American Institute of Aeronautics and Astronautics1

ORCHESTRATING A NEAR-REAL-TIME IMAGING MISSION IN NATIONAL AIRSPACEUSING A SOLAR-POWERED UAV

Stanley R. Herwitz∗Clark University UAV Applications Center, NASA Research Park

Moffett Field, CA

Lee F. Johnson†

California State UniversityMoffett Field, CA

Stephen E. Dunagan‡ and James A. Brass§

NASA Ames Research CenterMoffett Field, CA

Glen Witt¶

Technical Analysis & Application Center, New Mexico State UniversityLas Cruces, NM

∗ Professor† Senior Research Scientist‡ Senior Engineer§ Branch Chief, Research Scientist¶ Senior Staff Member

ABSTRACT

In September 2002, NASA’s solar-powered Pathfinder-Plus (PF+) UAV was used to collect digital imagery within the National Airspace System (NAS) over the 1400 ha Kauai Coffee Plantation on southern Kauai, HI. The U.S. Navy Pacific Missile Range Facility (PMRF), on westernmost Kauai, served as the range provider. The aircraft control station was established at PMRF, and a payload control station 25 km to the east at KCP. The transponder-equipped PF+ climbed to 21k ft within restricted PMRF airspace before entering the NAS above Kauai, where it was monitored by Honolulu Air Traffic Control. Pre-planned flight tracks were combined with spontaneous, controlled maneuvers to guide the UAV to cloud-free areas. PF+ loitered for four hours over KCP, continuously acquiring imagery with two solar-powered imaging systems. Image data were transmitted to the payload station tracking antenna at rates of 3-6 Mbit sec-1 over a line-of-sight wireless local area network, and were available for

ground station viewing, enhancement, and photo quality printing within five minutes after collection. Mission planning included development of an airspace management plan, an Application for Certificate of Authorization (COA), a Memorandum of Agreement with the FAA Honolulu Control Facility (HCF), and Notice to Airmen (NOTAM) data for issuance by the FAA Honolulu Automated Flight Service Station (AFSS).

INTRODUCTION

Unmanned aerial vehicles (UAVs) are beginning to offer new alternatives for the scientific and commercial remote sensing user community (Herwitz et al., 2002; Ambrosia et al., 2002, Seitzen, 2002). With respect to conventional photo-reconnaissance platforms, UAVs offer advantages in fabrication and operating cost, size, weight, and unique performance capabilities in terms of speed, endurance, and altitude. In September 2002, NASA’s experimental solar-powered Pathfinder-Plus (Table 1, Fig 1) was used to collect digital imagery in a proof-of-

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concept mission conducted within the U.S. National Airspace System (NAS) above Kauai, HI. The airborne campaign involved an effort to fly two missions above the 1500 ha Kauai Coffee Plantation (KCP) within the ten-day period 9/28/02-10/07/02. The first mission was designed to demonstrate wireless operation of the imaging payload and detect spatial differences in field ripeness levels. The second mission was designed as a repeat flight to add value by enabling the calculation of field ripening rates.

Two complementary CCD-array digital camera systems were configured for remote operation within the weight (68 kg) and power (500 w, solar generated) limitations of the UAV (Herwitz et al., 2003a). A color high-resolution camera was used to collect photographs for qualitative interpretation, and a narrow-band multispectral camera was used to explore automated spectral analysis of canopy color in relationship to field ripeness. Both systems recorded image frames, or “snapshots,” using 2-dimensional CCD arrays. The cameras were housed in lightweight, thermostatically controlled 0.05 m3

pressure pods. Each pod was attached to the central section of the airframe (Fig. 1) and integrated into the PF+ solar power system.

This paper provides an overview of the airborne campaign, including ground-based infrastructure, weather-related flight criteria, and procedures used by the UAV mission manager to gain FAA authorization and comply with airspace management regulations.

