A unique, modern instrument is described for resolving and measuring fine detail and transient changes in the angular structure of underwater radiance fields. This instrument makes use of modern developments in photographic wide-angle lens design, random access image analyzers and digital engineering tech-niques to provide a versatile instrument for measuring and recording radiance distributions. An implementation of this instrument is described which was deployed for two months in coastal waters of southern California. Examples of data acquired are presented and illustrate the versatility and features of the underwater radiance scanner. Fundamental radiometric measurements can be accomplished rapidly with a high confidence in the data. The ability to record time varying phenomena and analyze the data statistically is shown. Also, near real time presentations of the data to the experiment director in the field are possible. Storage of all data on magnetic tape allows later pro-cessing by computer and display of the data in a wide variety of formats.