Automated mapping of surface water temperature in the Great Lakes

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