EK60 Water Column Sonar Data Collected During FR1003

2010 California Current Ecosystem Survey. Measurements of volume backscattering strength (Sv; dB re 1 m) and target strength (TS; dB 1 m2) were made using four calibrated Simrad EK60 general purpose transceivers (GPTs) configured with split-beam transducers at frequencies of 38, 70, 120, and 200 kHz. To index the data by time and geographic position, a GPS receiver provided navigational data to the echosounder software (ER60). The echosounder system was tested and calibrated while FROSTI was anchored at Elliot Bay Anchorage (Washington) two days prior to the start of the cruise. EK60 data was collected to 250 m depths by transmitting 1024-µs pulses of the four frequencies simultaneously, every 0.5 seconds. The depth range was chosen to accommodate the depth distribution of CPS (i.e., ca. 70 m depth) and krill (i.e., ca. 250 m depth), and the fast pulse repetition allows multiple insonification of relatively small fish schools at the sampling speed of 8 kts.

The echoes were received with bandwidths of 2.425, 2.859, 3.026, and 3.088 kHz, respectively, and digitized every 256 µs (ER60; .raw data format) in a laptop computer. All the EK60 frequencies were triggered simultaneously, and all other echosounders, speed logs, and sonars operating at or near the survey frequencies were secured during survey operations. Exceptions were made during directed trawl operations when a net sounder was activated.