DARPA’S Autonomous Minehunting and Mapping Technologies (AMMT) Program

An Overview

Joseph G. Paglia William F. Wyman

C. S. Draper Laboratory, Inc. 555 Technology Square Cambridge, MA 02 139

Abstract - The C. S. Draper Laboratory, I n c . (Draper) recently completed the at-sea test phase of the Autonomous Minehunting and Mapp ing Technologies (AMMT) Program for the Defense Advanced Research Projects Agency (DARPA). The primary objective of this program is to develop and demonstrate advanced minehunting t echno log ie s that will enable Unmanned Undersea Vehicles (UUVs) to clandestinely survey an undersea area f o r mines and collect data for post mission mapping o f the surveyed area. The survey data must be o f sufficient quality to support selection of a n amphibious operating area and subsequent neutralization of mine or obstacle threats.

As integration contractor for the AMMT Program, Draper modified one of DARPA’s e x i s t i n g UUVs; which was previously designed and built b y Draper, and used for DARPA’s Mine Search Sys t em Program. State-of-the-art technologies in the a reas of Sonar Mapping, Navigation, Acoust ic Communications, Imaging, and Mission P lann ing were incorporated into the AMMT vehicle, resu l t ing in a system having the capability to perform a n autonomous survey and meet program ob jec t ives . The vehicle was subsequently tested at-sea t o demonstrate the advanced minehunting technologies and concepts.

This paper provides an overview of t h e AMMT Program and describes the development and integration of the technologies required to perform the clandestine AMMT mission.

I. INTRODUCTION

C.S. Draper Laboratory, Inc. (Draper) has been developing Autonomous Undersea Vehicles ( A W s ) and associated vehicle subsystem technologies for the Defense Advanced Research Projects Agency (DARPA) for several years. The DARPA Unmanned Undersea Vehicle (VW)

Program began in May 1988 when Draper was contracted to design, fabricate, assemble, test and deliver two UUVs. The goal of the joint DARPA/Navy U W Program was to demonstrate that UUVs could meet specific Navy mission requirements with emphasis on the use of state-of-the-art technology and “rapid prototyping” of hardware. Rapid prototyping of U W systems and subsequent at-sea test demonstrations of Navy mission concepts would allow the Navy to determine whether the concept should be taken to full scale development.

The first U W was delivered for at-sea testing 19 months after the start of the contract, and underwent preliminary performance testing and evaluation. Since these initial sea trials, the vehicles have been modified and configured to validate several Navy operational missions. The first mission to be validated was the Tactical Acoustic System (TAS), which was a classified mission and will not be discussed. The second mission demonstrated high data rate underwater laser communications between an AUV and a manned submarine. The third mission was the Mine Search System (MSS), which used a fiberoptic or acoustic data link between the UUV and a surface ship host for data transfers. The Program’s at-sea test demonstrated that a U W could guide a surface ship or submarine through a minefield in a semi-autonomous mode. In a fully autonomous test mode, the MSS vehicle performed a survey of an area and subsequently transferred mine target data from the surveyed area to a host via radio from a rendezvous point.

0-7803-351 9-8/96 $5.00 0 1996 IEEE 794

In recent years, DARPA has responded to the priority need for mine countermeasures clandestine reconnaissance with the Autonomous Minehunting and Mapping Technologies (AMMT) Program. The AMMT Program is a follow-on effort to DARPA’s MSS Program and builds significantly upon MSS achievements in five technology areas: Sonar Mapping, Inertial Navigation, Acoustic Communications, Undersea Imaging, and Mission

Planning. These minehunting technologies were integrated into a modified MSS vehicle and underwent a five month at- sea test program, which concluded in May of this year. The intent of the AMMT Program is to demonstrate the successful integration of these minehunting technologies into an autonomous vehicle, and in so doing gain insight and information which will support the Navy’s present off-board sensor programs; the Near Term Mine Reconnaissance System (NMRS) and Long Term Mine Reconnaissance System (LMRS), and also support other Navy UUV Program priorities.

Draper Laboratory was integration contractor for the AMMT Program and also responsible for providing the autonomous, fault tolerant testbed vehicle and a support equipment suite. In addition, Draper developed a vehicle launch and recovery system and set up a field site and maintenance facility for conduct of the at-sea test phase of the program at the South Florida Testing Facility, of the Naval Surface Warfare Center (NSWC), near Ft. Lauderdale, Florida.

