CA1057834A - Vehicle sensing apparatus - Google Patents
Vehicle sensing apparatusInfo
- Publication number
- CA1057834A CA1057834A CA218,238A CA218238A CA1057834A CA 1057834 A CA1057834 A CA 1057834A CA 218238 A CA218238 A CA 218238A CA 1057834 A CA1057834 A CA 1057834A
- Authority
- CA
- Canada
- Prior art keywords
- vehicle
- antenna
- signal
- vehicles
- area
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08G—TRAFFIC CONTROL SYSTEMS
- G08G1/00—Traffic control systems for road vehicles
- G08G1/01—Detecting movement of traffic to be counted or controlled
- G08G1/04—Detecting movement of traffic to be counted or controlled using optical or ultrasonic detectors
-
- G—PHYSICS
- G08—SIGNALLING
- G08G—TRAFFIC CONTROL SYSTEMS
- G08G1/00—Traffic control systems for road vehicles
- G08G1/01—Detecting movement of traffic to be counted or controlled
- G08G1/015—Detecting movement of traffic to be counted or controlled with provision for distinguishing between two or more types of vehicles, e.g. between motor-cars and cycles
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Traffic Control Systems (AREA)
- Geophysics And Detection Of Objects (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An improved road vehicle sensing system. The system has an antenna to collect microwave temperature signals from an area of a roadway. The system also includes signal processing means for providing an indication as to if there is a vehicle in the area depending on the signal received.
The system can provide a total count of vehicles received and can also differentiate between types of vehicles.
An improved road vehicle sensing system. The system has an antenna to collect microwave temperature signals from an area of a roadway. The system also includes signal processing means for providing an indication as to if there is a vehicle in the area depending on the signal received.
The system can provide a total count of vehicles received and can also differentiate between types of vehicles.
Description
~5~
`
; FIELD OF THE INVENTION
This invention is directed toward improved road vehicle sensing apparatus.
BACKGROUND OF THE INVENTION
Vehicle sensing apparatus is employed to provide a count of vehicles using a road or highway, usually within a specific time interval. These vehicle counts can be employed ;~
to provide vehicle traffic pattern data and/or to control the flow of vehicle traffic, locally or regionally, via traffic signals. The sensing apparatus can also be employed to provide data regarding the type and/or speed of each vehicle sensed if ~ desired.
j Many vehicle sensing systems, for carrying out the above, are known. Some systems employ buried magnetic loops or pneumatic tubes and plates. Others employ various sonic or ~ optical means. Still others employ electromagnetic waves -1 reguiring both a transmitter and a receiver. Thçse known systems are however, generally relatively complicated, expensive and bulky. In addition, the known systems are n~t always reliable in use under all operating conditions.
STATEMENT OF THE INVENTION
It is the purpose of the present invention to provide an improved vehicle sensing apparatus which is relatively simple and compact. It is a further purpose to provide an improved vehicle sensing apparatus which operates reliably under all weather conditions, day or night.
The improved road vehicle sensing apparatus of the present invention is particularly charac~erized in that it employs the principle of microwave radiometry.
jl~ 30 Microwave radiometry can be defined as the passive .1 .
detection of signals of thermal origin having wavelengths .
~.
.~ .
... ~ . .. . . -between one hundred centimeters and one millimetl~r. An ultra sensitive receiver is used to detect the signals picked up by a directional antenna, the beam of which is directed at the area to be observed. The magnitude of signal received can be generally said to be proportional to the temperature of, and reflected by, the area, or object in the area, observed.
As applied to vehicle sensing, the temperature signal received from an empty area of roadway would be different from the temperature signal received from a vehicle in the same roadway area since the vehicle reflects the sky temperature to a greater degree than the roadway. It is this principle in general which is employed in the present invention to provide an effective, reliable, vehicle sensing apparatus.
Broadly, the vehicle sensing apparatus of the present invention comprises an antenna for collecting microwave tempera-ture signals from an area of roadway, and means connected to the antenna for processing the collected signals to indicate , the presence of a vehicle in the roadway area due tG a change . , .
q in the magnitude of the temperature signals collected which change is caused by the presence of the vehicle in the roadway ~-area. ;
The processing means preferably includes means ~or detecting the amplitude of the signal to provide an indication of the size of vehicle sensed.
.
The processing means also includes means for providing a count of the vehicles sensed.
