Autosub Under Arctic Sea Ice
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RRS James Clark Ross Cruise JR106 Autosub under Arctic Sea Ice Cruise Report Peter Wadhams, Steve Ackley, Ken Collins, Pat Cooper, Terry Edwards, Jeffrey Evans, Gwyn Griffiths, Nick Hughes, Arthur Kaletzky, Steve McPhail, Duncan Mercer, Colm Ó Cofaigh, Kieran Rutherford, Andy Webb, Jeremy Wilkinson, Guy Williams and Doug Willis Grant NER/T/S/2000/00985 Autosub under Arctic Sea Ice JR106 Cruise Report (v1.00) CONTENTS CONTENTS...............................................................................................................................2 INTRODUCTION .....................................................................................................................3 SCIENTIFIC STAFF.................................................................................................................4 PURPOSE OF CRUISE.............................................................................................................6 CRUISE NARRATIVE .............................................................................................................7 AUTOSUB MISSION SUMMARY LOG ..............................................................................18 AUTOSUB NAVIGATION SYSTEM PERFORMANCE.....................................................19 AUTOSUB COLLISION AVOIDANCE................................................................................20 AUTOSUB HOMING SYSTEM AND ACOUSTIC TRACKING........................................22 AUTOSUB MECHANICAL REPORT...................................................................................24 AUTOSUB SCIENTIFIC SENSORS......................................................................................28 AUTOSUB - KONGSBERG EM2000 MULTIBEAM SWATH SYSTEM...........................31 AUTOSUB POST-PROCESSED NAVIGATION DATA FORMAT....................................35 AUTOSUB ADCP DATA DEFINITION (JR106) .................................................................36 SEA ICE VALIDATION PROGRAMME..............................................................................39 SATELLITE DATA ................................................................................................................40 SEA ICE WATCH...................................................................................................................45 PHYSICAL OCEANOGRAPHY............................................................................................49 MARINE TECHNOLOGY TESTS.........................................................................................58 ALONG TRACK MEASUREMENTS ...................................................................................60 EM120 MULTIBEAM SWATH BATHYMETRY AND TOPAS .........................................62 SHIPBOARD ADCP ...............................................................................................................71 LADCP.....................................................................................................................................74 CONTINUOUS PLANKTON RECORDER...........................................................................76 ITS REPORT ...........................................................................................................................77 APPENDIX A - ICE STATION DATA..................................................................................79 APPENDIX B – SALINITIES.................................................................................................89 APPENDIX C – LADCP SCRIPTS AND PROCESSING MESSAGES ...............................90 NERC Grant NER/T/S/2000/00985 Page 2 of 98 Autosub under Arctic Sea Ice JR106 Cruise Report (v1.00) INTRODUCTION Peter Wadhams (DAMTP/SAMS) Cruise JR106a was the second of four planned cruises by James Clark Ross to be carried out for the NERC Autosub-under-Ice (AUI) programme. The first cruise was in 2003 towards Pine Island Bay in the Antarctic. The third, in fact the second leg of JR106 (JR106b), is to south-east Greenland in September 2004; the fourth, JR97, will be to the Weddell Sea in January 2005. The purpose of AUI is to obtain data from beneath sea ice, glacier tongues and ice shelves using Autosub, and to develop Autosub’s capabilities as a cryospheric research tool. During the cruise reported here the Autosub was operated highly successfully under both moving pack ice and fast ice, obtaining some 400 km of high quality upward looking swath sonar data as well as oceanographic data. It undertook necessary avoidance manoeuvres for both deep pressure ridges and shallow seabed hazards in a classical manner as designed, and procedures for use of the acoustic homing system were