EM3002
- EM302 comparisons - Outer Beaufort Continental Slope
for Jose to work on ...
In August/September/October 2009
a collaborative mapping program took place between ArcticNet and
Imperial Oil. It involved mapping in the Beaufort Sea involving 3
multibeam platforms:
- CCGS Amundsen - EM302
- CCGS Nahidik - EM3002
- CSL Petrel - EM3002
and in previous years there has been a few transits through the region
with :
- CCGS Amnudsen with her older EM300
The specific focus of your research should be in the relative
performance of the multibeams (EM302 v. EM3002) in the overlapping
depth ranges (~70m to 200m). Also, possibly an assessment of the older
EM300 where available.
The comparison should include all of :
- bathymetry (resolution - achievable swath width - data
density etc..)
- backscatter ( ditto...)
- possibly water column imaging....
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Along the shelf break the following coverages were achieved:
Amundsen EM302 - normally ~ 13.5
knots
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Nahidik (pole-mounted) EM3002 -
normally ~ 5 knots.
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Petrel (launch) EM3002 -
normally ~ 8 knots.
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You need to select regions where there is suffficient overlap
and make grid and mosaics of the differning sonar data types ot
quantitativcely compare there relative resolution , coverage and
accuracy (through cross-line statistics). Two area examples
are presented below (from COMPARE_EM302_EM3002 directory) where a 5km
by 2.5km box was selected using a 2m resolution.
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SUN-ILLUMINATED
BATHYMETRY
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MULTIBEAM
BACKSCATTER
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EM302
EAST
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EM3002
Nahidik
EAST |
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EM3002
Petrel
EAST
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haven't made
the petrel backscatter..
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EM302
WEST
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EM3002
Nahidik
WEST |
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EM3002
Petrel
WEST |
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haven't made
the petrel backscatter.. |
As a precursor to the MEng report - a detailed description of
the relative capabilities of the two sonars should be well described:
- EM3002 - single sector, single swath - CW only (discuss choice of
centre fequency 297/300 or303 and pulse length), 300 kHz, 1.5x1.5
- older EM300 - 3 sectors in shallow, 9 sectors in deep CW only
(describe pulse lengths used by sector and mode). single swath 1x2
(poor flush mounting for icebreaker)
- EM302 - 4 secotrs in shallw, 8 secotrs in deep - dual swath
CW and FM pulses (describe pulse lengths/types used by sector and
mode)- - yaw, pitch and roll stabilized 1x2
DATA :
On:
/drives/nootka/disk1/Ajurak_Jose_302v3002
(you may need ot change permisisons to make it all owned by you...
you will find the following directories:
-
- Overview - a
series of overview images to register the surveys against.
- COMPARE_EM302_EM3002 -
some sample processing products that I created on board.
- html - the makings of
this web page
- Amundsen_EM302@ - a soft
link to the OMG format EM302 data
- Nahidik_Petrel_EM3002@
- a soft link to the OMG format Nahidik and Petrel data.
You need to get famniliar with the swathed philosophy for processing
the data - learn how to:
- grid bathymetry
- interactively edit the data (swathed -locate etc..)
- make strips of sidescan/backsactter
- mosaic thew sidescan.backsactter.
- view and compare differnt grids/mosdaics.
Issues to Research:
BATHYMETRY:
GRIDDING :
Learn how to choose a map sheet (rotated or north oriented) and
appropriate pixel size, -beamwidth footprint and beam angle
weighting.
Edit out fishfinder interference for Petrel.
ANALYSIS
Swath width v. depth for EM3002
Using cross lines in flat regions try to estimate the vertical
accuracy achieved
- must separate the unavoidable biases
due to working without good tides and imperfect draft measurments, from
the sounding noise
- can you see evidence of refraction residuals?
Comparison of spatial resolution of short wavelength targets...
Compare old EM300 with shorter pulse lengths on shallow shelf with
newer EM302 with longer pulses (no "very-shallow" mode)
Calculation of affect of attenuation (Arctic v. Mediterranean)
BACKSCATTER :
SIDESCAN STRIP CREATION :
learn how to make the various types of sidescan product (.ss, .ss_bp,
.ss_roll, .ss_degraz etc..)
(all have yet to be made for Petrel).
Specifically for the EM302 learn how to cope with the dual swath
mismatch - > downGrade..., perhaps suggest a better method?
Describe the problem with dealing with beam pattern statistics
with a very narrow angular sector..... (EM3002 in > 150m water)
For the em3002 - do the deTVG work.. - should see a significant
difference in the backscatter pattern around the pingoes.
- see if this will be useful for the EM302 (not tested yet - may not
work).
MOSAICING :
as with the gridding, select approiate resolution mapsheets and learn
how to make mosaics - try different options to deal with overlap.
make separate mosaics for the various types of beam pattern and grazing
angle correction options.
ANALYSIS :
Compare definition of textured seafloors.
Affect of frequency on whether seafloor appears rough or smooth
any evidence for subbottom penetration...
RECOMMENDATIONS:
Discuss - Pluses and Minuses of the choice of switch over depth.
Quantify whether the resolution is limited more by data density (due to
speed, no of swaths per ping cycle and choice of angular sector) or
beam dimension.
And lastly, but most importantly - become the shipboard expert in EM302
backscatter processing for the BP Amundsen operations in September!!!!!
thoughts by JEHC so far - April
2010
