WO2004106112A1

WO2004106112A1 - Device and method for vehicular invisible road illumination and imaging

Info

Publication number: WO2004106112A1
Application number: PCT/US2004/016906
Authority: WO
Inventors: Oleg Matveev
Original assignee: University Of Florida
Priority date: 2003-05-28
Filing date: 2004-05-28
Publication date: 2004-12-09

Abstract

A reduced glare imaging system (100) for motor vehicles which includes at least one pulsed light source (101). The system also includes a synchronization system (103) which has structure for obtaining a time reference (114, 104), and a trigger (102) for modulating emissions from the light source (101). The trigger (102) initiates emission of periodic light pulses from the light source (101) at fixed times relative to the time reference. The fixed times can be randomly selected or be selected based on a direction in which a vehicle using the system is moving. The light pulses can have a wavelength in the range in the visible light range.

Description

DEVICE AND METHOD FOR VEHICULAR INVISIBLE ROAD ILLUMINATION AND IMAGING

Field of the Invention

[0001] The invention relates to nighttime driving and illumination systems and methods to aid nighttime driving using pulsed laser and other non-laser sources of light.

Discussion of the Related Art

[0002] It is known that a large percentage of all nighttime car accidents occur due to inadequate illumination of the road. One of the most common reasons of crashes is because drivers are blinded by oncoming cars. The economic cost alone of motor vehicle crashes in 1994 in the U.S. was more than $150 billion and in 2000 it was more than $230 billion.

[0003] In 1996, there were more than 18,000 fatal nighttime car crashes. About 3,500 pedestrian and 368 bicyclists were killed. Although nighttime driving represents only 28 percent of total driving, it accounts for about 55 percent of all traffic fatalities. Of all pedestrian fatalities, about two-third occur at night. On a per mile basis, driving at night is more than three times as likely to result in a fatality as driving during daylight. While several factors affect these statistics, limited vision is one of the main reasons behind the high rate of accidents.

[0004] Several systems and related methods have been disclosed to improve nighttime driving safety. One method uses UN light, which is invisible for drivers and can be used with high beam headlights. This method is described in U.S. Pat. No 4,970,628 entitled "Headlamp for automotive vehicles" issued on November 13, 1990.

[0005] UN road illumination conception has several substantial drawbacks: 1. UN light does not eliminate the necessity to have at least low beam headlights in the visible region of spectrum, which can be disturbing, interfering and dangerous for oncoming cars because of impairing visibility glare.

2. Many natural obstacles on the road do not produce good yield of fluorescent radiation in the UN region of spectrum, such as human bodies, trees, tires, and stones. If a driver relies too much on the UN lamps, the driver can miss important information leading to a higher probability of crashes.

3. UN radiation can be hazardous from the environmental point of view. As known, people wear sunglasses as protection against UN radiation to eliminate this hazard. In comparison with UN radiation from the sun which is normally seen as a scattered radiation (the brightest sun is normally above us in the sky), UN radiation from cars will illuminate the eyes of pedestrians directly. The pedestrians will not see this radiation and will not close their eyes as if they were looking directly at the sun. At nighttime, the pupil of the eye at night is one to two order of magnitude larger than in the daytime. Because of this total exposure of people's eyes to UN can be much longer and more damaging. The brightness of the UN lamps is higher than the brightness of the sun and due to this, the total exposure of UN radiation per eye pixel can be one- two order of magnitude greater.

4. UN lamp introduction will require additional large expenses to install better fluorescing materials on and surrounding the roads.

5. UN lamps do not eliminate the blinding effect of early morning or evening glare from the sun.

[0006] A second method relates to infrared (LR) thermoimaging, generally in 9-10 μm region of electromagnetic spectrum. Thermal imaging has several significant drawbacks. 1. Since 9 to 10 μm radiation is 20 times longer in wavelength as compared to visible radiation, the spatial resolution of the image obtained will be 20 times worse. Currently available thermal IR imaging cameras have only about 76,800 pixels, which is about two orders of magnitude less than the number of pixels which human eyes or the best CCD cameras have. Also having such a small number of pixels it is practically impossible to build a future acceptable 3D stereoscopic vision system.

2. The road image contrast, sharpness and brightness provided by TR. thermoimaging systems depends on the ambient temperature. Objects on the road with equal temperature, for example tires, trees or stones on the road, might not be distinguishable.

[0007] Another type of invisible headlight was developed DaimlerChrysler. The DaimlerChrysler laser infrared active night vision system is similar to military laser- illuminating systems for viewing long-range details. Because infrared light is invisible for human eyes it cannot blind drivers of oncoming vehicles. Image detecting system of this device is protected by spectrally selective filter blocking visible radiation from headlamps of oncoming vehicles. Another important feature of DaimlerChrysler's imaging system is that it is activated synchronously with laser pulses illuminating the road. The gate of video camera is only open a short period of time immediately after laser pulse was fired. The duration of this time-gate can be several microseconds and because of this only limited amount of light from oncommg vehicles can penetrate to the imager.

[0008] The drawbacks of the DaimlerChrysler infrared laser road illumination and imaging system include the following:

1. Broadband radiation is used along with a small luminosity resolving power product spectrally selective imaging system. The imaging system thus acquires a rather large portion of unwanted light from headlights of oncoming vehicles with glare reducing factors of only about 50 - 100. 2. The period between laser pulses is not set with high level of precision. Therefore, when many oncommg cars are present the probability of becoming blinded is high and a driver may be forced to frequently switch off the laser illuminating system.

3. The road illumination system needs rather high energy per pulse to obtain an image which is not significantly distorted by the glare from standard headlights of oncoming vehicles.

4. The DaimlerChrysler system is not adapted for use with visible light to obtain color images.

SUMMARY OF THE INVENTION [0009] The invention relates to a reduced glare imaging system for motor vehicles. The reduced glare imaging system includes at least one pulsed light source. For example, the pulsed light source can be a laser, such as a Q-switched laser, a light emitting diode, and/or an electrode less radio frequency excited lamp. The pulsed light source can be configured as a vehicle headlight. In another arrangement, the pulsed light source can be configured as a head-mounded pulsed illuminator.

[0010] The system also includes a synchronization system which has structure for obtaining a time reference, and a trigger for modulating emissions from the light source. The synchronization system can utilize a wirelessly transmitted timing signal, such as time reference signals transmitted from a global positioning satellite system (GPS), a global navigation satellite system and an earth based time reference station. The timing signal can initiates emission of periodic light pulses from the light source in fixed time intervals relative to the time reference. The time intervals can be arbitrarily selected or have a predetermined duration. [0011] The light pulses can have a wavelength in the range of 0.19 μm to 5 μm, including the visible light range of from 400 nm to 750 nm to obtain color images. The average power of the light pulses can be less than 10 W, such as 1 W, 500 mW, 100 mW, 10 mW, 1 mW and/or 500 μW. In one arrangement, the period between light pulses can be constant for a plurality of vehicles. In another arrangement, the period between light pulses can be constant for all vehicles having imaging systems which are tuned to a frequency which is common to all vehicles.

