Project no. 018509 DAMOCLES Developing Arctic Modelling and Observing Capabilities for Long-term Environment Studies Instrument: Integrated Project Thematic Priority: 6.3 “Global Change and Ecosystems” D8.2-06 - Results from the Fram Strait acoustic tomography experiment and system evaluation Due date of deliverable: 30/05/2010 Actual submission date: 20/06/2010 Used Person/months: 9.75 Start date of project: 1 December 2005 Duration: 54 months Organisation name of lead contractor for this deliverable: NERSC Project co-funded by the European Commission within the Sixth Framework Programme (2002-2006) Dissemination Level PU Public PP Restricted to other programme participants (including the Commission Services) X RE Restricted to a group specified by the consortium (including the Commission Services) CO Confidential, only for members of the consortium (including the Commission Services) D8.2-06 - Results from the Fram Strait acoustic tomography experiment and system evaluation TITLE: D8.2-06 - Results from the Fram Strait acoustic REPORT IDENTIFICATION tomography experiment and system evaluation DAMOCLES Deliverable D8.2 CLIENT : CONTRACT DAMOCLES Contract Instrument: Integrated Project Grant agreement no.: 018509 Thematic Priority: 6.3 “Global Change and Ecosystems” CLIENT REFERENCE AVAILABILITY Open report within the DAMOCLES consortium. INVESTIGATORS AUTHORISATION Svein Arild Haugen, NERSC, Norway Hanne Sagen, NERSC, Norway Stein Sandven, NERSC, Norway Bergen, 20 June 2010 Matthew Dzieciuch, SIO, USA Peter Worcester, SIO, USA Emmanuel Skarsoulis, FORTH, Greece George Piperakis, FORTH, Greece Michael Kalogerakis ,FORTH, Greece Stein Sandven Date: 20/06/2010 i. D8.2-06 - Results from the Fram Strait acoustic tomography experiment and system evaluation Content 1 Introduction........................................................................................................................1 2 Observation System............................................................................................................2 2.1 Observation System Experimental Setup....................................................................2 2.2 Bathymetry...................................................................................................................2 2.3 Observation System Architecture................................................................................5 2.3.1STAR ....................................................................................................................7 2.3.2Acoustic source.....................................................................................................9 2.3.3Acoustic Transponders..........................................................................................9 2.3.4Acoustic releases................................................................................................10 2.3.5Acoustic Interrogation System............................................................................10 2.4 Participation in Preparations, Deployment and Recovery.........................................11 2.5 Provisional Quality Control........................................................................................12 2.5.1PQC system arrangement...................................................................................12 2.5.2Acoustic Recordings............................................................................................14 2.5.3Spectral analysis.................................................................................................14 2.6 Summary....................................................................................................................17 3 Data Treatment ...............................................................................................................18 3.1 Travel time sensitivity.................................................................................................18 3.2 Timekeeping..............................................................................................................21 3.3 Mooring Motion..........................................................................................................23 3.3.1Transponder geodesic positioning ....................................................................24 3.3.2Mooring instruments positioning.........................................................................27 3.4 Arrival Time estimation..............................................................................................30 3.5 Multipaths..................................................................................................................31 3.6 Sonar Equations........................................................................................................33 3.7 Pulse Compression....................................................................................................37 3.7.1Pulse Compression of Linear Frequency Modulated Sweeps ..........................38 3.8 Other issues...............................................................................................................42 3.9 Summary....................................................................................................................43 4 Acoustic Travel Time Measurements................................................................................44 4.1 Arrival Patterns, Damocles track, 21-26 September 2008........................................44 4.2 Travel time measurements, Damocles track, 2008-2009..........................................46 4.2.1Engineering data.................................................................................................46 4.2.2Travel times.........................................................................................................59 4.3 Preparation of data for inversion and data asimilation..............................................67 4.4 System errors............................................................................................................69 4.4.1Issues..................................................................................................................69 4.4.2Corrective actions................................................................................................75 4.5 Summary....................................................................................................................75 Date: 20/06/2010 ii D8.2-06 - Results from the Fram Strait acoustic tomography experiment and system evaluation 5 Inversion of ocean acoustic tomography ........................................................................76 5.1Introduction.................................................................................................................76 5.2The experiment ..........................................................................................................77 5.3Parameterization ........................................................................................................78 5.4Model relations ..........................................................................................................80 5.5Matched-peak inversion ............................................................................................81 5.6MCMC sampling ........................................................................................................83 5.7The tomography data.................................................................................................85 5.8Offset calibration.........................................................................................................91 5.9Inversion results..........................................................................................................93 Date: 20/06/2010 iii D8.2-06 - Results from the Fram Strait acoustic tomography experiment and system evaluation 1 Introduction This report describes the data treatment of acoustic tomography data and the results of using these data for inversion. Further, issues found about the experiemental equipment are decribed as well as some corrective actions taken. The data treatment of the acoustic tomographty data described in this report has been carried out by NERSC based on adaption of proven algorithms and methods provided by SCRIPPS. The inversions are carried out by FORTH/IACM. The major part of the data treatment tasks have been carried out as part of a Master's thesis conducted by NERSC. Date: 20/06/2010 Page 1 of 101 D8.2-06 - Results from the Fram Strait acoustic tomography experiment and system evaluation 2 Observation System The observation system which was deployed (and in operation) in the Fram Strait from 16 Aug 2008 until 01 Aug 2009 will now be described. The observation system obviously is only a part of the full tomography system which also includes the sub-systems needed for post recovery data treatment and implementation of the inversion schemes [Sagen et al., 2008a]. Thus, the observation system described here essentially comprises the instruments which were deployed on the moorings. The post recovery data treatment and travel time measurements will be described in the next chapters. Reference is made to [Skarsoulis et al., 2008] for using the travel time data for data oriented inversion, while [Sagen et al., 2008b] describes how the travel time data will be used for model oriented inversion. In addition to describing the tomography instruments, a system for provisional quality control that was designed,