Monday, 15 January 2007: 4:15 PM
The use of a wetness sensor in precipitation measurements for the U.S. Climate Reference Network
207A (Henry B. Gonzalez Convention Center)
The U. S. Climate Reference Network (USCRN) is a key element in climate monitoring for the United States. The stations in the network monitor temperature through redundant temperature readings and the precipitation by Geonor all-weather gauges. These gauges determine the depth of precipitation they hold by the vibration of three independent wires. Each wire is individually calibrated, with stable long-term behavior. However, there are small but significant variations in the wire vibrations and their implied precipitation depths, which are not related to precipitation. This paper discusses the use of a wetness sensor to distinguish Geonor depth changes due to precipitation from those from other causes. The precipitation from a Geonor gauge is determined by an algorithm which analyzes the depth changes of the three wires, makes a determination of the quality of measurement from each, and produces a single precipitation value. In a small number of cases, a non-zero value of precipitation is produced when other sources of information indicate a lack of precipitation. The recently installed wetness sensor is shown to provide a highly reliable source of this additional information. It is used to eliminate false precipitation from spurious depth changes, diurnal depth variations, and dew. Examples and statistics from USCRN sites and from the Sterling, VA and Johnstown, PA test sites are shown which indicate the wetness sensor's high value and reliability.