UAV RANGE PROVIDER

The Barking Sands Airfield of the U.S. Navy Pacific Missile Range Facility (PMRF) served as the UAV range provider. The aircraft control station was established at Barking Sands, and the associated protected airspace was used for aircraft climb and descent. Selection of PMRF was based on several considerations:

(1) Weather: Kauai has suitable and relatively predictable weather for flight operations year-round. PMRF is located in the island’s wind and rain shadow. It should be noted that frequent cumulus cloudcover on southern Kauai (typical of tropical and subtropical regions) is less suitable for optical remote sensing, due to ground obscuration. (2) Radio frequency environment: The number of users at PMRF is low; therefore, obtaining frequencies that ensure non-interference for flight operations is relatively easy.(3) Air traffic: PMRF is surrounded by restricted, special-use airspace (Restricted Area R-3101;

Warning Areas W-186, W-188) (Fig 2). Most military flight operations are conducted in the offshore Warning Area. Traffic in the NAS over southern Kauai is typically light, primarily involving local air tours and international carriers operating between Honolulu and Asia.(5) Latitude: At 22̊ N latitude, the Hawaiian Islands are located closer to the equator than any other part of the U.S., except remote territories. Elevated solar irradiance enhances energy generation from the UAV’s solar panels.(6) Logistics: Kauai is served by regular air service and commercial shipping from the mainland United States.(7) Impact zones: PMRF is surrounded by ocean on one side and the largely unpopulated interior of Kauai between PMRF and the Kauai Coffee plantation.(8) Heritage: For the above reasons, PMRF has hosted a number of prior test flights of PF+ and other solar UAVs.(9) Proximity to study site: PMRF is located in close proximity (25 km) to the KCP study site (Fig 2).

STUDY AREA

The Kauai Coffee Plantation produces more than half of all coffee grown in the U.S.A., and the 1400 ha property is one of the largest drip-irrigated coffee plantations in the world. The plantation includes over 40 fields, each of which is subdivided into 5-20 separate blocks. The blocks are typically further subdivided into irrigation and fertilization zones. The primary cultivar grown is yellow catuai (Coffee arabica), which ripens from green to yellow, then turning brown when overripe. Ground-based sampling is performed to monitor field ripeness levels. Mechanical harvesters are dispatched to the ripest fields, operating essentially 24 hours a day during harvest season.

PAYLOAD CONTROL STATION

A payload control station was established at the KCP processing plant, to handle all camera command-and-control aspects of the mission. A line-of-sight telemetry system using unlicensed wireless Ethernet bridge LAN (local area network) technology was configured to control both camera systems and enable near-real-time downloads of full -resolution, uncompressed image data (Herwitz et al., 2003b). The ground systems consisted of two Ethernet bridges attached to 21-db gain dish antennas mounted on a single computer-controlled azimuth-elevation tracking assembly. GPS data collected by the payload were sent by PPP (Point to Point Protocol) radio link to the PMRF aircraft control station, encapsulated into IP (internet protocol) packets, and transmitted over a wide area network through an encrypted tunnel to payload control.

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The packets were then decapsulated, re-converted to serial format, and the derived pointing instructions sent by hard wire to the tracking antenna assembly. All payload-related activities were coordinated with the U.S. Federal Communications Commission and PMRF frequency control.

AIRSPACE MANAGEMENT

A critical component of the overall project was the airspace management function. The first airspace management activity was to perform an airspace analysis. The primary purpose of the airspace analysis was to determine what airspace the UAV would occupy and which organizations had responsibility for authorizing flight operations in that airspace. The analysis concluded that flight operations would be performed in the Barking Sands Class D airspace, PMRF’s Special Use Airspace (SUA), restricted area R-3101 and warning area W-188, and within the NAS over Kauai. The Barking Sands Air Traffic Control Tower is responsible for operations in the Class D airspace, PMRF’s Range Safety Office is responsible for operations in theSUA, and the HCF, a combined en-route and radar approach control facility, is responsible for providing air traffic control services in the NAS over Kauai.

Approximately one year before the campaign, the mission manager traveled to Hawaii and visited each of the facilities that would be involved in the control of PF+ during its flight operations. Interviews were conducted with personnel from each of these organizations in order to determine what operational constraints existed and to determine what operational impact might transpire as a result of the flight of PF+ in their airspace. Using the information obtained from the affected organizations an airspace management plan was developed in concert with the HCF, PMRF, and the UAV provider. This airspace management plan enhanced safety, facilitated flight operations, and limited the impact on other airspace users’ flight activity.

To eliminate any conflict with aircraft operating under visual flight rules a flight profile was designed so that PF+ would make its initial climb in the Barking Sands Class D airspace, then transition to PMRF’s SUA for further climb to 21,000 feet (Flight Level 210). The UAV would then transition to the NAS over Kauai for image acquisition, and return to the SUA for descent and landing. FL210 was considered the optimal altitude from an Air Traffic Control (ATC) perspective, since the vast majority of aircraft operating in this same airspace are either at lower or much higher altitudes. FL210 was also desirable from a meteorological standpoint, as winds

are typically calm and are similar to those encountered at high altitude above the jet stream.

