Retrieval of Lake Bulk and Skin Temperatures Using Along-Track Scanning Radiometer (ATSR-2) Data: A Case Study Using Lake Tahoe, California

In 1999, four monitoring stations were permanently moored on Lake Tahoe, California–Nevada. Each monitoring station provides near-real-time measurements of the surface skin temperature and bulk temperature on a near-continuous basis. Day and night data, acquired over Lake Tahoe from March to August 2000 with the second Along-Track Scanning Radiometer (ATSR-2), have been analyzed, and sets of coefficients for recovering the skin temperature and bulk temperature of the lake have been derived. The field measurements indicate that there is a noticeable difference between the bulk and skin temperatures (skin effect), which varies over the diurnal cycle. At the time of the ATSR-2 daytime overpass, the skin temperatures are on average 0.118C cooler than the daytime bulk temperatures. At the time of the nighttime ATSR-2 overpass, the skin temperatures are on average 0.468C cooler than the nighttime bulk temperatures. The smaller skin effect during the day is attributed to strong solar heating and low wind speeds at the site in the morning. The standard errors for recovering the daytime bulk and nighttime bulk temperatures, by regressing the in situ measurements against the average ATSR-2 nadir 11and 12-mm channel brightness temperatures, are 0.408 and 0.188C, respectively. By comparison the standard errors for recovering the daytime skin and nighttime skin temperatures by the same approach are 0.338 and 0.288C, respectively. The lower standard error obtained for recovery of the skin and bulk temperatures at night is attributed to the lake surface being more homogeneous with the absence of solar heating. A comparison between the measured skin temperatures, skin temperature recovered by an ATSR-2 two-channel sea surface temperature algorithm, and the in situ regression indicates that the ATSR-2 algorithm has a similar scatter to the in situ linear regression but is offset with respect to the measured skin temperatures.