Sea Technology

JUN 2018

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www.sea-technology.com June 2018 | ST 21 the fish farming sector over the past two years. "We have definitely experienced a spike in interest from aquacul- ture organizations," said David Critchley, TCarta CEO. "They are on the lookout for more cost-effective sourc- es of bathymetric data in coastal areas where their fish farms will be located. For their purposes, they want data that's produced quickly, consistently and globally." TCarta built its business on creating terrestrial and marine geospatial products generated from diverse and often hard-to-find source data. Its flagship product line is satellite-derived bathymetry (SDB), which is extracted from high-resolution digital satellite imagery. TCarta had delivered SDB data, along with a related seafloor Habitat Map layer, of the Arabian Gulf to Envi- ronment Agency – Abu Dhabi (EAD) during a 2015 en- vironmental project. Just two years later, in 2017, EAD contracted BMT for the aquaculture siting study around the Island of Delma in the Gulf and offered the data sets for use in that project as well. Critchley explained that SDB prod- ucts are appealing to aquaculture orga- nizations because they deliver accurate water depth information in the relative- ly shallow coastal areas where many fish farms are located that can be dif- ficult to map with other methods. Op- eration of ship-borne sonar, for exam- ple, is often dangerous in the dynamic nearshore environment, while airborne LiDAR is expensive. Both methods can be time consuming to deploy. "Satellites have the advantage of capturing data very quickly on short notice with no impact on the ecosys- tem…in areas that might be inacces- sible for a number of reasons," said Critchley. "And the satellite-derived data costs about one-tenth of the ship and airborne methods. Just as impor- tantly, our process derives data sets that are consistent worldwide." TCarta uses a proprietary process- ing technique to extract seafloor in- formation from multispectral satellite imagery. Depending on the detail re- quirements of the project at hand, the geospatial firm has applied the tech- nique to most commercially available space-borne remote-sensing data sets. The point spacing and accuracy of the derived depth measurements correlate directly to the spatial resolution of the digital imagery. For broad-area planning projects re- quiring coarse detail, TCarta uses the 30-m-resolution U.S. Landsat data, while the 10-m Sen- tinel-2 data from the European Space Agency and 5-m RapidEye data from Planet suffice for planning in smaller areas, according to Critchley. But for a site selection proj- ect, where one or more specific locations must be se- lected for a given application, the most detailed seafloor information available must be used. "For some projects, we use a combination of image data," said Critchley. "We start with the less expensive lower resolution data to get a regional perspective for planning and then switch to finer detail data for final site selection." An aquaculture study like the one in the Arabian Gulf, as well as many engineering evaluations related to coast- al infrastructure and oil and gas development projects, requires high-resolution imagery. For these jobs, TCarta utilizes data acquired by the DigitalGlobe WorldView-2 and -3 satellites. From an orbit of 383 mi., these plat- forms capture 1.3-m-resolution data in eight spectral bands and 0.3-m data in one panchromatic band. Efforts are underway with a focus on the sustainable de- velopment of marine aquaculture. (Photos Credit: BMT Group)

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