[0012] The system also can include an imaging device for receiving light scattered from objects illuminated by periodic light pulses. The imaging device can be gated to receive the scattered light for defined gating periods. Each gating period can commence when a correlating periodic light pulse begins and can have a duration approximately equal to the sum of (2Ds/c) + ATPU_LSE, where AT_PUL_SE is a duration of at least one of the periodic light pulses, Ds is a distance correlating to a maximum desired observation range, and c is the speed of light. In another arrangement, the gating period can have a duration approximately equal to 2(D_B-D[)/C + AT_PUL_SE where _B is a distance correlating to a desired observation range maximum, D_L is a distance correlating to a desired observation range minimum. In yet another arrangement, each gating period can commence at a time approximately equal to + 2D_L/C and finish at a time approximately equal to 2Dβ/c + AT_PUL_SE, where t, = a time when a correlating one of said periodic light pulses begins, D is a distance correlating to a desired observation range minimum, D_B is a distance correlating to a desired observation range maximum, and c is the speed of light.

[0013] The imaging detector can have a luminosity-resolving power product of at least 10⁴ cm² sr. The imaging detector can be any suitable detector, such as an atomic vapor ultra narrowband imaging detector, a molecular vapor ultra narrowband imaging detector, an atomic magneto optical filter, a molecular magneto optical filter, a spectral hole burning filter, an image intensifier, an electron bombardment charged coupled device, or a resonance ionization imaging detector. The system also can include a display for displaying images contained in received scattered light.

[0014] Each of the gating periods can commence when a correlating one of the periodic light pulses begins. Accordingly, fixed times can be defined by time slots, each time slot having a duration equal to at least one gating period. The duration of time elapsing between a first one of the periodic light pulses and a next one of the periodic light pulses can be greater than the product of any number from 100 to 50,000 and the duration of the time slot. The imaging device can include an imaging detector for obtaining object images, and the imaging detector can detect the object images during each of the defined gating periods.

[0015] The system of also can include a suitable light filter. The light filter can be colored glass, an acousto-optic filter, a Liot type filter, an atomic resonance fluorescence imaging monochromator, a magneto-optical filter, or an interference filter.

[0016] The imaging system can be mounted to a vehicle wherein the trigger provides a particular time interval for the fixed times, whereby the imaging system emits light pulses which are not visible by unaided human vision during the time interval to signify an emergency condition. The emission of the invisible light pulses during the particular time interval can be detectable by an emergency service and can be detectable over a distance of at least 1 km. The particular time interval for the fixed times can be provided by the trigger upon the vehicle being operated while not being supplied a predetermined item or wherein the predetermined item is a unique key or a password.

[0017] The fixed times can be allocated between different groups of vehicles, such as when one buys an imaging system the fixed time can be allocated by some authority or a vendor. Different fixed time can be allocated for different types or makes of passenger vehicles, for police, for ambulances, and other vehicle classes or types. In another embodiment, the fixed times are allocated for different directions where the vehicles are moving, such that as the vehicle changes direction the fixed time can automatically change. In another embodiment, the different fixed times are allocated for different roads.

[0018] Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. The particular embodiments discussed below are illustrative only and not intended to be limiting. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a schematic view of an imaging system for object illumination and imaging, in accordance with an embodiment of the invention.

[0020] FIG. 2A is a timing diagram representing illuminating pulses and gating periods associated with an exemplary imaging system in accordance with an embodiment of the invention.

[0021] FIG. 2B is an exploded representation of illuminating pulses of FIG. 2 A.

[0022] FIG. 3 is a timing diagram representing illuminating pulses and gating periods associated with an alternate embodiment of an exemplary imaging system in accordance with the invention.

[0023] FIG. 4A is a diagram illustrating potential directions of travel which are associated with time slot groupings in accordance with the present invention.

[0024] FIG. 4B is a diagram illustrating roads which are associated with time slot groupings in accordance with the present invention.

[0025] FIG. 5 is a timing diagram representing exemplary time slot groupings in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The invention relates to an imaging system for motor vehicles. The imaging system includes a pulsed light source which emits electromagnetic pulses in one or more parts of the light spectrum, including the visible light spectrum. Objects receiving photons from the electromagnetic pulses producing scattering. Scattered radiation is received by the imaging system during specific light reception gating periods and processed to provide accurate images of the objects radiated. For example, the imaging system can provide accurate images of a roadway and oncoming vehicles on the roadway, preferably using visible light in a non-blinding fashion to obtain the images.

[0027] The amount of time that elapses in the light pulse cycle (period) can be divided into individual time slots. The light pulses and gating periods for each imaging system can be configured to occur in one of these timeslots. Notably, the time slots can be extremely short in duration so that a great number of time slots can be provided within a light pulse cycle. In particular, there can be significantly more than 100 time slots. For example, there can be more than 20,000 time slots in each cycle. Accordingly, a large number of imaging systems can operate in different time slots, thereby virtually eliminating glare being between oncoming vehicles. A timing signal, such as a RF timing signal, can be used by the imaging systems to keep the imaging systems synchronized. Light Pulse Generation and Detection

[0028] Referring to FIG. 1, a schematic view of an imaging system 100 for object illumination and imaging according to an embodiment of the invention is shown. The imaging system 100 includes a pulsed light source 101 which provides a light pulse 110. Light 110 is scattered by objects, such as automobile 111, to generate scattered light 113. The pulsed light source 101 can be positioned anywhere on a vehicle (not shown). For example, in one arrangement the pulsed light source 101 can be configured as a vehicle headlight. In another arrangement, the pulsed light source 101 can be positioned on the roof of a vehicle. In yet another arrangement, the pulsed light source can be worn on a human body, for example attached to head gear.

[0029] The pulsed light source 101 can be any source of pulsed light which generates light in a spectrum which is visible or invisible to the human eye. For example, the pulsed light source can generate light having a wavelength approximately in the range from 0.19 μm to 5 μm. This range includes the visible light spectrum, which is generally from about 0.4 μm to 0.75 μm. Color imaging information can be advantageously obtained from systems according to the invention when the pulse light source 101 provides visible light.

[0030] An exemplary pulsed light source 101 can be a laser, for example a Q-switched laser, a pulsed laser diode, a pulsed arc discharge xenon lamp, an electrodeless discharge lamp, an electrodeless radio frequency excited lamp, a light emitting diode, or other suitable source. If a laser generator is used as a pulsed light source 101, its output may be coupled to a fiber optic, a light pipe, or other equivalent device known by those skilled in the art to uniformly illuminate a target area and to eliminate the undesirable side effect of laser speckles.