Essentially, the plan to achieve flight safety was predicated on applying routine methods. All aircraft flying in the Barking Sands Class D airspace are under the control of the Barking Sands Air Traffic Control Tower. Non-participating aircraft are excluded from operations in R-3101. Such aircraft are not excluded from operating within W-188, although non-participating pilots are aware that experimental demonstrations may be conducted in the airspace, and tend to avoid flight in this airspace when the warning area is active. In the NAS airspace over Kauai, the HCF provided air traffic control service, ensuring that aircraft under their control were separated from the PF+. The UAV was equipped with a Mode3/A, 4096 code transponder, with altitude reporting (Mode C), to enhance the HCF’s ability to track the aircraft on radarscopes.

UAV proponents must obtain a Certificate of Authorization (COA) from the FAA for operation in the NAS. To date, the FAA has not published any guidelines that define the process civil proponents are to use in obtaining the COA. Currently, civil proponents are instructed to use the same criteria used by Department of Defense (DoD) UAV organizations, as contained in FAA Order 7610.4, Special Military Operations, Chapter 12, Section 9. This Order suggests that DoD proponents submit an “Application for COA” to the appropriate FAA Region’s Air Traffic Division (ATD) at least 60 days prior to the beginning date of the planned UAV flight operation. The application must include: (1) a detailed description of the proposed UAV operation, including the classes of airspace required, (2) the UAV’s physical characteristics and operational capabilities (e.g., cruise speed, climb/descent rate), (3) method used to control the UAV (remote or autonomous), (4) method used to avoid other aircraft, (5) coordination and communication procedures, (6) contingency plans, and (7) a statement that the UAV is “airworthy.”

The mission manager submitted the Application for COA to the FAA Western-Pacific Region ATD. The ATD then performed an airspace analysis in coordination with the HCF. The ATD issued a COA to the mission manager on 19-Apr-02. The COA contained some Special Provisions that required additional action on the part of the mission manager. Included in the Special Provisions was a requirement that the mission manager enter into a Memorandum of Agreement with the HCF and also to provide the FAA Honolulu Automated Flight Service Station (AFSS) specific information for each flight so the AFSS could issue a Notice to Airmen (NOTAM). The NOTAM contained information regarding the date, time, location, and altitudes to be used by the UAV and was available to all pilots operating aircraft in the Kauai vicinity. A project team member was stationed at FAA's Honolulu

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Combined Center/Radar Approach Control (CERAP) during flight, and a direct telephone link between CERAP and the PMRF aircraft control station was maintained.

CONTINGENCY PLANS/RISK MITIGATION

Safety factors involving unplanned descent of the UAV in an emergency situation were addressed. From an ATC standpoint, standard aircraft emergency procedures would apply, with other air traffic routed clear of the vicinity to the extent possible. Missions were to be conducted in such a manner that any in-flight emergency that prevented PF+ from returning to Barking Sands would not result in a fall point on a populated area. Predicted fall points, computed from aircraft position and vertical profiles of wind speed and wind direction, were mapped prior to take-off as a go/no-go criterion and updated during flight. In the event of unplanned descent, the UAV was equipped with a parachute to slow the aircraft and enhance visual display for pilots in the vicinity.

WEATHER MONITORING

Rollout and flight of PF+ was subject to a number of weather constraints: surface winds, winds aloft, air temperature, nearest precipitation, nearest thunderstorms, cloudcover during takeoff and climb, wind shear gradient, ceiling, visibility, nearest dust devils, and nearest hurricane. Weather conditions were monitored by meteorologists on-site at PMRF. Sounding balloons were launched approximately every two hours beginning at 0145 (Hawaiian Standard Time) on possible mission days. A SODAR 4000 system provided nearly continuous wind speed, direction, and turbulence measurements from 15 to 200 meters above ground level at PMRF. Meteorological updates were provided to the flight operations crew based on analyses of sounding data, SODAR data, geostationary satellite imagery, and regional forecasts. While PF+ is capable of achieving extremely high altitude (>80,000 ft), the lower altitude plan was adopted to increase chances of acceptable flight conditions, as higher-altitude jet stream winds could be discounted. Also, given its modest climb rate, this lower altitude allowed PF+ to be on-station near solar noon, which was desirable from a remote sensing standpoint.

