From 7–11 May, the GeoHab community met in Santa Barbara, California, for its annual conference. GeoHab, which stands for Marine Geological and Biological Habitat Mapping, is an international and multidisciplinary community of marine scientists that includes acousticians, biologists, ecologists, geologists, oceanographers, and spatial scientists, to name a few. One of the objectives of GeoHab is to maintain awareness of developments in marine surveying technologies and standards in order to better inform how biology, geology, and oceanography apply to marine habitat mapping in contexts like management and conservation.
Most marine habitat mapping exercises involve remote sensing, based on the general assumption that both absolute (i.e. depth) and relative (i.e. shape of the seafloor) bathymetry explain – at least partly – marine species distributions. At a broad scale, bathymetry can be derived from satellite radar altimetry data, while at a finer scale, optical remote sensing can be used to estimate bathymetry in very shallow waters. However, since 90% of the oceans are deeper than 200 m, most bathymetric data are now collected using acoustic remote sensing.
While the GeoHab conference is not remote sensing focused, the discipline is ubiquitous in the material that is presented. Bathymetric information is most often represented as a digital terrain model from which information like slope, orientation, and rugosity can be derived. Such data are critical in marine habitat mapping as they often can be the only source of environmental data available to characterize habitats at a relevant scale. In addition to bathymetry, acoustic remote sensing enables the collection of backscatter data, which provide information about substrate, an important driver of benthic species distribution.
New approaches to data collection
In the last decade, habitat mapping studies have mostly used multibeam echosounders and side-scan sonars to collect remotely sensed seafloor data. This year, however, the diversity of data collection approaches presented at the conference was particularly high. For instance, Dr. Charles Paull, a senior scientist at the Monterey Bay Aquarium Research Institute, presented in his keynote address the combined use of multibeam echosounders and dual LiDAR systems mounted on a remotely operated vehicle (ROV). The ROV surveyed the seafloor from about 3 m off-bottom in areas of the deep sea to provide bathymetric data at an outstanding 1 cm resolution! I was aware of bathymetric and topo-bathy LiDAR systems, which can provide bathymetric data from aerial surveys in shallow waters, but this was the first time that I had heard of underwater LiDAR systems. The data presented by Dr. Paull were simply incredible, not only capturing information about the seafloor, but also capturing directly the organisms living on it. While the georeferencing of data collected from ROVs is usually challenging and impacts the quality of the dataset, the position of his data was accurate enough to ensure monitoring surveys over the following years.
Despite how exciting those new opportunities for data collection are, they can be out of range for many scientists with a limited budget. Financial limitations, however, did not stop Dr. Kelly Kingon, from the University of Trinidad and Tobago, who presented a low-cost, kayak-based setup to map seagrass habitats with a side-scan sonar system. In the absence of high-end equipment and given the urgency to monitor seagrass beds that are facing anthropogenic threats, Dr. Kingon’s setup enabled the making of a map that will serve as the baseline for monitoring seagrass coverage in Trinidad.
With the increasing interest in mapping coastal environments, unmanned aerial systems (UAS) have also made their entrance into the GeoHab community’s toolbox. New algorithms and approaches now facilitate the creation of digital bathymetric models from optical data. This kind of application is promising as it enables data collection of both underwater and subaerial data, providing a more comprehensive picture of the coastal environment and its dynamics. The Marine Mapping Group at Deakin University (Australia) is a leader in coastal habitat mapping and uses both UAS and more traditional vessel-based acoustic systems to better understand the relationships between geomorphology and biological communities along the coastline.
Finally, the first applications of multispectral backscatter data were presented at this year’s conference. Up until last year, acoustic systems could only collect information at one frequency at the time, far behind the hyperspectral systems that are now found in optical remote sensing. However, at GeoHab 2017 in Halifax, Canada, the R2Sonic company introduced the first multispectral (3 frequencies) system. They provided free data to the community to encourage new applications for this type of data in habitat mapping. This year, a number of presentations introduced innovative ideas about how to use such data to classify seabed sediments and benthic habitats, including the use of multidimensional hypercubes to segment seafloor datasets by Dr. Craig Brown (Nova Scotia Community College, Canada).
Some trends in marine habitat mapping approaches were confirmed at this year’s GeoHab conference. First, object-based image analysis, which was first adopted by marine scientists a few years ago, has now become common in habitat mapping studies. Open source tools for remotely sensed underwater data processing are also increasingly being developed and made available to the community. For instance, Jared Kibele, from the University of Auckland (New Zealand), introduced the Marine Optical Remote sEnsing Map and Assessment Production System (MORE-MAPS.org), which facilitates the derivation of bathymetry and submerged habitat maps from optical remote sensing and the processing and analysis of underwater photo surveys. New approaches for mosaicking underwater videos and creating 3D models using structure-from-motion were presented, building on recent trends to automate the ground-truthing data analysis in marine sciences. Finally, it was interesting to see that awareness of concepts such as scale and data quality keeps increasing year after year within the community. The conference workshop included a discussion on the role of spatial and temporal scales in habitat mapping. The discussion highlighted recent progress toward a better understanding of how scale impacts habitat mapping studies and enabled the identification of many questions that remain unanswered. The importance and challenges of integrating socio-economic and management scales with the ecological and methodological (i.e. observational and analytical) scales were also discussed.
Another noteworthy trend is the new will by many nations and groups to increase efforts in seafloor mapping. While nations like Norway and Ireland are pioneers in national-scale seabed mapping and have been leading the way for many years now, many others are now realizing the importance of collecting seafloor data. At GeoHab 2018, a panel introduced the GEBCO 2030 initiative, an international effort to create a bathymetric map of the Earth’s oceans by 2030 to 100 m or 200 m resolution, depending on depths. Still in its infancy, this project will provide a framework for the identification of major gaps in current bathymetry and enable international collaborations to fill such gaps. It is estimated that an investment of the order of magnitude of the typical cost of a mission to Mars ($3B U.S.) would enable mapping 93% of the bathymetry deeper than 200 m. Given that we now have high-resolution topographic maps of many celestial bodies, it is time that we focus on Earth’s last frontier and get a better understanding of our oceans.
This is just a very quick overview of this year’s GeoHab conference; it is impossible to describe in a short post the extent and diversity of the work that was presented in Santa Barbara. The GeoHab community once again brought to the table some great innovations in marine habitat mapping through new technological and methodological developments and applications. There are very few meetings that so successfully integrate a multidisciplinary perspective, blending remote sensing technologies with disciplines like ecology and geomorphology for a variety of contexts, including conservation and management. I am really looking forward to attending what will be my fifth GeoHab conference next year, which will be held in St. Petersburg, Russia.
By Associate Editor Vincent Lecours, Ph.D., Assistant Professor in Marine Remote Sensing & Geospatial Analysis, Fisheries & Aquatic Sciences | Geomatics, School of Forest Resources & Conservation, University of Florida, Gainesville, FL, USA