[0031] The light 110 generated by the pulsed light source 101 can generally be pulsed at any repetition rate. In one arrangement, the light 110 can be pulsed at a repetition rate which is greater than a reciprocal time associated with eye inertia. For example, a repetition rate of 16 - 24 Hz can be used. Further, the duration of the pulse, or pulse width (AT_PU_LSE), can be chosen to be very short, such as from several femtoseconds to several microseconds. In any case, ATPU_LSE should be shorter than about Ds/c, where s is a desired illumination distance in the field of observation for the imaging system 100, and c is the speed of light. [0032] An imaging device 112 is provided to detect the scattered light 113 and form an image therefrom. As noted above, imaging device 112 can be mounted at or near the front of a vehicle, on the roof of a vehicle, or worn on the human body. In one arrangement, the imaging device 112 can include a lens assembly 108 and an image converter 106. The imaging device 112 optionally can include an imaging detector 107 which intensifies the scattered light 113 to improve the quality of received images and to perform gating of imaging information. Further, a light filter 109 also can be provided. The light filter 109 can be colored glass, an acousto-optic filter, a Liot type filter, an atomic resonance fluorescence imaging monochromator, an atomic or molecular magneto-optical (Faraday, Noigt) filter, a low or high resolution interference filter, or any other spectrally selective imaging filter.

[0033] The light filter 109 can be used to block light which does not have a spectral composition of scattered light 113. Accordingly, only light having the spectral composition of the scattered light 113 can pass through the light filter 109 to the lens assembly 108. The lens assembly 108 can focus the scattered light 113 on the imaging detector 107, or on the image converter 106 if an imaging detector 107 is not provided. In one arrangement, the focal length of the lens assembly 108 can be adjustable to optimize imaging resolution over a range of distances.

[0034] The lens assembly can be any suitable size. Nonetheless, for a given average light intensity I_R, image quality improves as the size of the lens assembly 108 is increased. Accordingly, to achieve a desired image quality, the average light intensity of the pulses generated by the pulsed light source 101 can be lower when a large lens assembly, for instance having a 10 - 15 cm diameter, is used in the imaging device 112 as compared to a lens assembly which is smaller. For example, in the visible region of the spectrum the light intensity I_R needed to achieve an image quality which is approximately equivalent to the image quality detected with a human eye receiving a light intensity Ih can be determined by

the following equation: I_R = I_h (d_h /d_iπ)²(η_h /η_im)(βh/βi_m),

[0035] where η is the quantum efficiency of the human eye, ηi_m is the quantum efficiency

the imaging detector, β_h is the ratio of the light intensity transmitted through the optical

system of the human eye to the input intensity of the light, βi_m is the ratio of the light

intensity transmitted through the optical system of the imaging detector to the input intensity of the light, d is the input aperture to a human eye, and dj_n is the diameter of the lens. Notably, the quantum efficiency of an imaging system can be much greater than the quantum efficiency of the human eye, especially in situations when the human eye is blinded by an

oncoming vehicle. In such instances the ratio η ηi can be as small as 10^"3 to 10^"4.

[0036] If it is assumed, for example, that βh/βim = 1, and that dh /d;_n = .05, the ratio Lχto Ih can be as small as 10^"5 to 10^"7. Thus, object illumination using an imaging detector and a pulsed light source generating several watts or microwatts of power can provide image quality equivalent to, or better than, a light source having 5 to 15 watts of power when being perceived by an unaided human eye. Importantly, the light pulses can have significantly less average power than the power of average low beam headlights. For example, an average power of the light pulses can be less than 10 W, such as 1 W, 500 mW, 100 mW, 10 mW, 1 mW, or less than 500 μW. Hence, even if the light pulses are white light in the visible part of the light spectrum, such light pulses will not blind oncoming drivers.

[0037] The imaging detector 107 can be gated so that it begins receiving image data at the time that the pulsed light source 101 generates a light pulse 110. The imaging device 107 should continue receiving images for a time duration (ATQAT_E ), which is approximately equal to about (2Ds/c) + ATP_UL_SE- Alternatively, the gating period can have a duration approximately equal to the sum of [2(D_B-D_L)/C + AT_PULSE , where AT_PU_LSE is a duration of at least one of said periodic light pulses, D_L is a distance correlating to a desired observation range minimum, D_B is a distance correlating to a desired observation range maximum, and c is the speed of light.

[0038] The time slot can be repeated at fixed times. Accordingly, the imaging device will receive image data only during the optimum light reception time slot, as noted. This mode of illumination also is beneficial when it is desired to increase a number of independent time slots, or while driving in low visibility conditions, such as from fog or rain. For example, 40,000 time slots can be provided instead of 20,000. In this case, the area of observation will be in far field, which is further than the area illuminated by low beam headlights. Since the near field area is illuminated by low beam headlights, only part of the distance Ds needs to be imaged with the imaging system of the invention.

[0039] The beginning of each time slot can begin, with respect to a time reference, at a time equal to the fixed time multiplied by an integer. In a preferred arrangement, the time slots are short, non-overlapping, time intervals. The time slots can have a predetermined duration and can be reproducible with predefined time shifts with respect to the time reference. For example, if the time slot is repeated 25 times per second, the period between pulses can be 40 ms.

[0040] Further, at least one instance of a repeating time slot can be timed to begin at a fixed time relative to a synchronization signal, such as a signal providing a time reference. The time reference can be, for example, at 0.000000000 second of every new year, at 0.000000000 second of every Greenwich time new day, at 0.000000000 of each new hour, 0.0000000000 second of every minute, the beginning of each second, or any other suitable time reference. [0041] A gating device 115 can be used to gate the imaging device. In this arrangement, it is preferable that the gating device 115 be fast enough to adequately activate imaging detector 107 reception upon the light pulse being generated and deactivate imaging detector 107 reception after a time slot equal to ATQATE has elapsed.

[0042] The image converter 106 can provide images of objects, either directly from the lens 108 or from the imaging detector 107, if provided. For example, the image converter 106 can be a charged coupled device (CCD), a charge injected device (CTD) or a complementary metal oxide semiconductor (CMOS) camera which is equipped with corresponding digitizing or analog converter. If the image converter 106 is sensitive enough to detect images without use of the imaging detector 107, then a fast light shutter (not shown) may be used to gate the image converter 106 so that the image converter 106 will be open approximately during the time slot equal to AT _GATE- Fast light shutters are known to those skilled in the art, for example a Kerr shutter or a Pockels cell can be used. Pockels cells are commercially available from Cleveland Crystals, Inc., Highland Heights, Ohio.

