Why The Guardian Alert® Uses Doppler Microwave Technology

There are various types of systems in consideration for discriminatory back up warning for trucks and automobiles. These systems must alert the driver/vehicle operator to potential collision situations while the vehicle is reversing. These are NOT back-up alarms that simply beep when a vehicle so equipped is in reverse; these are systems that warn a driver ONLY when necessary to avoid a collision.

Despite the best efforts of fleet operators and the common sense of private vehicle drivers, reversing incidents are all too common; there are about 500 fatalities each year, mostly young children. Vehicles with large blind spots to the rear, especially SUVs and vans, are becoming more prevalent in cities and suburban environments where reversing in constricted space is normal practice. The need for a technological solution to this dangerous situation has brought a number of, in our view, inadequate systems to market, some of which offer the illusion of solving the problem while only helping in marginal fashion under ideal circumstances.

As if reversing is not dangerous enough, the false sense of security that these systems give many drivers cause more accidents and in some cases more reckless reversing than with no system at all. Technology must provide a solution without adding false expectation. Currently, there are systems on the road with "holes" large enough for an adult to pass unnoticed and be run over during reversing. Other systems suffer chronic weather-related performance restrictions and need regular maintenance that is obviously not going to happen in the real world.

However, Doppler microwave radar offers excellent performance in all environments, is maintenance-free and is affordable. Also, as an additional incentive to automakers and vehicle owners, it is unobtrusive to vehicle styling as it can be hidden behind the rear bumper skin.

Sense Technologies, Inc. has drawn the conclusion that Doppler microwave radar is the only system that offers complete coverage to the rear of the vehicle without compromising detection in any way that allows people to go undetected. Additionally, it senses only diminishing distance between the vehicle and any object, because without the distance between the vehicle and object diminishing, a collision cannot occur. This is an important means by which nuisance notifications are reduced.

There are four basic areas of compromise with various back-up warning systems:

1. Environmental issues
2. Passive warning
3. Presence sensing
4. Vibration and durability issue

While each is a separate limitation, most systems suffer from more than one.

Environmental Issues cover a whole range of problems from precipitation to illumination levels, with condensation and road dirt causing the most and worst system failures and performance degradation.

Cameras and monitor systems, being optical in nature, often do not work well without sufficient light levels.  Ice, dirt and condensation may render these systems totally useless.  Condensation is a particular issue during early morning operation, and heaters are sometimes used to offset this issue. While some immediate maintenance may improve some situations, heavy precipitation may severely hinder their ability to detect or warn the vehicle operator of an obstacle in the path of a reverse-moving vehicle.

Infrared ranging systems suffer the same as cameras; optics get dirty and don't work. Cleaning without sufficient water causes scratches that over time further degrade performance.

Ultrasonic systems do not work in strong winds (over 12 mph) and suffer from the transducers "clogging up" with damp road dirt and salt. A major problem attributable to ultrasonic sensor systems having multiple transducers (currently the automakers are using such systems) is that the transducers won't all clog up at once and fail totally. If they did, the driver would stand some chance of realizing the system had problems; however, they clog up randomly during forward motion (regular driving). They fail to work (when called upon by engaging reverse) individually or maybe in pairs, but not as a whole set. For example, a vehicle equipped with the reverse sensing system suffers clogging (failure) in three sensors - passenger side outer, passenger side inner and drivers side inner. The drivers side outer is fine, and so when the vehicle is reversed back towards a flat wall, the system reports it's warnings correctly, and the driver has no idea that the system is suffering a 75% failure. Shortly thereafter, the driver backs towards a supposedly open area, unaware of a child in the blind spot behind the passenger side of the rear bumper. The three clogged transducers fail to detect.therefore, no warnings are given. Afterwards, the driver insists that the system worked just fine a little while earlier, and general testing will substantiate that statement. However, thorough testing will reveal the lack of detection on the passenger side. Ultrasonic sensors cannot self-test themselves individually. Such sensors either need to work in pairs looking at each other, or with a target behind the vehicle. Sensors that look at each other will false alarm in normal operation so they are either not arranged to see each other or are operated in a ripple (one at a time in sequence). Since the time of flight of a sound wave is slow, and the settling time of an inductive pulse circuit is long, this causes rapidly moving targets (over 5 mph) to go undetected before collision (see disclaimer #1, later).

