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Development of a sonar system to estimate the seafloor subsurface burial depth of a towed gamma-ray spectrometer

Development of a sonar system to estimate the seafloor subsurface burial depth of a towed gamma-ray spectrometer
Development of a sonar system to estimate the seafloor subsurface burial depth of a towed gamma-ray spectrometer
A sonar system and image processing method have been developed to continuously estimate the seafloor subsurface burial depth of a gamma-ray spectrometer that is towed along the seafloor by a ship. The towed gamma-ray spectrometer, called the RESQ hose, is an instrument designed to measure radiation levels in seafloor sediments that were contaminated as a result of the accident at the Fukushima-Daiichi nuclear power plant. In situ measurements of subsurface burial depth can increase the accuracy of the radionuclide concentration levels estimated by the RESQ hose by allowing for more accurate modeling of the measurement conditions. The reliability of the system is verified through sea trials performed near the outlet of the Abukuma River. Continuous measurements of burial depth are achieved with an outlier ratio of less than 5%. The burial depths measured by the device show a strong correlation with the acoustic backscatter intensity of side-scan sonar images obtained along the surveyed transect, indicating that burial depth is dependent on sediment type. We examine the influence of burial depth on the conversion factors between detected gamma-ray count rates and the concentrations of 134Cs and 137Cs. For both nuclides, the calculated factors increase by nearly 80% as burial depth increases from 0 to 11 cm. The converted results from the measured 137Cs count rates are compared with a core sample obtained near the transect, with the nearest point within a factor of two of the sampling result.
0025-3324
155-166
Hirao, Yoshihiro
072c864c-d916-460e-9e76-5d44fa19c43d
Ohnishi, Seiki
035c497a-ec02-4ce9-9879-a39a916b5d9a
Thornton, Blair
8293beb5-c083-47e3-b5f0-d9c3cee14be9
Yano, Yusuke
63d7a6f0-0757-4832-bd6d-7cbc0dede012
Odano, Naoteru
acead221-760b-421e-8c06-9907c2542f9e
Ura, Tamaki
b8fea5ba-e731-40fd-8544-1db1ca9f356b
Hirao, Yoshihiro
072c864c-d916-460e-9e76-5d44fa19c43d
Ohnishi, Seiki
035c497a-ec02-4ce9-9879-a39a916b5d9a
Thornton, Blair
8293beb5-c083-47e3-b5f0-d9c3cee14be9
Yano, Yusuke
63d7a6f0-0757-4832-bd6d-7cbc0dede012
Odano, Naoteru
acead221-760b-421e-8c06-9907c2542f9e
Ura, Tamaki
b8fea5ba-e731-40fd-8544-1db1ca9f356b

Hirao, Yoshihiro, Ohnishi, Seiki, Thornton, Blair, Yano, Yusuke, Odano, Naoteru and Ura, Tamaki (2014) Development of a sonar system to estimate the seafloor subsurface burial depth of a towed gamma-ray spectrometer. Marine Technology Society Journal, 48 (3), 155-166. (doi:10.4031/MTSJ.48.3.13).

Record type: Article

Abstract

A sonar system and image processing method have been developed to continuously estimate the seafloor subsurface burial depth of a gamma-ray spectrometer that is towed along the seafloor by a ship. The towed gamma-ray spectrometer, called the RESQ hose, is an instrument designed to measure radiation levels in seafloor sediments that were contaminated as a result of the accident at the Fukushima-Daiichi nuclear power plant. In situ measurements of subsurface burial depth can increase the accuracy of the radionuclide concentration levels estimated by the RESQ hose by allowing for more accurate modeling of the measurement conditions. The reliability of the system is verified through sea trials performed near the outlet of the Abukuma River. Continuous measurements of burial depth are achieved with an outlier ratio of less than 5%. The burial depths measured by the device show a strong correlation with the acoustic backscatter intensity of side-scan sonar images obtained along the surveyed transect, indicating that burial depth is dependent on sediment type. We examine the influence of burial depth on the conversion factors between detected gamma-ray count rates and the concentrations of 134Cs and 137Cs. For both nuclides, the calculated factors increase by nearly 80% as burial depth increases from 0 to 11 cm. The converted results from the measured 137Cs count rates are compared with a core sample obtained near the transect, with the nearest point within a factor of two of the sampling result.

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More information

Published date: May 2014
Organisations: Fluid Structure Interactions Group

Identifiers

Local EPrints ID: 400013
URI: http://eprints.soton.ac.uk/id/eprint/400013
ISSN: 0025-3324
PURE UUID: 02d7e920-9eef-4616-81bc-ca85690aa038

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Date deposited: 06 Sep 2016 15:57
Last modified: 07 Jan 2022 21:54

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Contributors

Author: Yoshihiro Hirao
Author: Seiki Ohnishi
Author: Blair Thornton
Author: Yusuke Yano
Author: Naoteru Odano
Author: Tamaki Ura

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