Profile soundings in lakes of the younger morainal area of Sleswick-Holstein with a sediment-echo-sounder of 30 kHz [Translation from: Wass.Boden 26, 135-138, 1974]

To be able to carry out physical, chemical and biological investigations on a lake, one needs a thorough knowledge of the volume of water and the shape of the lake basin. Little is known about the about the morphology of the lakes in Schleswig-Holstein and its ecological consequences. For this research a 30 KHz echo sounder with sediment transceiver was used to carry out profile determinations (echo soundings). This apparatus continuously records on paper the different reflexions and absorptions of the sediment and water body in the corresponding depth. By this, acoustically noticeable layers and different densities in the sediment and 'scattering layers' in the water body due to physical, chemical and biological reasons (e.g. plans and single fish) are made visible. Result are summarised here regarding the echo soundings in Blunker See.

Seabed classification for trawlability determined with a multibeam echo sounder on Snakehead Bank in the Gulf of Alaska

Rockfishes (Sebastes spp.) tend to aggregate near rocky, cobble, or generally rugged areas that are difficult to survey with bottom trawls, and evidence indicates that assemblages of rockfish species may differ between areas accessible to trawling and those areas that are not. Consequently, it is important to determine grounds that are trawlable or untrawlable so that the areas where trawl survey results should be applied are accurately identified. To this end, we used multibeam echosounder data to generate metrics that describe the seafloor: backscatter strength at normal and oblique incidence angles, the variation of the angle-dependent backscatter strength within 10° of normal incidence, the scintillation of the acoustic intensity scattered from the seafloor, and the seafloor rugosity. We used these metrics to develop a binary classification scheme to estimate where the seafloor is expected to be trawlable. The multibeam echosounder data were verified through analyses of video and still images collected with a stereo drop camera and a remotely operated vehicle in a study at Snakehead Bank, ~100 km south of Kodiak Island in the Gulf of Alaska. Comparisons of different combinations of metrics derived from the multibeam data indicated that the oblique-incidence backscatter strength was the most accurate estimator of trawlability at Snakehead Bank and that the addition of other metrics provided only marginal improvements. If successful on a wider scale in the Gulf of Alaska, this acoustic remote-sensing technique, or a similar one, could help improve the accuracy of rockfish stock assessments.

Echo location of fishes in Dhudawa reservoir (Madhya Pradesh)

An investigation was undertaken in order to locate fish using an echo sounder in Dhudawa Reservoir, Madhya Pradesh, India. In general, fish were found to be distributed either towards off-bottom or mid-water areas. Echo sounding is recommended for use in other reservoirs for fish detection.

Seabed Biodiversity on the Continental Shelf of the Great Barrier Reef World Heritage Area

The Great Barrier Reef is a unique World Heritage Area of national and international significance. As a multiple use Marine Park, activities such as fishing and tourism occur along with conservation goals. Managers need information on habitats and biodiversity distribution and risks to ensure these activities are conducted sustainably. However, while the coral reefs have been relatively well studied, less was known about the deeper seabed in the region. From 2003 to 2006, the GBR Seabed Biodiversity Project has mapped habitats and their associated biodiversity across the length and breadth of the Marine Park to provide information that will help managers with conservation planning and to assess whether fisheries are ecologically sustainable, as required by environmental protection legislation (e.g. EPBC Act 1999). Holistic information on the biodiversity of the seabed was acquired by visiting almost 1,500 sites, representing a full range of known environments, during 10 month-long voyages on two vessels and deploying several types of devices such as: towed video and digital cameras, baited remote underwater video stations (BRUVS), a digital echo-sounder, an epibenthic sled and a research trawl to collect samples for more detailed data about plants, invertebrates and fishes on the seabed. Data were collected and processed from >600 km of towed video and almost 100,000 photos, 1150 BRUVS videos, ~140 GB of digital echograms, and from sorting and identification of ~14,000 benthic samples, ~4,000 seabed fish samples, and ~1,200 sediment samples.