Radar systems are unaffected by all known environmental conditions. The only exception is a metallic bumper-sticker, such as on a AAA bumper sticker (and obviously this limitation can easily be avoided), as radar cannot see through metal.

Passive warning refers to the system's failure to alert the operator or driver to a dangerous condition while reversing. Camera and monitor systems do not beep or flash lights at the driver if a target enters the field of detection. If the driver is not looking (concentrating) on the image in the monitor, and/or if the driver is distracted by other vehicles or events and fails to see the target, a collision can occur. Active warning systems beep and flash lights. They do not need to be looked at to be effective because they are audible and visual.

Passive Warning systems (cameras) stick out of the rear of vehicles and look good to the general public who understand their function and see the fleet operator making an effort towards safety. They also gain favor with fleet operators because they make the entire decision-making process of the backing maneuver be that of the operator. There is no warning issued from the system for the driver to interpret. The operator must observe the situation (as best as can be done with the system performance and environmental conditions), make a judgment, and act accordingly. If he has an accident, it's the operator's fault not the owner's. From the owner's perspective, if the system doesn't work for whatever reason, it can be observed to be not working, and the operator should act accordingly (not reverse). If maintenance has failed to keep the system in good order, the operator can see this and abort the reverse maneuver. Fleet operators like "blame-free" systems that look good to the general public. Thus, many camera systems are installed despite their failings.

Presence Sensing systems (all ultrasonic and some radar) warn of things that are there in the field of detection even if they will never, ever, collide with the vehicle. They warn of targets that are stationary, relative to the vehicle, or are moving away from the vehicle. So, if for example the ground happened to be in the field of view, the system would continuously alarm. As a result, such a system is configured not to see the ground. Then, due to the possibility of a rearward up-ramp or incline (in a driveway for example), the clearance between the lower detection edge of the ultrasonic beam or presence sensing radar is increased to about 8-inches (a 6 degree up-ramp requires 8-inches of clearance for a 6-foot detection system), and allowing for road surface perturbations and vehicle height due to variances with loading, this clearance is raised to about 10 inches. The result is that an average 200-pound adult lying face up would go undetected under the beam. Children who have slipped on wet or icy pavement trying to get out of the way of backing vehicles will go undetected.

The ultimate conclusion to this situation is that the automakers have stopped referring to these systems as "reverse warning systems" and are now called them "parking assist systems". They actively specify them as going no lower than the lowest part of the vehicle (such lowest part that is not wheel or tire-related) and no higher that the top of the rear bumper. Somewhere in the owner's manual this is explained, along with all the other disclaimers these systems require. As we all know, generally an owner's manual is not well read so it is reasonable to assume that most drivers will think that such a system provides full coverage or are unaware of it's limitations (see disclaimer #2, later). Either way, it offers no safety-related benefits to reversing towards an unseen person unless the person is standing up.

It should be noted that most presence-sensing systems installed have an OFF button that overrides and defeats the system. This is because while a vehicle is stationary, with something in the detection zone and being in reverse gear causes endless, annoying warnings. The OFF switch cancels these annoying alarms and resets to normal operation the next time reverse gear is selected. This is to help limit the "nuisance" factor, but it does nothing to cause the operator to retain confidence in the reliability of the system to warn him/her when needed.

Vibrations and durability issues are very important. Sometimes, when parked and unattended, vehicles can be damaged by other vehicles, shopping carts, etc. Tree limbs can brush the top rear edge of vans and trucks, car washing systems (especially dryers) can misalign cameras and mirrors. Cross view mirrors are bumped and put out of alignment by loading docks and other vehicles from the same fleet during off hour loading and parking.

The reliability of optical (camera and mirror) systems is impaired by knocks and bumps that go undetected until it's too late. Vehicle vibration as well as jolting from bumpy roads can also cause misalignment if the mounting structure is not robust enough. Ultrasonic and radar systems also suffer problems due to their exposure, depending on mounting location; however, radar mounted behind the rear bumper is virtually indestructible unless a serious collision causes the bumper to be smashed.All Sense Technologies sensors are encased in an almost indestructible epoxy-type resin for long-term durability.