Patchy distribution fields: sampling distance unit and reconstruction adequacy

A mathematical model (Kriging) was used to examine the effects of choosing various units of sampling distance on the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches (or gaps ) of different shapes and spatial orientations, and an acoustic survey by p arallel transacts along which a unit of sampling distance is set. Conformit y of the reconstructed fields to those originally generated was evaluated b y calculating their correlations. If a priori information on patch orientat ion is available, the optimal ratios of the distance between transacts and the sampling distance unit to the corresponding autocorrelation radius for the field have been determined, ensuring the required match between the rec onstructed field and its original. The experiments with a certain unit of s ampling distance confirm that a posteriori determination of patch orientati on allows reconstruction of the best field attainable on the basis of the d ata from the survey conducted. In cases of field movement, the criterion fo r choosing a survey direction is based on the relationship between the dime nsion of moving patches in the direction of movement and that of the survey ed area; the criterion remains valid when a unit of sampling distance is se t along transects. (C) 2001 International Council for the Exploration of th e Sea.