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Eos,Vol. 85, No. 31, 3 August 2004 attack tactics were ineffective.Fire whirls were dramatic,as much as 800 m wide,crossing burned areas into unburned areas and caus- ing spot ignitions ahead of the fire by as much as 1200 m.Pilots reported burning debris as high as 450 m above ground.Fire and heat from burning structures and ornamental vege- tation were as much of a problem as any of the natural fuels. Many forested areas that burned in October 2003 probably burned much more completely than they would have in the absence of suc- cessful fire suppression over the past century. Dense vegetation fostered the rapid spread of high-intensity fires in the forest canopy.Wide- spread die-offs of this vegetation may help to reduce the risk of canopy fires in the future.In recent years,large portions of southern Cali- fornia have experienced substantial vegetation mortality resulting from drought, insects,and disease [Predictive Services, 2003].After the fine canopy fuels (needles, leaves,twigs,etc.) fall to the ground,the stand- ing dead trees may be less prone to spreading fires in the canopy (Craig Allen,pers.comm.). About 80% of the area burned in the October 2003 southern California fire siege,however, was in chaparral or grassland.Whereas healthy forests in southern California can sustain a low-intensity fire regime with regular surface fires in the absence of fire suppression,chap- arral always experiences canopy fires that consume much of the vegetation.Not only does chaparral regenerate quickly,but a rela- tively small proportion of the areas with homes proximate to wildland vegetation actually burned—only about 5% of southern California’s wildland-urban interface in total (S.Stewart, pers.comm.).Consequently,the risk of large regional-scale fires remains high. Acknowledgments Support for this research came from the U.S. National Oceanographic and Atmospheric Administration’s Office of Global Programs. We thank E.Bainto for assistance with the graphics and C.Allen and M.Moritz for their comments. References Mensing,S.A.,J.Michaelsen,and R.Byrne (1999),A 560-year record of Santa Ana Fires reconstructed from charcoal deposited in the Santa Barbara Basin,California,Quaternary Research 51,295–305. Mission-Centered Solutions (2003),Southern Califor- nia Firestorm 2003: Report for the Wildland Fire Lessons Learned Center,63 pp.,Mission-Centered Solutions,Inc.,Parker,Colo.; http://wildfirelessons. net/. Predictive Services (2003),Monthly Fire Weather/ Fire Danger Outlook,Southern California Geographic Area Coordination Center,Vallejo, Calif.,November. Pyne,S.J.(1997),Fire in America,654 pp.,University of Washington Press,Seattle. Schlobohm,P.and J.Brain (2002),Gaining an Under- standing of the National Fire Danger Rating System,National Wildfire Coordinating Group Publication: NFES # 2665,http://www.nwcg.gov. Author Information Anthony L.Westerling and Daniel R.Cayan,Scripps Institution of Oceanography,La Jolla,Calif.;Timothy J.Brown and Beth L.Hall,Desert Research Institute, Reno,Nevada; and Laurence G.Riddle,Scripps Insti- tution of Oceanography,La Jolla,Calif. A number of marine biological,geological, and archaeological applications share the need for high-resolution optical and acoustic imag- ing of the sea floor [Ballard et al.,2002; Greene et al.,2000; Shank et al.,2002].In particular, there is a compelling need to conduct studies in depths beyond those considered reasonable for divers (~50 m) down to depths at the shelf edge and continental slope (~1000–2000 m). Some of the constraints associated with such work include the requirement to work off of small coastal vessels or fishing boats of oppor- tunity,and the requirement for the vehicle components to be air-shippable to enable inexpensive deployments at far-flung oceano- graphic sites of interest. Over the last 2 and a half years,the Seabed Autonomous Underwater Vehicle (AUV) has been designed and deployed in support of such tasks off of Puerto Rico,Bermuda, Stellwagen Bank off Massachusetts,and the U.S.Virgin Islands. Components and Capabilities In designing the Seabed AUV (see http://www. whoi.edu/DSL/hanu/seabed),a decision was made to incorporate standard oceanographic sensors as far as possible to minimize costs and allow for easy maintenance.It currently supports a 300-kHz side-scan sonar,a 1200-kHz