A north-south interstate highway has been proposed for western Alabama primarily to spur development in what's locally known as "the Black Belt," which historically has lagged in jobs and income. The idea is that the new highway would help revitalize the area, provide a direct route from western Alabama south to the Port of Alabama at Mobile, and enhance economic opportunities along the Tennessee-Tombigbee Waterway. The $3 billion cost of that project would be partially offset by leasing the highway's right of way for pipelines, fiber optic cables and other utilities.

The proposed highway would follow U.S. 43 from Mobile north to Muscle Shoals via Tuscaloosa and then possibly enter Tennessee (Figure 1). Federal appropriations were secured to conduct a feasibility study. Originally planned between Muscle Shoals and Tuscaloosa, the freeway will be studied all the way south to Mobile. The total route, approximately 320 miles long, would extend from Mobile roughly along a line following the Tombigbee and Black Warrior Rivers to just west of Tuscaloosa, then northward through Fayette, Marion, Franklin and Colbert counties to Tuscumbia. It would connect to Corridor X/U.S. 78 and Interstate 65. The northern portion of the highway is considered in two segments: from Tuscaloosa to Corridor X (~ 60 mi.) and from Corridor X to Tuscumbia (~ 50 mi.). The boundaries of the corridor to be considered for siting the highway were defined by the Alabama Department of Transportation (Figure 1).

Georectification
The images were acquired in TIFF format with Universal Transverse Mercator projection with WGS 1984 horizontal datum. However, as is not uncommon, the georectification of the image pairs from the different dates did not agree. Using an independent source, the images from September were determined to be incorrectly rectified by 57 m in the easterly and 57 m in the northerly directions. An appropriate correction was applied to both September images.

Atmospheric Correction
The radiance observed by a space-borne sensor is comprised of a component of energy reflected or emitted from Earth's surface as well as from scattering of energy in the atmosphere. The amount of scattering that occurs is a function of wavelength and must be assessed and explicitly removed from each image band. The atmospheric contribution to each image was removed using a modified form of the dark object subtraction technique.

Segmentation and Classification
In the preliminary classification, the decorrelation stretch images from both March and September 2001 and the tassel cap transformation image from March 2001 were used in the classification. Use of transformation products is sometimes used to reduce the information content of images to a smaller number of bands. In this case, the benefit was minimal so that the final classification was based on the six bands from the March 2001 image and bands 2, 4, and 5 from the September image (Figure 2a).

First the image is segmented. That is, adjacent pixels with similar spectral characteristics are grouped into a segment or image object (Figure 2b). After training by the image analyst, the segments are then clustered into classes (Figure 2c). Thirteen land cover and land use classes were defined for the preliminary classification (Figure 3).

Figure 2a. True color image of a portion of the Western Corridor showing the Tennessee River at Tuscumbia, Alabama.
Figure 2b. Segmented image in which adjacent pixels have been grouped based on similar spectral characteristics. The yellow polygons delineate segments.
Figure 2c. Classified image in which each segment is assigned to a land cover type.