[0043] Object images converted by the image converter 106 can be forwarded to a display 105 for image presentation. The display 105 can be any type of display which can render images. For example, the display can be a microdisplay, such as a plasma display, a light emitting diode (LED) display, a liquid crystal on silicone (LCOS) display, an organic light emitting diode (OLED) on silicon display, a cathode ray tube (CRT), or other suitable displays. The display also can be a display worn by a driver of a vehicle, such as display goggles, or the display can be a heads-up display, for instance where images are projected onto a windshield of a vehicle. If display goggles, or any other type of head-mounted display is used, a stereoscopic image of the road can be obtained by using two imaging devices, one on each side of a vehicle. Accordingly, separate images can be generated for each side of the vehicle. Accordingly, images from the left side of the vehicle can be transmitted to the left eye and images from the right side of the vehicle can be transmitted to the right eye.

[0044] A trigger signal source 102 can control the gate timing of the image converter 106 and/or the imaging detector 107, if provided. The trigger 102 can be operatively connected to a synchronizing unit 103. The synchronizing unit 103 can include synchronization circuitry for maintaining time synchronization. Further, the synchronization unit 103 can include a processor for executing software algorithms, and a data storage upon which data and software programs can be stored.

[0045] The synchronizing unit 103 can provide a synchronizing signal to insure that the trigger 102 simultaneously activates the pulsed light source 101 and the gating device 115, thereby keeping the pulsed light source 101 synchronized with the image converter 106 and/or the imaging detector 107. For instance, if a laser is used as the pulsed light source 101, the synchronizing signals can be used to trigger a Q-switch element associated with the laser. If the laser is activated by a second laser, such as pulsed semiconductor laser or a pumping laser, the synchronizing signals can be used to trigger the second laser.

[0046] A receiver/timing signal processor (receiver) 104, which is operatively connected to an antenna 114, antenna array or satellite dish, can be provided. The receiver 104 can receive radio frequency (RF) timing signals and provide these signals to the synchronizing unit 103 for use in timing the pulsed light source 101 and the gating device 115. For example, the synchronizing unit 103 and/or receiver 104 can include an internal oscillator and software algorithms that process the RF timing signals received by receiver. There are a number of timing signal references from earth based time stations that can be used. For example, the RF timing signals can be timing signals received from either of the National Institute of Standards and Technology (NIST) time stations near Fort Collins, Colorado (WWV and WWVB) or the NIST time station in Kauai, Hawaii (WWVH). The timing signals transmitted by WWV and WWNH are specified as having a tolerance which is less than one microsecond at the transmitter site with reference to Coordinated Universal Time (UTC).

[0047] Timing signals also can be provided in desired geographic regions, such as large metropolitan areas, with the use of a local positioning system. A local positioning system can comprise three or more local transmitters winch can emanate RF signals carrying timing information and data from which synchronization times can be determined.

[0048] In another example, the RF timing signals can be timing signals received via a modern Global Positioning Satellite (GPS) receiver, which can provide even greater time synchronization precision. For instance, RF timing signals can be received from the United States GPS system, the Russian Global Navigation Satellite System (GLONASS), and/or any another global positioning system. Modern GPS receivers can produce time synchronization with a standard deviation often nanoseconds or less. Such receivers are available from a number of commercial providers, such as TrueTime, Inc. of Santa Rosa, CA. The use of GPS or GLONASS also can have the added benefit of providing vehicle location and tracking information. The use of GPS and GLONASS for providing vehicle location and tracking information is known to those skilled in the art.

[0049] In operation, imaging systems which are installed in vehicles can generate and receive uniquely timed light pulses. Accordingly, light pulses generated by a first vehicle will not overlap with light pulses generated by a second vehicle, and thus will not arrive at the second vehicle while the second vehicles imaging detector is activated to receive light. Likewise, in the case that the second vehicle uses a gated image converter in lieu of an imaging detector, light pulses from the first vehicle will not arrive to the second vehicle while the shutter of the gated image converter in the second vehicle is open. Accordingly, the amount of light received from other vehicles can be minimized, thereby reducing glare caused by the lights from other vehicles.

[0050] A diagram representing an exemplary pulse timing chart 200 is shown in FIG. 2A. The timing chart 200 shows a plurality of light pulse streams Si, S , S₃, S_n, each of which can represent the uniquely timed light pulses 202 generated by a different imaging system. The pulse streams Si, S , S₃, S_n can be synchronized using a time reference 206, such as an RF timing signal. The pulse timing chart 200 also shows the gating period (AT_GA_TE) 204 associated with each pulse 202. For instance, pulse stream Si includes light pulses P_1-sl, P_2-sl, P _-Sl, P_n-si and gating periods Gι-_Sι, G _-sl, G_3-sl, G_n-Sι, pulse stream S₂ includes light pulses Pι. s2_> P2-S2, P3-S2, Pn-s2 and gating periods Gι_-s2, G _-s2, G_3-s2, G_n-_S2, and so on. As noted, each gating period can begin when the pulse with which the gating period is associated begins.

[0051] Referring to FIGS. 2A and 2B, the time that elapses between the end of a gating period for a particular light pulse and the beginning of a next light pulse being generated, such as a light pulse generated in another light pulse stream, can be referenced as idle time

(ATID_LE)- Accordingly, the duration of one time slot (ATz) can be defined as Tz ~ ATGATE + AT_IDLE- Further, the time for one complete cycle in a light pulse stream can be defined as AT_CY_CLE, where AT_CYCLE can be measured as the time elapsing between the start time of a first light pulse and the start time of a second light pulse in the same light pulse stream. Ideally, assuming one pulse stream can operate in each time slot, the maximum number (Ns) of pulse streams that can operate without an overlap of gating periods can be determined by the number of time slots available. The number of time slots available can be determined by the formula Ns = AT_CYCLE/ AT_GATE- However, this formula assumes absolutely precise synchronization of light pulses and gating of the imaging detector and/or imaging converter.

[0052] Alternatively, the equation N_s = AT_CYCLE /(AT_GATE + ATIDLE) = ATCYCLE/ AT _τ can be used to determine the maximum number of time slots, thereby allowing for variations in timing signals and synchronization among imaging systems. For example, if AT_GAT_E ~ 1-2 μs, an appropriate value for AT_IDLE m y be 100-400 ns. It may be more desirable to make ATQATE and ATIDLE much shorter to maximize Ns. For instance, if AT_CY_CLE is 50 ms and ATz = 5 μs, lxlO⁴ time slots are provided and lxlO⁴ pulse streams can operate without overlap of gating periods. If AT_CYCLE is 50 ms and ATz ~ 2.5 μs, 2xl0⁴ time slots are provided and 2xl0⁴ pulse streams can operate without overlap of gating periods. Assuming an operational range D of 300 m, AT_CYCLE = 50 ms, AT_PULSE = 50 ns and AT_IDLE - 10 ns, 2.42xl0⁴ time slots can be provided. Notably, ATP_ULSE can be even shorter, for example as short as 10 ns.

