Applications of GIS and Remote Sensing in Ocean Exploration

Transcription

1 Applications of GIS and Remote Sensing in Ocean Exploration Geographic Information Systems (GIS) and Remote Sensing (RS) are critical to the success of Ocean Exploration. In the most basic sense, there is no point in exploring unless we can accurately and precisely measure the location of new features discovered. In order to make any data or samples collected in a new area of the ocean useful to the scientific community, everything has to be both time and geo-referenced. The most common way of presenting the results of an expedition and to plan future missions are typically expressed as a map. This allows scientists to demonstrate the survey area s location on the planet, identify topographical features of interest, display topological characteristics and conduct spacial analysis. Seafloor mapping is at the forefront of ocean exploration. Analogous to plugging in an address in a GPS before driving to a new city, scientists need maps of the seafloor to plan expeditions. Regions, features and targets of interest must be identified. Any available data for the area of interest is compiled and examined to determine how to use the expedition platform and schedule efficiently. There are three main ways that seafloor bathymetry data are obtained: sea surface gravity data (Smith et al., 1997), shipboard sonar (Weatherall et al., 2015) and submersible vehicle sonar. All three of these technologies are a form of remote sensing, and have a decreasing field of view with an increasing resolution, respectively. There are several key resources for bathymetric data, where exploration teams can determine if there is any existing, publicly available data in their area of interest. The General Bathymetric Chart of the Ocean (GEBCO) (Weatherall et al. 2015) and the Global Multi-Resolution Topography (GMRT) synthesis (Ryan et al., 2009) both use satellite altimetry data (Smith and Sandwell, 1997) as a base layer, with shipboard sonar data overlaid. In some areas, there may not be any sonar data, the data available may be old and/or at a low resolution, or of low quality (with artifacts). The resolution of the satellite data is coarse compared to sonar, but is very useful to predict the location and general shape of major seafloor features that are in areas that have not yet been surveyed with sonar (Smith and Sandwell, 1997). Features such as mid-ocean ridges, plate boundaries and seamount chains are visible, and their depths are within a reasonable range for the purpose of voyage planning. The Seamount Discovery Tool allows research vessels in transit to plot a mapping line that will go over features that are not surveyed, contributing to overall seafloor coverage with minimal planning effort or additional time (Sandwell and Wessel, 2010). The gravity data resolution is not, however, fine enough to execute further sampling. In order to make informed decisions to conduct site exploration, such as deploying sensors or submersible vehicles, a much higher resolution map is needed. 1

2 The first step in exploring a new area is seafloor mapping with shipboard multibeam echosounder. Multibeam is a very common and precise remote sensing system for measuring the topography of the seafloor (Armstrong et al, 2015). As multibeam technology continues to improve, so does the resolution of the data. At present, (depending on depth and frequency), the resolution will be in the range of meters or sub-meters. This allows scientists the ability to identify much smaller objects from the surface of the ocean. Once an area has been surveyed, the science team can then use GIS technologies to process, clean and interpret the data. Much of this workflow can be accomplished on board with the new data, hardware, software, people and procedures (Wright et al., 2000). Examples of software used to process sonar data are CARIS, Qimera and MBSystem. These systems allow the user to display the data in a variety of views to flag erroneous data. ArcGIS is often used when making the final mapping products, while Fledermaus is used to visualize the data in 4D. With an initial analysis, the science team can continuously re-strategize how to spend the remaining time onboard. Some cruises are dedicated solely to mapping, where sampling occurs on a subsequent leg. More commonly, mapping and sampling will happen on the same cruise, so the turn around on processing and analyzing the data needs to happen quickly. An area may be surveyed and processed overnight, with sampling beginning at daybreak. This level of processing is increasingly more successful due to the innovations of and automations of GIS softwares over the last three decades (Wright et al., 2000). The third stage of ocean exploration is to sample an area with sensors packages or submersible vehicles. There are three main types of vehicles: manned, remotely operated, and autonomous. While manned submersibles have been used in exploration, they are more commonly used for research. They are expensive to run, and there are only a handful around the world. Remotely operated vehicles (ROV) and autonomous underwater vehicles (AUV) are more common and more efficient to operate. AUVs may have multibeam sonar systems, sensors and imaging capabilities and are programmed with a mission. They are sent to work on their mission while the ship conducts other operations an efficient use of time and cost. ROVs are also common in ocean exploration because data are collected in real time. A team of scientists will interact with the vehicle pilots from a station on the ship to direct the dive. ROVs may also have multibeam sonar and sensors, but the most unique capability is to collect samples from the seafloor. Collecting higher resolution mapping data, sensor data, video and samples are all important methods for ground-truthing the shipboard and vehicle sonar data. In order to fully utilize mapping data for analysis, it is helpful to correlate the seafloor backscatter data to substrate material. Habitat mapping is crucial for determining where to dive, especially if the team are looking for a particular community such as corals. They will want to dive on an area that has a stronger 2

