IRSI Inter-Comparison Study

27 August 2007 - 23 September 2007

Lead Scientist: Victor Morris

Observatory: SGP

The principle objective of this campaign was to compare measurements of cloud fraction from different types of commercially available infrared sky imagers (IRSI) and to compare the daytime values with an operational Total Sky Imager (TSI).

In 2004, the Radiative Processes working group requested that an infrared sky imaging system be added to our measurement suite to provide a nighttime cloud fraction product. A Blue Sky Imaging Ltd. (BSI) All-Sky Thermal Infrared Camera (ASTIC) was purchased and deployed at the SGP Guest Instrument Facility in October 2005. The characteristics of the data were compared to the ARM TSI located at the site. The daytime images compare favorably with those from the TSI but the derived cloud fraction data significantly underestimate the TSI values when the sky is more than 50% cloudy. It is unknown whether the poor cloud fraction data is a product of the BSI software or the calibration of the imager.

Alternatives to the BSI instrument were investigated, including the Heitronics Nubiscan, Atmos Cloud Infrared Radiometer, and Solmirus All Sky Infrared Visible Analyzer. The respective vendors of these three instruments agreed to a simultaneous demonstration at the SGP site in the late summer of 2007 allowing an extended (about 1 month) inter-comparison with the ASTIC and TSI so that reliability and performance of the systems could be verified.

Related Publications


Morris V and D Klebe. 2011. Evaluation of Infrared Sky Imagers at the ARM Southern Great Plains Site. Presented at 2nd Atmospheric System Research (ASR) Science Team Meeting. San Antonio, TX.


Morris V and D Klebe. 2010. A Demonstration of the Solmirus All Sky Infrared Visible Analyzer. Presented at Atmospheric System Research (ASR) Science Team Meeting.

View All Related Publications

Campaign Data Sets

IOP Participant Data Source Name Final Data
Laurent Berger Cloud Infrared Radiometer Order Data
Chuck Long LW Flux Order Data
Hans Moeller NubiScope Order Data
Victor Morris All Sky Thermal Infrared Camera Order Data
Jeff Steele All Sky Infrared Visible Analyzer Order Data