User Manual - pancroma

this does not correspond to physical reality. If negative abundances arecomputed, PANCROMA TM will substitute a zero for the negative value in theendmember image. The number of substitutions is counted and reported to thedialog screen. A large number of negative abundances would cast doubt on thevalidity of the analysis.Spectral unmixing provides another interesting approach to multispectralanalysis. This is an area in need of more improvement but with a lot of potential.Watch for additional PANCROMA capabilities in this area.Landsat Change Distance TM Multispectral Change DetectionMany earth science disciplines required the detailed analysis of changes to theearth’s surface over a period of time. Examples include studies of deforestation,urban growth, desertification, glacier and ice pack change, agricultural land useand many others. Satellite data can be very useful to such studies. Often thesechanges are made on the basis of visual comparison of individual band files, truecolor or false color images composited from such band file data. Anotherapproach is to subtract one band image from another band image in order toobtain a quantitative measure for the degree of change.PANCROMA TM offers a powerful multispectral tool for assessing such changes.Rather than using a single multispectral band, the Change Distance TM tool usesall available Landsat multispectral bands in order to determine the degree ofchange. This can often be more accurate than relying on a single band, becauseapriori knowledge of the most affected band is not necessary in order to detectthe change. The utility considers each pixel in the scene as a vector in sixspace,and computes the vector distance between the top of atmosphere (TOA)reflectance value of each pixel. Using the TOA reflectance provides a moreaccurate comparison between the two scenes than using raw digital numbers(DNs). Those pixels with near zero vector distances may be assumed to beunchanged, while those with larger vector distances are identified as changed.Using the tool requires two multispectral Landsat data sets, one representing thebase scene and one for the changed scene. Each set should include bands 1, 2,3, 4, 5, and 7. Because a pixel-by-pixel comparison will be made between thetwo scenes, it is important that they are correctly co-registered. The registrationrequirements are exactly the same as those required for gap filling, and any andall of the PANCROMA TM tools that are used for preparing Landsat gap fill datacan be used for change detection.The first step in the process in to obtain two Landsat scenes with at least someoverlapping area, i.e. two scenes with the same path and row number. Makesure that you download the metadata files with the Solar Elevation Angles andAcquisition Dates, as these will be needed in the process.272