developed to the point where the vehicle could be returned with confidence to an area covered with loose moving pack ice in the knowledge that it could be sent to a holding pattern out of which it could be steered towards the ship and recovered. This is a cause of increased confidence for the future use of the vehicle in regions covered with sea ice. Thanks are due to Steve McPhail and the entire AUV technical team for the quiet efficiency and hard work which underlay every mission and which was the chief cause of success. We are grateful for the contribution of all the other scientific groups on board, including the ice drilling teams, the ice watch, the SPRI group which ran the swath sonar system, and the CTD operators. We thank those who came as observers – Steve Ackley, Ken Collins and Gwyn Griffiths – but who willingly undertook onerous watchkeeping tasks. Especial thanks are due to the Captain, Chris Elliott, and the officers and crew of James Clark Ross for their unending support. We are grateful also to the Alfred Wegener Institute and to Professor Peter Lemke for the assistance of Polarstern in the ice thickness validation exercise on 25 August. For help in Reykjavik we offer special thanks to Professor Ingibjorg Jonsdottir, University of Iceland. The cruise was carried out under NERC grant NER/T/S/2000/00985 to Professor Peter Wadhams at Department of Applied Mathematics and Theoretical Physics, University of Cambridge, currently on leave at Dunstaffnage Marine Laboratory, Oban. NERC Grant NER/T/S/2000/00985 Page 3 of 98 Autosub under Arctic Sea Ice JR106 Cruise Report (v1.00) SCIENTIFIC STAFF Peter Wadhams DAMTP/SAMS [email protected] Jeremy Wilkinson SAMS [email protected] Nick Hughes SAMS [email protected] Duncan Mercer SAMS [email protected] Russell Ladkin SAMS [email protected] Arthur Kaletzky DAMTP [email protected] Gwyn Griffiths Autosub [email protected] James Perrett Autosub [email protected] Kieran Rutherford Autosub [email protected] Mark Squires Autosub [email protected] Andrew Webb Autosub [email protected] Dave White Autosub [email protected] Peter Stevenson Autosub [email protected] Stephen McPhail Autosub [email protected] Dr. Colm O Cofaigh SPRI [email protected] Dr. Jeffrey Evans SPRI [email protected] Ruth Mugford SPRI [email protected] Ken Collins SOC [email protected] Zoe Roberts SOC [email protected] Terry Edwards UKORS [email protected] Guy Williams ACECRC [email protected] Steve Ackley USA [email protected] Pat Cooper BAS Doug Willis BAS SAMS – Scottish Association for Marine Science Dunstaffnage Marine Laboratory Oban Argyll PA37 1QA Scotland DAMTP – University of Cambridge, Department of Applied Mathematics and Theoretical Physics Centre for Mathematical Sciences Wilberforce Road Cambridge CB3 0WA United Kingdom Autosub – Autosub Mission Team Southampton Oceanography Centre Waterfront Campus European Way Southampton SO14 3ZH United Kingdom NERC Grant NER/T/S/2000/00985 Page 4 of 98 Autosub under Arctic Sea Ice JR106 Cruise Report (v1.00) SPRI – Scott Polar Research Institute University of Cambridge Lensfield Road Cambridge CB2 1ER United Kingdom SOC – Southampton Oceanography Centre Waterfront Campus European Way Southampton SO14 3ZH United Kingdom UKORS – United Kingdom Ocean Research Services Southampton Oceanography Centre Waterfront Campus European Way Southampton SO14 3ZH United Kingdom ACECRC - Antarctic Climate and Ecosystems Co-operative Research Centre Marine Ecosystems Group University of Tasmania Private Bag 80 Hobart 7001 Australia USA - Clarkson University Potsdam, New York. NERC Grant NER/T/S/2000/00985 Page 5 of 98 Autosub under Arctic Sea Ice JR106 Cruise Report (v1.00) PURPOSE OF CRUISE Peter Wadhams The purpose of the cruise was to obtain ice thickness distributions from the upward- looking swath sonar system aboard Autosub, to validate the thickness values against other data collected simultaneously from the surface and the air, and to conduct transects across and within Fram Strait so as to obtain estimates of ice flux. An important aspect of the cruise also was the development of operating methods which are suitable for ice-covered waters. The moving sea ice in Fram Strait in August 2004, following a long period of calm weather, was a very diffuse cover which spread far to the east but with a coverage of only 1- 2/10. This was an unfavourable type of ice for Autosub for three reasons. Firstly the low concentration meant that not much ice was profiled per hard-won mile of Autosub mission track, with additional problems arising from the extensive calm water causing a loss of lock in the sonar (described later by Arthur Kaletzky). Secondly, the concentration, while diffuse, was sufficient to make surfacing of the Autosub dangerous, so the homing