NBP09-01 Cruise Report - British Oceanographic Data Centre

enough number to be able to regionally charcterize ice growth and melt processes. The design consistsof a single wire of addressable digital temperature sensors with 1/16 of a degree resolution. Each stringconsists of 144 sensors with a 4 cm spacing mounted on a thin flexible PCB that was weatherproofed inheatshrink. Each has a surface mounted resistor that heats the sensor when a voltage is applied, allowingthe thermal response of the sensor to be monitored. This ”hot-wire anemometer” mode will in principle allowdiscrimination of the medium that the sensor is in (i.e. snow, ice, air or water) and hence determination ofsnow and ice thickness without the need for acoustic sounders. A particularly advantageous feature of thissystem is the potential to continuously monitor surface processes such as flooding, snow ice formation, andsnow melt. These processes are a particular focus of the sea ice program.Data is recorded using a Persistor CF2 logger and transmitted via Iridium modem. To reduce power consumptionand data transmission costs, temperatures are recorded 4 X daily, and a heating cycle is appliedonce per day. Power is supplied by 80 alkaline D-cell batteries. All components other than the sensor chainare enclosed in a 1550 Pelicase (20 cm x 35 cm x 50 cm).This is the first deployment of these systems in the Antarctic. Modifications from the design used in theArctic include a longer chain to accommodate thick ice and snow and finer sensor spacing to resolve surfaceprocesses.To deploy the IMBs, 2 meters of the sensor chain were cable tied to a 2” diameter ABS pipe to supportthe sensors in the snow and air. This was fixed in the field via a threaded joint to a second pipe that wassecured in a 2” auger hole in the ice. The remaining sensors were run along the ice surface to a hole 40 cmaway and dropped through a drill hole through the ice.Two systems were deployed. A third failed during testing on the helo-deck due to failures in both the sensordriver module and the Persistor logger. The cause of the first failure is unclear, but it is probable that ashort damaged the logger. The first system was deployed at ice station 11 on the Northwest side of theThwaites iceberg tongue. This site was chosen as it was well protected by icebergs and fast ice to the east sohad a fair chance of surviving into the winter. High Resolution ASAR data was provided by BAS under theauspices of the European Polarview project was particularly useful in locating the site and finding a routethrough the iceberg tongue. The IMB was deployed in 2.7 m of sea ice about 1/2 mile from the fast ice edge.At this site, the snow was removed in blocks prior to drilling and then replaced around the snow mast. Thisprevented wetting of the snow, but it is likely that there were air gaps between sensors and replaced snowso that detection of snow in the heating cycle is difficult. The second IMB was deployed at ice station 13 ona roughly 500 m floe in the middle of the pack ice band. The ice was 2.0 m at this site. Rather than clearthe snow, holes were carefully drilled through both the snow and ice. Crushed snow was packed in the gapsaround the sensors to ensure good contact. Both sites were flooded. Deployment of each station took about2 hours.Initial analysis of the data show that the different layers can be resolved, but the thermal response of snowand air are only slightly different. This may be because the response is detected using the temperature riseafter a one minute heating cycle. This may not be sufficient time for the heat to flow through the heatshrink on the sensor chain and deeply into the snow. It may be better to transmit temperature informationat several points during a cooling cycle, similar to what is done with needle probe measurements of thermalconductivity. Further testing of alternative potting methods to reduce thermal mass of the chain would beworthwhile.5.5 Remote Sensing SupportHigh-resolution satellite data has proved indispensible on previous cruises to support navigation through iceand to find suitable ice floes for sampling and instrumentation deployment. Useful satellite data availableon NBP0901 consisted of near-real time acquisition of visible OLS (0.55 km resolution) and SSM/I passivemicrowave (12-25 km resolution), and visible band AVHRR (1.1 km resolution) using the Terrascan system.NBP09-01 Cruise Report (p. 41 of 83) Revised February 27, 2009