Field testing and performance evaluation of the Long-term Acoustic Real-Time Sensor for Polar Areas (LARA)

In the Arctic, in-situ measurement of the upper water column properties (e.g., salinity and temperature) has been a challenge because of the seasonal sea ice coverage. A Long-term Acoustic Real-Time Sensor for Polar Areas (LARA) was developed, field-tested in the shallow water off Oregon and its performance evaluated. The LARA utilizes a commercially available underwater profiler winch from NiGK, conductivity-temperature-depth (CTD) sensors, and a passive acoustic monitoring (PAM) systems. The sensor section consists of two modules: 1) a satellite antenna with a temperature and depth sensor (TD) and 2) a sensor buoy with a controller, a CTD, and a PAM. Using the two vertically separated temperature and pressure sensors, it is capable of detecting the presence of sea ice by sensing the oceanographic conditions in the upper water column. In addition, using the acoustic sensors, (1) surface wind speed can be estimated from the ambient noise level and (2) enable monitoring of marine mammal calling activity. The winch can be fully controllable from the sensor buoy by acoustic commands. It is capable of aborting an ascent in case sea ice coverage or a high sea state was detected. Although the sea ice detection algorithm could not be tested in Oregon waters, the LARA successfully repeated 94 profiles and transmitted CTD and acoustic detections data via satellite. The wind speed estimates by the PAM were in good agreement with the nearby buoy data. The PAM recorded various biological signals from 10 Hz to 60 kHz including vocalizations of fin, humpback, sperm whales and calls of Pacific white-sided dolphins. The system is capable of repeating 365 profiles or one profile per day for 1 year making it suitable for collecting high-resolution water column data in the extreme weather and water conditions of the Arctic.