Lake Michigan and the Mississippi River
Clear skies over the upper Midwest allowed an unobstructed view of the surface for VIIRS instrument on NOAA-20 and Suomi NPP. An ice-free Lake Michigan is apparent. Small patches of snow remain over Iowa, Illinois and Wisconsin (ice-covered lakes remain as well); snow-covered surfaces and snow and ice-covered lakes appear bright white in the visible (0.64 µm) imagery, but dark in the near-infrared 1.61 µm because solar radation at 1.61 µm is absorbed by ice.
These images can be used to deduce where the Mississippi River is ice-free. The zoomed-in images below (0.64 µm on the left, 1.61 µm on the right), shows ice (mostly white in the visible, dark in the near-infrared 1.61 µm) north of Lock #13 at Fulton (Click here to see the visible image with city names). The river south of the Lock and Dam is dark in the near-infrared because of strong absorption of radiation by water (land is more reflective of 1.61 µm radiation than of 0.64 µm radiation, so there is greater contrast between land and water). The smaller reflectivity south of the Dam in the visible suggests open water.
Clear skies also allowed for an accurate estimate of lake-surface temperatures of Lake Michigan, shown in a toggle below with true-color imagery. The warmest surface temperature: 39o F.
VIIRS imagery and products are available from CIMSS via an LDM feed.