Remote sensing: Using the spatial domain

Objects in the terrestrial environment interact differentially with electro magnetic radiation according to their essential physical, chemical and biol ogical properties. This differential interaction is manifest as variability in scattered radiation according to wavelength, location, time, geometries of illumination and observation and polarization. If the population of sca ttered radiation could be measured, then estimation of these essential prop erties would be straightforward. The only problem would be linking such est imates to environmental variables of interest. This review paper is divided into three parts. Part 1 is an overview of the attempts that have been made to sample the five domains of scattered radia tion (spectral, spatial, temporal, geometrical, polarization) and then to u se the results of this sampling to estimate environmental variables of inte rest. Part one highlights three issues: first, that relationships between r emotely sensed data and environmental variables of interest are indirect; s econd, our ability to estimate these environmental variables is dependent u pon our ability to capture a sound representation of variability in scatter ed radiation and third, a considerable portion of the useful information in remotely sensed images resides in the spatial domain (within the relations between the pixels in the image). This final point is developed in Part 2 that explores ways in which the spatial domain is utilized to describe spat ial variation in remotely sensed and ground data; to design optimum samplin g schemes for image data and ground data and to increase the accuracy with which remotely sensed data can be used to estimate both discontinuous and c ontinuous variables. Part 3 outlines two specific uses of information in th e spatial domain; first, to select an optimum spatial resolution and second , to inform an image classification.