With a goal of maintaining an efficient measurement system that meets the data and information needs of
scientists, policy-makers, educators, and the public, NADP committees in 2006 passed two resolutions requiring
equipment changes for all NTN, MDN, and AIRMoN sites. The first resolution requires all sites to install
an approved electronic rain gage by the end of 2011. The second resolution requires those sites receiving at
least 20 percent of their annual precipitation as snow to install an Alter-type wind shield.
How were gages selected?
NADP conducted bench and field tests of several commercially-available gages to determine which models best meet the following performance criteria.
- Range (liquid capacity): 25 cm depth or greater
- Resolution (sensitivity): 0.02 cm depth or less
- Accuracy (calibration test): +/- 0.05 cm over entire range
- Accuracy (field): within 0.05 cm or 5% of Weather Service standard
- Real-time reporting: report within 5 minutes of start of precipitation
- False reporting: no false positive reports in dry weather
- Wind and temperature limits: operate at 15m/s (25m/s gusts) windspeed and in -45 C to +50C temperatures
- Reliability: more than 500 days with no failures
- Maintenance: maintenance interval more than 90 days
- Power supply: 110 VAC or 12 VDC (less than 5 amps at 12 VDC)
Why is NADP replacing its rain gages?
In addition to accurately measuring all types of precipitation, NADP requires a gage that
allows site operators to quickly and easily evaluate gage and collector performance
in the field. With the Belfort B5-780, this involved the time-consuming and often innacurate
task of reading the rain gage chart. With an electronic gage, the operator gets a report
from the gage that details the equipment's performance.
Also, eliminating the charts, ink, and the need to replace mechanical components such as clocks,
should help minimize the long-term costs of maintaining the gages