Network of Infrared Thermometers Nearly Complete at SGP

 
Published: 28 February 2006

Red dots indicate extended facilities at SGP with the new IRTs installed; green dots indicate future installations.

As reported in April 2005, a network of infrared thermometers (IRT) is being installed throughout the ARM Southern Great Plains (SGP) site for the purpose of measuring cloud base temperature and inferring cloud base height across the domain. These measurements will enhance existing SGP surface and satellite cloud measurements to help scientists improve their calculations of heating rate profiles on the scale of global climate models. The first set of IRTs was successfully deployed to four extended facilities in May 2005. In August, eight more IRTs were installed at additional extended facilities throughout the SGP domain. Following a short period for system testing and data quality review, integrated data collection began in November 2005, with information soon flowing to the Data Archive.

These photos of the prototype IRT show the system from both inside and out. A filtered fan pressurizes the enclosure, with venting through an open port in the top of the enclosure. The IRT views the sky through this port with the aid of a gold mirror.

Every ARM site includes an IRT as part of its instrument suite for obtaining upwelling and downwelling radiation measurements. On-site technicians clean the instrument every day to make sure its optical properties are not compromised. However, because of the range covered by the new IRT network at SGP, a significant design modification was needed. The new IRT is housed in a steel enclosure to prevent contamination of the lens and mirror, lengthening the maintenance schedule to once every two weeks. In addition to the contamination resistant design, the new IRTs obtain sky brightness temperature measurements at a rate of 5 Hz (5 times per second), compared to 1-minute averages produced with the other IRTs. This rate allows the IRT network to more accurately capture the variability under cloudy and partly cloudy conditions across the SGP domain.

To ensure adequate coverage of the SGP domain throughout the installation schedule, IRT deployments have been carefully selected among the extended facilities to eliminate “clustering” effects. This plan helps to minimize large gaps in the coverage area until the balance of the IRTs can be installed. Deployment of the remaining IRTs is planned to begin in FY2007.