Victor R. Morris — Pacific Northwest National Laboratory
Dimitri Klebe — Solmirus Corporation
Category
Instruments
Description
Three of the four instruments deployed in the Infrared Sky Imager Intercomparison Study conducted in 2007 are visible in this photo taken on the Guest Instrument Facility platform at the SGP site. They are the Solmirus All Sky Infrared Visible Analyzer (foreground), Heitronics Nubiscope (top right), and Atmos Cloud Infrared Radiometer-4 (far left).
Uncertainty in the characterization of clouds in general circulation models (GCMs) is one of the major causes of the broad spread of future climate change predictions (ASR Science and Program Plan, January 2010). Cloud fraction, which is closely related to cloud coverage, has been an integral part of the observational data set that feeds these GCMs. Cloud fraction, however, has only been reliably determined at the ARM sites during daytime hours utilizing the Total Sky Imager (TSI). Nighttime cloud fraction has been and remains a critical programmatic gap in ARM’s observational data set. It has long been recognized that infrared sky imaging technology has held great promise in closing this gap. In addition, this technology has the distinct advantage that its ability to characterize clouds is identical for day or night conditions. Therefore, instrument demonstrations were conducted at the ARM Climate Research Facility Southern Great Plains site in 2005, 2007, 2009, and 2010 to evaluate measurements of cloud fraction from different types of infrared sky imagers and to compare the daytime values with an operational TSI. The most promising of the instruments tested is Solmirus Corporation’s All Sky Infrared Visible Analyzer (ASIVA). Preliminary analysis of the hemispheric infrared sky images captured by the ASIVA, using simple techniques to provide cloud fraction, shows very good agreement with the TSI results during daylight hours. A comprehensive data analysis of observations made during the 2009 campaign has been performed using more sophisticated algorithms to attain an even better correlation with the TSI instrument. Also in development is a robust nighttime cloud fraction data product utilizing the radiometrically calibrated data from ASIVA’s two infrared channels.
