Calculating change curves for multitemporal satellite imagery: Mount St. Helens 1980-1995

We developed and tested a method for analyzing multitemporal satellite imag ery using change curves. The method is flexible and allows an analyst to ex tract specific change parameters from the curves depending on the research question of interest. Eight Landsat TM images of the Mount St. Helens, Wash ington, blast zone from 1984 to 1995 were geometrically and radiometrically corrected. They were then transformed to estimates of green vegetation cov er. Unsupervised clustering was performed on the set of eight transformed i mages and polynomial curves were fit to the cluster means. From these fitte d curves, parameters of interest were extracted and returned to GIS layers, including number of years to reach 10% cover, the greatest rate of cover i ncrease during the study period,, and time-integrated cover. Statistical an alysis indicated that the curves did a good job of representing the change trajectories of unclustered pixels. We demonstrated he nse of change curve analysis by analyzing the importance in the revegetation of Mount St. Helen s of the different types of disturbance resulting front the volcanic erupti on. The change curve analysis is useful in a variety of applications rc;he re the data are continuous, more than two dates of data are available, and the underlying question of interest relates to trends in the data. (C) Else vier Science Inc., 1999.