[0053] It may appear that a pulse width AT_PULSE of 10 ns would not give adequate image quality because for every second of operation only 200 ns of image data for a particular point in a road is received, assuming AT_CYCLE is 50 ms. However, the distance of effective illumination does not correlate to pulse width. Accordingly, a series of images which are received with a repetition rate of at least 16-20 images per second will appear like a continuous image stream, even if each image gating period AT_GA_TE is extremely short.

[0054] Additionally, short light pulses and short gating periods which are time shifted with respect to the light pulses can be used to improve visibility of objects or a roadway when the visibility is deteriorated due to clouds, fog, dust, or any other airborne molecules or particulates which can scatter light (hereinafter referred to as particulates). In operation, the short gating periods can be used to reduce or eliminate the reception of light which has been scattered by the particulates. In particular, the gate can be timed to close immediately after receiving light scattered by objects being illuminated, but before significant radiation from light scattered by the particulates is received. In consequence, the use of short light pulses and gating periods can provide much higher image quality when airborne particulates are present. For example, a pulse duration (AT_PULSE) which is less than Ds/c can be advantageous. [0055] As noted above, the light pulses can be synchronized using RF timing signals. For example, the light pulses emanating from an imaging system in a vehicle can be timed so that each light pulse and its associated gating period occur within a time slot AT_Z allocated for the particular vehicle. This allocation of the light pulses into defined time slots prevents light pulses and gating periods from overlapping into multiple time slots. Accordingly, a pulse emanated by a first vehicle will have significantly dissipated before a gating period begins for a second vehicle, thereby significantly reducing the likelihood of the second vehicle receiving glare caused by the first vehicle. In one arrangement, time slots may be assigned for a selected groups of vehicles, for example vehicles used by the military, the government, law enforcement agencies, ambulance services, fire rescue services, tractors, and so on. Vehicles also can be grouped by the type of vehicle, for example luxury vehicles, small vehicles, large vehicles, etc.

[0056] Different time slot duration can be used for different vehicle types. For instance, the duration of a time slot AT can be 2-3 times longer for emergency vehicles as compared to other types of cars. Correspondingly the distance which is illuminated and observed in front of vehicle can be 2-3 times larger. In another arrangement, the imaging systems in different groups of vehicles can be configured to emit light pulses at different wavelengths.

[0057] In another example, it is assumed that a first imaging system is operating in a first vehicle and specified to illuminate a region in front of the first vehicle for a distance (Ds) of 300 m. It is also assumed that the light pulses are synchronized with the UTC. Accordingly, the gating period AT_GATE for the first vehicle should be (2 x 300)/(3 x 10⁸) = 2 x 10^"6 seconds. Further assume that the imaging system generates a light pulse having a duration AT_PU_LSE ⁼ 100 ns and a repetition rate (R_c) of 25 Hz. Further, assume that the idle period ATI_DLE is significantly shorter than the gating period AT_GATE so that the time slot ATz is approximately equal to AT_GAT_E- Accordingly, the probability (P_m) of the first vehicle meeting an oncoming second vehicle which emanates light pulses during the gating period of the first vehicle is given by the equation P_m = AT_GATE R_c = (2 X 10^"6) x 25 = 5 x 10^"5 . In other words, approximately one out of 20,000 cars will emanate a light pulse which may be detected by the first illumination system during a given gating period.

[0058] Next, assume that R_M is the average rate of the first vehicle encountering a second vehicle which has the same type of illuminating system and which operates in a randomly selected time slot. Further, assume that T_TR represents the amount of time the first vehicle is being operated on the road. Accordingly, the probability (P_m) of the imaging system of the first vehicle receiving significant glare at least once from light pulses of the second vehicle can be estimated by the equation P_m = ATGate cTτ_R. _M, where P,„ < 1. Hence, the likelihood of a vehicle receiving significant glare from another vehicle's illumination system is extremely low.

[0059] In contrast, if the pulses are not synchronized into time slots, such as those synchronized with a UTC time reference, the equation for the probability (P_m) of a first vehicle receiving significant glare from an oncoming second vehicle will be different. In this case, the probability P_m should be multiplied by the number of pulses (Np) emanated by the second vehicle as it approaches the first vehicle. Np can be determined by equation Np = [Ds/(vι + V₂)] R_e (where ; + ₂ is the mutual velocity of two cars towards each other). Depending on the mutual velocity of cars, N may vary. For example, assume that Ds = 250 m, v; = 20 m/s, v₂ = 10 m/s and R_c = 50 Hz. hi this example N = 416. Hence, in comparison to a situation when two approaching vehicles emit light pulses in pre-defined time slots, the probability of glare increases significantly when pre-defined, synchronized time slots are not used. Accordingly, the use of a timing signal for pulse synchronization substantially decreases the probability of an imaging system receiving glare from an imaging system of an oncoming vehicle. Imaging Detector Considerations

[0060] The Doppler effect caused by vehicles moving toward each other is preferably considered when implementing the invention. In particular, the minimal detection bandwidth which is required for the imaging detector 107 to detect a particular frequency of light can be estimated from the amount of frequency shift that is likely to occur due to the Doppler effect (Doppler shift). The Doppler shift can be determined by the equation Δ v = 2 v (V/c)= 2V/λ,

where vis the frequency of the light, Δ v is the change in frequency of the light, Fis the relative velocity of the vehicles with respect to each other, and λ is the wavelength of the light. For example, if the maximum velocity of each of two vehicles as they approach each other is 50 mph, the relative velocity between the vehicles is V= 100 mph (44.7 m/s) since the cars are moving toward each other. If the wavelength (λ) of the light pulses emanated by a first vehicle are 700 nm, the Doppler shift Δv associated with those light pulses computes to be 127.7 MHz. If the wavelength (λ) of the light pulses emanated are 1500 nm, the Doppler shift Δv is 59.6 MHz. Further, the Fourier transform of short light pulses can be evaluated and taken into consideration. Accordingly, for this example, a detection bandwidth of 100 MHz - 300 MHz will be adequate if pulses with duration 1 to 10 ns are used.