BRIEF DESCRIPTION OF THE INVENTION
The invention will now be described in detail having reference ta the accompanying drawings in which:
Figure l is a schematic view of a simple sensing . . .
~ apparatus of the present invention;
.
1~5~
Figure 2 is a schematic view of a more sensitive sensing apparatus;
Figure 3 is a schematic view of a preferred sensing apparatus;
, 5 Figure 4, appearing on the same sheet as Fig. 1, is a graph illustrating the nature of the signals received by the `~apparatus;
Figure 5~ appearing on the same sheet as Fig. 1, is a schematic view of one form of sensing apparatus for sensing vehicles in a plurality of lanes; and Figure 6, appearing on the same sheet as Fig. 1, is a schematic view of another form of sensing apparatus for sensing vehicles in a plurality of lanes.
DESCRIPTION OF A PREFERRED EMBODIMENT
:1 -1~ The vehicle sensing apparatus 1 of the present invention, can, in its simplest form as shown in Fig. 1, comprise a directional antenna 3 mounted above a road or ;~
' highway 5 for picking up temperature signals fro~ an area 7 of the highway 5, and means 9 for processing the received signals. The processing means 9 essentially comprises, a signal detector 11, connected to the antenna 3, ~or detecting the temperature signals, an amplifier 13 for amplifying the detected signals, a threshold circuit 15 for passing signals of a predetermined magnitude indicating the detection of a vehicle, and a counter 17 for providing a count of the detected vehicles. ~ -The area 7 of the highway, covered by the beam 19 of the antenna 3, is substantially equal to the area of a car 21 so that maximum utilization is made of the detected signal.
In this arrangement a car 21 gives the same signal as a truck `~
23 which is larger than the car. The apparatus 1 can of course, 1~ ~
in this arrangement, provide a total co~lnt only of the vehi-cles sensed, without distinguishing between cars and trucks.
The temperature signal, T received by the antenna 3 from area 7 is in general a combination of three temperature signals. More specifically the temperat~re signal T is given by the equation:
T = aTa + sTs ~ bTb where a, s and b are emissive, reflective and transmissive coefficients respectively, and Ta~ Ts and Tb are the ambient temperature of the area, the reflected sky temperature from the area and the background temperature of the area, re-spectively. In viewing area 7 alone, being a part of the roadway 5, the ambient and transmissive values are relatively ~
high and the reflective value is low. The temperature signal ~ `
in this case might be representative of a temperature in the range between 200K and 300K. When a car or truck is viewed -in this area however, the signal received, because the car or ;i-j .
truck is reflective is primarily the reflected sky temperature which is relatively low and might be representative of a temperature in the range between 10K and 50K. The differ-ence in the values of the temperature signals received oper-ates signal detector 11 in a manner to generate a signal in the system indicative of the presence of a car or truck.
To obtain sharper signal definition, the processing i 25 means 9 shown in Fig. 1 can instead comprise a radiometer 109, l such as the one commonly known as a Dicke T.M. radiometer shown -' :
in Fig. 2. The radiometer 109 operates by comparing the signal at the antenna 103 with that from a reference road 125 alterna-tiyely by operation o~ a switch 127. Both signals are detected by a detector 129 and either directly, or after conversion to an IF frequency, are ampli~ied by an amplifier 131 to a ,., .. :
.,'' ~.
convenien~ level to assure that only desired signals are observed. The amplifier 131 is followed by a synchronous ~
detector 133, which is sensitive only at the switching rates of switch 127, and by an integrator 135, a threshold circuit 137 and a counter 139 as before.
While the time sharing of the antenna 103 reduces the signals by one half, the detection process greatly enhances the detection of weak signals and reduces unwanted noise and gain fluctuations. In many instances a second switch, not shown, is placed between the reference load 125 and the first switch 127, such that the load may be compared to a second I load of a known controlled temperature. In this manner signals can be derived from a second synchronous detector to be used as a calibration value by placing the second switch in the port containing the load. The degradation in the sensitivity , of the system is minimized as ~he signal path length still ~¦ contains but one switch.
The temperature sensitivity of a miorowave radiometer used for ground mapping is normally defined by the following ¦ 20 expression9 (which relates to a signal-to-noise valu of unity) , aT = K NF To ~t where l<K<2. For most Dicke radiometers K is approximately equal to 2 . NF relates to the noise figure of the radiometer9 To is its ambient temperature (usually 290K), B is the pre-detection bandwidth, and t is the integration time in seconds.
l As can be seen from the expression, sensitivity is proportional ¦ to the noise figure of the system but inversely proportional to I the square root of the predetection bandwidth and integration time, - ., ~ ~. ~ . . . .
