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Unmanned Ground Vehicle
Reconnaissance
Sensor Systems
Laboratory 1. INTRODUCTIONIncreased world peacekeeping activity has
increased the need for reconnaissance, frequent surveillance and even constant
monitoring, with reduced public acceptance of danger to peacekeepers. This may already drive the market for
advanced land vehicle reconnaissance technologies, such as those found in the
Canadian Light Armoured Vehicle Reconnaissance (LAV Recce) and other
programs. It has been commonly
speculated that future battlefield and other hot-spot situations will see
increased use of telerobotic or even autonomous vehicle systems for remote
information gathering and monitoring.
While universities, private research institutes, and even the Defence
Research Establishments have been pursuing Unmanned Ground Vehicle (UGV)
developments, UGV Reconnaissance (UGV Recce) will require surveillance
systems, including sensors, signal processing, communications and man-machine
interfaces, from those who are now developing such technologies for the LAV
market. This paper will discuss a number of
elements and technology challenges that may be important to future UGV Recce
systems, drawing on a large quantity of work that has already been done in
separate areas of autonomous vehicles (robotics) and surveillance sensor
technology. An attempt has been made
to cover a fairly broad collection of technologies, both to consider missing
background, and perhaps to point to areas of particular interest to the
intended reader. The main purpose of
this discussion paper is simply to begin exploring an area, UGV Recce, that
many may already be involved with through work on related technologies, but
which seems rather unexplored as a whole. The next section introduces UGV Recce,
with attention to the move toward unmanned vehicles and the characteristics
of autonomy. Section 3 introduces and
discusses autonomous vehicles, highlighting aspects of mobility, power and
navigation, and how technology in these areas may relate to autonomous
vehicular reconnaissance. Section 4
discusses reconnaissance sensor technologies, including sensor deployment,
and offers for consideration a few characteristics and possibilities of
command, control and communications in future UGV Recce systems. Section 5 concludes this work by
summarizing what has been discussed. 2. BEYOND LINE-OF-SIGHT RECONNAISSANCE TO UGV RECCEBeyond line-of-sight (LOS) reconnaissance
requires the ability to acquire information from an area not directly
observable from the current location.
To go beyond the current LOS one could go on foot or by vehicle. Safety issues aside, one would choose to
go by vehicle to be able to transport more surveillance, communications or
other equipment more quickly and easily, and to be able to return or move to
some other position, again more quickly and easily. Admittedly, if little equipment is needed, and one only needs
to survey an area that is literally ‘just over the hill’, it may be better to
do it on foot. It is pointed out in [1] that unattended
ground sensing is seen to be a major need by the Canadian Forces for beyond
LOS surveillance. Admittedly, this
need does not explicitly require vehicles or autonomy. However, surveillance installations in
hostile territory require initial movement to, and possibly within, that
territory. Once in place, the greater
the autonomy of the remote system, the less direct attention (monitoring/servicing)
required by personnel. Finally, it is
highly desirable that any required removal and/or relocation of surveillance
equipment does not require risk of exposure of personnel. Sophisticated land reconnaissance is
performed by sending vehicles to remote areas to be investigated. Questions that may be asked once the choice
to use a vehicle has been made include: Should the vehicle be air-borne or
land based, should it be manned or unmanned, and (in this work) how might
autonomy come into play? The
following two subsections briefly consider and propose answers to these
questions. 2.1 Unmanned VehiclesAerial land reconnaissance facilitates
rather fast, deep penetration into remote areas (ex. search and rescue
planes/helicopters). Low-level manned
reconnaissance (i.e. slow) flights can however be overly hazardous when
investigating hostile areas.
Considering a remedy to this problem, we note that an area that is
undergoing active development is that of air-borne Remotely Piloted Vehicle
(RPV) reconnaissance [2]. Without
attempting to balance an argument, it is immediately noted that unlike
powered air vehicles, ground vehicles can operate for much longer periods
(days or conceivably weeks) without servicing, while remaining completely
undetected. It would seem to be
rather difficult to sneak-up, cross front lines, perform covert surveillance
for an extended period, and finally return undetected, using an air-borne
RPV. The Light Armoured Vehicle Reconnaissance
(LAV Recce) system [3] is representative of the state-of-the-art in land vehicle
reconnaissance. The basic standalone
system consists of a manned, 8-wheeled Armoured Personnel Carrier (APC), that
has been outfitted with an extensive suite of surveillance and targeting
sensors, operator’s console and communications equipment. LOS sensors, including radar and thermal
imaging devices, can be extended on a mast to about 10 m above ground. In addition, other non-standard
surveillance equipment or techniques could also implemented on short notice,
since additional equipment would likely not affect the vehicle’s ability to
maneuver and bring sensors to bear. Considering overhead to manned ground
vehicle reconnaissance, note that in addition to armour, the LAV Recce APC
has a turret-mounted canon and machine guns, assorted protection and survival
equipment, and crew supplies for extended missions. In fact, perhaps the greatest amount of effort and cost in
developing, procuring and supporting the LAV Recce system is not the
surveillance technology, but the bringing of the operators to the
surveillance site. Unmanned ground
vehicle reconnaissance, UGV Recce, on the other hand, would not require
on-site crew, heavy armour, turret, guns, ammunition, fire-control system,
shrapnel containment and flame suppression, substantial heating and air conditioning,
survival gear or food supplies. Also,
there would be much less system weight and more free space, reducing the
vehicle profile and leaving more room for fuel, backup power, surveillance
sensors and communications systems.
