Establishing a Relationship between Aspirated and Non-Aspirated Temperature Sensors in Support of CRN Power Management

The United States Climate Reference Network (USCRN) was established in 2003 to provide the necessary accuracy in measurements of air temperature to determine the climate trends over the next 50 – 100 years. In addition to the primary measures of surface air temperature, and precipitation, the stations also provide observations of solar radiation, wind speed, surface temperature, and relative humidity. In order to obtain accurate and representative data, some of the stations are positioned in locations where line power is not available. These stations are powered using solar panels. However, there have been a few periods over the past several winters in which the system batteries in the solar systems have become highly discharged and power management of the total CRN system becomes an issue. The fans of the aspirated shields draw a majority of the power (~1.5 amps at 12 VDC), but aspiration of the shield is important to obtain accurate measurements of surface air temperature. If the fans were operated only part of the hour, could a correction be applied to the remaining data in the hourly period to correct the bias?

In this project, a CRN site in Wolf Point, MT named Give Out Morgan ,was examined due to an aspirated shield fan cutting off at 7am on January 31, 2009, till 11pm May 11, 2009. This provided aspirated and non-aspirated temperature readings. This data was examined to determine the difference between aspirated and non- aspirated temperatures, to find a correction factor, and to determine a solution for power management.