FLIGHT DAY

A successful flight was performed on 30-Sep-02, with no safety or performance anomalies noted by the aircraft operations crew. While in the

NAS, the mission was seamlessly integrated into regional air traffic operations of the FAA’s Honolulu ATC Facility. Four other possible flight days within the 10-day campaign timeframe were scrubbed due to weather. The two immediate post-flight days were devoted to aircraft turnaround and crew rest. The Range was unavailable due to support of unrelated activity on one day and, by prior agreement, no flights were attempted on Sundays (Table 2).

On the flight day, a trough of low pressure and an associated semi-stationary cold front 100 nautical miles to the northwest of Kauai resulted in a weak east-southeasterly trade wind pattern. The forecast called for a fairly normal wind pattern at PMRF with scattered low clouds at takeoff and at least scattered cumulus cloud cover likely over the KCP study site throughout the day. Early morning conditions at PMRF were generally favorable with only scattered low clouds and little development expected. Winds aloft were less than 20 knots between surface and 21,000 feet (Fig 3, top). Surfacewinds were generally 6 knots or less before 0400 HST, varying from the northeast and southeast between midnight and 0810 HST, time of land breeze transition. Winds at takeoff (0845 HST) were 5 knots from the west (270°). Wind speeds experienced at FL210 during image acquisition were on the order of 1-2 knots (Fig 3, bottom), and were similar to the benign wind conditions typically encountered at high altitude above the jet stream. The aircraft landed at 2015 HST, with winds averaging 7 knots from the southeast (120°) (Figs 4, 5).

The primary on-station flight plan called for negotiation of parallel tracks above the plantation, a standard approach used for airborne remote sensing. To minimize yaw, the final flight track specification was established (literally on-the-fly upon entry to the NAS) so that the aircraft was flying, to first approximation, directly upwind and downwind. The tracks were in sufficiently close proximity to allow image collection with cross-track overlap for production of a seamless image mosaic. The UAV faithfully navigated the prescribed tracks, though with variable yaw and speed as a function of ambient winds. The influence of instantaneous aircraft positioning (pitch, roll, and yaw) on sensor pointing vector is not a particular problem for frame-based camera systems as used in our mission. However, it is worth noting that image data from line scanners or linear arrays, which use platform forward motion to compile an image, would have required relatively sophisticated georectification post-processing (e.g., Hammer et al., 2001).

Cumulus cloud obscuration of the target area was extremely challenging while PF+ was on-station. Observers at KCP estimated total cover at 70% throughout most of the overflight, with highly dynamic spatial pattern of cloud development and cloud dissipation. Therefore, after the first hour on-station, an

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alternate strategy was invoked (with ATC clearance) to enhance acquisition of cloud-free imagery. Video feeds from forward-, side-, and downward-looking video cameras mounted on the UAV were available to the mission manager at the PMRF ground control station and KCP payload control station, who then interacted with flight navigators to direct PF+ to cloud-free parts of the study area (Fig 6).

Both cameras performed successfully throughout the mission. In total, about 50 Kodak and 300 DuncanTech frames were acquired over the KCP, totaling in excess of 2 GB of image data. The imagery was used to quantify field ripeness, map weeds, and detect fertilization and irrigation anomalies.

CONCLUSION

In summary, the campaign required extensive team coordination and regulatory compliance. Extensive research of regulatory requirement was needed before the campaign could be effectively planned. The FAA process for authorizing UAV operations in the NAS can be quite lengthy depending on the nature of the proposed flight(s). Under the current regulatory climate, it is suggested that UAV proponents allow ample time to develop an airspace management plan, prepare an “Application for COA,” and mitigate any FAA or other airspace user concerns that may surface.

The PF+ flight operations described here were successful from an airspace utilization standpoint, posing no problem for air traffic control or airspace users. Mission success was assured by extensive coordination performed with both PMRF and HCF well in advance of flight operations.

The experimental UAV used in this study imposed additional constraints in the form of weather limitations, primarily with regard to takeoff and landing operations. Once aloft, the aircraft accurately navigated specific flight tracks and provided a sufficiently stable platform for frame-based (“snapshot”) imaging. Moreover, its loitering and spontaneously maneuvering capability ultimately allowed for collection of cloud-free imagery over much of the target area. Constraints on takeoff, landing, and flight turnaround will assume relatively less importance as energy storage solutions, combined with demonstrated high altitude capability (above air traffic and jet stream), enable descendants of this prototype UAV to function as an extreme (multi-day and longer) endurance platforms.