Finally, the UGV Recce system could operate for long periods in the
field without service or supply, and may be left if need be, without
consideration for personnel. 2.2 AutonomyAssuming that one has an unmanned vehicle
for reconnaissance, there are different levels of autonomy that might be
desired of the system. For example, a
highly autonomous (robotic) UGV may be instructed to move about a range while
performing relatively high-level monitoring, doing further surveillance and
reporting when necessary. A less
independent system might be described as semi-autonomous, where the vehicle
is remotely guided or piloted to some degree. The UGV might automatically track a path and avoid obstacles
without supervision, but it might not ‘know’ a final destination, goal or
mission, and specific path segments along the route might be chosen and
actively supervised by the operator.
In the least autonomous mode, an operator might remotely drive the
vehicle, which would seem to be reminiscent of RPV reconnaissance
applications. This may represent the
entry level for development of UGV Recce systems. The labeling of a system as fully autonomous or
semi-autonomous, or somewhere in between, seems to depend on how much
teleoperation (real-time remote control) the system requires. It is noted that two broad areas of
autonomy appear to be available for pursuit; that of vehicular activity and
that of surveillance. This work will
not attempt analysis of an appropriate balance of autonomy between these two
areas, or to determine if there may be more levels or regimes of autonomy to
explore. (Admittedly, such analyses
might be very interesting and useful.)
Suffice it to say that there are various reasonable scenarios or
configurations for the UGV Recce system concept, and that it is also interesting
and useful to simply pick applications and system scenarios at hand. Therefore, it is noted that two items
recently highlighted in [1] as requiring unattended activity are 1) the
ability to differentiate between vehicles and personnel, and 2) 24-hour,
all-weather monitoring of perimeters, and early warning; Gross differentiation between vehicles
and personnel would seem to be an activity that could indeed be done
automatically. In fact it should not
require highly speculative future technologies. It is noted that various automatic target detection [4] and
classification [5] capabilities are already under investigation. Requirements for all weather, 24-hour
perimeter monitoring and early warning would seem to match the inherent
capabilities of an unmanned surveillance vehicle. It is noted in [1] that the LAV Recce system [3], on which the
vehicle and sensor capabilities for this UGV Recce work are heavily based, in
fact already partly meets these very needs.
The required autonomous monitoring and reporting activities could be
seen as challenging extensions of developments in commercial security robot
technology. It is again noted that the above are
simply recent applications development examples that were close at hand. However, it seems noteworthy that they are
already considered to be needed, appear achievable, and would lend themselves
nicely to desired initial UGV Recce applications. 3. AUTONOMOUS VEHICLESThe development of new autonomous vehicle
concepts and related technologies has increased dramatically over the last
decade or so. Greatly increased
high-speed computational capabilities have supported relatively high-level
autonomous road vehicle applications development, an example of which has
been described in [6]. Such work has
obvious applications to future intelligent vehicle/highway systems
development, which is documented in [7] and elsewhere. Complementary to this, the development and
proliferation of inexpensive microcontrollers, as well as novel sensors, has
supported and encouraged new low-level architectures for smaller autonomous
mobile robots [8,9]. The discussion here will be limited to
high-level considerations of autonomous vehicles, with occasional connections
made to lower-level issues where it is believed to be necessary or particularly
interesting to do so. Therefore, it
is noted that primary considerations for an autonomous vehicle include its
physical mobility, the availability of power, and the ability to guide and
control its own actions, referred to here as navigation. Points of interest in these areas are
discussed below, with the intent that they offer useful background and
perhaps spark further interest in UGV Recce systems-level considerations of
autonomy. 3.1 MobilityMobility may be defined as the cumulative
measure of agility (acceleration/deceleration), maneuverability (turning
capability), gradability (slope climbing/descending), trafficability (soft
soil, ditch/boulder crossing) and ride quality (shock/vibration
isolation). A vehicle’s required
mobility may be based primarily on only a subset of the above factors. Given two different vehicles designed with
similar capabilities in the above, the vehicle that can move more rapidly,
through terrain that comprehensively tests the corresponding factors, would
be considered to have the higher mobility. For a manned LAV Recce system, high speed
travel with high performance in all five of the above areas would seem to be
desirous (required), whereas for future UGV Recce, perhaps agility, ride
quality and top speed might be sacrificed for higher performance in the
remaining mobility factors. This is
perhaps practically realized through a few general vehicle parameters such as
size, weight, traction and ground clearance, and by a collection of specific
capabilities such as vertical stepping, climbing and ditch crossing. Certainly typical road vehicle performance
parameters such as acceleration, speed and deceleration distance could be of
significantly less importance for typical UGV Recce off-road activities. The mobility of a vehicle generally
increases with its size and number of degrees of freedom in its frame. Generally, a vehicle can overcome
obstacles of a size comparable to a characteristic dimension (say wheel
diameter for a rolling vehicle), with variation in capability determined by
the vehicle’s structural variability (degrees-of-freedom). For instance, a three-axle, highly
articulated vehicle (i.e. single-axle front, centre and rear cabs, with an
actuated joint between cab pairs), might climb over a rock about as high as a
wheel diameter, and cross a ditch about a half of a vehicle length
across. If articulations are removed,
the maximum obstacle size might reduce to say less than half a wheel
diameter, and if two axles are used (like a road car), maximum ditch crossing
width could reduce to less than a wheel diameter. Articulated vehicles are somewhat popular in planetary
exploration endeavors. A proposed
three-segment, multi-wheeled planetary rover, described in [10], has 1 m
diameter wheels, and is indeed expected to climb over 1 m diameter
obstacles. On a much smaller scale,
the 11.5 kg Sojourner rover, intended for the Mars PathFinder mission
[11], has 13 cm diameter wheels, and will also apparently overcome
13 cm obstacles. This work has so far assumed rather
conventional notions of mobility.
