Introduction The quick change process is a simple, fast method to map vegetation change using Landsat 5 or 7 thematic mapper (TM) imagery for two dates. It differs from the change detection methodology of the Region 5 Land Cover Mapping and Monitoring Program (LCMMP) by not requiring radiometrically corrected/normalized images, by using one simple algorithm to produce a raw change layer ready for labeling (there is no classification step), and by producing a less rigorous map of vegetation change: the classes are relative, and not directly comparable from area to area since there are no canopy cover classes. Instead the quick change map uses an intuitive continuous color scheme, depicting decreasing vegetation ranging from pale orange to red, increasing vegetation from pale to dark green, and little or no change in gray.
Preprocessing Terrain corrected image pairs are acquired and coregistered using a nearest neighbor resampling method to maintain the spectral integrity of the data.
GIS Database Building If multiple path/rows are required, an index layer is developed to avoid clouds and smoke in the overlap areas and to develop processing areas along natural boundaries. Agriculture, urban, and water are masked from analysis. Other reference layers are assembled, such as NAIP imagery, and fire and forest activity layers.
Quick Change Calculation A thematic "PC4" image for labeling is created using an Imagine model to perform a principal components analysis. The model stacks bands 3 and 4 from both input TM images and then creates a thematic 8-bit image for the 4th principal component. The PC4 image has 255 classes in a continuum (usually!) from extreme decrease to little or no change (the center of the histogram) to extreme increase.
Labeling and Cause The thematic PC4 image is labeled by "coloring up" into a continuum of decreasing and increasing vegetation. Change of less than 15% (approximately) is labeled little or no change. The cause of change attribute may be determined by modeling with existing layers or noted during labeling. In addition to real vegetation change, the quickchange image picks up change from unmasked agriculture or development as well as "nonveg" change (water levels, snow-levels, etc.) and "seasonal" change due to phenology differences.
The quickchange image was stratified by lifeform and the classes colored up depicting a continuum of vegetation change. Tree lifeforms use one color scheme and non-tree lifeforms use another color scheme:
ALL LIFEFORMS:
Gray Little or no change Beige Usually little or no change (borderline decrease) Pale green Usually little or no change (borderline increase) Magenta Extreme decrease which may represent AGR (agriculture) or non-veg change (due to changing moisture or water levels or snow level) Purple Extreme increase; may be AGR or non-veg change.
TREE LIFEFORMS (CON/MIX and HDW)
Red Usually large decrease Orange Usually moderate decrease Pastel orange Usually small decrease Pastel green Usually small increase Green and Dark green Usually large increase
SHRUB, HERBACEOUS AND BARREN LIFEFORMS (SHB, HEB or BAR)
Yellow-brown and Mustard yellow Usually decrease Yellow-green, Olive green and Dark green Usually increase
Tan AGR Agriculture Cyan URB Urban Blue WAT Water