Sense and Avoid Sensor Selection
Mark C. Hardy
UNSY 605 Unmanned Systems
Sensing, Perception, and Processing
Embry-Riddle Aeronautical
University
Unmanned
aircraft systems (UAS) possess unique abilities which could have transformative
effects on entire commercial industries.
However, in order to realize this potential UAS must be able to comply
with applicable rules and regulations relative to the airspace in which the UAS
will be operating. The Federal Aviation Administration has indicated that UAS
operating in the United States must fulfill the requirements specified by 14
CFR §91.111, §91.113 and §91.181 that govern operations near other aircraft and
various right-of-way rules. Key to the UAS airspace integration discussion, is
language found in 14 CFR §91.113 that mandates all persons operating aircraft
to maintain vigilance “so as to see and avoid other aircraft” (General
Operating and Flight Rules, 2015). As a result, an effort is underway to
develop sensor based technologies which will enable UAS to sense and avoid
(SAA) potential collision hazards. SAA systems for large UAS such as the Global
Hawk and Predator B are already in the operational test phases, however, a full
source SAA solution for small UAS (sUAS) that weigh less than 55 pounds has yet
to emerge (Carey, 2014).
Researchers
at the University of Kansas have developed a prototype for a radar based SAA
system that may be sufficiently compact enough to meet the size, weight and
power limitations (SWaP) of some sUAS (Allen, Ewing, & Keshmiri, 2015).
Radar is an active remote sensing technology that emits pulses of
electromagnetic energy and uses the reflected returns to determine the relative
position of objects in the surrounding environment (Austin, 2010). Radar offers
distinct advantages for SAA. Radar is essentially an all-weather technology
capable of day/night detection of non-cooperative targets such as aircraft not
equipped with transponders, birds, parachutists, or terrain obstacles
(Barnhart, Marshall & Shappee, 2011).
The system developed
at the University of Kansas employs a multichannel frequency-modulated,
continuous wave (FMCW) radar to sense targets within its field of interest (+/-
110 degrees azimuth, +/- 15 degrees elevation). The system utilizes programmable, radar -ready
chipset technology originally developed for FMCW radars used in automobile
collision-avoidance systems. Processing for the SAA system is conducted by an
Xlinix Spartan 6 field-programmable gate array (FPGA) which provides rapid
processing and added flexibility. Objects within range are painted by a single
low gain transmit antenna, while a set of four low-gain antennas, which combine
to create a virtual anechoic chamber, form the receiving array. Target range is gauged by the echo signal’s
beat frequency and velocity is determined by measuring phase variation over
successive radar returns. Target azimuth and elevation data are calculated by
correlating the signal phases captured by the individual antennas of the
receive array. Initial laboratory and flight tests indicated that the system
could detect an object with a 1 square meter radar cross section (RCS) at a
distance of approximately 430 meters. However, subsequent laboratory testing of
the miniaturized system revealed significant improvements in sensitivity,
leakage signal tolerance, and noise floor. These improvements could potentially
extend the device’s detection range for a target with a 1 square meter RCS to
860 meters. Targets with larger RCS values could be detectable at greater
ranges (Allen, Ewing & Keshmiri, 2015).
The prototype’s
processing components and the radio frequency (RF) front end assembly weigh
approximately 6 ounces and are housed in a 6.5” x 4” x 2.25” shielded container.
The system operates at 2.37 gigahertz which enables the use of smaller
commercial off the shelf (COTS) antennas. The prototype antenna array measures
7.5” tall x 3.4” diameter and weighs approximately 12 ounces. The FMCW
architecture reduces transmit power requirements, during testing, the system’s RF
front end assembly was shown to consume approximately 10 watts of power (Allen,
Ewing & Keshmiri, 2015).
Further refinement and testing of
the system is required before it can become a market ready SAA solution.
Additional data processing requirements may force developers to switch from the
FPGA to a multi-core processor capable of managing an auto-pilot algorithm
which is also under development at the University of Kansas (Allen, Ewing &
Keshmiri, 2015). Additional miniaturization of the system’s components would
increase its feasibility for use with a wide variety of sUAS. Pricing
information for this system is not yet available; however, a miniature phased
array radar developed at the University of Denver’s Unmanned Research Institute
was recently licensed by Integrated Robotics Imaging Systems Ltd. which plans
to offer the devices at a price point of $7,000-$10,000 (Brehmer, 2014).
References
Allen,
C., Ewing, M., & Keshmiri, S. (2015, January). Multichannel Sense-and-Avoid Radar for Small UAVs. Retrieved from http://nari.arc.nasa.gov/sites/default/files/Allen_LEARN%20Final%20Report%20-%20Kansas%20-%20Jan%202015%20%20%28v2%29.pdf
Austin,
R. (2010, March). Payload Types. Unmanned
Aircraft Systems : UAV Design, Development and Deployment (pp. 136-137).
United Kingdom: John Wiley & Sons.
Barnhart,
R., Marshall, D., & Shappee, E. (2011). Detect, Sense and Avoid. Introduction to Unmanned Aircraft Systems (pp.138-151).
Boca Raton, FL: CRC Press.
Brehmer,
E, (2014, May 22). Kenai Company Leading the Way on Unmanned Aircraft Radar. Alaska Journal of Commerce. Retrieved
from http://www.alaskajournal.com/Alaska-Journal-of-Commerce/May-Issue-4-2014/Kenai-company-leading-the-way-on-unmanned-aircraft-radar/
Carey,
B. (2014, July 11). U.S. Firms Advance
UAS ‘Detect and Avoid’ Capability. Retrieved from http://www.ainonline.com/aviation-news/2014-07-11/us-firms-advance-uas-detect-and-avoid-capability
General
Operating and Flight Rules, 14 C.F.R. §91 (2015).