3 backscatter reflection because that is correlated to hard rock substrate where corals attach themselves to the seafloor. Although bathymetry data collected via ship or submersible may be the focus of a map, there are a number of other important GIS data sets that are incorporated into ocean exploration. Country borders, exclusive economic zones (EEZ) and monument boundaries are very important for both the planning and execution phases of an expedition (Armstrong et al., 2015). Ships must obtain permission to conduct research within a country s EEZ or territorial waters. Not all countries will grant this permission so it is important to be able to delineate where the data is relative to these borders. These boundaries are monitored closely by the ship s bridge officers, who navigate the vessel with their own GIS system Electronic Chart Information Display System (ECDIS). Many of these polygons are used as overlays when examining and presenting the data. Additionally, plotting the ship s scientific activities (such as points representing vehicle dives and sensor deployments) are useful to demonstrate which areas were sampled. Compiling these data into one map or GIS database provides context to the expedition which areas were explored more or less thoroughly, and which ones should be explored in subsequent missions. Data management is critical for post-expedition analysis. It is imperative to ensure the data is organized and cataloged in a way that scientists, students and public can find the information they need. NOAA s public data archives, hosted by the National Center for Environmental Information (NCEI) have a interface that allows scientists to easily search for and download meteorological, geophysical and oceanographic data. Since a national video archive does not exist, the NOAA Office for Ocean Exploration and Research (OER) developed the OER Video Portal (also hosted by NCEI). All of the underwater footage collected by the NOAA Ship Okeanos Explorer is made publicly available and searchable with a user-friendly interface, including an interactive map of the expeditions (Mesick et al., 2017). The more the data can be widely used by the scientific community, the more valuable it is. Exploration is a high-risk and high-cost venture. Although there is typically a high probability that the science party will make new and interesting discoveries in a place that was previously unexplored, there is no method for predicting how successful it will be. Scheduling ship time to conduct exploration is expensive, because areas that are unknown are typically quite far from a practical port it may take several legs of transit to get to the area that scientists want to explore, so voyage planning is a major consideration. It is imperative that any available data for the area is assembled for the team to plan and execute the expedition effectively. Having the ability to process and analyze new data during the cruise with GIS software allows the science party to monitor data quality and utilize time on site as efficiently as possible. Post-expedition, the recently collected data can be archived and compared to pre-existing data to highlight new discoveries as well as present a justification for the next expedition. 3

4 Annotated Bibliography Wright, D.H and D.J. Bartlett Down to the Sea in Ships: The Emergence of Marine G IS. Marine and Coastal Geographical Information Systems, GIS had been used primarily in terrestrial studies until the early 1990s, where there was an explosion of popularity in the use of GIS for marine applications. The first known American graduate thesis in marine GIS was earned by a student at the University of Rhode Island (Hatcher, 1992), with support from the Ocean Mapping Development Center. Hatcher developed a raster marine GIS as well as the mapping, collection and processing of geological data from Narragansett Bay. Marine Data Sampler was one of the earliest commercially available collections of marine GIS data. Soon after, a software package was developed by CARIS, to process and visualize large amounts of bathymetric data. In 1993, the first version of Electronic Chart Information Display Systems (ECDIS) were released, which revolutionized the production nautical charts and maritime industry. As technological advances improve the systems used to collect data, the amount of data collected has also increased. It becomes more imperative to have software that can handle such large datasets and can automate some of the processes. Smith, Walter H. F. and David T. Sandwell Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings. Science, 277: Walter Smith and David Sandwell have been leaders in developing the technique of using high-resolution marine gravity data from the Geosat and ERS-1 spacecraft to estimate seafloor topography. This method of utilizing gravity data provides a significant advancement to revealing seafloor features of which previous bathymetry modeling was not capable. Multibeam data is expensive to collect, and is sparsely distributed, where the entire globe can be covered via satellite. The topography/gravity ratio varies from one region to the next due to the differences in substrates and thicknesses, so accurate depth soundings are required. Existing bathymetry data, found in the NOAA archives were utilized to calibrate the model. The purpose of this model is to reveal the largescale and intermediate structures of ocean basins, which was not possible with previous modeling methods. The Foundation Seamount chain was revealed by this data, which were previously unknown, as confirmed by sonar data collected by the RV Atlante. Armstrong, A., L. Mayer, J.V. Gardner Seamounts, Submarine Channels, and New Discoveries: Benefits of Continental Shelf Surveys Extend Beyond Defining the Limits of the Shelf. Journal of Ocean Technology, 10(3)1-14. The exclusive economic zone (EEZ) for a country with a maritime border is 200 nautical miles from shore. In the case of countries that share a border on a body of water, the difference is split between the countries, like a Theissen polygon. In 2002, the authors proposed a project to thoroughly map areas of the United States continental shelf 4