ACKNOWLEDGMENTS

The work was sponsored by NASA’s Suborbital Science Office, UAV Science Demonstration Program. AeroVironment, Inc. (Simi Valley, Calif.) maintained and operated the UAV. The UAV/Coffee Project team based at NASA Ames performed the payload physical and electronic integration onto the UAV. PMRF and NASA Dryden staff collected and analyzed meteorological data. NASA Dryden also provided flight safety oversight. We thank the Kauai Coffee Company for their participation.

REFERENCES

Ambrosia, V.G., Wegener, S.S., Sullivan, D.V., Buechel, S.W., Dunagan, S.E., Brass, J.A., Stoneburner, J. and Schoenung, S.M., 2002. Demonstrating UAV-acquired real-time thermal data over fires. Photogrammetric Engineering & Remote Sensing, 69:391-402.

Hammer, P.D., Johnson, L.F., Strawa, A.W., Dunagan, S.E., Higgins, R.G., Brass, J.A. Slye, R.E., Sullivan, D.V., Smith, W.H., Lobitz, B.M. and Peterson, D.L. 2001. Surface reflectance mapping using interferometric spectral imagery from a remotely piloted aircraft. IEEE Transactions in Geoscience & Remote Sensing, 39: 2499-2506.

Herwitz, S.R., Johnson, L.F., Arvesen, J.C., Leung, J.G., Dunagan, S.E., 2002. Precision Agriculture as a Commercial Application for Solar-powered UAVs, Proceedings 1st AIAA UAV Conference, Portsmouth, VA.

Herwitz, S.R., Dunagan, S.E., Sullivan, D.V., Higgins, R.G., Johnson, L.F., Zheng, J., Slye, R.E, Brass, J.A., Leung, J.G., Gallmeyer, B.A., Aoyagi, M., 2003a. Solar-powered UAV mission for agricultural decision support. Proceedings Int’l Geoscience & Remote Sensing Symposium, Toulouse, France.

Herwitz, S.R., Leung, J.G., Aoyagi, M., Billings, R.L., Wei, M.Y., Dunagan, S.E., Higgins, R.G., Sullivan,D.V., and Slye, R.E., 2003b. Wireless LAN for operation of high resolution imaging payload on a high altitude solar-powered unmanned aerial vehicle. Proceedings Int’l Telemetering Conference, Las Vegas, NV.

Seitzen, F., 2002. New blueprint for NASA aeronautics. AIAA Aerospace America, August, pp. 24-27.

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Table 1. Pathfinder-Plus UAV specificationsSpecification DescriptionOwner NASAManufacturer AeroVironment, Inc. (Simi Valley, Calif., USA)Structure Composites (carbon, aramid & glass fiber), mylar, styrofoamMotors Eight (8) solar-electric propellersEnergy Source Solar (lithium sulfur dioxide batteries as backup)Wing Span 37 mWing Chord 3 mWing Area 90 m2

Takeoff Weight 350 kg (including payload)

Table 2. Daily flight status log during campaign period.Date Status Reason09/28/02 scrub excessive winds on surface and at 15,000’09/29/02 not attempted Sunday09/30/02 successful flight10/01/02 not attempted aircraft operations in turnaround mode10/02/02 not attempted aircraft operations in turnaround mode10/03/02 scrub surface winds; T-storms predicted10/04/02 not attempted PMRF range unavailable10/05/02 scrub weather system in vicinity; potential for wing icing10/06/03 not attempted Sunday10/07/03 scrub weather system in vicinity; potential for wing icing

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Figure 1. Pathfinder-Plus UAV in flight over Kauai on 30-Sep-02. Cameras are housed in two environmental pods suspended on underside of central wing section.

W-186

PMRF KCP

Figure 2. Site map, showing locations of the U.S. Navy Pacific Missile Range Facility (location of the aircraft ground control station) and the Kauai Coffee Plantation study site (location of the payload control station). Distance

between PMRF and KCP is ~25 km. PMRF airspace Warning Areas W-186 and W-188 also shown.

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Figure 3. Vertical wind profile measured by sounding balloons launched from PMRF at 0145 HST (top) and 1143 HST (bottom) on flight day, 30-Sep-02. Note relatively calm conditions at operating altitude of 21,000 ft.

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a)

b)

Figure 6. On-station flight track. Bright green arrow shows current UAV position. a) Navigation of parallel flightlines during first hour on-station. b) Cumulative track for 4-hour period, showing fixed flightlines (as above) followed by

maneuvers to cloud-free zones guided by ground based monitoring of downlooking on-board video feed.