In the program’s technology development areas, Draper developed the mission planner which provides real- time vehicle trajectory planning based on data input from the vehicle’s multiple sensors. The Applied Research Laboratory at the University of Texas (ARL:UT) developed the program’s mapping sonar, using the vehicle’s Ahead Looking Sonar (ALS) as the primary sensor. Lockheed Martin Tactical Defense Systems, formerly LORAL, provided the program’s navigation system, which is a doppler-aided inertial system with enhanced Kalman filtering and automatic at-sea erection and alignment capability. The Acoustic Communications System was developed by the Woods Hole Oceanographic Institution (WHOI), and was used for two way communications between the vehicle and support ship host. WHOI also developed compression algorithms to allow high bandwidth image and map data to be transmitted to the host in a short period of time.

Two Imaging Systems were integrated into the AMMT vehicle; a Laser Line Scanner System (LLSS) originally developed by Applied Remote Technology Inc., a company purchased by Raytheon during the program, and a CCD Camera. The LLSS is capable of providing high resolution images of objects autonomously, at altitudes to 15 meters. Since this was the first time a LLSS was used in an autonomous imaging mode, the camera system was integrated into the vehicle as an imaging system backup and risk mitigator.

Completing the team of program participants are the Applied Physics Laboratory at Johns Hopkins University (JHWAPL), and Vail Technology Corporation (Vail). JHU/APL developed the program requirements and data

analysis plan, and assisted Draper’s Test Director in carrying out the at-sea test program. Vail, and previously PRC, provided support to DARPA’s Tactical Technology Office, formerly the Maritime Systems Technology Office, in managing the AMMT Program. Fig. 1 is a chart illustrating the program organization and participants.

DARPA TTO

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Integration Cnntractor B Vehicle System Acoustic McKlem

RAYTHEON

Nivi go ti on Se nwr

Fig. 1 AMMT Program Operations

11. GOALS AND OBJECTIVES

The AMMT Program has four major objectives in demonstrating its effectiveness as a mine countermeasures system:

Develop and demonstrate complementary technologies that will enable an autonomous UUV to clandestinely survey an undersea area and collect data for post mission mapping of the surveyed area

Provide data products of sufficient quality to support selection of an amphibious operating area and subsequent neutralization of mine or obstacle threats

Transmit, in near real time to a host, mission maps and images of targets identified as having a high probability of being mines

Provide a post-mission map of the surveyed area

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In meeting the overall program objectives, a test program was developed to demonstrate and validate advanced vehicle technologies for the following:

- Mine detection and classification

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- Acoustic communication of mine/obstacle images to the surface for near real-time identification

Precise mine and obstacle localization

Optical Imaging of underwater objects

- Mapping bottom topography with locations of mines/obstacles

- On-line mission planning

In order to meet program objectives and perform the technology demonstrations, there were four program requirements, generated early in the program. These requirements were successfully met during the course of the program and are as follows:

- Provide a reliable, fault tolerant integrated testbed vehicle

Develop a support equipment suite -

- Provide the capability to launch, recover, perform diagnostic tow, and maintainhervice the vehicle

Select a test site and mobilize for conduct of the at-sea test program

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111. SCHEDULE AND MILESTONES

The AMMT Program originally began in April 1993, as a follow-on effort to DARPA’s MSS Program. The program was stopped in October 1993, due to a congressional delay in GFY 1994 funding, and restarted in July 1994. Following in-laboratory systems integration, mobilization for the program’s at-sea test phase at NSWC’s South Florida Testing Facility began in December 1995. The at-sea test phase of the program occurred over a five month period ending with demobilization of the test site in mid-May 1996. During the test program, many of the subsystem test demonstration milestones were successfully met. However, full mission demonstrations of the integrated AMMT system were not completed due to program schedule and cost considerations.

IV. VEHICLE AND MAJOR SUBSYSTEMS

The AMMT vehicle, as shown in Fig. 2, is a modified version of the MSS vehicle. The 1.1 m diameter hull was extended to an overall length of 12.5 m, by the addition of a new 0.7m titanium hull insert. The additional insert volume houses two mapping processors for the sonar subsystem. The basic MSS vehicle and control system remain intact along with the Ahead Looking Sonar System. Mechanical mounts were added to the bow of the vehicle to allow a bridle to be used for vehicle towing, and to provide for attachment of a tow cable for submerged sonar diagnostic towing. A GPS system is integrated into the vehicle with the antennaadded to the vehicle’s 1.1 m erectable mast, also used for the radio antenna. The acoustic modem’s two projectors are installed in the vehicle’s aft free-flood section. The modem’s eight receivers are mounted in the vehicle’s forward free-flood section and the modem’s computer is installed in the vehicle’s electronic section. The Doppler aided-inertial navigation system components include a broadband Doppler Sonar, located in the forward free flood area, and an inertial reference unit, navigation computer and recorder located in the vehicle’s payload section. Power to the various subsystems is distributed from the vehicle’s 300 Kw- Hr silver-zinc battery. In the AMMT configuration the vehicle is capable of diving to 460 m, and achieving speeds of 2-7 knots.

