Automated mapping of surface water temperature in the Great Lakes

A procedure for producing daily cloud-free maps of surface water temperatur e in the Great Lakes has been developed. It is based on satellite-derived A VHRR (Advanced Very High Resolution Radiometer) imagery from NOAA's Coast W atch program. The maps have a nominal resolution of 2.6 km and provide as c omplete as possible coverage of the Great Lakes on a daily basis by using p revious imagery to estimate temperatures in cloud covered areas. Surface wa ter temperature estimates derived from this procedure compare well with wat er temperatures measured at the eight NOAA weather buoys in the lakes. The mean difference between the buoy temperature and the satellite-derived temp erature estimates is less than 0.5 degrees C for all buoys. The root mean s quare differences range from 1.10 to 1.76 degrees C. As one example of the possible applications of this product, the daily surf ace water temperature maps for 1992 to 1997 were analyzed to produce daily estimates of average surface water temperature for each lake. Results are c ompared to the long-term (28 year) mean annual cycle of average surface wat er temperatures. The average surface water temperatures vary from as much a s 4 degrees C below climatology in 1993 to 2 to 3 degrees C above climatolo gy in 1995. The new analysis procedure also provides a more realistic depic tion of the spatial distribution of temperature in the springtime than the climatological maps.