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The availability and use of remotely sensed digital image data have increased rapidly over the last two decades. One application where remotely sensed image data are a critical component is environmental analysis and monitoring. In our case it involves using sidescan sonar images to detect and map the location of 55‐gal drums that were disposed of near the Farallon Islands (about 50 nautical miles west of San Francisco). About 48,000 drums containing low‐level radioactive waste were dumped in water depths ranging from 100 to 2500 m covering 1400 km2. The high number of drums littering the seafloor and the rather large area involved makes remotely sensed image data one of the few promising tools to detect and map drum locations. In our analysis, sidescan sonar images collected by the SeaMarc IA and having about 1‐m pixel resolution were used. Spatial variability analysis (SVA) and other digital processing procedures were applied to the sidescan sonar images to automatically detect and map the location of t...