The 320M Marine Echosounder was developed to meet demanding requirements of field work. Its low maintenance modular construction, together with advanced features and easy configuration, make the 320M the most flexible sounder available. Using either the high or low frequency channel, or both simultaneously, the 320M produces a high resolution record accurately depicting bottom profiles and sediment layers with 32 shades of grey. The thermal printer uses easily loaded 21.6cm (8.5") plastic film for permanent, high-quality records. The annotated depth grid is printed with reverse shading for clarity. Digitized water depth is shown on two large 4-digit LCD displays, visible in direct sunlight and backlit for night operation. Serial RS232 depth data is continuously available in NMEA format as well as user defined string formats, and in operator selectable time and position tagged formats. An LCD menu display with simple 2-button control provides access to parameters such as sound velocity, draft, TX blanking, serial port assignment, time and date setting, and many more, as well as a variety of self-test, communication and configuration features. All settings are retained in non-volatile memory and recalled on power-up. Three RS232 ports support communication with personal computers, NMEA input and output devices, GPS receivers, sound velocity sensors, heave sensors, remote depth displays and survey data loggers. The standard 320M firmware includes drivers for all these devices above and can be field upgraded where updated firmware can be downloaded through a serial port into "flash" program memory. In addition to traditional "hands-on" operation, an optional upgrade allows the 320M to be operated remotely through the built in SCSI interface and Windows application software.