st 15 minutes of hour for vibrating wire #2 mm
D24 Gauge depth at end of 2nd 15 minutes of hour for vibrating wire #2 mm
D24 Gauge depth at end of 3rd 15 minutes of hour for vibrating wire #2 mm
D24 Gauge depth at end of 4th 15 minutes of hour for vibrating wire #2 mm
F2avg Average frequency for vibrating wire #2 for hour Hz
F2min Minimum frequency for vibrating wire #2 for hour Hz
F2max Maximum frequency for vibrating wire #2 for hour Hz
P31 Precip for 1st 15 minutes of hour for vibrating wire #3 mm
P32 Precip for 2nd 15 minutes of hour for vibrating wire #3 mm
P33 Precip for 3rd 15 minutes of hour for vibrating wire #3 mm
P34 Precip for 4th 15 minutes of hour for vibrating wire #3 mm
P3tot Precip hourly total for vibrating wire #3 mm
D34 Gauge depth at end of 1st 15 minutes of hour for vibrating wire #3 mm
D34 Gauge depth at end of 2nd 15 minutes of hour for vibrating wire #3 mm
D34 Gauge depth at end of 3rd 15 minutes of hour for vibrating wire #3 mm
D34 Gauge depth at end of 4th 15 minutes of hour for vibrating wire #3 mm
F3avg Average frequency for vibrating wire #3 for hour Hz
F3min Minimum frequency for vibrating wire #3 for hour Hz
F3max Maximum frequency for vibrating wire #3 for hour Hz
IRavg IR temp average for hour °C
IRstdev IR temp standard deviation for hour  
SRavg Solar radiation average for hour Watts/meter2
SRstdev Solar radiation standard deviation for hour  
WSavg Wind speed average for hour meters/sec
WSstdev Wind speed standard deviation for hour  
FGBV Voltage for fan and GOES transmitter battery volts
FGBVfull Voltage for fan and GOES transmitter battery under full load volts
DLBV Voltage for datalogger battery volts
DLDO Number of minutes datalogger door was open minutes