| Overview |
| Site Selection |
| Parameter Measured |
| Air Temperature |
| Moisture |
| Wind |
| Solar Radiation |
| Systems Architecture |
| Site Maintenance |
| Metadata |
| Data Quality |
Overview
The Kentucky Mesonet operates upon a foundation comprised of monitoring sites, instrumentation, and computing and communications architecture. That foundation supports quality assurance operations consisting of site maintenance, metadata collection, and data quality assessment. The integrity of the Kentucky Mesonet is contingent upon each of these elements.
Site Selection
The selection of Kentucky Mesonet environmental monitoring sites follows extensive community outreach. By enlisting the help of local officials and stakeholders who know their communities best, monitoring sites can often be found that both meet scientific criteria and provide added benefits to local communities. Candidate sites are surveyed and scored in accordance with criteria for monitoring temperature, precipitation, wind, and soil that are based on World Meteorological Organization standards. Final site selections reflect input from the state climatologist, a Kentucky-based representative of the National Weather Service, and the state soil scientist.
Air Temperature Sensors
Thermometrics Corporation Platinum Resistance Thermometer (PRT)
PRTs are the source of official temperature record of the network. Three Thermometrics PRTs are installed at each station inside of an aspirated radiation shield. The shield is mounted such that the sensor measures the air temperature at 1.5 meters above ground. The sensors sample air every three seconds. The reported temperature is the five minute average of the three-second samples. After being received by the Kentucky Mesonet Network Operations Center, the three PRT values are averaged together to calculate the official five-minute temperature value (TAIR) for the station. The redundancy of the sensors allow for the quick recognition of a sensor that needs to be recalibrated.
Variables | Standard | Range | Resolution | Accuracy |
|---|---|---|---|---|
TA01, TA02, TA03 | °C | -60°C to +300°C | 0.01°C | °0.4% over range |
Vaisala HMP45C Temperature and Relative Humidity Probe
A Vaisala HMP45C probe is installed inside of an unaspirated radiation shield at 1.5 meters above ground. Relative humidity (RELH, see Moisture Sensors) and air temperature (THMP) are measured. THMP is not the official source of site temperature data but aids aspects of quality assurance. The sensor is sampled every three seconds by the datalogger. The five minute temperature value is a five minute average of the three second temperature samples. Due to the lack of artificial aspiration of the radiation shield, the temperature sensor will possess an error that is pronounced with calm winds and strong solar radiation.
Variables | Standard | Range | Resolution | Accuracy |
|---|---|---|---|---|
THMP | °C | -39.2°C to +60°C | 0.1°C | °0.2°C (at +20°C) |
°0.3°C (at 0°C and +40°C) | ||||
°0.4°C (at -20°C and +60°C) | ||||
Moisture Sensors
Vaisala HMP45C Temperature and Relative Humidity Probe
A Vaisala HMP45C probe is installed inside of an unaspirated radiation shield at 1.5 meters above ground. Relative humidity (RELH) and air temperature (THMP, see Air Temperature Sensors) are measured. The sensor is sampled every three seconds by the datalogger. Every five minutes, the most recent three-second humidity sample is used as the official relative humidity value for the five-minute period. The five minute temperature value is a five minute average of the three second temperature samples. Due to the lack of artificial aspiration of the radiation shield, the temperature sensor will possess an error that is pronounced with calm winds and strong solar radiation.
Variables | Standard | Range | Resolution | Accuracy |
|---|---|---|---|---|
THMP | °C | -39.2°C to +60°C | 0.1°C | °0.2°C (at +20°C) |
°0.3°C (at 0°C and +40°C) | ||||
°0.4°C (at -20°C and +60°C) | ||||
RELH | % | 0 to 100% | 1% | °2% RH (for 0 to 90% RH) |
°3% RH (for 90 to 100% RH) | ||||
Vaisala VRG101 All Weather Weighing Bucket Precipitation Gauge
The Vaisala VRG101 is installed 20 feet southeast of the site tower. Every five minutes, the gauge calculates a differential in the precipitation accumulation in the bucket.
Several preventative measures have been taken to minimize the exposure error of the instrument. The gauge is surrounded by an alter shield to decrease any adverse effects from the wind. To prevent any ice or snow accumulation, the rim of the gauge is heated when specific conditions are met.
