Case study: LiDAR system provides helicopter pilots a clear line of ...

Technology: 3D situational awarenessCase study: LiDAR system provides helicopterpilots a clear line of sight in brownoutsBy Maureen CampbellSingle Print OnlyPhoto courtesy of U.S. ArmyToday’s combat zones are inundated with threats. Enemyfire, Improvised Explosive Devices (IEDs), and mines area few of the imminent dangers that war fighters face. Onethreat that has become a major focus in recent yearsis vision obstruction in a helicopter’s landing zone, causedby brownouts and whiteouts. However, a new modifiedLiDAR system is providing 3D images to help increasepilots’ situational awareness.As the war on terrorism continues, helicopters play a crucialrole in both combat and civilian missions, in everything frommedical evacuations to crew transportation. Due to the threatof IEDs, helicopters are now becoming the preferred method oftravel to and from mission coordinates. But in arid environmentslike Afghanistan, landing visibility is constantly obstructed bybrownout conditions.“Brownouts” occur when a helicopter takes off or lands in sandor onto dust-covered sites, while snow-covered sites produce“whiteouts.” The spin of the helicopter’s rotors cause clouds ofdust (or snow) particles to form in the air, obscuring the pilot’sview and, consequently, their situational awareness. When pilotsdo not have the visual cues they require to safely land the helicopter,the results can be fatal.In recent years, the U.S. Army has recorded more than 40 casesof brownout conditions causing accidents at various trainingfacilities within the U.S. In conjunction with in-theatre operations,this number jumps to 230 cases of aircraft damage and/or injury since 1991. Between 2001 and 2007, 80 percent ofthe accidents happened during landing procedures, while only20 percent occurred upon takeoff. Brownouts are costing theU.S. an estimated $100 million per year.[1]Investigating solutions to this problem has become a highpriority for the military. Until recently, no definitive solution hasbeen developed. However, a new modified LiDAR vision systemis emerging, the Obscurant Penetrating AutosynchronousLiDAR, known simply as OPAL. Its early prototypes have beentested in a variety of environments and have proven to be robustand powerful.OPAL’s ability to penetrate brownouts and whiteouts is provenmore effective than conventional LiDAR. When used in conjunctionwith an infrared camera and a terrain database in a systemsuch as Augmented Visionic System (AVS), a powerful syntheticvision system is created for helicopter pilots – enabling a lineof sight through brownout and whiteout conditions and ensuringsafe takeoffs and landings.OPAL versus conventional LiDARSeveral systems exist that are aimed at improving helicopterpilot visibility. Although these sensors have some merit, they areinefficient in brownout and whiteout conditions. For example,infrared cameras are effective in poor visibility conditions, suchas fog, but are limited when operating in dust clouds holdingparticles of size comparable to the operational wavelength ofthe camera. Additionally, Millimeter-Wave (MMW) radar, flashLADAR, and Range-Gated Cameras are also ineffective withinbrownout and whiteout conditions. For example, because of itslonger wavelength, MMW radar penetrates deeply into a brownoutor whiteout but has poor spatial resolution, failing to clearly