~ 8 ~
Atmospheric attenuation plays a large role in the radiometric temperature seen by a microwave radil~meter. Thus, it is exceedingly important that the proper operating frequency be selected within one of the so-called window fnequencies in the upper centimeter or lower,millimeter portion of the electromagnetic spectrum. Window frequencies are character-istics of an attenuation curve as a function of frequency for electromagnetic waves in the atmosphere. Window frequencies '~
below 10 GHz are not suitable as the aperture si~es necessary 'lO for good resolution are too large. Above 90 GHz, the sensitivity of the system is so low and the cost so great that all-weather capabilities cannot be fully utilized.
Frequency bands at 10 GHz and 35 GHz are a good compromise ~ because they are within a window frequency. ', 3 15 A preferred system 201, utilizing a 10 GHz radiometer 'I is shown in Fig.3. This system is also designed to distinguish , types of vehicles as will be described. The system has an '~
antenna 203 of a size and beamwidth commensurate with the , height of the system and the vehicle size to be detected. A
horn antenna with a beamwidth of 32 at the 3db points can be ' used for example. The traffic system is suspended over the highway 205 at a distance which allows a truck 207 to fill the area 209 on the highway illuminated by the beam 211 when ' `'I passing under the sensor. This is the area encompassed on the ' 25 highway by the 3db beamwidth of the antenna. When the traffic I sensor is observing the highway 205 in the absence of a vehicle, it views the radiometric temperature of the highway which is ~! Tr = Tke ~ '' Where Tr ~ radiometry temperature '~
Tk = kinetic temperature e - emissivity of the highway . ~ . . . ... . .
~57 ~ ~
This temperature on a warm summer day is approxi-mately 200~ Kelvin. When a truck 207 enters the beam 211, the truck 207 reflects the sky temperature which is approximately 10K. This gives rise to a temperature signal oF 190K. This signal (centered at the band around 10 GHz in the present system~ is collected by the antenna 203 and is ct~upled to a pin diode switch 213, toggled by a square wave of plus and minus one volt at a rate of 1 KHz. In the closed position it has an attenuation of 2db and in the open position its attenuation is 60db. In one position of the switch 213 it connects the antenna 203 to the isolator 215. In the other position it connects a reference load 217, which it is at ambient temperature, to the isolator 215. Appearing at the isoiator 215 is a square wave signal of an amplitude pro-1 15 portional to the difference between the antenna signal (antennabrightness temperature) and the reference load. The isolator 215 couples the signal to the mixer-preamplifier 219. The isolator has a forward attenuation of 0.3db and la reverse attenuation (isolation) of 20db, resulting in a low attenuation for a signal passing from the antenna to the mixler-preamplifier.
..
1 However, a s;gnal passing from the mixer to the ,~ntenna is ~ ;~
attenuated heavily. Since the receiver is a supler-heterodyne l type, the local oscillator 221 supplies energy at or near the -l incoming signal frequency. Some of this energy used to down-convert the incoming signal is coupled through the mixer to the antenna. If there is a mismatch between the antenna and mixer, energy is reflected back to the mixer and is down converted as a signal. By placing the isolator 215 between the switch 213 and mixer 219, the energy coupled out of the mixer is absorbed by the isolator preventing the energy from getting to the mismatch and re~lecting back to the mixer as ~,' .,.
.~ ...... . . ., ~
~(35~3~
a signal. The attenuator 223 reduces the local qscillator signal to the proper power level for the mixer. It also provides isolation between the mixer 219 and local oscillator 221 and prevents local oscillator pulling with s1gnal amplitude.
The down converted signal (10 MHz to 4~0 MHz) is amplified by the preamplifier 219, having an overall gain of 23db. This signal is coupled to a main IF amplifier 225, with a gain of 43db and a bandwidth of over 500 MHz. The output of the IF amplifier 225 is coupled to second detect~r 227 which j10 envelope detects the double side band IF signal, producing DC
and a noisy 1 KHz square wave. The second detector 227 has a tangential sensitivity of -52 dbm when coupled t~ an amplifier with a noise figure (NF) of 2db and a bandwidth of 2 MHz. The output is AC coupled to a low noise (NF 2db) witb a bandwidth ¦15 of 30 KHz. Its output feeds a synchronous detector and JI integrating amplifier. The overall gain of this amplifier chain 229 is 60db. After synchronous detection and integration, I the output signal is DC with an AC signal (noise). The AC
; signal represents an rms variation about the DC signal.