Vehicle guidance and control is enhanced by addition of a Draper-developed mission planner, which provides real- time optimal planning for vehicle trajectories based on input from the sensor suite. The mission planner software incorporates terrain following and obstacle avoidance algorithms, and is run in the vehicle’s Mission Data Processor (MDP). The MDP is an extension of the vehicle’s three channel Fault Tolerant Processor and contains the vehicle’s navigation filter and acoustic ping management software. The MDP is also used to control and communicate with the new AMMT Program subsystems added to the MSS vehicle.

The mapping sonar utilizes the MSS Ahead Looking Sonar and performs additional functions of bathymetric mapping and precise navigation. Computer aided detection enhancements were added to the sonar data processing, which also generates bottom relief profile maps. A byproduct of the mapping process is the ability to improve vehicle navigation using sonar data. The Acoustic Tracking and Navigation (ATN) function of the mapping sonar, which estimates vehicle position based on ping-to-ping correlation and tracking of bottom features, provides input to the vehicle’s navigation filter for integration with the navigation estimates from the inertial navigation system.

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Fig. 2 AMMT Vehicle

Acoustic communications at rates to 10 kbps over ranges up to 10 km were goals for the program. The acoustic communications system also had the additional function of image management. Prior to transmission of the laser line scanner images and sonar maps topside, images and map data were compressed to reduce transmission time. Subsequent decompression and enhancement of the transmissions was provided in the host communications support equipment.

The primary imaging system on the AMMT vehicle is a Laser Line Scanner System (LLSS) provided by Raytheon. The system uses a 400 mw laser and has the ability to provide sampling resolutions of 512, 1024, 2048, and 4096 pixels over a 70” field of view with 14 bit amplitude resolution. The laser sensor is mounted to the underside of the vehicle hull in a faired, fiberglass pod. For the AMMT Program application, the LLSS was designed to provide high resolution images at altitudes of 11.3 - 14.0 m over the target at speeds up to 6 knots. Because the LLSS had not been previously used in autonomous operations and to mitigate the potential risk that the system might not operate satisfactorily in the vehicle, a second imaging system was integrated into the vehicle. The backup system utilizes an electronic still camera and strobe lights, which were mounted in the aft and forward freeflood sections of the vehicle respectively.

V. TEST AND SUPPORT FACILITIES

The Naval Surface Warfare Center’s South Florida Testing Facility was selected as the site for the AMMT Program’s at- sea tests and mission demonstrations. Located in the Ft.

Lauderdale area of Florida, the facility was selected for its proximity to the open ocean, and the suitable bottom features and water depths available in it’s test area. The size, availability, and launch/recovery capability of NSWC’s support ship, M/V Seacon, was also a major reason for selection of the test site. The site is located on the Port Everglades channel and permits rapid access to the open ocean without the penalty of a long surface transit. The MIV Seacon is equipped with a 22 ton crane which is capable of lifting the AMMT vehicle for launch and recovery operations and a winch capable of supporting vehicle diagnostic tow operations. The M N Seacon is also large enough to permit the AMMT Control Van, a standard 40 foot IS0 container, to be mounted on its deck along with pedestals for vehicle support during transits to and from the test area. The Control Van housed the control and tracking equipment to support the AMMT vehicle and was the central monitoring location for vehicle performance and data collection. The Seacon also housed and deployed the V-Fin assembly which carried the topside (host) acoustic modem’s array, amplifier, and projector .

In addition to the equipment mounted on the M/V Seacon, a temporary shelter was constructed dockside to house the vehicle during assembly, disassembly, maintenance, repair, and battery charging. The vehicle was rolled out of the shelter on its handling carts and then shore-craned onto a set of support cradles dockside where the LLSS pod was mounted to the vehicle. The vehicle was then either crane launched or transferred to the pedestals on the Seacon for travel to the test site and launch at-sea. Fig. 3 shows the vehicle in the maintenance shelter on it’s handling carts.

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Fig. 3 UUV in Maintenance Shelter

In the water, the vehicle was handled with the use of inflatable support craft, including a pontoon type inflatable boat developed by Draper, to control the vehicle during surface tow operations. The vehicle could be surface towed from the dock to the test site using the pontoon boat; or carried to the test site on the pedestals onboard the Seacon, and craned into the water, sea-state permitting. The vehicle was able to be handled using the pontoon boat in seas to sea- state 3, and launchedrecovered using the support ship crane in sea-states of 1 or less. Generally, the vehicle was towed either to or from dockside using the pontoon boat. After being towed dockside, the vehicle was lifted to the pedestals on the support ship using the support ship crane for subsequent transfer to the shore cradles. Fig. 4 shows the vehicle in the water with the pontoon boat, and Fig. 5 shows the vehicle and M N Seacon at-sea.

