Sense and Avoid Sensor Selection

            Sense and avoid technologies are in a nascent stage.  There are efforts in academia, government and industry working together to come up with solutions to address the sense and avoid issue particularly as it pertains to integrating unmanned aerial systems into the National Air Space.  As of this date, the Air Force as a system for the Global Hawk that they hope to transition to smaller Category 2 and 3 UAS programs (Insinna, 2014).  The Air Force, as well as the other services, are also working with industry on other sense and avoid technologies in the hopes to reduce the size of the equipment so that it can be used in smaller platforms (Eshel, 2013; Airborne Sense, n.d.).  These systems are radar based, with other sensors such as cameras, traffic collision avoidance systems (T-CAS) and automatic dependent surveillance-broadcast (ADS-B) integrated into the solution.  These systems will not provide the smallest UASs with the capabilities to sense and avoid target.  

Application to sUAS

            While there are numerous technologies that can be applied to the sUAVs, there is not one that can provide a complete solution.  As with the larger UAVs, it is going to be a combination of several technologies.  Unfortunately, most of the sensors today do not meet with size, weight and cost (SWaP) requirements for the sUAS, or are still immature, complex and process-intensive solutions. 

            There are several products that address some of the challenges posed in sensing and avoidance by sUAS.  They include radars, ultrasonic sensors, LiDAR and camera. Each has its advantages and disadvantages.  Of these technologies, LiDAR has proven to be useful for other unmanned systems, particularly in ground and maritime surface systems.  Most LiDAR used in these applications tend to be larger in size and have moving parts.

LeddarTech

Of the solutions that have promise to use today is the LiDAR produced by Leddar.  They have a solution that has been proven in other industries that provide detection and ranging, which are important components in solving the sense and avoid problem. Unlike the LiDAR used in the self-driving cars, this one has no moving parts.  LeddarTech, based in Quebec City, Canada, is focused on small form factor LiDAR sensors for use in the automotive, smarter cities initiatives, smart homes and buildings. They now have a multi-beam sensor that is ideal for multi-rotor aerial vehicles (Leddar Sensors, n.d.; Leddar Optical, n.d.)).

            Their technology is based on optical time-of-flight sensing, which is a new approach to detecting and ranging.  It combines fast, high resolution analog-to-digital conversion and signal processing that has advantages when compared to other technologies.   Most active and passive sensors, identify multiple objects within the field of view.  Energy measured by the sensor that was emitted by any object measured infer a positional information, which are known as ‘time-of-flight measurements’.  In passive sensors, it normally requires the employment of an algorithm to determine a triangulation of the various images to determine position.  In the active systems, this can be accomplished by measuring the return signal from radio frequency, acoustic or light waves.  Each of these waves have their limitations, particularly in taking exact measurements because the distance travel and time measurement of the analog signal (Leddar Optical, n.d.)

            The unique feature of the Leddar optical time-of-flight sensing technology is that it iteratively expands the sampling rate and resolution of the sampled analog signal.  It then analyzes the resulting discrete-time signal to extract the distance for every object. Unlike other methods that may see the echo returns as noise, Leddar can process and extract the distance for every object found in the field of view.  This applies to even to objects that return a weak signal. The importance to a sense and avoid application, is that these sensors are highly sensitive, immune to noise, and have a powerful data extraction capability.   The core processer is an ultra-low-power device that integrates the photodetector, pulsed light source and optics into one sensor package (Leddar Optical, n.d.).

Multi-Element Sensor Module

            In detecting and providing a range to objects in the field of view, the Leddar multi-element sensor provides spatial awareness of the environment, and processing efficiency for a sense and avoid solution.  The sensor works both in and outdoors.  It works well in an GPS and barometric pressure denied areas.  The sensor array is capable of providing information about the environment around the drone, with accurate distance information for the drone to autonomous maneuver to avoid the objects.  Unique features of the M-16 Sensor Module include:

a.     16 independent segments with simultaneous acquisition and lateral discrimination capabilities.

b.     Sensor field of view:  9 to 95-degrees, 360-degree coverage with four sensors

c.     Range: up to 100 meters

d.     Accuracy < 5 cm

e.     Rapid data acquisition rate of 50 Hz.

f.      Weight: 180 grams

g.     Power consumption: 4 W

h.     Immune to light, wind and vibration.

i.      Price for the M-16 retails for $895.  It is currently advertised for $540. 

This sensor is only part of a complete sense and avoid solution.  Integrated with the proper behavioral-based software and another complementary sensor, such as a camera, it is a viable solution for sUAVs today.