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REPORT NO. 141007.1
Headword:
acoustic profiling (boomer)
Task no.:
141007
Report no.:
1
Employer:
Statens Vegvesen
Task/
report:
E39 STATE MUNICIPAL PLAN AKSDAL-BERGEN
Acoustic profiling with boomer to map bedrock horizon
Date:
12. November 2014.
Abstract
In connection with the E39 state municipal on the section Stord-Os have Geomap
AS performed acoustic surveys in the area Rekstern and Sørøyanene of Haljem.
Survey area had been divided up to five smaller areas.
Sediment thickness hardly exceeds 20m anywhere in the area. Sediment is present
only in small patches.
Country/county:
Norway/Hordaland
Municipal:
Os
Locality:
Halhjem.
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REPORT NO. 141007.1
SUMMARY:
PAGE
ABSTRACT
1
1.
INTRODUCTION
3
2.
FIELDWORK
3
3.
PROCESSING AND INTERPRETATION
4
4.
RESULTS
4
AREA 1
5
AREA 2
7
AREA 3
9
AREA 4
11
AREA 5
12
TECHNICAL INFORMATION
14
5.
APPENDIX:
A1
MARINE ACOUSTIC PROFILING
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REPORT NO. 141007.1
1. INTRODUCTION
In connection with the E39 state municipal on the section Stord-Os have Geomap AS
performed acoustic surveys in the area Rekstern and Sørøyanene of Haljem.
2. FIELDWORK
The acoustic survey had been carries out between 19th and 21st of May, 2014. Weather
conditions were appropriate for data acquisition. No accidents happened during the
survey.
A high resolution real-time corrected differential GPS receiver had been used for
positioning.
The whole survey area consisted of five smaller areas, referred to as Area 1, Area 2,
etc. (see later in Chapter 4 “Results”).
For acoustic source, a 105J energy boomer source and a four-hydrophon stacked
streamer cable had been used. Data was acquired digitally using 16-bit 50kHz A/D
conversion. An 80Hz–2.5kHz analog bandpass filter ensured the removal of DC
component and the 50Hz noise, and also to ensure the suppression of any frequencies
higher than the Nyquist-frequency in the spectra.
The equipment arrangement used during the survey is shown on Figure .
12,7
boomer
boomer towing point
GPS antenna
1
0,57
boat
1,95
streamer towing point
streamer
13,3
(13,55)
Figure 1 –Eqipment arrangement. All dimensions are in meters.
Note – The streamer cable towing distance was 13.30m during the whole survey except
on the 19th of May, when it was only 13.55m. It affected half of Area 3.
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REPORT NO. 141007.1
3. PROCESSING AND INTERPRETATION
Acoustic raw data had been converted to standard SEG-Y format. Then, a tidal
correction had been applied. Finally, after adding positions, acoustic profiles were
loaded into a seismic interpretation system, where water bottom horizon and a typical
intra-sediment horizon had been picked. A 1485m/s value from literature was applied
as water velocity. To calculate sediment thickness, an average value of 1800m/s taken
from literature has been applied.
To stabilize interpolation when creating water bottom horizon grid, land data has been
added to the dataset. Land data has been created using ±0m height isoline of the base
map provided by the client.
Bedrock horizon was created by subtracting thickness map from water bottom map.
4. RESULTS
The results displayed in the following subchapters displayed as height above sea level
and thickness maps. Coordinates are in UTM system, zone 32. The survey layout is
shown in Figure 2.
Figure 2 – Overview map. Red lines represent survey path. (Base map had been exported from
Google Earth.)
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REPORT NO. 141007.1
In Area 1 and 2, water depth reaches or even exceeds 200m, but only in marginal
places of the areas. Sediment is present in a trench running along the shoreline and
some deeper spots, but sediment thickness rarely exceeds 20m.
In Area 3 and 4, water depth goes down only to approximately 100m, while the deepest
point of Area 5 is cc. 120m. Sediment is present only in some small patches, with a
thickness of maximum approximately 20m. The widest horizontal sediment
distribution can be observed in the well protected Northern bay in Area 4, and the two
North-South running trenches in Area 5.
Legend for detailed result maps is shown on Figure 3.
Figure 3 – Legend for detailed result maps
Area 1
Figure 4 – Area 1 water bottom horizon height above sea level
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REPORT NO. 141007.1
Figure 5 – Area 1 bedrock surface horizon height above sea level
Figure 6 – Area 1 sediment thickness
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REPORT NO. 141007.1
Area 2
Figure 7 – Area 2 water bottom horizon height above sea level
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REPORT NO. 141007.1
Figure 8 – Area 2 bedrock surface horizon height above sea level
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REPORT NO. 141007.1
Figure 2 – Area 2 sediment thickness
Area 3
Figure 9 – Area 3 water bottom horizon height above sea level
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REPORT NO. 141007.1
Figure 10 – Area 3 bedrock surface horizon height above sea level
Figure 11 – Area 3 sediment thickness
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REPORT NO. 141007.1
Area 4
Figure 12 – Area 4 water bottom horizon height above sea level
Figure 13 – Area 4 bedrock surface horizon height above sea level
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REPORT NO. 141007.1
Figure 14 – Area 4 sediment thickness
Area 5
Figure 15 – Area 5 water bottom horizon height above sea level
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REPORT NO. 141007.1
Figure 16 – Area 5 bedrock surface horizon height above sea level
Figure 17 – Area 5 sediment thickness
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REPORT NO. 141007.1
5. TECHNICAL INFORMATION
Employer
Contact man
Field personnel
Fieldwork
Boat
Subsea deposit mapping (acoustic
profiling)
Horizontal datum
Projection
Bathymetry, altitude basis
GEOMAP a. s.
Robert Vida
Statens Vegvesen
Bjørn Alsaker
Mr. Morten Urhaug, Mr. Robert Vida
Week 21, 2014
”Øyen”
EG&G/ORE, Boomer 105 Joule
EG&G hydrophone
Euref 89 (in field)
Zone 32
http://sehavniva.no, shoreline from basemap