In May 2001, MIT's Nicholas Makris and his then postdoctoral fellow Purnima Ratilal were searching for the ancient riverbeds buried within the continental shelf off the New Jersey coastline. Although hidden in muck when the sea level rose during the last ice age, those ancient channels had been previously mapped using high‐frequency sonar that distinguished the slight density differences in the sediment. Researchers sent a signal, listened for its echo, and then deconvolved the spectral components to resolve underwater features.