Loranger
Scott
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Scott
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ArticleImplosion in the Challenger Deep: echo sounding with the shock wave(Oceanography Society, 2021-04-19) Loranger, Scott ; Barclay, David R. ; Buckingham, MichaelSince HMS Challenger made the first sounding in the Mariana Trench in 1875, scientists and explorers have been seeking to establish the exact location and depth of the deepest part of the ocean. The scientific consensus is that the deepest depth is situated in the Challenger Deep, an abyss in the Mariana Trench with depths greater than 10,000 m. Since1952, when HMS Challenger II, following its namesake, returned to the Mariana Trench, 20 estimates (including the one from this study) of the depth of the Challenger Deep have been made. The location and depth estimates are as diverse as the methods used to obtain them; they range from early measurements with explosives and stopwatches, to single- and multibeam sonars, to submersibles, both crewed and remotely operated. In December 2014, we participated in an expedition to the Challenger Deep onboard Schmidt Ocean Institute’s R/V Falkor and deployed two free-falling, passive-acoustic instrument platforms, each with a glass-sphere pressure housing containing system electronics. At a nominal depth of 9,000 m, one of these housings imploded, creating a highly energetic shock wave that, as recorded by the other instrument, reflected multiple times from the sea surface and seafloor. From the arrival times of these multi-path pulses at the surviving instrument, in conjunction with a concurrent measurement of the sound speed profile in the water column, we obtained a highly constrained acoustic estimate of the Challenger Deep: 10,983 ± 6 m.
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ArticleBroadband acoustic quantification of mixed biological aggregations at the New England shelf break(Acoustical Society of America, 2022-10-25) Loranger, Scott ; Jech, Michael J. ; Lavery, Andone C.At the New England shelf break, cold, less saline shelf water collides with warmer saltier slope water to form a distinct oceanographic front. During the Office of Naval Research Sediment Characterization Experiment in 2017, the front was mapped by narrowband (18 and 38 kHz) and broadband (70–280 kHz) shipboard echo sounders. The acoustically determined cross-shelf velocity of the front ranged in amplitude from 0.02 to 0.33 m/s. Acoustic surveys revealed aggregations of scatterers near the foot of the front. Acoustic backscatter in conjunction with Northeast Fisheries Science Center bottom trawl surveys identified longfin squid (Doryteuthis pealeii) and mackerel (Scomber scombrus) as the most likely scatterers in the aggregations. A mixed species scattering model was developed and further refined by the use of a matching method used for distribution of the lengths of each species. The mean length of squid and mackerel, respectively, using the matching method was 4.45 ± 1.00 and 20.25 ± 1.25 cm compared with 6.17 ± 2.58 and 22.76 ± 1.50 cm from the trawl data. The estimated total biomass of the aggregation was a factor of 1.64 times larger when using the matching method estimated length distribution compared to the trawl length distribution.
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ArticleA model for the fate of carbon dioxide from a simulated carbon storage seep(Elsevier, 2021-03-11) Loranger, Scott ; Pedersen, Geir ; Blomberg, Ann E. A.Offshore geological carbon storage (GCS) is a rapidly developing technology essential for meeting international climate goals. While the likelihood of leakage from a properly planned geological sequestration site is low, assurance that CO stays contained will require robust monitoring programs. While seismic imaging methods are used to monitor the geological reservoir, the ideal method for monitoring the water column above the reservoir depends on the fate and transport of CO. Whether CO is likely to be present as a rising seep of bubbles or dissolved in the water column near the seafloor will determine the appropriate monitoring technology and lead to a better understanding of the environmental impact of a potential leak. In this study, high definition video of a laboratory release of a carbon dioxide bubble seep recorded the size distribution of bubbles as a function of flow rate and orifice diameter. The transport of CO from different bubble size distributions was then modeled using the Texas A&M Oil Spill Calculator modeling suite. Model results show that the most important factor determining the rise height and transport of CO from the simulated leak was the maximum initial bubble size. For a maximum bubble radius of 5 mm, 95% of CO in the simulated seep reached a height of 17.1 m above the seafloor. When the maximum bubble radius was limited to 3 mm, 95% of CO dissolved by 7.8 m above the seafloor. The modeled results were verified during a controlled release of CO in Oslo Fjord.
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ArticleShipboard acoustic observations of flow rate from a seafloor-sourced oil spill(American Geophysical Union, 2020-10-15) Loranger, Scott ; Weber, Thomas C.In 2004 a debris flow generated by Hurricane Ivan toppled an oil production platform in Mississippi Canyon lease block 20 (MC20). Between 2004 and the installation of a containment system in 2019 MC20 became an in situ laboratory for a wide range of hydrocarbon in the sea‐related research, including different methods of assessing the volumetric flow rate of hydrocarbons spanning different temporal scales. In 2017 a shipboard acoustic Doppler current profiler (ADCP) and high‐frequency (90 to 154 kHz) broadband echosounder were deployed to assess the flow rate of liquid and gas phase hydrocarbons. Measurements of horizontal currents were combined with acoustic mapping to determine the rise velocity of the seep as it moved downstream. Models of the rise velocity for fluid particles were used to predict the size of oil droplets and gas bubbles in the seep. The amplitude and shape of the broadband acoustic backscatter were then used to differentiate between, and determine the flow rate of, hydrocarbons. Oil flow rate in the seep was estimated to be 56 to 86 barrels/day (mean urn:x-wiley:jgrc:media:jgrc24228:jgrc24228-math-0001 barrels/day) while the flow rate of gaseous hydrocarbons was estimated to be 98 to 359 m3/day (mean urn:x-wiley:jgrc:media:jgrc24228:jgrc24228-math-0002 m3/day).