5 regions that may be suitable for extending the country s EEZ, for areas along the 2,500- meter isobath. This study was in conjunction with a provision of Article 76 of the United Nations Convention on the Law of the Sea. This law proposes formulae and constraints for determining a new delineation of an EEZ. Several expeditions were conducted around the US coast as well as its territories. The team had to be able to demonstrate the 2500m contour of any questionable features in the bathymetry data in order to make a case for extending the US territory. Although the premise of the study was to increase the US territory, there was an exploration component as well. Many of the areas that were mapped with shipboard multibeam sonar uncovered new and unexpected features, which changed the understanding of geological processes in particular regions. Only vessels with high quality sonars and navigational installations were used for this study, as the accuracy requirement for the results were quite high. Calibration and training were conducted at the beginning of the expeditions to ensure that the highest quality of data were collected. All of the data collected for this study were made available in the national data archives within six months of collection. Ryan, William B.F., S.M. Carbotte, J.O. Coplan, S. O Hara, A. Melkonian, R. Arko, R.A. Weissel, V. Ferrini, A. Goodwillie, F. Nitsche, J. Bonczkowski, and R. Zemsky Global Multi-Resolution Topography Synthesis. Geochemistry Geophysics Geosystems, 10(3)1-9. Global Multi-Resolution Topography Synthesis (GMRT) is now a widely-used data resource. This compilation of sonar data is viewable in the native resolution in which it was collected. As new data is collected and edited, it is ingested into the system and made available via web services such as Google Earth. Only the affected tiles for the region in which the data was collected need to be updated (as opposed to the entire database), which makes this a very agile system, constantly expanding with new data. This synthesis allows users to access all of the processed (edited) data rather than having to download each raw bathymetry file from the national archives and spend exorbitant amounts of time cleaning the data to conduct analysis. GMRT utilizes the gravity data set from Smith and Sandwell as the base layer of the interface, with sonar bathymetry overlayed above. Scientists can use an application called GeoMapApp to view, select, project and download files pertaining to a specific area, with all of the available bathymetry data incorporated into the files. Sandwell, D.T. and Paul Wessel Seamount Discovery Tool Aids Navigation to Uncharted Seafloor Features. Oceanography, 23(1): Since ocean exploration expeditions are typically cost-prohibitive, it is beneficial to acquire new information whenever possible. Ships that are transiting through unknown areas of the ocean can use the Seamount Discovery Tool to make informed planning decisions for transits. Transits are typically a point A to point B voyage, but taking small detours along the route could lead to the uncovering of numerous unknown seafloor 5

6 features that would otherwise remain undiscovered. This low-impact effort can adds great value to the transits, and provides valuable additional data to the scientific community. The satellite-derived gravity data used to identify seamounts can only resolve those that are 2km tall, so it is imperative that they be measured by shipboard sonar. There is a great potential for these transit cruises to uncover a variety of other seamounts and seafloor features smaller than 2km. The Seamount Discovery Tool allows the ship s crew and science party to determine a track that would map areas of the ocean along the route that has not been previously mapped. Mesick, S., S. Gottfried, C. Wall-Bell and J. Jackson Exploring the Ocean Through Data. Oceanography, 30(1)S: The authors of this article highlight the importance of data management in ocean exploration. Every bit of information gathered on an exploration expedition is valuable data, and needs to be handled properly. The NOAA Office of Ocean Exploration (OER) and Research Data Management Team, led by NOAA s National Centers for Environmental Information (NCEI) hosts all of the data collected by the NOAA Ship Okeanos Explorer (America s only ship for ocean exploration) as well as a number of unique interfaces in which to find data. The data is only as valuable as it is accessible by the science community (and public) for analysis. The NOAA OER Video Portal is an interface customized to enable easy search-ability for the underwater video collected by the Okeanos Explorer s remotely operated vehicle. The video can be searched using common metadata parameters such as keywords, an interactive map or cruise and dive IDs. All of the video is time stamped for correlation with other key sampling data. NOAA OER continues to work with its partners to incorporate new data sets into the archives. Weatherall P., K. M. Marks, M. Jakobsson,T. Schmitt, S. Tani, J. E. Arndt, M. Rovere,D. Chayes, V. Ferrini, and R. Wigley A new digital bathymetric model of the world s oceans. Earth and Space Science, 2: General Bathymetric Chart of the Ocean (GEBCO) provides an elevation data set that covers both terrain and bathymetry. The GEBCO model uses the SRTM30_PLUS (Shuttle Radar Topography Mission, 30 arc second/1 kilometer) altimetry data set as the base grid, with any available shipboard sonar merged. The Global Multi-Resolution Topography (GMRT) grid, also incorporated into the GEBCO map includes a large amount of processed shipboard sonar data. This map displays the elevation data with mean sea level as the vertical datum. Although the database of shipboard sonar data has increased in recent years, the majority of the deep ocean basins and pole regions remain sparsely mapped. The Sub-Commitee on Regional undersea mapping (SCRUM) was formed to encourage collaboration and coordinate and the inclusion of related datasets into the model. Through this committee, the contribution of a regional grid of the northwestern Pacific Ocean region from the Japan Hydrographic Oceanographic Department substantially improved the portrayal of the region compared to previous 6

7 versions of the GEBCO model. In addition to the development of this model, the map is made publicly available for the scientific community to utilize in a variety of standard formats. GEBCO also provides additional educational resources and courses to assist researchers of all levels succeed in the collection, processing and gridding of bathymetric data. 7