Remotely Piloted Vehicles as Fire Imaging Platforms: The Future is Here!
Vincent G. Ambrosia
During military operations in Bosnia and, more recently Afghanistan, the use of Remote Piloted Aircraft (RPAs) or Unmanned Aerial Vehicles (UAVs) has increased dramatically and caught the attention of the public. These aerial platforms have served as imaging payload stations as well as Air-to-Ground missile launch platforms. With their increasing utility in non-military situations, the UAV will undoubtedly become a workhorse of civilian government and private industry in the not too distant future.
NASA, tasked with developing UAV utility in the aerospace and research community, has embarked on an ambitious program to push the technological "envelop" of UAV use in research and applications. The NASA program, ERAST (Environmental Research Aircraft and Sensor Technology) seeks to develop and flight-demonstrate remotely piloted aircraft for cost-effective science missions. Further goals are to demonstrate the utility of UAVs in situations that would be deemed most appropriate for the technology. These parallel applications efforts seek to "concept-prove" UAVs as data gathering platforms to agencies and public entities in need of such technology. Since the mission of UAVs are to provide an unmanned airborne platform in situations that would put a pilot at risk (what we tend to call the 3D missions: dull, dirty and dangerous), the use of these aircraft in both data gathering over wildfires and possibly as a airborne fire suppression tool are enticing.
NASA-Ames Research Center (Moffett Field, California) is leading the ERAST applications activities and recently completed a demonstration of the UAV as a wildfire remote sensing platform, gathering thermal data over fires and relaying that information through a satellite communications telemetry system in real-time to fire management personnel on the ground. The FiRE (First Response Experiment) experiment demonstrated the combined use of a thermal multi-spectral scanner, integrated on a large payload capacity UAV, a satellite image data telemetry system, near-real-time image geo-rectification, and rapid Internet data dissemination to disaster managers. The FiRE demonstration occurred in El Mirage, California in September 2001 and involved imaging a controlled burn and relaying the imagery in near real time. This brief paper describes the exciting results of that demonstration and provides the framework for future endeavors with long-duration UAVs as fire imaging payload platforms.
The FiRE demonstration was a close collaboration among federal and state agencies and private industry. General Atomics Aeronautical Systems Inc. (GA-ASI) developed, built and flew the ALTUS® II UAV airborne platform (Figure 1), while NASA-Ames supplied the Airborne Infrared Disaster Assessment System (AIRDAS) thermal infrared scanner for integration as the imaging payload on the ALTUS® II (Figure 2). Full system integrations (as well as the experimentation flight) were performed at the GA-ASI Flight Operation Facility in El Mirage, (San Bernardino County) California. The data telemetry system, a modified NERA World Communicator M4 portable satellite telephone terminal and antenna offering ISDN functionality and pure digital interface, was provided by Remote Satellite Systems, Inc. of Santa Rosa, California. The telemetry system was modified for remote aircraft operations by NASA-Ames and integrated into the fuselage fairing of the ALTUS® II by GA-ASI. Terra-Mar Resource Information Services of Mountain Ranch, California, performed image geo-rectification in near real time. The U.S. Forest Service and the State of California Resources Agency (disaster managers) participated as technology reviewers and provided feedback on the resultant fire image data sets. The goals of the demonstration were to:
The overarching objective was to provide the right information to the right people, at the right time. Based on these criteria, the FiRE team proposed delivery of a fully geo-rectified image file within 15 minutes of acquisition aboard the UAV!!