¦ 20 The output of the synchronous detector and integrator 229 is coupled to a dual threshold circuit block 231. As a car or a truck enters the beam, the resulting temperature seen by ~' the antenna is the average of the ground and sky temperatures weighed by the rdtlo of the surface of the vehicle to the total area. Total temperature is given by the expression Ttot - Te Av ~Tv - Te) Where Te = temperature of earth or highway v ~ temperature of vehicle or sky temperature Av = area of vehicle Atot = area of beam on highway . . .
For any given time Te can be considered a constant and Ttot changes by the ratio Av Since a truck and a car have tot different areas, the amplitude of the s-igna1 is proportional to the areas.
~ 5 This amplitude difference is detected by the dual ; threshold circuits 231 which consist of parallel comparators having their thresholds set for car and truck amplitude respectively. The output of each comparator is ooupled to their respective counter. Since a car has a smaller area than a truck~ its signal will only exceed the first threshold and one counter 233 will count. A truck whose signal is larger than a car will exceed both thresholds and will cause both counters 233, 235 to count. The low threshold counter counts total vehicles and the high threshold counter only trucks.
By subtracting the count for trucks from total v,ehicle count, the total car count can be obtained.
~, The counter outputs are fed to seven segment decoders :;! which drive seven-segment pin lights for a visual display 237.
A clock circuit drives a seven segment pin light to show elapsed time as well in the display 237.
A multivibrator 239 generates a square wave signal, used to toggle the switch 213 and the synchronous detector 229.
Fig. 4 illustrates the type of signals received by `~
the system 201 just described when sensing vehicles in a time . i interval. The signals illustrate graphically, small vehicles, ~ small trucks and large trucks and trailers. The amplitude of j the signals are proportional to the size of the vehicles.
If it is desired to measure the velocity of each vehicle sensed3 the system shown in Fig. 3 can be modified to do so. The system can include an operational amplifier in a differentiating mode to measure the slope of the vehicle signal .. . . . . . . . .
, ~ ; . . ..
~ 7~
received. The slope in the signal is due to the fact that the signal varies in amplitude at a rate proportionall to the velocity at which a vehicle enters the antenna beam. In addition, means are provided for measuring t-he amplitude of the signal since the slope is also prop~rtional to this amplitude. The combination of these two measurements gives the velocity of the vehicle sensed.
The system of Fig. 3 can be used as we`ll to identify emergency vehicles. This is useful if the system is controlling traffic lights so that upon sensing an emergency vehicle, the system will set the traffic lights to give the vehicle a non-stop route. To identify emergency vehicles the ~ystem is frequency multiplexed and equipped with a PCM demodulator.
Approximately four megahertz of the system bandwidth IS will be used to receive radiated PCM signals transmitted by an emergency vehicle or vehicle to be identified. The PCM
demodulator will decode the PCM signal and operate the traffic light or interrogate a control computer. To interrogate an emergency vehicle the local oscillator can be coupled to the ;
antenna through a power split~er and perform as a low power PCM transmitter.
It should be noted that the vehicle count operation observes "cold" signals about an average background. The e~ergency signal is a "hot" radiated signal which is easily separated and distinguished ~rom the cold vehicle signal.
Conversely, the hot signal does not interfere with or cause a count in ~he vehicle count mode.
The systems have been described as sensing vehicles in one lane of traffic. The antenna could however be used to ` 30 sense traffic in two or more lanes simultaneously. As shown in Fig. 5 the antenna 401 has a beam width to cover three :: - 1 0 -: ~.
~ 57~3~
traffic lanes 403, 405 and 407. A vehicle in any lane is sensed by signal processing means 409 and counted by a counter 411. This system gives an average vehicle count for each lane (by dividing the total counter by the number of lanes).
I~ a traffic count for each lane is desired, the system shown in Fig. 6 can be used. Here an antenna 501, 503, - 505 is provided for each lane 507, 509, 511 respectively. A
counter 513~ 515, 517 is also provided for each lane S07, 509, 511 respectively. A single processing means 519 is provided connected by switches 521, 523 to the antenna and counters respectively. The switches are operated in a time-sharing mode to connect each antenna to its reSpeCtiYe counter.