[0061] The resolution R of an imaging detector is equal to λ/Aλ, where λ is the wavelength of the light pulses being detected and Aλ is variation in wavelength due to Doppler shift. It is preferable that the imaging detector have a resolution of approximately R = c/2N or 3.35 x 10⁶ in the example. Further expanding the example, if the area of the imaging detector is approximately 3 to 5 cm² and the field of view is 1 - 2 steradians (sr), it can be estimated that the ideal luminosity-resolving power product (LRPP) for imaging a moving object using a very narrowband light pulse is approximately 10 - 10 cm sr. A number of imaging detectors which provide the necessary LRPP are currently known to those skilled in the art. [0062] In one arrangement, the imaging detector 107 can be a resonance ionization imaging detector (RIID). A suitable RILD is disclosed in U.S. Patent No. 6,008,496 to Winefordner et al., which is incorporated herein by reference. When a RIID is used, the RIID can be activated to detect images when the atoms of an atomic vapor in an RIID cell are excited into their Rydberg states. To decrease or eliminate the RIID noises, atoms can be excited into Rydberg states with a lifetime which is more than 2D c. h the case, a high voltage pulse, for example 1 to 50 kV, can be applied when the λ₂ pulse is ended. To excite the atoms into their Rydberg states, the atomic vapor can be illuminated by a trigger light source which emanates light having a wavelength of λ₂. For example, if Cs is used for the atomic vapor, the wavelength λ₂ can be about 535 nm to 510 nm to excite one or several Rydberg states.

[0063] Hence, the pulsed light source 101 can generate narrow band light pulses which are tuned to an appropriate resonance transition for the atomic vapor within the RILD cell. For example, cesium (Cs) vapor has resonance transitions of 894.35 nm and 852.11 nm, rubidium (Rb) has resonance transitions of 794.76 nm or 780.02 nm, potassium (K) has resonance transitions of 769.90 nm or 766.49 nm and mercury (Hg) has a resonance transition of 253.7 nm and a non-resonance transition 438.5 nm. In order to effectuate the gating action in the RHD, the trigger light source can be pulsed for a length of time equal to about ATG_ATE- It should be noted that any other atomic or molecular vapor which can selectively absorb specific frequencies of light can be used and the present invention is not so limited.

[0064] Notably, the RIID can provide spectral selection since the atomic vapor absorbs fairly narrow bands of light which correspond to the resonance transitions. For example, the RΠD can have a selection bandwidth can be approximately from 200 MHz up to 1 GHz. Accordingly, filter 109 is not required if a RIID is used, which can be beneficial since filters are usually limited as to the amount of LRPP. For example, filters such as acoustooptic filters, can pass a maximum LRPP of approximately 3 x 10³ cm² sr. As noted, the RIID has a much greater value of LRPP, which reduces image distortions, noise and glare from oncoming vehicles, thereby providing images with higher quality.

[0065] The ability of the RIID or other imaging detectors to process images from light which has a very narrow frequency bandwidth provides further advantages. For example, the probability of a first vehicle having a first imaging system receiving glare from a second vehicle having a second imaging system can be reduced by operating the first and second imaging systems at different frequencies. Accordingly, the first imaging system can be configured so that light pulses emanating from the second imaging system are not detectable by the first imaging system, and vice versa. In this manner, different light pulses can be used by different groups of vehicles to expand the number of vehicles that can use the imaging systems without excess glare being generated. If, for example, the imaging device has a bandwidth approximately 300 MHz, and the center frequency has a wavelength anywhere in the spectral range 1.52 μm - 1.76 μm, almost 90,000 independent spectrally separated channels may be provided to decrease the probability of the imaging system receiving glare from oncoming vehicles. Thus, combining spectral selection with time slot allocation substantially decreases the probability of an imaging system receiving glare from an imaging system in another vehicle. Combining the above spectral selection example with our previous time slot example, the total probability of encountering a vehicle operating with an imaging system operating in the same time slot and at the same wavelength will be 1/(90,000 x 20,000) = 5.55 x 10^"10. Notably, the reciprocal number of this probability is at least three orders of magnitude greater than total number of cars on the Earth.

[0066] Other imaging detectors can be used and the invention is not limited to a RIID. For example, the imaging detector can be an atomic and/or molecular vapor ultra narrowband imaging detector, an atomic and or molecular magneto optical filter. Regardless of the type of imaging detector which is used, images captured by the imaging detector 107 can be utilized for any number of purposes. For example, as noted, the images can be presented on a display 105. The images also can be stored to a storage medium. For example, the images can be stored to a hard disk drive, a video tape, a digital video disk, or any other suitable storage suitable for storing images. Accordingly, the images can be available for viewing and analysis at a later time. The images also can be analyzed in real-time using an image processing system. For instance, the images can be analyzed and processed as part of an accident warning or accident avoidance system. Still, the images can be used for other purposes and the present invention is not so limited.

Imaging System Use as Anti-theft System

[0067] The imaging system of the present invention may also serve as an efficient emergency notification system and/or antitheft system. In particular, a vehicle can be pre- configured to emit light pulses in a specific time slot if it is detected that the vehicle has been stolen, or if there is some other emergency situation. For example, the light pulses can be emitted in the specific time slot if a unique key has not been used in the vehicle ignition to start the vehicle, if a proper password has not been entered prior to operating the vehicle, or if a hazard switch has been activated.

[0068] The specific time slot can be an emergency time slot 309 as shown in FIG. 3. Light pulses emitted during the emergency time slot 309 can be referred to as emergency pulses. To effectuate the detection of stolen vehicles, or other vehicles requiring a response by an emergency service, an emergency service vehicle, watercraft, and/or aircraft (hereinafter referred to generally as emergency response vehicle) can be pre-configured to identify vehicles generating the emergency pulses. For example, an emergency response vehicle can be fitted with a suitable light detection system that detects the emergency pulses, such as an imaging device synchronized to receive light pulses emitted during the emergency time slot 309. Notably, the light pulses can be detectable at any time of day.

[0069] The light detection system also can be configured to detect light pulses over large distances. For example, the light pulses can be detectable over a distance greater than one kilometer, five kilometers, 10 kilometers, and other distances. If the emergency time slot 309 has a duration which is relatively short in comparison to a time delay between the moment an emergency pulse is generated and the moment the emergency pulse is received by a emergency response vehicle, the light detection system should compensate for the time delay when identifying emergency pulses.

[0070] For example, a light pulse (range finding light pulse) can be emitted from the imaging system of the emergency response vehicle towards a target vehicle and the elapsed time (ATg) to receive scattered radiation resulting from the illuminated object can be measured. The range finding light pulse can have a different wavelength than the light pulses used for object imaging, thereby insuring that the range finding light pulses do not create glare for the imaging system.

