Hawaii Ocean Time-series (HOT)
in the School of Ocean and Earth Science and Technology at the University of Hawai'i at Manoa
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Currents in the upper ocean (0-1200 m) during 2018 were measured using shipboard Acoustic Doppler Current Profilers (ADCP) on board R/V Kilo Moana and R/V Ka'imikai-O-Kanaloa.
Onboard ADCP data are collected and preliminarily processed in real-time using the University of Hawaii's CODAS processing system. This system allows for automatic quality control of the data and real-time graphic display of current profiles and other data products while at sea. Should any ancillary data stream be disrupted at sea or found to be in error, raw data are saved and a complete re-processing of the data is possible at a later time.
The R/V Kilo Moana was used during HOT-299, 300, and 305 through 308. The ship is equipped with two ADCP systems. A Teledyne RD Instruments Ocean Surveyor 38 is located on the starboard side of the ship, and an RD Instruments WorkHorse 300 is located on the port side; both feature a transducer depth of 7 m. The Ocean Surveyor operates at 38 kHz and is able to profile up to 1200 m in broadband mode (OS38BB) with a bin size of 12 m averaging ensembles every 5 minutes. In narrow band mode (OS38NB) with 24 m bins, profiles can reach as deep as 1500 m. The WorkHorse (WH300) operates at 300 kHz, typically profiling to a maximum of 100 m with a bin size of 4 m and averaging ensembles every 2 minutes. Heading information is taken from the gyrocompass and corrected using a TSS POS/MV 320 (an integrated inertial and GPS system). An Ashtech ADU5 is used as a heading-correction device should there be a problem with the POS/MV. Position data are provided by the POS/MV system with an Ashtech ADU5 and a Trimble GPS as backups.
The R/V Ka'imikai-O-Kanaloa was used during HOT-301 through 304. The ship is equipped with a WorkHorse 300 that was enabled to sample to depths of 150 m and bin sizes of 4 m. Ensembles were taken every 2 minutes.
Final processing of shipboard ADCP data involves applying small heading corrections to the velocity data based on watertrack calibrations, trimming unnecessary data from the beginning and ends of the cruise followed by a visual inspection of the final dataset with manual data flagging of suspicious points.
ADCP data were collected using OS38BB, OS38NB, and WH300 onboard R/V Kilo Moana during HOT-299, -300, and from HOT-305 to -308. The WH300 had problems and was repaired before the HOT-306 cruise, but still displayed problems and its measurements were not reliable. The OS38 data was not available during HOT-308 because its deck box unit failed during the previous ship’s cruise. WH300 data were collected during HOT-301 to -304 cruises onboard the R/V Ka'imikai-O-Kanaloa.
An overview of the shipboard ADCP data is given by the plots of velocity as a function of time and depth while on station (below-left) and velocity as a function of latitude and depth during transit to and from Station ALOHA and Station Kaena, combined (below-right). As in previous years, currents were highly variable from cruise to cruise and within each cruise.