Hence, a microwave radiometric traffic sensor made in accordance with the present invention is a simple passive all weather device. It does not radiate energy to generate a signal. It also operates day or night and in every type of weather. It does not require modification to the road bed ~;
nor does it require surface sensors. It has the capability to distinguish various catagories of vehicles by the amplitude and shape of the signal. It can measure velocity. Road wetness can be determined by monitoring the road temperature.
It does not have the disadvantage of pressure sensors or treadles which become inoperative in snow or ice. It will not wear out by constant vehicle passage. Optical and infrared -;
devices become inoperative in fog since the attenuation of the radiation becomes quite high. Doppler radar devices are all-weather but exhibit problems in resolution both in distance and amplitude when se t-up for appropriate speed measurement and resolution.
While specific types of antennas and signal -'7831~ .
processing means have been described in this application, other suitable antennas and signal processing means ma\~ be used as well, without departing from the scope of the invent~on.
~.
... ~.~
- 12- ~ ;
`
; FIELD OF THE INVENTION
This invention is directed toward improved road vehicle sensing apparatus.
BACKGROUND OF THE INVENTION
Vehicle sensing apparatus is employed to provide a count of vehicles using a road or highway, usually within a specific time interval. These vehicle counts can be employed ;~
to provide vehicle traffic pattern data and/or to control the flow of vehicle traffic, locally or regionally, via traffic signals. The sensing apparatus can also be employed to provide data regarding the type and/or speed of each vehicle sensed if ~ desired.
j Many vehicle sensing systems, for carrying out the above, are known. Some systems employ buried magnetic loops or pneumatic tubes and plates. Others employ various sonic or ~ optical means. Still others employ electromagnetic waves -1 reguiring both a transmitter and a receiver. Thçse known systems are however, generally relatively complicated, expensive and bulky. In addition, the known systems are n~t always reliable in use under all operating conditions.
STATEMENT OF THE INVENTION
It is the purpose of the present invention to provide an improved vehicle sensing apparatus which is relatively simple and compact. It is a further purpose to provide an improved vehicle sensing apparatus which operates reliably under all weather conditions, day or night.
The improved road vehicle sensing apparatus of the present invention is particularly charac~erized in that it employs the principle of microwave radiometry.
jl~ 30 Microwave radiometry can be defined as the passive .1 .
detection of signals of thermal origin having wavelengths .
~.
.~ .
... ~ . .. . . -between one hundred centimeters and one millimetl~r. An ultra sensitive receiver is used to detect the signals picked up by a directional antenna, the beam of which is directed at the area to be observed. The magnitude of signal received can be generally said to be proportional to the temperature of, and reflected by, the area, or object in the area, observed.
As applied to vehicle sensing, the temperature signal received from an empty area of roadway would be different from the temperature signal received from a vehicle in the same roadway area since the vehicle reflects the sky temperature to a greater degree than the roadway. It is this principle in general which is employed in the present invention to provide an effective, reliable, vehicle sensing apparatus.
Broadly, the vehicle sensing apparatus of the present invention comprises an antenna for collecting microwave tempera-ture signals from an area of roadway, and means connected to the antenna for processing the collected signals to indicate , the presence of a vehicle in the roadway area due tG a change . , .
q in the magnitude of the temperature signals collected which change is caused by the presence of the vehicle in the roadway ~-area. ;
The processing means preferably includes means ~or detecting the amplitude of the signal to provide an indication of the size of vehicle sensed.
.
The processing means also includes means for providing a count of the vehicles sensed.
BRIEF DESCRIPTION OF THE INVENTION
The invention will now be described in detail having reference ta the accompanying drawings in which:
Figure l is a schematic view of a simple sensing . . .
~ apparatus of the present invention;
.
1~5~
Figure 2 is a schematic view of a more sensitive sensing apparatus;
Figure 3 is a schematic view of a preferred sensing apparatus;
, 5 Figure 4, appearing on the same sheet as Fig. 1, is a graph illustrating the nature of the signals received by the `~apparatus;
Figure 5~ appearing on the same sheet as Fig. 1, is a schematic view of one form of sensing apparatus for sensing vehicles in a plurality of lanes; and Figure 6, appearing on the same sheet as Fig. 1, is a schematic view of another form of sensing apparatus for sensing vehicles in a plurality of lanes.