Fig. 4 UUV and Pontoon Boat

An exercise minefield was installed in the offshore test area, to provide targets for the Ahead Looking Sonar. Approximately 40 bottom and moored test mines were deployed in water depths ranging from 46- 180 m. A pattern of mine lines parallel to the shore was used to represent a mine barrier which might be used to deter an amphibious assault from the sea. Special optical targets were also placed on the ocean bottom to evaluate the dimensional and contrast resolution of the vehicle’s imaging systems.

Fig. 5 M N Seacon and UUV

and validation. Mission software for each individual test day was verified in the simulation facility before its use at-sea. In addition, the facility was used to troubleshoot and resolve the problems and anomalies, encountered during at-sea testing, by recreating the actual test conditions in simulation and running the tactical software.

Draper’s simulation facility provided support to the program during laboratory vehicle integration and at-sea testing. All vehicle software, including the mission planner, was run in the high fidelity hybrid simulation for verification

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VI. ACCOMPLISHMENTS

Significant accomplishments were achieved during the test program. In addition to meeting the four major program requirements; provide a reliable, fault tolerant integrated testbed vehicle; develop support equipment suite; provide capability to launch, recover, perform diagnostic tow and service vehicle; and select test site and mobilize for conduct of tests; many program objectives were met and test demonstrations conducted. At-sea tests included subsystem demonstrations of the various advanced technologies. However, full mission demonstrations of the program’s integrated minehunting and mapping capabilities were not accomplished due to time and cost considerations.

On-line adaptive mission planning was implemented, and successful generation and execution of mission plans in varying ocean environments was demonstrated. The vehicle achieved trajectories and maintained safe operating conditions. All preplanned mission planner activities were demonstrated at-sea, except for data upload; with the planner’s contingent activities demonstrated in simulation, as the program ended before these activities could be executed at-sea.

The sonar system demonstrated the ability to perform real-time mine detection and classification by detecting all deployed targets. The ability to autonomously map bottom topography was demonstrated by generation of maps which agreed with surveyed data. The ability to track and navigate, using bottom features in the acoustic tracking navigation mode, was demonstrated over short intervals. However, the acoustic tracking navigation data was not integrated with the inertial navigation system data before the program ended.

The navigation system demonstrated it can be operated in an autonomous mode and can perform erect and align sequencing. Test data indicated performance accuracies which approached the desired goal of 0.02% of distance traveled, exceeding state-of-the-art systems in use. The results are based upon limited test data and require additional at-sea testing to establish firm quantitative values.

The acoustic communications system demonstrated reliable uplink communications from the vehicle to the host at data rates of 5 kbps up to ranges of 2 km. Uplink rates of 10 kbps were demonstrated up to ranges of 700m. Downlink communications from the host to the vehicle, typically at 2.5 kbps, were not demonstrated due to the thermal layer in the operating area and the geometries of the V-Fin positioning on the host and the directional receiver patterns of the vehicle.

Image processing demonstrations showed the ability to compress optical images by either of two methods, JPEG or EPIC, and transmit the images acoustically to the host. The system was used to compress and transmit a sonar map post mission but not in real-time, before the program ended.

Optical imaging was not successfully demonstrated during AMMT Program testing. Although both the LLSS and camera were integrated into the vehicle and operated correctly producing images dockside in air, the LLSS did not produce a suitable image at desired altitudes at-sea due to environmental conditions. Autonomous imaging runs were made at conservative altitudes of 15 m, which proved to be too great for the water conditions. LLSS images were obtained at non-optimal altitudes during surface tow operations but they lack detail and recognizable objects.

Originally, the at-sea test program was designed to include an overall demonstration of the fully integrated vehicle conducting a clandestine reconnaissance mission profile, utilizing all of the advanced technologies. Specifically, the vehicle would autonomously transit 25 nautical miles, over-the-horizon, perform a minehunting and mapping survey of an area, revisit one or more of the previously detected minelike objects, image the objects with the LLSS, and compress and acoustically transmit the image and mapping products to a host. The detailed maps and images would be generated post-mission to support “quick- look” data products. Although pieces of this mission profile were demonstrated individually, they were not demonstrated collectively in one autonomous mission due to test schedule limitations.

VII. CONCLUSIONS

The AMMT Program was conceived and executed in the DARPA tradition of having aggressive goals with an aggressive schedule. At-sea testing was terminated in May 1996 before all goals were completely met, because of funding limitations and other commitments for the NSWC facility and support ship. At termination, the Program was proceeding toward completion of all goals. At the time, there were no known technical challenges which were considered insurmountable. All goals were met or were close to being met. The AMMT Program went a long way towards proving the concept that a complex, autonomous vehicle, integrating several state-of-the-art technologies, could perform a clandestine survey of an undersea area and transmit information in near real time such that it could be used as an effective mine countermeasures asset.

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