Identification of Gypsy Moth Defoliation in Ohio Using Landsat Data

The gypsy moth is one of the most devastating forest pests in North America. In late spring, gypsy moth larvae hatch from eggs laid the previous summer. During the next forty days, tens of thousands of these caterpillars eat up to one square foot of foliage each. The gypsy moth has established populations in several states, and dangerously fast-growing populations in several others. The state of Ohio is a critical area in the suppression of the gypsy moth because the front of gypsy moth advance passes through the state. Besides diminishing the aesthetic value of Ohio’s forests, gypsy moths also cause substantial economic damage to the Ohio timber industry, which is estimated to be a $7 billion per year industry. The Ohio Department of Agriculture currently uses aerial sketchmapping each year to assess the damage done by the gypsy moth. This procedure is difficult, time-consuming, and somewhat imprecise. The results obtained from Landsat 5 and Landsat 7 data can be compared to locations determined by aerial sketchmapping to locate gypsy moth infestations in Ohio. Since vegetation reflects infrared light and absorbs visible light, the health of vegetation can be assessed using a haze-adjusted ratio of Landsat spectral band 4 (near-infrared) to Landsat spectral band 3 (visible red). To determine the change that has occurred between two dates, the ratio values from two dates are subtracted. To identify change that has been caused by the gypsy moth, an area should exhibit defoliation between early June and late June and subsequent refoliation between late June and late July. This type of change results in large positive ratio subtraction values between early June and late June and large negative ratio subtraction values between late June and late July. Pixels that exhibit these attributes are candidates for locations of gypsy moth damage. These ratio subtraction values are further analyzed using change vector analysis to more effectively isolate areas where change has been caused by the gypsy moth. The use of three frames to analyze both defoliation and subsequent refoliation results in a stronger, less ambiguous signal of gypsy moth damage and pinpoints the locations of the most severe defoliation. The most severe defoliation often marks the location of egg masses. Although the use of three frames reduces the ambiguity caused by agricultural anomolies, this procedure also detects areas with significant wild grapevine infestations