Specifically, proposed future UGV’s and their characteristics have
been assumed to be based on vehicles that roll. This class of vehicles includes road cars, motorcycles,
snowmobiles, tanks, and virtually all other land vehicles used today. A second class, those that step rather
than roll, are not conceptually new.
Land animals, including elephants, horses, cheetahs and humans, have
inspired efforts to develop walking vehicles. Although progress has indeed been made [12], and certainly
continues, the problem of dynamic stability is a very challenging one. As an alternative to dynamically stabile
legged motion, development programs pursuing insect-like mechanisms have
progressed further in a practical sense, by using lighter structures capable
of static stability. Essentially, if
power, computational or otherwise, runs low, the vehicle doesn’t fall
over. One example is the six legged
robot referred to as Ambler [13].
Conceived for planetary exploration, it can manage step heights of 1.5
m, but has a top speed less than 0.1 km/h.
Recent field work involving a similarly capable eight legged stepper,
named Dante II [14], saw it climb into (and out of) the mouth of a volcano in
an effort to gather data too dangerous to gather on foot. Traversal of the inner wall at the mouth
of a volcano would likely not be safely accomplished using a typical rolling
vehicle. In fact, legged locomotion
would seem to allow access to virtually all land on the earth, while a U.S.
Army study, quoted in [15], suggests that about 50% of the earth land mass is
inaccessible to wheeled or tracked vehicles. The following terrain traversal
characteristics are described mainly in terms of advantages of legged
vehicles over rolling (wheeled or tracked) vehicles. Although rolling vehicles would be the
natural extension of current LAV Recce systems to UGV Recce systems, the
legged-versus-rolling framework may help highlight considerations and desired
capabilities for all land vehicles. maneuverability/trafficability A legged vehicle is able
to move in three dimensions, while a wheeled or tracked vehicle must move in
two [16]. A legged vehicle is able to
utilize isolated footholds [12]. speed Average speed in rough
terrain is noted to be about 5-8 km/h for a wheeled vehicle, 8-16 km/h
for a tracked vehicle, and up to about 55 km/h for an animal [15]. In addition, some rolling vehicles achieve
animal speeds, but only with very high power consumption and damage to the
environment [15]. (Admittedly, many
current walking vehicles achieve speeds of only about 0.1 km/h, as noted
earlier.) efficiency De-coupling (or otherwise
minimizing) vehicle interaction with the terrain avoids unnecessary work [12]
(ex. a car suspension system). It is
noted that a leg/foot tends to step on the ground, while a wheel often
ploughs and is continually digging itself out of its own rut [17]. Superiority of one system over another may
still vary however, depending on specific foot and wheel interaction with
each soil type. vehicle vibration/shock Passive suspension, often
found on a rolling vehicle, leaves that vehicle subject to unpredictable
dynamics. Adaptive legged vehicles
are inherently actively stabilized, and can isolate the vehicle from terrain
irregularities [16], especially during fast motion. Additionally, during step height changes, wheeled vehicles may
be forced to sustain substantial shocks, whereas legs may step up/down. terrain impact Rolling vehicles cause
surface abrasion and even ploughing, and tracked vehicles typically tear-up a
surface using grousers. In peaceful
surveillance applications, or during movement between operational theaters,
it is highly desirable to avoid surface damage. During covert reconnaissance, this may be doubly
desirable. Although both legged and
wheeled vehicles may cause surface indentation, on reasonably firm soil the
legged stepping action should leave less identifiable traces, and in
difficult terrain, obstacles that can be stepped past must often be rolled
over or through. 3.2 PowerThe primary power source required for a
vehicle is strongly dictated by desired drive characteristics. A large vehicle like a manned LAV, that
moves fairly quickly, requires the high specific power of a fuel engine. If one can use a lighter vehicle and/or
accept lower speed, other alternatives, most notably electric or fuel cell
technologies, become viable. We will
not examine primary source, generation or conversion technologies, however we
will try to estimate what the power requirements might be for future UGV
Recce systems. To put power levels into perspective, we
can examine a few specifications from across a range of vehicles. Considering engine power and vehicle
weight, we note: Abrams Tank: 1100 kW,
55 t (20 W/kg), Bradley APC: 450 kW, 30 t
(15 W/kg), LAV Recce: 200 kW, 13 t (15 W/kg), road car
100 kW, 1000 kg (100 W/kg), Landscaping Tractor 15 kW,
600 kg (25 W/kg). A future
reconnaissance UGV, with a frame of a size and weight similar to one of the
above examples, would likely require comparatively less power to address its
performance requirements; there are no heavy armaments/implements and no
people to quickly move about. As an
aside, planetary exploration might be looked to as an extreme application of unmanned
low power rovers. The 11.5 kg
rover proposed for the Mars PathFinder mission [11] uses a 16 W peak
solar-electric array (1.4 W/kg), while on the other end of the weight
scale, a 1000 kg planetary explorer, proposed in [18] and similarly
elsewhere, might use a 500 W radio isotope thermal generator
(0.5 W/kg). Generation of motive power is a less than
covert operation, due to acoustic and/or thermal emissions. It seems then that the above power ranges
should represent extreme upper boundaries for continuous power for
surveillance and other equipment. In
fact, since part of an UGV Recce mission is likely to consist of extended,
isolated surveillance, energy resources should also be conserved, pushing
still harder for designs that do not require continuous high power. (Intermittent power requirements could be
allowed to exceed the maximum power available from the primary source, or
intermediate conversion system, using a large battery or other storage
buffer.) To facilitate a systems
level consideration of power, one could note some of the following power
requirements that may impact near future UGV Recce: computers If all high-level vehicle
and surveillance related activities could be handled by two high-performance
computers (2 ´ 250 W), and a two-channel
high-performance signal processing system with DSP cards, I/O and A/D
peripherals (250 W), we might estimate a continuous power of say 750 W. communications Assuming that normal
continuous reconnaissance activities use low data-rate networked
communications, perhaps only a few Watts (maximum) would be required to
sustain a radio communications transceiver.
