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âOcean Mappingâ in 2025 Larry Mayer* It is both exciting and intimidating to speculate about where our field will be 16 years from now. While I will not be so bold as to try to address the entire field let me start my comments with some overarch- ing statements and then drill down and focus on those areas that I have most experience withânamely seafloor mapping and the use of acoustic and other sensors to quantify the deep-sea environment and understand deep-sea processes. In the broadest sense I firmly believe that over the next few decades we will see a greatly increased permanent presence for instruments and sensors in the ocean. This will be facilitated by both NSFâs research observatory efforts (OOI) and NOAAâs more operational observatory system (IOOS). The combination of the observatory infra- structure and advanced remote sensing tools with evolving modeling and visualization capabilities will revolutionize our predictive capabili- ties. Most importantly it will probably demonstrate how little we really understand about the small scale temporal and spatial variability of ocean processes. Lessons learned from these large scale experiments will inevi- tably be transferred to smaller scale efforts (and vice-versaâe.g., we are presently building a âmini-observatoryâ to monitor Portsmouth Harbor and innovations developed in our and other small scale efforts may also be adopted in the larger programs). Along with this I believe we will see a rapidly increasing role for autonomous vehicles (both powered and gliders and both large and very small) providing a cost-effective *âCenter for Coastal and Ocean Mapping, University of New Hampshire 153
154 OCEANOGRAPHY IN 2025 way to compromise between spatial and temporal coverage. Finally, I also strongly believe that with increased satellite communication capa- bility we will be able to transfer much of the processing, interpretation and even decision-making load from the ship (or AUV) to shore-based facilities. We are experimenting with this now through âTelepresence Consolesâ which provide multiple high bandwidth audio, video and data channels to a shore-based facility. In our work with NOAAâs Ocean Exploration program, multibeam sonar data is transmitted in real time to our lab (where we stand watches as if we were on the vessel), where it is processed and 3D maps are returned to the ship in near-real time. The potential of this capability for support of many types of sea-going opera- tions is tremendous. With respect to my own field of âocean mapping,â our goal is to make the ocean as transparent as possible, yet we are faced with the fun- damental limitations of an optically opaque medium and the tradeoffs between acoustic resolution and propagation. Over the past 25 years, concomitant advances in sonar design, positioning systems, computing power, and visualization capabilities have led to the development and application of multibeam sonar technology, and with it, an evolution from sparse 2D profiles of the seafloor to full coverage 3D images that have revolutionized our understanding of a range of seafloor-interacting pro- cesses. We are now poised for the development of the next generation of swath mapping systems. These systems will evolve from current narrow- band systems to broad-band, multi-frequency or chirp-based systems. The increased bandwidth of the next generation of swath mapping sys- tems will increase spatial resolution but more importantly will provide a âmulti-spectralâ look at the seafloor (and water column) and with this the possibility for the remote derivation of quantitative seafloor or mid-water (e.g., fish) properties (think of this as the difference between a black and white satellite image and a full-color image). Along with broader band- width, the next generation of swath mapping systems will use multiple phase detections within each beam footprint, evolving to the point where lateral resolution will be limited by the pulse length rather than the cur- rent limitation of beam footprint. Additionally, these new systems will use 2D arrays that will allow multiple beams to be formed in both the along- track and across-track direction. Finally, the new generation of systems will allow information to be collected from the entire water column (not just the seafloor), resulting in an evolving real time high-resolution 3D image (when combined with appropriate real time visualization software) of the seafloor and targets in the water column (e.g., fish, oceanographic frontsâincluding Doppler measurements, or other targets of interest). Many of the technological advances described here are underway in some form or another (Figure 1), but it will take at least 10 years bring them to
Larry Mayer 155 FIGURE 1â Interactive 3D visualization of multibeam sonar collected both seafloor and mid-water data. Midwater targets are open-ocean aquaculture cages and anchor lines. full fruition. These efforts would benefit greatly from research leading to the development of efficient and very broad-band acoustic transmitters. While the developments described above will greatly aid in the abil- ity to characterize both the seafloor and the water column, resolution of the finest scale features will always require bringing the sensor closer to the target. Remotely operated vehicles offer one approach to bringing the sensors close to the target (with little constraint on power and data trans- mission), but ROV surveys are time consuming and costly. AUVs (both powered and gliders) offer a tremendous opportunity to deliver sensors anywhere in the medium and while power and data transmission com- promises are inevitable, they open up a vast new range of opportunities to monitor and capture ocean processes at a range of scales (as well as stealth). Thus I hope to see in the coming decade rapid evolution of AUV capabilities. Critical amongst needed developments will be more efficient power supplies, sensors that require less power, and development of more sophisticated control software that will allow adaptive behavior of
156 OCEANOGRAPHY IN 2025 AUVs depending on mission requirements (e.g., modify mission plan in response to detection of particular target or parameter). I also suspect we have only begun to scratch the surface on capabilities for non-powered AUVs (e.g., gliders) or devices that use solar-, wind-, or wave-power as an aid. For an AUV, intermittent visits to the surface have many advantages including boosting power, transmitting data and updating position. A constraint on many AUV-based surveys is the loss of high resolu- tion positioning capability once submerged. Long-baseline transponders are the current solution but these are expensive and time consuming. An area ripe for progress is the development of âhybridâ modes of high- resolution positioning for AUVs. Current kinematic GPS capability allows cm-level positioning as long as the satellites can be viewed. The combi- nation of free-floating kinematic GPS buoys and some sort of acoustic ranging system may offer the possibility of greatly extending the posi- tional accuracy of AUV-based surveys in an unconstrained (geographi- cally) and cost-effective manner. An important research area associated with this will be improved underwater acoustic communications. Once againâincreased bandwidth (along with clever compression algorithms) will be the key.