Acoustic Doppler Current Profiler, a Seabird pumped Con- ductivity, Temperature and Depth sensor, a 675-kHz mechanically scanned pencil beam sonar, and a 12-bit (high dynamic range) camera sys- tem.A 2-kWhr lithium-ion battery pack provides an 8-hour endurance for Seabed running at speeds between 0.3 m/s to 1 m/s.Its size— each of its two torpedo-shaped hulls is 1.5 m in length—and weight of 250 kg permit easy deployment off small coastal or fishing vessels of opportunity,and it can be shipped by air at a very reasonable cost to most departure ports. Optical Imaging and Navigation and Control Seabed has been designed specifically to further the growing interests in the area of sea floor optical imaging; specifically,high-resolu- tion color imaging and the processes of pho- tomosaicking and three-dimensional image reconstruction.In addition to high-quality sen- sors,this imposes additional constraints on the ability of the AUV to carry out structured surveys,while closely following the sea floor. The distribution of the four thrusters,coupled with the passive stability inherent in a two-hulled vehicle with a large meta-centric height,allows the Seabed AUV to survey close to the sea floor,even in very rugged terrain. Figure 1 illustrates vehicle performance in such challenging applications.The vehicle (top left) can follow steep gradients at constant altitudes; in this case,on a coral reef off the U.S.Virgin Islands,and follow a greater than 45° slope at 3 m (top center) while obtaining high-resolution imagery with good color fidelity. Figure 2 shows an image obtained from the vehicle using its camera and lighting system at night in 65 m depth,in the absence of ambient lighting.The nonlinear preferential attenuation of different parts of the visible spectrum underwater led to images that are not color-balanced.However,the 12 bits of dynamic range provided by the camera allow us to compensate and color balance the imagery as shown in Figure 2 (bottom) by using methods including frame averaging and parametric surface fitting in the homomorphic domain. To accomplish high-resolution,large-area surveys,the AUV is run under closed loop control [Whitcomb et al.,2000].Navigation in shallow water (down to a few hundred meters) is accomplished by using a doppler velocity log in combination with Global Positioning System data before and after the dive.Algorithms for bottom-following in rugged terrain also allow the AUV to carry out autonomous surveys in regions of high relief while running precise track lines.The results of such a task are illus- trated in Figure 3.Here,the AUV was imaging a boulder pile with a series of closely spaced track lines,while maintaining a constant 3-m altitude off the bottom in an area where the relief was also of that order. Photomosaicking Underwater Imagery Photomosaicking underwater is a challeng- ing task [Pizarro et al.,2003].The nonlinear attenuation of color underwater,the absence of uniform ambient lighting,an unstructured Seabed AUV Offers New Platform for High-Resolution Imaging BY HANUMANT SINGH,ALI CAN,RYAN EUSTICE, STEVE LERNER,NEIL MCPHEE,OSCAR PIZARRO, AND CHRIS ROMAN PAGES 289,294–295 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 03 AUG 2004 2. REPORT TYPE 3. DATES COVERED 00-00-2004 to 00-00-2004 4. TITLE AND SUBTITLE Seabed AUV Offers New Platform for High-Resolution Imaging 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Woods Hole Oceanographic Institution,Deep Submergence Laboratory,Woods Hole,MA,02543 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT Same as Report (SAR) 18. NUMBER OF PAGES 4 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 Eos,Vol. 85, No. 31, 3 August 2004 Fig.1.The Seabed AUV (top left) has been designed for high-resolution imaging close to the sea floor.It is capable of working very close to the sea floor,as illustrated by the mission depth profile (top center) at a coral reef in the U.S.Virgin Islands.During this mission,it followed the sea floor bathymetry at a height of 3 m across a steep cliff in varied terrain.Even in such challenging environs,the Seabed AUV can obtain high-resolution, high-quality color imagery (bottom row). terrain,and backscatter from the water column all combine to make image registration under- water a difficult task.Our systems-level solu- tion to the problem (as described above) has been to