[0071] The time delay (AT_D) associated with the distance between the target vehicle and the emergency response vehicle can be computed by the equation ATD=AT_E 12. A processor and a data storage having a software algorithm stored thereon can be provided to compute a time delay (AT_D). For instance, the processor and the data storage of the synchronization unit can be used to compute AT_D. Alternatively, the distance (D_R) between the target vehicle and the emergency response vehicle can be determined using a range finder, which is known to those skilled in the art, and the time delay (AT_D) can be computed by the equation AT_D = D_R/c. [0072] Regardless of the method used to determine the time delay (AT_D), the time value corresponding to the moment that the light pulse was transmitted (T_TRAN) can be determined by subtracting the value of the time delay (AT_D) from a time value corresponding to the moment a light pulse is received (TRE_C), i.e. TTRAN -TRE_C-ATD- If the moment correlating to T_TRAN falls within the emergency time slot 309, then the light pulse can be identified as an emergency pulse.

[0073] In another arrangement, the light pulses can be emitted at a particular frequency (emergency frequency) to signify a vehicle has been stolen. In this arrangement, police vehicles can be equipped with a suitable light detection system which detects the emergency frequency. A light filter can be provided to block light which does not have a spectral composition of the emergency frequency. Alternatively, a RIID can be used to detect light. As noted, a light filter is not required if a RIID is used.

[0074] The present invention can also include an anti-collision option to decrease the probability of vehicles colliding. For example, the present invention can include a processor which receives vehicle coordinate data from GPS, GLONASS, WAAS, or any other suitable positioning system. Vehicle coordinate data can be provided for a vehicle with which the imaging system of the present invention is associated, and for other vehicles which are proximate to the vehicle associated with the imaging system. A software algorithm can be provided for use by the processor to evaluate the vehicle coordinate data. The vehicle coordinate data can be presented on a display. Further, vehicle trajectories can be computed and a warning signal can be generated upon predefined conditions of possible danger being present. A condition of possible danger can be, for example, a vehicle stalled on a road, a vehicle driving in an incorrect lane, or any other driving condition which can represent potential danger. [0075] hi another embodiment, groups of time slots can be allocated to vehicles traveling in a particular direction on a particular roadway. Thus, vehicles approaching each other on a roadway will utilize time slots from different time slot groups. Vehicles approaching an intersection from two different roadways can also utilize time slots from different groups. Accordingly, glare from the oncoming vehicles can be virtually eliminated. [0076] Referring initially to FIGS. 4 A and 5, the directions of travel can be divided into two or more groups. For example, the directions of travel can be divided into four directional groups 401, 402, 403, 404, with each directional group representing those directions that are within +/- 45° of a particular direction, for instance north, south, east and west. Importantly, the invention is not limited to this example. In another arrangement there can be two directional groups representing those directions that are within +/-90° of a particular direction. In other arrangements the number of directional groups can be three, five, six, seven, eight, and so on. Importantly, a great number of directional groups can be provided. For instance, if there are 40,000 available time slots, there can be up to 40,000 directional groups. It should be noted, however, that the number of time slots and the number of groups need not have a one to one correspondence because a plurality of time slots can be allocated to any directional group. Further, the time slots can be grouped in any way. For instance, time slots can be sequentially grouped. For example, the first 100 time slots can be assigned to time slot group 1, the next 100 time slots can be assigned to time slot group 2, and so on. In another arrangement, the time slots can be distributively grouped. For example, every 10^th time slot can be assigned to time slot group 1, and each time slot following a time slot in group 1 can be assigned to time slot group 2, etc.

[0077] Still, other time slot allocation systems can be used. For instance, if there are 20,000 available time slots, but only 100 time slots are needed for each roadway, 100 time slots can be allocated for that roadway while at least a portion of the remaining time slots can be left to operate in an alternate time synchronized mode, for example as described above. [0078] Vehicles traveling in a direction falling in a particular directional group can use a time slot from a group of time slots which are allocated to that directional group. For example, vehicles traveling in a direction which is within directional group 301 can use any of the time slots 511, 512, 513, 514 within a first group 501, while vehicles traveling in a direction which is within directional group 403 can use any of the time slots 531, 532, 533, 534 within a third group 503.

[0079] The imaging system can be preconfigured to associate the time slot groups 501, 502, 503, 504 with particular directional groups 401, 402, 403, 404. For example, the imaging system can receive a directional heading from a compass, WAAS, or a satellite positioning system, GPS or GLONASS, and then process this data to determine the appropriate time slot group. Further, timing signals also can be proved in desired geographic regions, such as large metropolitan areas, with the use of a local positioning system. A local positioning system can comprise three or more local transmitters which can emanate RF signals carrying timing information and data from which coordinates can be determined. [0080] In another arrangement, indicators 480, 482 can be provided in, on or proximate to roadways to provide roadway, lane and/or directional information to imaging systems. For instance, the indicators can be mounted under the roadway surface, in roadway reflector assemblies, on guard rails, on traffic signals, on street lamps, and so on. The indicators 480, 482 can propagate a low level RF signal containing roadway, lane, directional information and/or other information. The RF signal can be received by a vehicle's imaging system, for example using an RF receiver. The indicators 480, 482 can include a data storage and an RF transmitter, which can be low power. The indicators 480, 482 also can include a wired or wireless modem for communicating with a control center if it is desired that the indicators 480, 482 be updateable. Alternatively, the indicators 480,482 can include a communication port which can be accessed by a service technician. The indicators can be connected to utility power, use photovoltaic cells and a storage battery, or any other power source. [0081] In yet another arrangement, time slots can be selected manually. For example, when a driver of a vehicle changes from a first road to a second road, a driver of the vehicle can activate a switch which changes the time slot manually.

[0082] Referring to FIGS. 4B and 5, time slots also can be allocated based upon which roadway and/or lane on the roadway a vehicle is traveling. In one example, all vehicles traveling in lane 452 can use a time slot selected from the first time slot group 501, while all vehicles traveling in lane 454 can be use a time slot selected from the third time slot group 503. h this arrangement, absolute directional information is not required. Rather, only information which is relative to the road upon which the vehicle is traveling is required. Further, information relative to a lane on the road also can be provided. For example, a road may have lanes identified as northbound lanes and lanes identified as southbound lanes, although some portions of the road may follow a path that is not consistently oriented north and south.

[0083] Nonetheless, so long as vehicles traveling in a first direction on a roadway are using time slots from a different time slot group than vehicles traveling in an opposing direction on the same roadway, the probability of an imaging system in a first vehicle receiving glare from an imaging system in a second vehicle is substantially reduced. In this case, based on the direction of the road the time slot allocation will be always the same, but can be changed according a predetermined schedule or area allocation. For example, time slots can be changed when a vehicle cross a state line.

[0084] In a congested region, such as an urban area, a road may cross many other roads. Hence, in such a case it may be desirable to have a large number of groups of time slots available for use by vehicles traveling on different roadways. Further, time slots and groups of time slots can be shared by vehicles which are on roadways which do not cross near the present location of the two vehicles.