ALTUS® II Description
The ALTUS® II was developed by GA-ASI under the NASA AeroSpace Enterprise, ERAST program as a scientific research and applications platform. The ALTUS® II is powered by a Rotax 914-2T dual-turbo-charged piston, liquid cooled, four cylinder engine that is rated at 100 HP at 52,000 feet (15,853 meters). The aircraft has a wingspan of fifty-five feet, is 24 feet long, and 10 feet high. The ALTUS® II has a maximum altitude capability of 65,000 feet (19,817 meters) with a total flight endurance of eight (8) hours at 60,000 feet, eighteen (18) hours at 30,000 feet, and twenty-four (24) hours at 25,000 feet. The aircraft has a maximum speed of 100 knots indicated air speed (KIAS), with a cruise / loiter speed of 65 KIAS. The aircraft lands on normal tricycle type retractable landing gear. A large payload capacity of 330 pounds (150 kg) and size of 58"L x 48"H x 27"W is standard on the ALTUS® II. For avionics controls, the UAV communicates with the remote pilot and payload operator via a C-band line-of-sight radio frequency (RF). The aircraft is also adaptable for over-the-horizon (OTH) operations via a satellite communications link. This command and control (C2) link is separate from the data telemetry link, and is used strictly for flight and instrument operations. Remotely piloted flight operations for the ALTUS® II UAV platform are performed on the ground at the GA-ASI Ground Station (Figure 3). The ALTUS® II, and all GA-ASI aircraft are controlled by a portable common solid-state digital ground control station (GCS) through a C-Band line-of-sight (LOS) data link. The GCS is capable of direct control of the UAV and passing real-time payload data at ranges up to 150 NM. In addition to the LOS link, a high data rate Ku-Band satellite data link for routine over-the-horizon operations is available and has been used by the military and will be expanded for civilian use shortly.
AIRDAS Thermal Imaging Payload
The AIRDAS thermal scanner was flown on the ALTUS® II for the FiRE demonstration. The AIRDAS is a four-channel line-scan instrument designed for airborne imaging of wildland fires and other natural and man-induced disasters. The AIRDAS has been laboratory-calibrated to accurately resolve fire intensities up to 873° K (600° C). AIRDAS data is collected in four filterable EM channels: band 1, 0.61-0.68m m; band 2, 1.57-1.70m m; band 3, 3.60-5.50m m; and band 4, 5.50-13.0m m. Each of the specific AIRDAS bands provides useful information for fire analysis. The visible band 1 is suitable for monitoring smoke plumes as well as distinguishing surface cultural and vegetative features not obscured by smoke or clouds. Band 2 is suitable for analysis of vegetative composition, as well as very hot fire fronts, while still penetrating most associated smoke plumes. Band 2 is sensitive to fires and hot spots at temperatures above 573° K (300° C). Band 3 (mid-infrared thermal) is specifically designed for estimating high temperature conditions. Band 4 is designed to collect thermal data on earth ambient temperatures and on the lower temperature soil heating conditions behind fire fronts, as well as the minute temperature differences in pre-heating conditions. The Field-of-View (FOV) of the scanning optics is 108° cross-track, with an Instantaneous Field Of View (IFOV) of 2.62 milliradians. The system operates at a designed scan rate of 5-24 scans/second. The AIRDAS has a digitized swath width of 720 pixels in the cross-track direction, with continuous data flow acquired in the along-track direction. These parameters provide a ground resolution of 8.0 meters at an aircraft altitude of 10,000 feet AGL, although fires, smaller than 8.0 meters can be detected due to the design of the detectors and the instrument calibration criteria. The AIRDAS fit easily into the payload bay of the ALTUS® II, but received minor software modifications to optimize remote instrument operations.
Remote Operations of Payload
The AIRDAS payload operator and all system controls were located in the command and control trailer. This allowed direct communication with the pilots and flight engineer and access to the same forward and downward-looking video data. A downward-looking video camera, placed in the nose of the ALTUS® II, provided real-time coverage information of the potential target areas. By incorporating this camera view with the streaming GPS and moving map display, the payload operator was able to ascertain the UAV position and select the optimum AIRDAS data capture time. When the ALTUS® II was over the controlled burn site, the instrument operator in the GCS initiated the AIRDAS data capture and saved the resultant thermal multispectral scene and an associated platform / payload navigation file. The AIRDAS image data were saved as jpg-compressed files of 720 x 640 pixels x 3 bands (approximately 100 Kb). The associated "navigation" file composed of sensor profile and attitude data (pitch, roll, yaw, time, heading, etc.) was also captured and telemetered to a ground receiving location along with the image file. The associated navigation files were 9 Kbs. The "navigation" files were necessary for AIRDAS image geo-rectification.