define the target image. The flash LADAR and the Range-GatedCamera work together to create a full Field-Of-View (FOV) inone laser shot pulse. Although this provides a high resolution, itlacks the ability to penetrate deep inside aerosol clouds becausethe light sources in these devices have to be spread into the FOVfor each shot pulse.Additionally, there are several systems on the market aimed atimproving helicopter pilot visibility. While various combinationsof Infrared (IR) cameras with synthetic terrain databases provideeffective solutions to deal with environmental conditions and pollutions,they are not always efficient in brownouts and whiteouts.Akin to driving in a thick fog with high beams, when dust cloudscontain particles of a comparable size to that of the operationalwavelength of the camera, the vision system cannot penetrate theaerosol cloud to determine if there are any objects within it.Many active sensors, such as LiDARs, have the ability to penetratefurther into brownouts and whiteouts than passive sensors.Emitting their own energy, LiDARs use a laser shot pulse togather data. Using Time-Of-Flight (TOF) – that is, measuringthe time it takes to travel back and forth from the objects/targetsin its path – the image of a flightpath or a landing site is createdby gathering the sensor data and using the dataset to create a 3Dimage or model.Because conventional LiDARs are triggered by the rising edge ofa return pulse without a separated pulse from the target buried inan aerosol, this LiDAR can only report on the range of the closestaerosol under the brownout or whiteout situation. The OPALwas, therefore, developed specifically to address this problem.How the system worksOPAL offers a higher signal-to-noise ratio than conventionalLiDAR, resulting in a higher probability of detection and/ora greater range of depth capability. Its bistatic optical designprovides robust results, and a proprietary design enables OPALto scan full FOV and acquire 3D data quickly – something traditionalactive sensors using bistatic designs have been incapableof. Using OPAL with an IR camera and a terrain database in asystem like CAE’s AVS, pilots gain a powerful synthetic visionsystem.The terrain database must be pre-populated using data collectedby the AVS system on an initial scan, or using data purchasedfrom an organization dealing in cartography, or a combinationof both. With the ability to accurately map a highly detailed andaccurate representation of the helicopter’s landing zone priorto and during descent into a brownout or whiteout, this systempresents a stable heads-up/heads-down view of the world aroundthe aircraft to the pilot for optimal situational awareness duringhover, landing, and takeoff situations.This is critical as the terrain database creates an accurate geospecificrepresentation of the world, and the information gatheredby OPAL and the IR camera is compared to the information containedwithin the database. Quite simply, the scanned areas areoverlaid onto the synthetic world and changes are quickly andeasily detected.This type of synthetic vision system provides the pilot with completeperception of the physical/geographic environment. Whencombined with a helmet mounted vision system in a heads-downdisplay, the pilot gains an almost infinite, instantaneous field ofregard, independent of the current geographic conditions.Single Print OnlyTesting for helicopter systemsInitial tests using the Aerosol Research Corridor at DefenceResearch and Development Canada (DRDC) in Valcartier, Quebec,involved comparing OPAL’s performance to that of a variety ofpassive sensors including the human eye (visible camera) and anIR camera.The aerosol chamber, which is a long, narrow building, hostedvisible and IR targets. The visible target was a board with blackand white stripes for the visible camera to focus on. The IR targetfor the IR camera was a frame with heated bars. The targetswere placed at the back of the chamber, and the doors were shutto disperse the aerosol within the chamber. The visible camera,IR camera, OPAL, and transmissometer were located about100 meters away from the chamber. When the doors opened, thesensors began gathering data within 0.5 seconds and continuedto collect data until the density of the aerosol cloud became toothin to gather further measurements.A detection factor – the defined parameter that is the ratio ofaerosol density at the moment of target detection by the OPALor IR camera to the aerosol density at the moment of targetdetection by the visible camera – was used to compare OPAL’sperformance to the passive sensors.The OPAL penetrated farther than the eye and the IR camera undersand, dust, and fog aerosol conditions. In fact, the OPAL was ableto see through 50 micrometers of sand dust that is 4 times denserthan what the eye penetrates, through 6 micrometers of dustwhich is 6.6 times denser than what the eye can penetrate, andthrough fog that is more than 7.6 times denser. This is attributed toOPAL’s timing discrimination, which reduces the scattering effect.Nevertheless, the results demonstrated that the OPAL can be usedto detect obstacles in brownout conditions more effectively thanthe other options tested.To further evaluate the system prototype under regular andwhiteout conditions, a test flight was carried out in February2007 at Crash Lake, just north of Ottawa, Canada. The AVSsystem was mounted under the National Research Council’sCanada Bell 412 helicopter, which then flew to a landing siteconsisting of an open field. The center of the field featured anarea with bushes and rocks, while the field was surroundedwith trees on the one side and a flat frozen lake on the other.The system was used to scan the landing site under differenthelicopter maneuvers: A push-broom scan was used in fly-byor approaching operation, and a raster scan mode was used inhovering operation.To create a whiteout condition, the helicopter hovered close tothe ground in order to generate snow clouds with its rotor motion.In this test, the OPAL, developed by Neptec Design Group, andAVS provided outstanding results. The ground and trees behind

Technology: 3D situational awarenesssnow clouds are clearly visible to pilots as shown in Figure 1.The bottom part of Figure 1 shows the side view of the 3D OPALimage under whiteout conditions.The results of the pushbroom scan clearly illustrate the 3Dlandscape of the fly-by path and the tree and obstacles on thelanding site (Figure 2). This demonstrated the OPAL’s ability tomechanically sustain the vibration during flight while integratedas the active sensor of the AVS system. It also indicated that theOPAL data and the helicopter navigation data can be sucessfullyfused together to generate geo-referenced 3D images.Gaining a clearer perspectiveA very specific application, the OPAL/AVS system was developedexplicitly to combat the detrimental effects of brownout and whiteoutconditions. OPAL’s unique capabilities provide pilots a clearview of what is in their landing zone. The visibility and situationalawareness is critical in terms of landing or taking off, therebypreventing accidents that can sometimes prove deadly.Maureen Campbell is the technicalmarketing specialist at Neptec DesignGroup. With more than 10 years of experiencein the technology industry, she workswith the research and development team atNeptec. Maureen has been with the companyfor three years. She can be reached atmcampbell@neptec.com.Figure 1Neptec613-599-7602 • www.neptec.comReferences:1. “Owning the Aviation Edge: NVGPID: A Simple Device to TrainCrucial Skills,” Army Aviation, United States Army, 2007-04, p. 22.Figure 2© 2008 OpenSystems Publishing. Not Licensed for distribution. Visit opensystems-publishing.com/reprints for copyright permissions.