[0085] At this point it also should be noted that allocations of time slot groups for a particular roadway can change over a length of a road. For example, the time slot groups allocated for the second road 460 can be changed for a portion of the road which is at, or near, an intersection 470 of the second road 460 with the first road 450. Accordingly, if lanes 462, 464 have the same respective time slot allocations as lanes 452, 454, the time slots can be re-allocated to prevent vehicles approaching the intersection 470 on the second road 460 from causing glare for vehicles approaching the intersection on the first road 450, and vice versa.

[0086] Algorithms which determine an appropriate time slot group for a vehicle on a roadway can be processed by a control center and wirelessly transmitted to the vehicle's imaging system, or processed by the imaging system itself. For example, the synchronizing unit can include a processor and a data storage. Alternatively, a second processor and/or a second data storage can be provided in the imaging system for storing and processing data and algorithms. In any case, the algorithms can be used to process road map data and mapping coordinates, such as local positioning system data, WAAS data or GPS and/or GLONASS coordinate data, using a database to determine an appropriate time slot group for the vehicle. Once an appropriate time slot group is selected, a second algorithm can select a time slot from the time slot group if the time slot group contains more than one time slot. [0087] In another arrangement, the indicators 480, 482 can be used to provide the proper time slot information to a vehicle's imaging system. For example, the indicators 480, 482 then can sequentially assign the time slots to vehicles as the vehicles pass the indicators. In another arrangement, the time slots can be provided randomly or following some prescribed algorithm. The indicators 480, 482 can be programmed to operate autonomously using a predetermined time slot group from which to issue time slots, or the indicators 480, 482 can be communicatively linked to a control center to receive operational instructions.

[0088] As electronics systems currently are not 100% reliable, it is conceivable that an indicator 480, 482 can fail, or that a receiver or compass being used to establish direction can fail or lose communication with the imaging system. Hence, the imaging system can be predisposed to switch to a backup time slot should there be a problem identifying the appropriate time in which the imaging system should be operating. For example, a portion of available time slots can be reserved as backup time slots. Thus, one of these time slots can be randomly selected by an imaging system when the imaging system cannot otherwise determine in which time slot it should be operating. Further, the backup time slots can be utilized by vehicles operating on roads which have not yet been allocated time slot groups, for instance roads which are new or lightly traveled. The reliability of the directional systems being used and the number of roads not having a time slot group allocation should be evaluated to determine the appropriate number of backup time slots.

[0089] While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as described in the claims.

Claims

CLAIMS We claim:

1. A reduced glare imaging system for motor vehicles, comprising: at least one pulsed light source; a synchronization system including a time reference; a trigger modulating emissions from said light source, wherein said trigger initiates emission of periodic light pulses from said light source, said periodic light pulses emitted at fixed times relative to said time reference; and an imaging device for receiving scattered light from objects illuminated by said pulsed light source, wherein said imaging device is gated to receive said scattered light only during defined gating periods.

2. The system of claim 1 , wherein said light pulses have a wavelength in the visible light range of 400 nm to 750 nm.

3. The system of claim 1 , further comprising a display coupled to said imaging device for displaying images generated by said received scattered light.

4. The system of claim 1, wherein said gating periods each have a duration approximately equal to the sum of (2Ds/c) + AT_PULSE, where AT_PUL_SE is a duration of at least one of said periodic light pulses, Ds is a maximum desired observation range, and c is the speed of light.

5. The system of claim 1 , wherein said gating periods each have a duration approximately equal to the sum of 2(D_B-Dι)/c + AT_PUL_SE, where ATPULS_E is a duration of at least one of said periodic light pulses, D_L is a distance correlating to a desired observation range minimum, D_B is a distance correlating to a desired observation range maximum, and c is the speed of light.

6. The system of claim 1 , wherein each of said gating periods commences at a time approximately equal to + 2D/c and finishes at a time approximately equal to 2D_B/c + AT_PULSE, where t, = a time when a correlating one of said periodic light pulses begins, D_L is a distance correlating to a desired observation range minimum, D_B is a distance correlating to a desired observation range maximum, and c is the speed of light.

7. The system of claim 10, wherein said imaging detector has a luminosity- resolving power product of at least 10⁴ cm² sr.

8. The system of claim 1, wherein a period between light pulses is constant for a plurality of vehicles.

9. The system of claim 1 , wherein a period between light pulses is constant for all vehicles having imaging systems which are tuned to a light frequency which is common to all of said vehicles.

10. The system of claim 1, wherein said time reference is a wirelessly transmitted timing signal.

11. The system of claim 1 , wherein said time reference is a timing signal transmitted from a global positioning satellite system, a global navigation satellite system or an earth based time station.

12. The system of claim 1, wherein said fixed times are allocated between different groups of vehicles.

13. The system of claim 1, wherein said fixed times are allocated for different directions where vehicles are moving, wherein as said vehicle changes direction said fixed time automatically changes.

14. The system of claim 1, wherein said fixed times are allocated for different roads.

15. A motor vehicle, comprising the imaging system recited in claim 1.

16. A method of providing reduced glare imaging for motor vehicles, comprising the steps: receiving a time reference; triggering a light source to emit periodic light pulses at fixed times relative to said time reference; during gating periods correlating to said light pulses, receiving light scattered from objects illuminated by said periodic light pulses; and displaying images obtained from said received scattered light.

17. The method of claim 16, wherein said light pulses have a wavelength in the visible light range from 400 nm to 750 nm.

18. The method of claim 16, further comprising the step of defining said gating periods to be approximately equal to the sum of (2D s/c) + AT_PULSE, where AT_PULSE is a duration of at least one of said periodic light pulses, Ds is a desired illumination distance for the imaging system's field of observation, and c is the speed of light.

19. The method of claim 16, wherein said gating periods each have a duration approximately equal to the sum of [2(D_B-D_I)/C + AT_PU_LSE], where AT_PULSE is a duration of at least one of said periodic light pulses, DL is a distance correlating to a desired observation range minimum, D_B is a distance correlating to a desired observation range maximum, and c is the speed of light.

20. The method of claim 16, wherein a duration of time elapsing between a first one of said periodic light pulses and a next one of said periodic light pulses is greater than the product of a number between 100 to 50,0000 and said duration of said time slot.

21. The method of claim 20, wherein a duration of time elapsing between a first one of said periodic light pulses and a next one of said periodic light pulses is greater than the product of 1,000 and said duration of said time slot.

22. The method of claim 16, wherein said time reference is a wirelessly transmitted timing signal.

23. The method of claim 16, wherein said time reference is a timing signal transmitted from a global positioning satellite system, a global navigation satellite system or an earth based time station.