Lake Superior Ice Facies from AVHRR and SSM/I

Lake Superior Ice Regimes from AVHRR and SSM/I

Abstract

Coregistered AVHRR (Advanced Very High Resolution Radiometer) thermal infrared and SSM/I (Special Sensor Microwave/Imager) passive microwave imagery reveals patterns in Lake Superior ice cover at the 1-50 km scale. Three principal classes emerge from analysis of microwave emissivity data and are interpreted as: older, colder, thicker, deformed ice; young, thin, warm congelation ice; and new, thin ice and polynya. This interpretation is supported by spatial patterns of occurrence and basic principals of thermal emission.

AVHRR and SSM/I Images Lake Superior, February 4, 1996

The presence of ice and snow on the earth is relatively easy to detect from satellite due to the large change in a landscape's reflection, emission and transmission characteristics upon introduction or removal of an ice/snow cover. This stems primarily from the strong dielectric contrast between liquid water (real part of the dielectric constant (epsilon) = ~80), and solid water (ice) (epsilon=3.17). Beyond simple detection are efforts to measure parameters such as thickness, snow water equivalent, ice cover concentration, onset and melt, and duration of ice/snow cover.

Great Lakes ice cover monitoring is currently conducted by the U.S. National Ice Center and the Canadian Ice Service through a combination of satellite observations (RADARSAT, AVHRR, GOES), aerial reconaissance with trained ice spotters, and ship and shore reports. Satellite monitoring of Great Lakes ice cover was initiated in the 1970s. The emphasis to date has been on visible and thermal infrared imagery, but this is now shifting towards fusion with active microwave data from RADARSAT C-band radar satellite, and perhaps with complementary passive microwave data from SSM/I. Microwave radiation is sensitive to physical properties such as surface roughness, ice/snow thickness, grain size and moisture state, and as such offers some exciting avenues for research of Great Lakes ice cover little explored to date. Also, the capability to acquire microwave imagery day or night and independent of most weather conditions provides a higher temporal resolution than infrared and visible imagery.

AVHRR and SSM/I Data

Two February 4, 1996 images were combined in this analysis. The AVHRR image was acquired by the NOAA 14 satellite at 08:14 UTC (03:14 EST). Only thermal bands are available in this image due to the non-daylight time. The SSM/I image was captured by the F10 satellite at approximately 08:13 UTC. AVHRR has a nominal resolution of 1.1 km per pixel. Figure 1. AVHRR Band 4 TIR Tb

Thermal infrared brightness temperature image of Lake Superior. Dark=cold, bright=warm. Ice emissivity is approximately 0.96-0.98, so physical temperature is approximately equal to Tb.