A Comparison of the TSI/WSI Cloud Fraction Estimates at the SGP
Slater, D.W.(a), Long, C.N.(a), and Tooman, T.P.(b), Pacific Northwest National Laboratory (a), Sandia National Laboratory (b)
Twelfth Atmospheric Radiation Measurement (ARM) Science Team Meeting
Beginning with the installation of the Total Sky Imager (TSI) at the ARM Southern Great Plains site in July, 2000, both the TSI and the Whole Sky Imager (WSI) have operated simultaneously in close proximity to one another. Both systems produce all-sky cloud fraction estimates as part of their primary products, though each uses distinctly different methods to arrive at these estimates. The purpose of this study is to provide a link between the large body of estimates produced by the WSI before the installation of the TSI at the SGP as well as the continuing operations. A secondary purpose is to provide assurance of the cloud fraction estimates for the Island Effect Study currently underway on Nauru Island. Beginning with the commencement of TSI operations in July, 2000 until September, 2001, all available cloud fraction estimates from the SGP WSI and TSI have been compared for this 15 month period. All comparisons were made with estimates of cloud cover during periods that the solar elevation exceeded 10 degrees. The primary results show that consistent estimates of cloud fraction can be routinely generated with current analysis techniques, and that although the TSI does favor a slightly higher estimate that the WSI, we attribute this to user-defined thresholding that identifies the 'thin' cloud classification. The probability of agreement between the TSI and WSI for specific cloud conditions will be illustrated.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