At high levels of direct-to-operator data transmission, for example in
close-range detailed surveillance, perhaps 50 W would be required for
sustained transceiver operation. sensors At the core of current
and proposed LAV Recce systems are high resolution thermal and visible light
imagers, and some form of scanning radar unit. In addition to pan-tilt and stabilization systems, mechanical
drive is required for most land reconnaissance radar systems, and thermal
imagers typically require some form of active cooling. With these and a few other specific
systems engaged, one can expect to require say 500 W for normal
operation. Additional sensors would
of course add to this requirement. deployment While sensor (head)
deployment may not require continuous power, initial deployment and
intermittent (but frequent) adjustment could outweigh all other surveillance
power requirements. Assuming the UGV
Recce system is used in a direct-view telepresence mode, one would expect
that the distant operator would desire deployment control and speed of the
order of that required for manned vehicle reconnaissance. Experience with mast-mounted deployment
for LAV Recce suggests elevation of just the few pieces of equipment noted
above can require power of the order of 2.5 kW with a practical
telescoping mast. Calculations have
shown that this requirement is almost an order of magnitude higher than
should be expected for a loss-less drive system. One might therefore assume a future improved requirement of say
500 W - 2500 W for intermittent elevation of a sensor suite. Summing the above equipment power
requirements, one can estimate that surveillance activities might require
continuous power of about 1.3 kW, with intermittent peaks in the range
of 1.8 kW - 3.8 kW. While
intermittent peaks may not greatly affect energy reserves, it may alternatively
be possible to benefit from intermittent or extended drops in power
requirements. During low apparent
target activity it may be reasonable to power-down sensors for some period,
or to cycle them off and on in some optimum (perhaps random) manner. This energy conservation tactic could be
commanded during teleoperation, or executed by a highly autonomous system
during isolated auto-detection, tracking and early warning activities. Although power consumption may tend to
fall for any given technology, and with introduction of new operating
techniques, there are likely to be new technologies (and tasks) to add to a
future UGV Recce system, again pushing power requirements upwards. In the past, high mobility and heavy (LAV)
systems would seem to have dictated the primary power source design, with
other on-board equipment needs being secondary (and less). In the future, much less power may be
required for UGV’s, while the same or more power may be required to use the
current sensors with new ones that may become available. On-board equipment may dictate future
power requirements, with drive power being secondary. 3.3 NavigationIn the context of autonomous land vehicle
operations, navigation might best be described as encompassing the two
functions of motion planning and motion control. This very broad definition attempts to include the many
elements required to move a vehicle intelligently. Table 1, adapted from consideration of autonomous planetary
vehicle navigation [18], illustrates how these elements might be broken out
to reveal various operations and parameters.
Activities towards the left in the table are at a higher command level
than those toward the right, and are where an operator would tend to
interface with a sophisticated UGV.
Low-level interface points, toward the right in the table, would
likely be required for a near-future UGV Recce system, but would become
decreasingly necessary with progress in robotics, cybernetics, and other
areas of artificial intelligence. To
place this scheme into perspective, it is noted that somewhat mid-level (left
to right) elements, such as use of a magnetic compass, the Global Positioning
System (GPS), and dead reckoning, are central elements of current manned LAV
Recce systems [3]. Table 1: Autonomous Navigation Considerations for UGV
Reconnaissance
Navigation schemes for autonomous or
semi-autonomous vehicles are frequently arranged such that higher-level
path-planning activities specify paths to be taken, with no concern for the
path traversal (motion control). A
desired path is defined in some coordinate system, and the motion control
system steers the vehicle along the path, using some system of reference to
indicate its error in doing so.
Knowing the path in absolute world coordinates, the motion controller
could use the GPS, Inertial Navigation (IN) and even odometry to determine
its relative error in following a given path. A fairly straightforward steering algorithm can be used to
track the target path. Alternatively, an UGV might move toward a
goal without following a pre-planned path.
If a specific goal is chosen at some distant point, the UGV would
simply head toward the goal (likely measuring its progress using the GPS, IN
and odometry as before) in much the same way as a human might. Travel occurs then with little regard for
the path taken, and obstacles are simply dealt with (circumvented) as
encountered. With little
pre-planning, such techniques are often referred to as reactive or reflexive
motion control. Each of the above path tracking
approaches involves a somewhat straightforward method of approaching a goal;
the first by staying on a path, and the second by keeping a heading in the
direction of a goal point. Each
technique also requires a method for avoiding and circumventing minor obstacles,
much as a human steps to the side of a hole or rock, and deviates from his
intended direction for short periods to pass an obstacle. These obstacle avoidance techniques can
simply involve slight modification of the progressing motion using some type of
bias signal to the steering controller.
