TY - JOUR T1 - Map-guided classification of regional land-cover with multi-temporal AVHRR data JF - Photogrammetric Engineering and Remote Sensing Y1 - 1998 A1 - Stoms, D. M. A1 - Bueno, M. J. A1 - Davis, F. W. A1 - Cassidy, K. M. A1 - Driese, K. L. A1 - Kagan, J. S. KW - accuracy assessment KW - AVHRR KW - gap analysis KW - Intermountain Semidesert ecoregion KW - map-guided classification KW - National Vegetation Classification Standards KW - NVCS KW - remote sensing AB - Cartographers often need to use information in existing land-cover maps when compiling regional or global maps, but there are no standardized techniques for using such data effectively. An iterative, map-guided classification approach was developed to compile a spatially and thematically consistent, seamless land-cover map of the entire Intermountain Semi-Desert ecoregion from a set of semi-independent subregional maps derived by various methods. A multi-temporal dataset derived from AVHRR data was classified using the subregional maps as training data. The resulting regional map attempted to meet the guidelines of the proposed National Vegetation Classification Standards for classification at the alliance level. The approach generally improved the spatial properties of the regional mapping, while maintaining the thematic detail of the source maps. The methods described may be useful in many situations where mapped information exists but is incomplete, compiled by different methods, or is based on inconsistent classification systems. VL - 64 UR - ://000075109200012 ER - TY - JOUR T1 - Viewing geometry of AVHRR image composites derived using multiple criteria JF - Photogrammetric Engineering and Remote Sensing Y1 - 1997 A1 - Stoms, D. M. A1 - Bueno, M. J. A1 - Davis, F. W. KW - AVHRR KW - cloud removal KW - compositing KW - NDVI KW - Normalized Difference Vegetation Index KW - satellite zenith angle AB - The U. S. Geological Survey currently generates composites of AVHRR imagery based on a single objective--maximizing the Normalized Difference Vegetation Index--as a means of reducing cloud contamination. Our research supports the findings of others that in some cases, NDVI is maximized at the expense of optimal viewing geometry; that is, satellite zenith angles are often further off-nadir than necessary to ensure cloud-free viewing. We explore various compositing methods by systematically varying weights on NDVI, satellite zenith angle, and maximum apparent temperature. A test composite of California from September 1990 appears to be superior to the maximum NDVI and maximum apparent temperature composites in several respects. First, the satellite zenith angle distribution is more closely clustered about nadir, which minimizes atmospheric path length, spatial distortion, and bidirectional reflectance effects. Second, neighboring pixels are more frequently selected with similar viewing geometry and atmospheric conditions. VL - 63 UR - ://A1997XC40700004 ER -