The original NERON datalogger code used a first generation GEONOR algorithm developed for the USCRN to compute precipitation accumulation inside each individual datalogger. The accumulation calculated by the datalogger was reported by the site for dissemination to users. Because sensitive vibrating wires were used, the GEONOR required a solid foundation. Limitations of the first generation algorithm and numerous unstable foundations caused many reports of erroneous precipitation across New England. Personnel at the NERON Operations and Monitoring System and field technicians have downloaded a much improved, second generation logger program to many sites which changes the way precipitation accumulation is calculated. Instead of calculating accumulation in the datalogger, these sites now report each vibrating wire frequency and precipitation depth at five-minute resolution. During post-processing, the three vibrating wire depths are passed through a Quality Assurance (QA) system designed to flag those values that meet any of the following criteria: out of range, do not agree with like instruments (e.g., vibrating wire data from one wire does not agree with the other two wires at the site), coincident with a site visit, or manually flagged as erroneous by QA personnel. If data pass the QA process, the second generation GEONOR algorithm processes the resulting data to calculate an ‘official' five-minute accumulation. At the time of this writing, the new algorithm has proven to significantly reduce the number of false precipitation reports across the New England network.
In addition to the implementation of the new GEONOR algorithm, NERON staff conduct a number of manual QA procedures. Each day, NERON precipitation data are compared to storm total radar estimates. Software developed for the NERON program automatically compares the radar estimate for each site using the site's latitude and longitude. The radar estimates are then compared to the precipitation recorded by the NERON site coincident with the times listed in the radar file. A map displays the radar estimate, NERON precipitation total, and radar image which allow QA personnel to view the data and find anomalies between the radar estimates and NERON precipitation accumulations. Although radar comparison provides a good spatial overview of precipitation accumulation, some areas tend to have poor estimates because of limitations in radar coverage.
To complement the radar analysis, nearby COOP sites are also used for rainfall comparisons. For near real-time comparison, daily hydrologic reports issued by each New England Weather Forecast Office are saved and used for comparison with NERON gauge reports. For data more than two-months old, COOP monthly summaries are obtained from NOAA's National Climatic Data Center.
In summary, quality precipitation measurements are dependant on several factors. NERON users have found that the quality of precipitation data has improved notably since the vibrating wire data are now quality assured before being processed by the latest USCRN GEONOR algorithm. In addition, NERON staff have been able to monitor precipitation gauge problems successfully by manually comparing the data with radar estimates and nearby manual COOP reports. By combining these processes, NERON has significantly improved the accuracy of precipitation measured in New England.