A SATELLITE-BASED ASSESSMENT OF THE 2001 FLOOD EVENT FOR 
LA CROSSE, WI.

Cynthia J. Berlin.
Department of Geography and Earth Science and River Studies Center, University 
of Wisconsin-La Crosse, La Crosse, WI 54601.

This research examines the spatial extent of the Spring 2001 flood event for the 
La Crosse, Wisconsin region using satellite images. The 2001 flood was the third 
highest in recorded history for the La Crosse area and provides an excellent 
opportunity for assessing the utility of satellite imagery in flood research.  
The Landsat Enhanced Thematic Mapper (ETM) satellite passed over this region on 
April 18, 2001, the day the flood peaked in La Crosse. Atmospheric conditions 
were extremely favorable for satellite observation, with cloud-free skies and 
low aerosol interference.  

The two April 18, 2001 ETM images that cover the La Crosse area were compared to 
Landsat TM images from September 18, 1984 and May 19, 1992.  Comparatively, the 
1984 and 1992 dates represent lower and higher Mississippi River water level 
conditions.  The images were subsetted to include the City of La Crosse and 
nearby communities along the Mississippi River and then classified using a 
multi-step, “cluster-busting” unsupervised classification approach.  For the 
analysis, land cover/use classes were reduced to three major categories:  open 
water (includes flooded areas for 2001), non-developed lowlands (primarily 
wetlands), and other land areas (includes all urbanized areas as well as 
agricultural and non-developed upland areas).  The results indicate that 
although there was slightly more non-developed  lowland area and less open water 
in 1984 than 1992, statistically they are not significantly different.  Using 
either the 1984 or 1992 image classification as representing non-flood 
conditions, the 2001 flood covered 100% of the areas classified as non-developed 
lowlands but only 0.42% of the areas classified as other land areas.  A matrix 
analysis of the classified images suggests that of these flooded areas, over 90% 
are urbanized floodplain areas.  This study represents an initial investigation 
into the utility of satellite images in flood research.  A more comprehensive 
study that includes aerial photography and ground-based data along with 
satellite images is scheduled for Spring/Summer 2003.  Ground observations 
obtained at the time of a satellite fly-over for non-flood conditions (assuming 
a flood does not occur this Spring or Summer) will be combined with ground-based 
data and aerial photography available for the 2001 flood event.   

Keywords:  2001 flood, Landsat, remote sensing, La Crosse, Mississippi River