Airborne Data Telemetry System
The data telemetry system was derived from the NERA mobile handheld system that communicates through the INMARSAT series of geo-stationary satellites (figure 4). The INMARSAT system currently operates at 64Kbs, sufficient for the FiRE project data telemetry activities. The AIRDAS scene data and navigation file were sent from the AIRDAS control computer to the NERA system onboard the UAV. Data were telemetered through a pair of phased array antennas mounted into the skin of the ALTUS® II fuselage, pre-positioned (in elevation) to acquire signal lock with an appropriate INMARSAT geo-stationary communications satellite. For the FiRE demonstration, both the Atlantic Operating Region West (AOR-W) satellite located at 54° West longitude over the equator and the Pacific Operating Region (POR) satellite at 178° East longitude at the equator were used. The data were then telemetered via a File Transfer Protocol (FTP) login to a file server for INTERNET distribution. Individual image file transfer procedures required approximately two minutes for full data delivery.
Geo-Rectification and Data Distribution
AIRDAS data and the associated navigation data file, transmitted via from the ALTUS® II UAV through INMARSAT were received at a workstation server at NASA-Ames Research Center, Moffett Field, California. The data were accessible by fire managers immediately at the UAV FiRE website (http://geo.arc.nasa.gov/sge/UAVFiRE/). At the same time, the two data files were used to create the geo-rectified data sets using the Terra Mar Data Acquisition Control System (DACS) software package. The DACS system utilizes the aircraft / payload attitude information and a sensor model to geo-rectify the data. If terrain data is available (Digital Elevation Model (DEM) or Shuttle Radar Topographic Mapping (SRTM) data), the geo-rectification improves greatly and the resultant data sets can be easily draped over other registered files such as maps, etc, in a GIS or used to create 3-D perspectives of the fire.
The FiRE demonstration mission occurred on 6 September 2001 at the GA-ASI Flight Operations Facility in El Mirage, California. Disaster managers and fire management personnel were invited to El Mirage, CA. to view the FiRE demonstration and participate in an evaluation of the products and procedures. Immediately prior to the ALTUS® II launch, the controlled burn was ignited adjacent to the aircraft runway. The mission plan was for the ALTUS® II to make numerous passes over the controlled burn during a one-hour allocated flight and burn time. Full aircraft system and payload checks were initiated at 7:00 AM (PST) with "hands off" all systems at 7:30 AM. The controlled burn was ignited and ALTUS® II was launched at 8:00 AM (Figure 5). After attaining planned data collection altitude (6000 feet MSL), the ALTUS® II flew "racetrack" patterns in an east / west orientation over the controlled burn. The first data collection pass was made at 8:22 AM (PST). A total of five data collection passes were made over the fire and data were relayed to the ground receiving station for geo-rectification. At the same time, fire managers were able to view the data via a remote login to the NASA-Ames server, with the data displayed on a theater projection system at the GA-ASI El Mirage Flight Facility. The geo-corrected images were sent back to the server and available within ten (10) minutes of being collected (Figures 6, 7 and 8)!!
The ALTUS® II completed the FiRE mission data collection and the aircraft landed at 9:30 AM (PST) and was available for viewing by the disaster managers following system and payload shutdown. Greatly exceeding our expectations of one hour for full data dissemination, the ALTUS® II UAV had launched, attained altitude, made five passes over a controlled burn, AIRDAS payload data were telemetered from the UAV to INMARSAT over the horizon (>400 miles) to NASA-Ames, data were geo-rectified, and distributed to the World Wide Web (WWW) and were available to disaster managers around the globe.