Variables | Standard | Range | Resolution | Accuracy |
|---|---|---|---|---|
PRCP | mm | 0.0 to 999.0 mm | 0.1 mm | 0.2 mm (for precip event >0.5 mm) |
Texas Electronics TE525 Tipping Bucket Rain Gauge
At select stations (currently, only RSVL), a tipping bucket rain gauge has been installed. It is not the offical source of site precipitation data but is an aid to precipitation quality assurance. While the resolution of the gauge is limited to the amount of water each bucket can hold, the long term precipitation totals are comparable to the weighing bucket. Tipping bucket gauges are widely used in meteorological networks and therefore provide valuable data for intercomparison.
Variables | Standard | Range | Resolution | Accuracy |
|---|---|---|---|---|
PTIP | mm | 0.000 to 999.000 mm | 0.254 mm | °1% (up to 25.4 mm hr-1) |
+0, -3% (25.4 to 50.8 mm hr-1) | ||||
+0, -5% (50.8 to 76.2 mm hr-1) | ||||
Wind Sensors
RM Young 05103-5 Wind Monitor
The Wind Monitor is a propeller anemometer mounted on the site tower at ten meters above the ground. Wind speed and direction are measured by the revolution of the propeller and vane body, respectively. The instrument is sampled every three seconds by the datalogger. The reported values (WSPD and WDIR) are five-minute averages of the three-second samples. In addition, when the five-minute average wind speed is zero (calm conditions), all other wind variables are automatically set to zero.
Maximum three-second wind speed value (WMAX) within the five minute period is reported. On the data pages, this appears as a gust if it is more than five miles-per-hour higher than a minimum 25 mile-per-hour five minute average wind speed.
Variables | Standard | Range | Resolution | Accuracy | Starting |
|---|---|---|---|---|---|
WSPD, WSMX | m s-1 | 0.0 to 60.0 m s-1 | 0.3 m s-1 | °0.3 m s-1 | 1 m s-1 |
WDIR | ° | 0 to 360° | 1° | °3° | 1.1 m s-1 |
Solar Radiation Sensors
Apogee CS300 Silicon Pyranometer (PYR-P)
An Apogee PYR-P pyranometer, mounted at two meters above ground on the site tower, measures incoming solar radiation in Watt-hour per square meter. Every five minutes, the sensor is sampled for the most recent three-second value. The sample is multiplied by the number of seconds in five minutes (300) to get an estimate of the solar radiation over the past five minutes. This also gets rid of the time factor in the units.
Variables Measured | Standard Units | Range | Resolution | Accuracy |
|---|---|---|---|---|
SRAD | W m-2 | 0.0 to 2000.0 W m-2 | 0.2 mV per W m-2 | °5% |
Systems Architecture
The selection of Kentucky Mesonet environmental monitoring sites follows extensive community outreach. By enlisting the help of local officials and stakeholders who know their communities best, monitoring sites can often be found that both meet scientific criteria and provide added benefits to local communities. Candidate sites are surveyed and scored in accordance with criteria for monitoring temperature, precipitation, wind, and soil that are based on World Meteorological Organization standards. Final site selections reflect input from the state climatologist, a Kentucky-based representative of the National Weather Service, and the state soil scientist.
Site Maintenance
Kentucky Mesonet technicians visit each station a minimum of three times a year: Spring, Summer, and Fall. During each scheduled maintenance visit, technicians perform the required tasks to keep the instrumentation within manufacturer specifications. When a sensor fails this test, it is brought back to the Kentucky Mesonet instrumentation laboratory to be recalibrated or decommissioned. Due to the design of the weighing bucket precipitation gauges, antifreeze must be added to the bucket during the fall site visit before the first expected freeze. The antifreeze is later removed during the spring site visit.
Upon recognition of a problem, the quality assurance specialist issues a trouble ticket describing the situation. The ticket notifies the technicians of the problem and provides a deadline for the fix. When the technicians have finished the repair, the ticket is submitted back to the quality assurance specialist for approval and archival.
Metadata
Metadata, or data about data, are recorded for each station in multiple stages. During the initial site survey, metadata such as latitude/longitude and elevation are recorded. Other metadata, like calibration coefficients and serial numbers, are recorded in the instrumentation laboratory and assigned to the appropriate station's dataset. Metadata relating to physical site characteristics, instrumentation, and site maintenance activities are combined in a metadata database. In turn, the metadata database is integrated with the database for meteorological data.
Data Quality Assessment
Standard data visualization tools are currently the primary means of manual data quality assessment. Data that has been flagged as bad are not included in the historical data. Knowledge of system behavior developed using these tools will aid in the development of algorithms for assessing data quality. In the future, both automated algorithms and interactive data visualization tools will be used to assess the quality of all incoming data.