Motivation:
The Great Lakes exert profound influences on local and regional weather patterns. Ice extent and duration control regional shipping and snowfall, and may be used as indicators of climate conditions and climate change. Snow pack is a major part of the hydrologic cycle in this region, and ice cover is the dominant control on lake effect snows; i.e., as ice cover develops, the opportunity for evaporation and snow generation diminishes.SSM/I (Special Sensor Microwave/Imager) is a microwave remote sensing instrument on the Department of Defense F series satellite platforms. It measures upwelling microwave radiation emitted by the earth and atmosphere, in seven frequency-polarization combinations in the millimeter-wavelength portion of the electromagnetic spectrum.
Microwave frequencies are particularly valuable for hydrologic remote sensing for a number of reasons:
- sensitivity to water state and content
- (nearly) all-weather imaging
- day/night imaging
Ice Cover
Lake effect snows in the Great Lakes region are heavily influenced by ice cover. As ice cover extent increases, the water surface area available for evaporation decreases and, consequently, so does lake effect snow precipitation.
- Ice cover animation(278 kb)
This mpeg animation shows the development of Great Lakes ice cover in January 1994. The animation is a time series of daily SSM/I 85 GHz horizontal polarization images. Numbers in the upper left (e.g., 1.4) indicate the date (January 4). Ice cover is seen as bright tones developing on the previously black lake surfaces (ice is radiometrically brighter than water). Land surfaces grow darker with time, indicating decreasing physical temperatures and accumulation of snow cover, which attenuates the signal coming from the radiometrically warmer soil (hence, the image brightens going from north to south where snow cover is less and/or ephemeral). (The animation should be a greyscale. If you get a strange colormap, try exiting Netscape and restarting it using the -install option. You need an mpeg player at your end as well.)
Data smoothing
The SSM/I data used here are from a series of CDs produced by the National Snow and Ice Data Center NSIDC (The CD series is the "DMSP F-11 SSM/I Brightness Temperature Grids: Polar Regions".)
The raw data on CD are degraded by missing values due to tape recorder failure on board the F11 satellite. The raw data image shows what the imagery looks like without any smoothing or averaging.
The raw data can be smoothed using a med ian filter. Missing data are interpolated from the values of surrounding pixels for that day.
SSM/I Connections:
SSM/I Imagery of Lake Superior
