Multibeam Echosounder Metadata and Quality Statistics

Transcription

1 Multibeam Echosounder Metadata and Quality Statistics Dave Mann, Survey Support Manager, Gardline Geosurvey

2 Gardline MBES Systems Sea Explorer EM1002 RV Triton EM1002(S) Ocean Seeker EM1002(S) Ocean Endeavour EM1002 / EM120 Sea Profiler EM1000 Sea Surveyor EM1000 / EM12 Portable EM3000 Sea Trident ELAC 1050

3 Metadata What is it? A complex topic in itself IGGI Guidelines Principles of Good Metadata Management The Dublin Core Metadata Initiative (DCMI) is an organization dedicated to promoting the widespread adoption of interoperable metadata standards A technical word for Data about Data Structured information that describes, explains, locates or otherwise makes it easier to retrieve, use, or manage an information resource.

4 Metadata Why do we want it? To catalogue data To provide an abstract of the data To search for data To learn more about data

5 Metadata Why do we want it? Geophysical Site Survey 9 Kms 2 Hydrographic Survey 9,000 Kms 2

6 Metadata Why do we want it? CONTRACTOR shall fill out the following swath coverage tables as an integral component of their bid. The swath coverage tables shall detail the seafloor coverage of the multibeam bathymetry and backscatter system(s) as a function of water depth and survey speed, with a minimum accuracy of 0.5% of the water depth. Swath coverage tables should be based upon experience, preferably with the vessel proposed, and not manufacturer s specifications.

7 Metadata - Survey Data Client Details Survey Vessel Crew List Project Information Geodetic Parameters Survey Plan Equipment List

8 Metadata - Multibeam Data Equipment Specifications Interface Details Installation Parameters Calibration Details Operating Parameters Quality Statistics

9 Equipment Specifications Equipment Specifications MBES Frequency 95 KHz Number of Beams 111 Beam Width 2 x 2 Swathe width 150 Pulse Length 0.2, 0.7, 2.0 msec Sample Rate 9 KHz Survey Sensors Motion/Heading Sensor SVP Probes DGPS

10 Survey Sensors Seapath 200 Attitude/Heading System Pitch/Roll 0.03 RMS Heave 5cm or 5% Heading RMS Transducer Velocity Probe (AML) Velocity 0.05 m/sec Temperature C Depth 0.05 % Velocity Probe (Valeport) Velocity 0.03 m/sec Temperature 0.01 C Depth 0.04 % DGPS

11 Interface Details Format Data rates Baud rates Demodulator RTCM Seapath 200 CoG Velocity Heading DGPS Attitude Heading PPS MRU5 Transducer EM1002 Processor Unit Attitude Heading Transducer CTD Velocity Temperature EM1002 Workstation MBES Datagrams Voyager5 PC

12 Integrated Survey System

13 Installation Details Installation Survey Hardware versions Software versions

14 Operating Parameters Operating Parameters MBES Mode Draught / Waterline Sound Velocity Profile Filter Settings Motion Sensor Filter Settings Positioning System Reference Station

15 MBES Quality Plan Installation Survey Report Harbour Tests Instrument Tests Calibrations Heading/Motion Sensor Positioning System Velocity Probes Offshore Calibration (Patch) Tests Acquisition Statistics Processing Statistics

16 MBES Quality Statistics What is Quality? Fitness for Purpose Verification Is it working correctly? Manufacturers Specification Validation Is it providing the required data? Clients Specification

17 Clients Specifications Different Clients Different Specifications Oil / Gas Exploration Site Surveys Pipeline Route Surveys Inspection Cable Companies Cable Route Surveys Government Agencies Hydrographic Surveys EEZ Surveys

18 Quality Control Statistics Depth data Acquisition Statistics Noise data Motion Sensor data Velocity data Timing data Percentage of Valid Soundings Mean Swathe Width Ping Rate IHO statistics a/b are : User# Total # fail % fail # pass % pass ===== ===== ====== ======

19 Mean Depth per Beam MBES Quality Statistics

20 MBES Quality Statistics Fortunately, the Earth is flat(ish)..

21 But not always MBES Quality Statistics

22 MBES Quality Statistics Beam Errors may be derived from Best Fit Curve Beam Errors -> Corrections, if desired.

23 MBES Quality Statistics If the Earth is not Flat, the Surveyor may Frown

24 MBES Quality Statistics Persistent Frown, or Smile, indicates Velocity Problems

25 MBES Quality Statistics Quantify Error wrt Depth and compare with Specification

26 MBES Quality Statistics Differencing depths enables a Noise figure to be calculated

27 MBES Quality Statistics Peaks in Noise coincide with change in Amplitude/Phase detection

28 MBES Quality Statistics Consistent figures are expected at same depth (50m)

29 MBES Quality Statistics But will vary with water depth (220m)

30 MBES Quality Statistics And with type of system 220m)

31 MBES Quality Statistics Change in Noise values may indicate change in sea conditions

32 MBES Quality Statistics Motion data may be analysed to indicate sea conditions

33 MBES Quality Statistics Scatter plot will show Magnitude and Period

34 MBES Quality Statistics Histogram will show Frequency Distribution

35 MBES Quality Statistics Comparison of Lines indicated change in sea conditions

36 Transducer velocity is critical MBES Problems

37 MBES Problems Long term trends can highlight problems

38 MBES Problems Mean Depths show general problem, plus exaggerated effect

39 MBES Problems Problems within a line have instantaneous effect

40 MBES Problems Time synchronization with GPS can be problematic

41 MBES Problems Loss of GPS Pulse can introduce large offset errors

42 MBES Problems Two options for synchronization System Use Processor Unit (PU) Time to time-tag position data. 4No need for PPS 6Must have consistent latency Datagram Synchronize PU to GPS using Pulse per Second (PPS). Then use the Time reported in the (GGA) datagram to time-tag position data. 4Most accurate (in theory) 6Requires PPS

43 MBES Problems An apparent shift in seabed features, could be caused by a number of problems

44 MBES Problems Monitor difference between System time and GPS time

45 MBES Problems If the GPS-System time difference is greater than 1 second, a potential problem exists

46 MBES Problems Care taken when calibrations show unexpected results

47 MBES Problems A Rule of Thumb : System Use Processor Unit (PU) Time to time-tag position data. Most Reliable, IF LATENCY IS CONSISTENT Datagram Synchronize PU to GPS using Pulse per Second (PPS). Then use the Time reported in the (GGA) datagram to time-tag position data. Most Accurate, IF PPS IS RELIABLE

48 Conclusions The concept of Metadata appears to suited to the problem of multibeam data management. Quality statistics should form an important part of such Metadata. Analysis of relatively simple statistics can help to verify the quality of acquired data. Useful implementation requires agreed standards

49 THANK-YOU Dave Mann, Survey Support Manager, Gardline Geosurvey