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www.sea-technology.com March 2015 / st 27 I n 2008, the Alfred We- gener Institute Helm- holtz Center for Polar and Marine Research (AWI) in Bremerhaven, Germany, started refocusing its ro- botic exploration pro- gram in the Arctic. Since then, under the general term of "Biogeochemical Research," a Bluefn-21 AUV from Bluefn Robot- ics (Quincy, Massachu- setts) has been deployed to investigate such things as primary production and the distribution of nutri- ents in the Arctic marginal ice zone. The vehicle is equipped with various sen- sors and a water sample collector. Its main site of operation in the Arctic has been the Fram Strait between Svalbard and Greenland where AWI has run the permanent deep-sea ob- servatory "Hausgarten" since 1999. Here, we describe a correction algorithm used during post-processing of the vehicle's navigation data. Using posi- tion data of an external tracking system, this algorithm re- constructs the actual dive track of the AUV and provides reliable navigation data to georeference scientifc measure- ments accurately. Basic Preconditions The majority of biogeochemical processes in the sea are closely related to the uppermost meters of the water col- umn. Concerning the distribution of biogeochemical pa- rameters, the Arctic marginal ice zone features high spatial variability in small areas. In order to investigate these steep gradients correctly, the assigning of the measurements to reliable navigation data is crucial. However, operating in these conditions entails a number of problems for the ve- hicle, as it has to navigate close to the surface, and thus, depending on the respective water depth, it might be unable to establish bottom tracking with its Doppler velocity log (DVL). As a consequence, the vehicle will not have a refer- ence to determine its exact velocity and heading. AWI's AUV also conducts foat maneuvers that place an additional burden on the vehicle's navigation system. Dur- ing this maneuver the thruster of the AUV is deactivated, making it behave like a foat and record a high-resolution vertical profle of the water column as it ascends. Due to the missing bottom lock and the foat maneuver, the navigation accuracy is reduced. External tracking systems can improve the quality of AUV navigation data. It is common to use long baseline (LBL) networks to support the navigation of a vehicle, although the exact deployment of the acoustic beacons is a time- consuming operation. In a fast-changing environment such as the Arctic marginal ice zone, with the ice achieving drift speeds of 1.5 kilometers per hour and more, these kinds of operations are diffcult to carry out. Ship-bound ultrashort Correcting Navigation Data Of Shallow-Diving AUV in Arctic Algorithm Improves Data Quality of Biogeochemical Research By Uwe Wulff • Thorben Wulff Raw data of the AUV and GAPS (left) and phase one AUV data (right).