DETECTION AND REMOVAL OF CLOUD CONTAMINATION FROM AVHRR IMAGES

This paper describes the characteristics and performance of an algorithm designed to remove the effects of cloud contamination from AVHRR composite images over land. Using information in the temporal NDVI profile, the algorithm detects cloud-contaminated pixels, and optionally replaces these with interpolated values of individual AVHRR channels or channel transformations. As tested, the algorithm detects only those effects of residual clouds that result in a temporary decrease of the NDVI. It was found that the algorithm is capable of identifying cloud, of varying opacity as well as cloud shadows present in the composites, and that its use appears preferable to compositing over longer periods. The algorithm can be applied without the need for ancillary information, e.g., on expected surface radiance conditions. Although developed for use in biospheric studies in Canada, it could also be applied at other latitudes where the seasonal trajectories of satellite-derived variables exhibit a single maximum or, by extension, a single minimum.