Close-range remote sensing, or field spectroscopy, involves the use of hand-held or boom-mounted radiometers to study relationships between spectral characteristics of Earth surfaces and their biophysical properties as measured in the field environment. Such data often provide the basis for remote sensing work conducted at broader scales, such as those monitored by modern Earth-observing satellites. However, spatial and temporal variation in the relationships between spectral response and surface characteristics usually are not considered in the analysis of remotely sensed data