The FiRE project successfully demonstrated the potential for utilizing UAVs for real time disaster management remote sensing data gathering. From a UAV operating at an altitude of 6000 feet (MSL), five fully geo-rectified fire status images from an imaging payload were collected, uplinked via a satellite telemetry system, and delivered to an Incident Command Center and over the WWW. Our objective to deliver accurate geo-rectified data via this methodology in less than one hour was achieved. Overall collection, telemetry, geo-processing, and delivery were achieved in less than fifteen (15) minutes. The five images were obtained over a one-hour flight profile while the ALTUS® II UAV "lingered" in the airspace above the controlled burn site.
The GA-ASI ALTUS® II UAV proved to be a capable platform for this disaster support mission. The uniqueness of remotely piloted operations facilitates hazardous operations during critical data gathering conditions. The capability of UAVs to safely acquire and deliver data during hazardous missions greatly enhances the disaster management communitys ability to monitor and mitigate a broad range of disasters. The development and refinement of remote payload operations enhances the use of those payloads on UAVs and other platforms where weight or safety precludes the use of an on-board systems engineer. With the ability to switch out pilots easily, the aircraft can remain on-station over a disaster event such as a fire for extended periods of time. This becomes critical in long duration missions, or where monotonous, long-term data collection missions would stress an aircraft pilot. A UAV operates very efficiently within the airspace of hazardous fire conditions (unstable air, large obscuring smoke plumes, and possible rugged terrain conditions); safety of a pilot operating within that same airspace is at risk under those conditions.
Where Do We Go Next?
The FiRE project team is focused on the further advancements of UAV, payload, telemetry, and information processing for disaster management. The next phase of that research, development, and demonstration will involve the use of a GA-ASI ALTAIR® UAV. The ALTAIR® is a scientific variant of the GA-ASI PREDATOR B® UAV for use by NASA and other organizations. The ALTAIR® has more than an 750 pound (340 kg) internal payload weight capacity, an endurance of 32 hours (with 700 lb payload), a cruise airspeed of 151 KIAS, an operating altitude above 50,000 feet (15,244 meters) MSL and a range of over 4000 miles (6437 km). The ALTAIR® also employs OTH command and control via a high data rate (500 Kbs) commercial Ku-band satellite (SATMEX 5) communications datalink system.
The FiRE project team is planning a large-scale demonstration of enhanced disaster management capabilities using the ALTAIR® platform in 2003. The ALTAIR-FiRE project will demonstrate 24-hour coverage of fires throughout the Western United States. This long-duration mission will allow a fire management organization to request multiple AIRDAS thermal IR digital data acquisitions over numerous fires spread throughout an area stretching from Mexico to Canada and the Pacific Ocean to Colorado. The >4000 nautical miles (>6437 km) endurance of the ALTAIR will allow lingering over many of these potential fire events. Data will be transmitted via the aforementioned high data rate (500 Kbs) commercial Ku-band satellite (SATMEX 5) communications datalink system to a fire data management facility. All data will be geo-rectified in near real time and GIS-compatible. This long-duration, large area coverage demonstration mission will exceed the capabilities currently employed to capture tactical fires data over large regions.
The disaster management community is on the cusp of a great technological leap forward compared to the methods that have been employed during the last thirty years. The FiRE team is committed to assisting and advancing that technology curve through research and development on new UAVs, development and integration of new payloads, data telemetry, and information processing for use by the disaster management community. Only through these technological breakthroughs can we foresee a day when the danger to both wildfire pilots and firefighting personnel on the ground is greatly minimized.
Brief Author Bio
The author (Vince Ambrosia) has been involved in remote sensing research and applications at NASA-Ames Research Center since 1980. His research interests include thermal imaging of fires, hyperspectral analysis and development of remote sensing applications. He can be contacted at: email@example.com