use a combination of technologies to collect color-balanced images that can be coupled with precision navigation and closed loop control associated with the vehicle,to allow automatically constructed photomosaics,such as the 27-image mosaic shown in Figure 3. Typically,overlapping imagery with a struc- tured survey is collected,and after color com- pensation of each image,features based on the Harris corner detector are extracted,and they are encoded individually using Zernike basis functions.Features in Zernike space can then be compared across an overlapping image pair to estimate the transformation for that pair of images.In a sequential manner, image topologies can thus be generated,and in a final step,combined into a single photo- mosaic [Shank et al.,2002]. These efforts highlight the possibilities asso- ciated with such work for underwater imaging platforms in general.Small AUVs,such as Seabed,are necessarily constrained in the amount of light available for optical imaging. They are also constrained by their size,to hav- ing a limited camera-to-light separation.Our ability to provide high-color fidelity and reso- lution for imagery obtained from a small AUV highlights the possibilities associated with optical imaging from other platforms such as the Jason ROV and the DSV Alvin. A number of these imaging technologies have been suc- cessfully transitioned to other assets within the academic community,including the Jason ROV and the Abe AUV.Efforts are also currently underway to make these photomosaicking technologies widely available for academic users. Further details about the Seabed AUV can be found at Web site: http://www.whoi.edu/ DSL/hanu/seabed.Our efforts with regard to the use of this asset are continuing through funded work on the engineering aspects as well as through scientific research cruises.The low costs associated with using this AUV make Eos,Vol. 85, No. 31, 3 August 2004 Fig.2.A typical raw (top) and color-compensated (bottom) image obtained by using the Seabed AUV off Stellwagen Bank in 65 m of water.The image footprint covers an area of approximately 3 m x 3 m. Eos,Vol. 85, No. 31, 3 August 2004 it an ideal platform for conducting long-term, repeatable time series surveys at sites of inter- est.Collaboration with those interested in using this asset is encouraged. Acknowledgments This work was funded in part by the Office of Naval Research under grant #N00014-01- 10310,in part by the Censsis Engineering Research Center of the U.S.National Science Foundation under grant EEC-9986821; and in part by the Woods Hole Oceanographic Insti- tution,through a grant from the Penzance Foundation.We thank D.Fornari and R.D. Ballard for their invaluable suggestions and comments regarding this manuscript.We also thank Rob Reves-Sohn,Page Valentine,James Lindholm,Ken Foote,Roy Armstrong,and Rick Nemeth for their support during our initial cruises. References Ballard,R.D.,et al.(2002),The discovery of ancient history in the deep sea using advanced deep submergence technology,Deep Sea Res.,1(47), 1591–1620. Greene,G.H.et al.(2000),Mapping and Classifica- tion of Deep Sea floor Habitats, ICES 2000 Annual Science Conference,(CITY),Bruges,Belgium, September. Pizarro,O.and H.Singh (2003), Towards large area mosaicing for underwater scientific applications, IEEE J.Ocean.Eng.Underwater Image and Video Proc.,28 (4), October. Shank,T.et al.(2002),Time-series exploration and biological,geological,and geochemical character- ization of the Rosebud and Calyfield Hydrothermal Vent Fields at 86°W and 89.5°W on the Galapagos Rift (abs.),Eos,Trans.AGU,83(47), Fall Meet.Suppl. Whitcomb,L.L.,et al.(2000),Advances in Underwater Robot Vehicles for Deep Ocean Exploration: Naviga- tion,Control and Survey Operations, The Ninth International Symposium on Robotics Research, Springer-Verlag,London. Author Information Hanumant Singh,Ali Can,Ryan Eustice,Steve Lerner, Neil McPhee,Oscar Pizarro,and Chris Roman For additional information,contact Hanumant Singh,Deep Submergence Laboratory,Woods Hole Oceanographic Institution,Woods Hole,Mass.; E-mail: hsingh@whoi.edu. Fig.3.A 27-image photomosaic of a rock pile in Stellwagen Bank,off of the Massachusetts coast,along with two of the original color-equalized images that went into constructing it.Each image encompasses an area of 3 m x 3 m,with the total mosaic spanning 35 m in length.