Berit Horvei, Project Manager, SW Hydrography, Subsea Division Seabed image processing and datacleaning of the EM 3002 Common Data Set Berit Horvei, Project Manager, SW Hydrography, Subsea Division WORLD CLASS – through people, technology and dedication

Outline Data collection Tide / realtime heave Sound speed variation Seabed Image processing Datacleaning 19-Apr-19

Data collection R/V Coastal Surveyor EM 3002 D mounted to the existing ram system onboard All other sensors supplied by UNH Used RTK 3 ½ Day with surveying 19-Apr-19

Tide / realtime heave Problems with realtime heave Measured tide from NOAA homepage. Height values extracted in Neptune Established modified tide values 18. sept, RTK stasjon 1, svakt signal, falt tidvis ut. 19-21 sept. Ny RTK stasjon, montert på toppen av et fyr. 19-Apr-19

Real time heave in the data  Modified tide file 1 m corridor x5 Depth scale factor Calib, 1 m corridor Gridnavn: 19-Apr-19

Sound speed at transducer Gridded measured sound speed at transducer head. Small part(red) with wrong sound speed. 19-Apr-19

Seabed image processing Seabed image datagram, corrected for incidence angle Backscatter, one value / beam Target, lobster pots, not visible in seabed image frame Can be identified in the grid. 19-Apr-19

Seabed image processing Seabed image data gridded with a higher resolution than the depth values. Overlay on top of the ordinary grid Hvilke parametre brukte jeg. 19-Apr-19

Seabed image processing Seabed image data Backscatter values gridded 19-Apr-19

Seabed image processing 19-Apr-19

Seabed image processing 19-Apr-19

Datacleaning Line based: Looks at every depth in the current ping. Removes time- and overhangs errors. Grid based: Uses the Tukey-algorithm to construct a curved surface that fits as good as possible to most of the depths in the cell unit. Does cell splitting and merging to find best possible cell size first. Reconsiders all depths from previous lines every time the same geographical area is processed. Uses statistics to remove spikes based on standard deviation, but can also use grazing angle and calculated error estimates for each depth to flag out depths. 19-Apr-19

Datacleaning Raw data gridded Selected area where the sound speed profile created problems. 19-Apr-19

Datacleaning Data cleaned in Neptune. Removed on beam angle, manual inspection and descision xyz-data from Neptune is gridded in SIS 19-Apr-19

Datacleaning Residue standard deviation rule. Noise removed, but effect of sound speed still visible. 19-Apr-19

Datacleaning Residue std. rule Point data. Red invalid points. Blue valid points. 19-Apr-19

Datacleaning Grazing angle rule For each depth the angle between the beam and the bottom surface is calculated. 19-Apr-19

Datacleaning Grazing angle rule Point data. Red invalid points. Blue valid points. 19-Apr-19

Datacleaning Upper left, raw data Upper right, xyz data, cleaned in Neptune Lower left, standard deviation rule Lower right, grazing angle rule 19-Apr-19

Summary Tide / realtime heave Sound speed variation Seabed Image processing Datacleaning 19-Apr-19

Kongsberg Maritime 19-Apr-19