ATLAS Self-Siphoning Rain Gauge Error Estimates

Abstract

This report describes sampling and error characteristics of self-siphoning rain gauges used on moored buoys designed and assembled at NOAA's Pacific Marine Environmental Laboratory (PMEL) for deployment in the tropical Pacific and Atlantic Oceans in support of climate studies. Self-siphoning rain gauges were chosen for use on these buoys because they can be calibrated at PMEL before and after deployment. The rainfall data are recorded at 1-min intervals, from which daily mean rate, standard deviation, and percent time raining are calculated and telemetered to PMEL in real time. At the end of the deployment, the 1-min, internally recorded data are recovered and processed to produce 10-min rain rates. Field data from a subset of these rain gauges are analyzed to determine data quality and noise levels. In addition, laboratory experiments are performed to assess gauge performance. The field data indicate that the noise level during periods of no rain is 0.3 mm h?1 for 1-min data, and 0.1 mm h?1 for 10-min data. The estimated error in the derived rain rates, based on the laboratory data, is 1.3 mm h?1 for 1-min data, and 0.4 mm h?1 for 10-min data. The error in the real-time daily rain rates is estimated to be at most 0.03 mm h?1. These error estimates do not take into account underestimates in accumulations due to effects of wind speed on catchment efficiency, which, though substantial, may be correctable. Estimated errors due to evaporation and sea spray, on the other hand, are found to be insignificant.