Seabed discrimination data from SeaScan™

Raw data from SeaScan™ transects off Wide Bay (south Queensland) taken in August 2007 as part of a study of ecological factors influencing the distribution of spanner crabs (Ranina ranina). The dataset (comma-delimited ascii file) comprises the following fields: 1. record number 2. date-time (GMT) 3. date-time (AEST) 4. latitude (signed decimal degrees) 5. longitude (decimal degrees) 6. speed over ground (knots) 7. depth (m) 8. seabed roughness (v) 9. hardness (v) Indices of roughness and hardness (from the first and second echoes respectively) were obtained using a SeaScan™ 100 system (un-referenced) on board the Research Vessel Tom Marshall, with the ship’s Furuno FCV 1100 echo sounder and 1 kW, 50 kHz transducer. Generally vessel speed was kept below about 14 kt (typically ~12 kt), and the echo-sounder range set to 80 m. The data were filtered to remove errors due to data drop-out, straying beyond system depth limits (min. 10 m), or transducer interference.

Bi-annual environment monitoring technical report for the SON cage fish culture site at Bugungu, Napoleon Gulf, northern Lake Victoria, December 2012

The first year-round quarterly surveys were completed for the year 2011. For the year 2012, SON management decided to change the frequency of the surveys from quarterly to biannual and the first such survey, was undertaken in June 2012. The second survey was undertaken in December 2012 and is the subject of this report: Results/observations made are presented in this technical report along with a scientific interpretation and discussion of the results with reference to possible impacts of the cage facilities to the water environment and aquatic biota. SON cage study sites were coded as downstream of cages (DSC), within cages (WIC) and upstream of cages (USC). Physical-chemical parameters (water column temperature, dissolved oxygen, pH, conductivity, were measured in-situ with a pre-calibrated hydrolab at each site. A digital Echo Sounder was used to determine the total water column depth at each site. A black and white Secchi disc was used to determine water column transparency. Coordinate locations were determined with a GPS device.

Gas seepage on the sea floor of Okinawa Trough Miyako Section

A marine geophysical survey was carried out, on the RN Science 1 of the Institute of Oceanography, Chinese Academy of Sciences (IOCAS), in 2000, at the Miyako Section of Okinawa Trough. Here we present seismic and acoustic evidence of a gas seep on the sea floor on the western part of the Okinawa Through, near the lower slope of the East China Sea Slope and discuss the possibility of related formation of gas hydrate. A gas column reflection was observed in echo-sounder data above a section where the sea floor reflector was missing, on both the echo-sounder and the seismic data for line H14. The seismic data also show an acoustic curtain reflection and a turbidity reflection at this section. These anomalies are the evidence of the existence of a gas seep, which occupies an area 2.2 km in diameter. Based on the acoustic curtain on line H14, we believe that the amount of gas contained in the sediments below the gas seep is larger than 1 % by volume of sediment. Tectonically, the gas seep developed in a small basin controlled by basement uplift in the north, south and east. The thickness of the sediment layer can be greater than 3.5 km. A mud diapir structure was found in layer D beneath the gas seep. Over-pressure may occur due to the large sediment thickness and also the tectonic basement uplift in the north, south, and east. The mud diapir could be the preferential pathway for methane-rich fluids. The acoustic curtain may indicate that free gas related to the gas seep can be formed on the sea floor. We also note that the layer above the acoustic curtain on profile H14 may contain gas hydrate.

Characteristics of shallow gas hydrate in Okhotsk Sea

Multidisciplinary field investigations were carried out in Okhotsk Sea by R/V Akademik M.A. Lavrentyev (LV) of the Russian Academy of Sciences (RAS) in May 2006, supported by funding agencies from Korea, Russia, Japan and China. Geophysical data including echo-sounder, bottom profile, side-scan-sonar, and gravity core sample were obtained aimed to understand the characteristics and formation mechanism of shallow gas hydrates. Based on the geophysical data, we found that the methane flare detected by echo-sounder was the evidence of free gas in the sediment, while the dome structure detected by side-scan sonar and bottom profile was the root of gas venting. Gas hydrate retrieved from core on top of the dome structure which was interbedded as thin lamination or lenses with thickness varying from a few millimeters to 3 cm. Gas hydrate content in hydrate-bearing intervals visually amounted to 5%-30% of the sediment volume. This paper argued that gases in the sediment core were not all from gas hydrate decomposition during the gravity core lifting process, free gases must existed in the gas hydrate stability zone, and tectonic structure like dome structure in this paper was free gas central, gas hydrate formed only when gases over-saturated in this gas central, away from these structures, gas hydrate could not form due to low gas concentration.