This signal can be generated from medium to low-level sensing, such as
identification of object position from image analysis, laser scanning,
infrared and acoustic proximity, and even tactile sensing. Finally, it is speculated that
complementary to the notion that planning and high-level control operations
might be augmented by operator input, the navigation system may incorporate
various aspects of behavioral control schemes [8]. For instance, if the autonomous UGV is stopped to use its radar
for surveillance, a minor detection of motion might cause deployment or
pointing of other sensors in the general direction of the detection. This would then not be a hard system
trigger for any particular action or operating mode, but simply the addition
of a parameter that influences the general scanning characteristics
(attention) of the system, which may still scan other directions and move
from location to location. Further
signals by ‘enough’ other sensors might extend the UGV’s stay in one place,
allowing for more detailed sensing, analysis and operator notification. Alternatively, the increased probability
of a threat might discourage the system from using certain types of active
sensors, encourage some sort of silent running, or even encourage a move
toward more cover. 4. RECCONAISSANCE TECHNOLOGYBeyond line-of-sight reconnaissance,
discussed earlier, may be taken in a broad sense to imply the gathering of
many types of information about an area beyond ones current location. These types of information might extend
from radar imagery, to sound, air and soil samples. Gathering data from such diverse sources not only requires
various sensors, but brings to the forefront the consideration of deployment
methods and related technologies.
Also, remote deployment, sensing and other operations seem to mandate
some consideration of other systems issues.
The following subsections briefly discuss possible UGV Recce sensors
and their deployment, and consider a few possibilities for command, control
and communications characteristics for the UGV Recce system operation. 4.1 SensorsA very common approach to sensor system
design, somewhat akin to biological systems, is to choose a suite consisting
of sensors that complement each other.
This may be contrasted with choosing a single high performance sensor,
or several sensors of a similar type.
The complementary approach not only ensures that a single failure
stands little chance of cutting-off the information gathering ability, but
also that few surveillance targets would be able to elude detection of all
sensor types. In addition, a single
high performance sensor can be prohibitively expensive, and may not be mature
enough for field applications. Sensor fusion, which may be considered to
be a similar but perhaps lower level process from data fusion, might be
described as an elegant use of complementary sensors and their outputs, with
some form of fusion process taking place close to the source. The resulting output can simplify the burden
on higher level systems (including operators), as well as simplifying systems
design. To accomplish this, one could
choose complementary devices at the beginning of the systems
development. For example, in the case
of the motion control system, infrared proximity and tactile sensors, collocated
on the vehicle, might combine their outputs, such that the higher level
system receives only a single three-state output: low (clear), close
proximity, and contact. In later
development, this one signal source can be used in obstacle avoidance processing,
in place of two. Fusion processes can
also be extended to higher-level separated surveillance sensors, or to
entirely different types of data.
There are numerous teleoperated systems (RPV’s) that have required
developers to come to grip with the remote vehicle sensor and data fusion
challenge. Recent consideration of
data fusion issues relating to teleoperated remote landmine detection are
described in [19]. The following points describe a number of
sensor types and their variants, in an attempt to cover as wide a detection
range as possible. A number of the
sensors listed may seem somewhat esoteric or simply impractical, however the
choice to list these technologies stems from a desire to encourage future systems
debate, while at the same time keeping in mind what would be possible for
future UGV Recce. Visible Light Imaging The LAV Recce system [3]
has a high-resolution visible light camera (monochrome) with zoom
capability. The camera is mounted on
a pan-tilt platform, which in turn is elevated above the vehicle using a
powered free-standing mast. Initial
UGV Recce applications could certainly utilize a similar system for
teleoperated activities, however deployment and pointing control may pose a
challenge for highly automated systems at this time. Fixed-focus roof-mounted systems would
likely represent a good entry level approach for automation. Thermal Imaging The LAV Recce system [3]
has an 8-12 um wavelength thermal imager (TI). It is mounted parallel to the visible light camera, on the same
pan-tilt platform mentioned above. A
thermal imager is a very likely candidate sensing technology for UGV Recce
applications. In fact, for automated
target detection (hot vehicles for instance) this may be the line-of-sight
sensor of choice. Intensified Light Imaging The commander’s sight on
the LAV Recce system [3] contains an intensified light imager for very low
light-level viewing. These systems
are also now becoming a common tool for the individual soldier, in the form
of night-vision goggles. Although it
is currently a valuable alternative to using much more expensive thermal
imagers, thermal imager costs are currently dropping, and any savings over
TI’s would not likely represent much of the total cost for initial UGV Recce
production systems. Stereo Vision Stereo vision is now
frequently applied in robotics developments.
