The FAU (FArvandsvæsenets UTM) is a hydrographic binary file format developed and maintained by DGA with contributions from several hydrographic stakeholders.
The FAU format was originally designed to store data collected by one of the first commercial multibeam system. That system operated by simultaneously transmitting four beams (each seperated by a fixed angle), shifting and repeating the transmission to create a whole swath of beams. This origin influenced the adopted data structure.
The FAU format is in use by various hydrographic agencies, and is supported by several commercial and open source hydrographic data processing applications. The latest release of the open FAU Format Specifications is available here.
The content of a FAU file can be explored using the SUSSIE app.