Since 2000 the international Argo project has been conducted in order to provide a real-time monitoring system of temperature and salinity profiles for the global upper ocean (The Argo Science Team, 2001). However, duo to the existence of sea ice, we were not able to obtain any data measured by Argo-type profiling float (Argo float) in sea ice region before. Instead, main method for year-round observation in the multi-year ice region is ice-drifting buoy while only a few are equipped with sensors for measuring the sea under the ice. The first buoy to measure the sea under the ice was the SALinity ARGOS (SALARGOS) buoy developed in 1986 (Burke and Morison, 1987). After that, some buoys were developed and deployed in the Arctic Ocean, e.g., Polar Ocean Profiler (POP) buoy (e.g., Morison et al., 1991), and Ice Ocean Environmental Buoy (IOEB) (e.g., Hatakeyama et al., 1994).
Development of JAMSTEC Compact Arctic Drifter (J-CAD) began in 1999 in collaboration with METOCEAN (Hatakeyama and Monk, 2001). Since 2000, the J-CADs have been deployed in the multiyear ice area of the Arctic Ocean once or twice a year, to understand the going Arctic Ocean change. We have been sampling a broad suite of oceanographic and atmospheric data from the Arctic multiyear ice region (e.g., Kikuchi and Hosono, 2004). Recent results from the J-CAD observation have highlighted not only interannual variability of oceanographic condition (Kikuchi et al., 2004; 2005), but also atmospheric forcing on ice and ice-albedo feedback (Inoue et al., 2005; Inoue and Kikuchi, 2006). Based on J-CAD successful performance, JAMSTEC and METOCEAN started collaboration again in the development of a new buoy system tethering an Argo float. The new buoy is named as Polar Ocean Profiling System, POPS. In this article, we introduce a system description of the POPS.
Figure 1 shows schematic view of the POPS. The POPS consists mainly of an ice platform and a subsurface CTD profiler. Hull of the ice platform is constructed of aluminum with an ionomer foam collar for floatation in case of ice flow break up. The tubular hull has a diameter of 8.0 inches and is intended to be placed into a hole drilled in the ice, which provides excellent stability. The ice platform contains system controller, meteorological sensors (sea level pressure and atmospheric temperature), GPS (latitude and longitude), and Iridium satellite communication system. The system controller of the ice platform manages all data acquisition, processing, formatting, and messaging. Iridium transceiver provides bi-directional satellite communication not only for sending observation data from the buoy but also for sending a remote command to the buoy.
The subsurface CTD profiler system is based on an Argo float technology. Decent and ascent of the profiler depends upon buoyancy, i.e., a precision hydraulic system of the profiler is used to adjust its volume. The major differences from the Argo float are that the profiler is mounted on an oceanographic steel cable and that it moves between upper and lower bumpers along the cable. The cable has a diameter of 0.156 inches and interfaced to the ice platform. To keep the cable as vertical as possible even in the case of an ice drift velocity reaching 30 cm/sec or faster, terminal weight with a weight of 20 kg is used at the lower termination of the cable based on calculations of the cable catenary. Upper and lower rider attached on the profiler are designed with
Figure1. Schematics of Polar
OceanProfiling System, POPS
Both meteorological and oceanographic profiling data acquisitions are configurable even after the deployment using the Iridium communication system. The power budget calculation indicates an expected lifetime of more than two years for meteorological data acquisition with GPS position every three hours and oceanographic profiling data acquisition every five days.
Figure 2. Cartoon of the POPS deployment
The deployment at the NPEO 2006 was conducted on April 17 on the Arctic multiyear ice near the North Pole. At first, we build a tripod and made an ice-hole with 10-inches diameter. Drilling the ice-hole, we fixed a terminal-weight, lower bumper, and CTD profiler to the oceanographic steel cable, and then completed the preparation for putting into seawater (Figure 2a). Once we punctured the ice-hole through, we put the weight, profiler, and cable into seawater in order (Figure 2b). As the cable came closer to the end, we stopped it once. We connected the cable and the buoy platform so that the observation was ready to start anytime.
We connected the buoy to a computer and turn on the POPS to start observation (Figure 2c). Once confirmed the data acquisition and transmission, we put the buoy platform into the hole on sea ice and completed the deployment (Figure 3).
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