Pacific Southwest Region

Quick Change Methodology

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.

Quick Change Image	Quick Change Legend
Time1 1999 Landsat	Time2 2000 Landsat

USDA Forest Service - Pacific Southwest Region
Last Modified: Friday, 13 April 2012 at 10:10:40 EDT