It operates under the same principal as mammalian two-eye systems,
using parallax of two viewing angles to give depth information. Such a system would lend itself well
perhaps to advanced UGV telepresence applications for surveillance, in
addition to image (scene) analysis required for obstacle avoidance techniques
noted earlier. Laser Range Finding The LAV Recce system [3]
uses an eye-safe laser range finder that is mounted and aligned parallel to
the visible-light and thermal imagers, on their common pan-tilt cradle. In UGV Recce applications, such a device
would likely be used during teleoperated surveillance. However, difficulties in aiming and
interpretation of results may require modification of typical systems for
autonomous operation. Scanning Range Finding These systems, which are
scanning versions of the above, with surface profiling capabilities, are typically
used in mobile robot applications to locate and define objects at close
range. Such devices may be of value
in highly autonomous UGV Recce navigation systems. Radar The LAV Recce system uses
a 17 GHz sector scanning Doppler radar system, capable of detecting a moving
vehicle at a range from 50 m to about 20 km. The radar head is attached near the
electro-optic sensors at the top of the mast mentioned above. Radar such as this is likely to remain
desirable for teleoperated ground surveillance, and for use in early
warning. Target tracking would likely
be a more local activity for the autonomous UGV system, with range
requirements of an order of magnitude less, out to say 2000 m. It is also noted that remote or even
autonomous deployment of equipment favours simpler mechanisms, due primarily
to the difficulty in precise equipment positioning in close quarters. Fully shielded reflectors or perhaps
future phased arrays would be encouraged. Acoustic For outdoor surveillance,
acoustic sensors have been used for detection of aircraft (helicopters), and
for seismic vibration from moving ground vehicles. For silent surveillance, or more specifically early warning,
such sensors should be easily implemented in a UGV Recce system. Low frequency acoustic sensors would not
be particularly sensitive to orientation on the UGV, and seismic units could
use a fairly simple actuator for ground penetration and coupling. Multiple remote acoustic sensors might
also be ‘laid’ and left behind using the teleoperated UGV Recce system. Landmine Detection The Improved Landmine
Detection Project (ILDP) involves using a teleoperated vehicle to bring
various sensors to bear on an area of road that is suspected of being mined
[19]. In addition to a visible-light
camera for general inspection, the remote sensor suite includes a thermal
imager to examine heat flow disturbances at the road surface, a road-width
metal detector array, a ground penetrating radar array, and a thermal neutron
activation detector that can be placed over a suspect location to examine
subsurface nitrogen content. This
system may resemble near-future UGV Recce systems when they are
teleoperated. Efforts are now being
made to make the data fusion and mine detection process more automated. However, aside from visible-light and
thermal imaging, the other landmine detection technologies are not currently
well suited to off-road applications, autonomous deployment or covert
missions. The large number of buried
landmines (estimated > 100 million) may however encourage sufficient
near-term developments to make these technologies more fieldable. Chemical and Elemental The LAV Recce system [3]
is equipped with a chemical sensor and crew alerting system. A more proactive detection device is used
for dismounted point detection [3].
This would seem to be an excellent type of detection and warning
capability for an unmanned reconnaissance system. In fact, along similar lines, the teleoperated ILDP rover
mentioned above was considered for fitting of a Trace Element Detector
(TED). This device, although
currently somewhat cumbersome, uses a mass spectrometer to analyze airborne
chemical components released form air and soil samples. Teleoperated manipulation of the sampling
head could however allow point investigation of dangerous sites. Radiation The LAV Recce system is
equipped with a radiation detector [3], and alerting system similar to the
chemical sensor above.
Vehicle-mounted and tele-manipulated sensor heads could be used in
parallel with the above chemical sensing system for area and point
investigations, respectively. Nuclear Event Battlefield systems,
including manned reconnaissance vehicles, use nuclear event detectors to
trigger system protection measures, in case of a nuclear detonation. Radiation hardening and careful attention
to electromagnetic pulse shielding might be desirable for unmanned
reconnaissance, considering that UGV’s are perhaps the most desirable vehicle
to send into an escalating conflict. Biological Remote air and soil sampling
for dangerous biological agents is now desired in some conflicts. Operation Desert Storm required rapid
deployment of portable field analysis laboratories. New thin-film membrane and other bio-electrical technologies
may allow for portable detectors to be mounted to UGV’s for autonomous early
warning. Additionally, teleoperated
sampling and analysis might be performed using more elaborate equipment if
the need arises. Navigation and Sighting In addition to the more
common surveillance sensors, UGV Recce will require a number of other common
sensors for navigation and sighting operations. Navigation will likely use a magnetic compass, GPS, and
possibly a combination of odometry and inertial sensors for accurate short
term navigation estimates for motion control. Surveillance and sighting activities would certainly make use
of GPS to measure position and elevation of the UGV. Sight angle could then be measured using
inclinometers, as well as a magnetic compass for approximate azimuth. If more accurate surveying is required,
other vehicle-transportable geodetic equipment is available. 4.2 Sensor DeploymentSensor deployment for reconnaissance or
surveillance involves the bringing of a sensor head to bear on the
environment in which it is to sense.
