comparisons to be made between satellite imagery and CASI, three
considerations were made: (1) Data for use in habitat categorisation
were drawn from a wide area to represent the range of habitats
present in all image types (2) To obtain replicate pixels of each
habitat type and mitigate spatial autocorrelation (Cli and Ord
1973), a larger area was visited for satellite sensors than for CASI
(i.e. a single seagrass bed may represent hundreds of CASI pixels
but only a few, relatively autocorrelated pixels in a satellite image)
(3) The high costs associated with ¯ying and processing CASI
dictated that only a relatively small area of Caicos Bank could be
surveyed. Cockburn harbour was chosen because most habitats
were represented in a microcosm of the bank (Fig. 1: inset).
Imagery-acquisition dates were June 1992 for Landsat MSS,
November 1990 for Landsat TM and March 1995 for SPOT XS and
SPOT Pan. CASI data were obtained in July 1995 (see Clark et al.
1997; Mumby et al. 1997c). The CASI data presented here are for
comparison purposes: a full analysis is presented elsewhere (Mumby
et al. 1997b). Aerial photographs were not available for the Caicos
Bank, but the results of Sheppard et al. (1995) from Anguilla are
comparable to the habitats examined in the present study. These
authors used colour aerial photography at a scale of 1:10 000.