For UGV Recce, many chassis-mounted sensors might remain deployed at
all times, while mast or manipulator-mounted equipment would likely require
some amount of extension to properly expose and orient the sensor head. Additionally, some sensors might be
particularly delicate or suffer degradation from dirt or unnecessary
exposure, and some may require vehicle isolation and active stabilization to
perform properly. The following notes
consider issues of chassis-mounting sensors, extending them to some distance
from the vehicle, and orienting or pointing them. Chassis Mounting Considering the desire
for mobility, stealth and reliability, it would seem that the ideal location
for the mounting of reconnaissance equipment would be the inside of the UGV
hull. This is of course not suggested
to be practical for many surveillance activities, but it would seem to be a
good starting point for deployment considerations. Sensors that could in fact be mounted internally include those
for UGV engine or other system status monitoring, inertial navigation,
vehicle attitude (inclinometers) and even barometric pressure. The next best mounting location, for the
same reasons as stated above, would seem to be on the outside surface of the
hull. Indeed this is a reasonable
location for many practical sensors, especially those that are
omnidirectional in nature, or that may be left in some fixed alignment. Vehicle motion control sensors for
proximity or contact could certainly be fixed to the chassis. Mobile robotic systems typically use
peripherally mounted arrays of acoustic and infrared transducers, and use
appropriate signal processing for directivity. Considering an early warning function of the UGV Recce system,
it is noted that chemical, biological and perhaps radiation sensors might not
require anything more than hard-mounting with wide-angle external exposure. Extension The need for extension of
a sensor, from the UGV vehicle to the working environment, would seem to be
about the least desirable requirement to have to meet, considering the desire
for mobility, stealth and reliability, as noted earlier. Nevertheless, most line-of-sight (LOS)
sensors will require at least some elevation above the vehicle for reasonable
performance, and any point detection activities will likely require some kind
of manipulation of a sensor head. The LAV Recce system [3] does in fact use
turret-mounted LOS sensors, including intensified-visible and thermal imagers
for driving, fire-control sighting and surveillance. However, the primary surveillance sensor
suite is mounted to the top of a free-standing telescoping mast. This power-driven mast extends from the
rear quarters of the vehicle, to elevate a radar unit, imagers and a laser
range finder, to a height of about 10 m above the ground. Such deployment generally restricts the
vehicle to stationary operation. Stationary surveillance is intended not
only to benefit sensor deployment and performance, but to facilitate covert
operations. In fact, it is highly
desirable for the reconnaissance vehicle to conceal or camouflage itself
within surrounding trees or other close terrain features. Extension and retraction of a mast or
other elevating device will likely be a significant reliability problem for
UGV Recce systems. Teleoperated
deployment in cluttered areas may suffer from lack of feedback during
extension, and automated systems will certainly have to be robust,
algorithmically as well as mechanically. In addition to typical surveillance
activities, reconnaissance may require site investigations and point
detection or sampling for chemical, biological or radiological agents, or to
move or manipulate the surroundings during the course of investigation. Fully automated manipulation in the near
future would likely be restricted to simple activities, such as driving a
coring tube into the soil, or lowering a sensor head close to the ground at
some distance from the vehicle. More
sophisticated manipulators might however be practical for teleoperated activities. Pointing and
Stabilization The difference between pointing and stabilization control is
really just a matter of degree of the same operation. Pointing control usually refers to rather
macroscopic placement and orientation of a sensor head, while stabilization
refers to keeping the sensor accurately positioned and directed on target
using some form of active motion isolation.
To facilitate rapid large-scale moves, the pointing device, or
director, many not be practically able to achieve the precision in position
or velocity control that the sensor requires. A second stage, the stabilizer, may be used to perform small
angular displacement correction, and to dampen the system to reduce angular
velocities. For line-of-sight systems, the most
common device for pointing control is the pan-tilt platform, which
facilitates yaw and pitch (azimuth and elevation) motion. For imagers, the direction and
stabilization of roll motion is usually unnecessary, since the base platform
can be designed to be acceptably horizontal, image rotation is not usually
required, and image sensors do not magnify roll disturbances. The LAV Recce [3] and other vehicular
reconnaissance systems have imagers and laser range finders mounted to
pan-tilt platforms for directing their gaze and to track targets. UGV Recce systems will also require
directors for both teleoperated and fully autonomous detection and
surveillance. Many current pan-tilt
devices and related remote operation technologies should be adaptable to UGV
activities. Further active stabilization of systems might
be performed by appropriate sensing and feed-back control of the
director. If the director
characteristics are insufficient to allow for such control, it may be
necessary to install an additional stabilizer interface between the base and
the director, or the director and the sensor head. Such feedback stabilization was not found to be necessary for
the LAV Recce system, however many other systems do in fact require such
additional complexities. Noting that
UGV Recce systems are likely to be less massive and more structurally
adaptable (flexible), it would seem prudent to expect to need to combine some
active stabilization with at least all high performance line-of-sight
sensors. Operators should have (and
may expect) performance similar to established manned systems during
teleoperation. Also, near-future
autonomous detection and tracking algorithms should not be expected to handle
image loss or distortion (ex. image blurring) better than human operators. 4.3 Command, Control and CommunicationAutonomy for unmanned vehicles and
surveillance, outlined earlier above, would seem to be encouraged not just by
the fact of the expected UGV isolation, but by the inadequacies of still
developing teleoperation technologies, limited communication bandwidth, and perhaps
even manpower constraints. On the
other hand, current technologies of autonomous systems are also far too
inadequate to allow one to simply instruct the UGV to head out into the field
and perform reconnaissance. Taking a
lead from decades of systems design for planetary exploration, a blend of the
fully independent with directly controlled (teleoperated) machine will be
necessary. Command The commander of an UGV
Recce unit will of course not be physically at the surveillance site. While lack of on-site command presence may
seem to be a drawback initially, if one can assume that teleoperation and
telepresence capabilities for one UGV Recce unit are sufficient, then in fact
a single commander might access multiple UGV’s. This not only reduces manpower requirements, but should
facilitate more rapid wide-area data acquisition with greater coordination. It was noted earlier that autonomous
capabilities in vehicular and surveillance activities will be limited in
near-future systems. In addition, it
is still an open question as to how much autonomy would in fact be found
acceptable to a commander. Perhaps it
should be expected that for single UGV applications, the commander will want
fairly direct knowledge and control (via his operator) of the vehicle movement
and the surveillance activities, and in a multiple UGV scenario, he would be
willing (and required) to give autonomy to many operations while
concentrating on the activities of one UGV in a critical situation. Control While the UGV Recce system
commander may be free to work with more than one UGV at a time, it would seem
that multiple UGV’s would require multiple operators. At the lowest levels of system autonomy,
perhaps two operators per UGV system would be sufficient; one for UGV operations
and one for surveillance activities.
Eventual elevation in autonomy levels for the vehicle and/or
surveillance activities would seem to naturally facilitate reduction to one
operator per UGV. In practical terms, one could therefore
see an initial UGV Recce system requiring two operator consoles (vehicle and
surveillance), each with a high resolution display, keypads, joysticks, and
perhaps a suite of mission recorders (VCR and data recorder). The dual console system would also seem to
offer a couple other benefits.
Firstly, single operator loads would free one ‘seat’ for observers,
namely a commander. Secondly, as
autonomy allows one operator to run one UGV Recce system, the second operator
then has the equipment to control a second UGV. This last point has yet another interesting systems
effect. Assuming sufficient network
or other communications are in place, it may be possible to pass UGV’s from
one station to another, for logistics reasons or perhaps when a control
station must go off-line. Communication Two paradigms for
tele-command of UGV Recce systems are direct transmission, and network
messaging. The first appears rather
straightforward (traditional), while the second touches on ideas of wide-area
networks and the “digitized battlefield”.
Communications schemes that tend toward this second idea have some
interesting possibilities. First of
all, one would expect that all future reconnaissance or even other military
communications systems will incorporate encryption of information that is
transmitted. With this data security
mechanism in place, compatibility with existing commercial and other
available communication links can be pursued. This would include virtually all allied satellite and land
links, for which the UGV would have to have appropriate transceivers on
board. A few other general concepts, introduced
earlier, seem to work well with this networking idea. Increased UGV autonomy allows for a
minimum of command and control transmission, and sensor fusion at the UGV
would help to keep the returned surveillance data-rate to a minimum. While an UGV can move out of range of some
given radio transmitter, low data-rate messages can be passed via network
and/or other limited bandwidth systems, regardless of physical location of an
UGV or its operators. This brings out
the idea that UGV’s could pass from one operational area to another, while
remaining under the same operator control, or being transferred to another
control station as suggested earlier. Finally, using a fairly ‘open’ type of
secure communication facilitates allied unit reception of surveillance data,
without needing full involvement in the UGV Recce system, or having to wait
for data processing. Command/control
centres may not process information with attention to items which other
locations or allied forces have interest.
A very similar idea is proposed for air-borne RPV reconnaissance in
[2], using a specialized remote access device. In any case, such a system is then perhaps more of an
information resource. Combined with
portable computing and sundry digitized battlefield equipment, isolated
sections/units/soldiers might be able to utilize surveillance information
more directly when necessary. 5. CONCLUSIONThis paper has discussed the concept of
Unmanned Ground Vehicle Reconnaissance (UGV Recce). Beyond line-of-sight land reconnaissance requires ground
vehicle activity in hostile areas, where substantial costs of the required
systems are incurred by the need to transport operators. Unmanned aerial vehicles, already in use
for land reconnaissance, would seem to have limitations for extended covert
surveillance. It is suggested that
teleoperated UGV’s are appropriate for land surveillance, and that increasing
levels of autonomy may ease the operational burden, as well as add new
capabilities. Mobility for UGV Recce is seen to be
dictated more by say maneuverability than by acceleration or speed. It is noted that the weight and primary
power for UGV Recce vehicles may be very much less than that of the current
manned LAV Recce systems, and on-board surveillance systems may therefore
require much more power relative to the total budget of future systems. Navigation, encompassing motion planning
and control, pulls together vehicular elements of the system, and is perhaps
the central location or embodiment of the characteristic of autonomy. Initial UGV Recce systems may move under
direct (teleoperated) control, however future developments may allow an
operator to issue higher-level mission goals, leaving the UGV to handle all
motion planning and execution. In addition to line-of-sight
surveillance, other UGV Recce activities may include detection, monitoring
and inspection of explosives (landmines, ordnance) and other chemical,
radiation and biological hazards. In
addition to chassis- and mast-mounted surveillance equipment, various robotic
manipulator and teleoperation technologies may then be required. Finally, although commanders and operators
will no longer be on-site, UGV Recce in fact offers expanded
capabilities. These include
coordinated, multi-UGV wide-area reconnaissance, using a single command
point, hand-off of UGV’s from one control station to another, and low
data-rate network communications for system control and reception of
surveillance data, facilitating long range operation and direct information
access by allies. 6. ACKNOWLEDGMENTSThe author would like to thank Vic
Aitken, Chris Brosinsky, Robert Chesney and Doug Hanna of Defence Research
Establishment Suffield (DRES), Blair Cain of Computing Devices Canada (CDC)
Calgary, and Phil Church and Jim Lougheed of CDC Ottawa, for reviewing the
draft paper and making suggestions to improve it. The contributions of numerous other CDC colleagues, mostly
through casual conversation, are also gratefully acknowledged. 7. REFERENCES[1] Capt.
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