DESCRIPTION OF A PREFERRED EMBODIMENT
:1 -1~ The vehicle sensing apparatus 1 of the present invention, can, in its simplest form as shown in Fig. 1, comprise a directional antenna 3 mounted above a road or ;~
' highway 5 for picking up temperature signals fro~ an area 7 of the highway 5, and means 9 for processing the received signals. The processing means 9 essentially comprises, a signal detector 11, connected to the antenna 3, ~or detecting the temperature signals, an amplifier 13 for amplifying the detected signals, a threshold circuit 15 for passing signals of a predetermined magnitude indicating the detection of a vehicle, and a counter 17 for providing a count of the detected vehicles. ~ -The area 7 of the highway, covered by the beam 19 of the antenna 3, is substantially equal to the area of a car 21 so that maximum utilization is made of the detected signal.
In this arrangement a car 21 gives the same signal as a truck `~
23 which is larger than the car. The apparatus 1 can of course, 1~ ~
in this arrangement, provide a total co~lnt only of the vehi-cles sensed, without distinguishing between cars and trucks.
The temperature signal, T received by the antenna 3 from area 7 is in general a combination of three temperature signals. More specifically the temperat~re signal T is given by the equation:
T = aTa + sTs ~ bTb where a, s and b are emissive, reflective and transmissive coefficients respectively, and Ta~ Ts and Tb are the ambient temperature of the area, the reflected sky temperature from the area and the background temperature of the area, re-spectively. In viewing area 7 alone, being a part of the roadway 5, the ambient and transmissive values are relatively ~
high and the reflective value is low. The temperature signal ~ `
in this case might be representative of a temperature in the range between 200K and 300K. When a car or truck is viewed -in this area however, the signal received, because the car or ;i-j .
truck is reflective is primarily the reflected sky temperature which is relatively low and might be representative of a temperature in the range between 10K and 50K. The differ-ence in the values of the temperature signals received oper-ates signal detector 11 in a manner to generate a signal in the system indicative of the presence of a car or truck.
To obtain sharper signal definition, the processing i 25 means 9 shown in Fig. 1 can instead comprise a radiometer 109, l such as the one commonly known as a Dicke T.M. radiometer shown -' :
in Fig. 2. The radiometer 109 operates by comparing the signal at the antenna 103 with that from a reference road 125 alterna-tiyely by operation o~ a switch 127. Both signals are detected by a detector 129 and either directly, or after conversion to an IF frequency, are ampli~ied by an amplifier 131 to a ,., .. :
.,'' ~.
convenien~ level to assure that only desired signals are observed. The amplifier 131 is followed by a synchronous ~
detector 133, which is sensitive only at the switching rates of switch 127, and by an integrator 135, a threshold circuit 137 and a counter 139 as before.
While the time sharing of the antenna 103 reduces the signals by one half, the detection process greatly enhances the detection of weak signals and reduces unwanted noise and gain fluctuations. In many instances a second switch, not shown, is placed between the reference load 125 and the first switch 127, such that the load may be compared to a second I load of a known controlled temperature. In this manner signals can be derived from a second synchronous detector to be used as a calibration value by placing the second switch in the port containing the load. The degradation in the sensitivity , of the system is minimized as ~he signal path length still ~¦ contains but one switch.
The temperature sensitivity of a miorowave radiometer used for ground mapping is normally defined by the following ¦ 20 expression9 (which relates to a signal-to-noise valu of unity) , aT = K NF To ~t where l<K<2. For most Dicke radiometers K is approximately equal to 2 . NF relates to the noise figure of the radiometer9 To is its ambient temperature (usually 290K), B is the pre-detection bandwidth, and t is the integration time in seconds.
l As can be seen from the expression, sensitivity is proportional ¦ to the noise figure of the system but inversely proportional to I the square root of the predetection bandwidth and integration time, - ., ~ ~. ~ . . . .
~ 8 ~
Atmospheric attenuation plays a large role in the radiometric temperature seen by a microwave radil~meter. Thus, it is exceedingly important that the proper operating frequency be selected within one of the so-called window fnequencies in the upper centimeter or lower,millimeter portion of the electromagnetic spectrum. Window frequencies are character-istics of an attenuation curve as a function of frequency for electromagnetic waves in the atmosphere. Window frequencies '~
below 10 GHz are not suitable as the aperture si~es necessary 'lO for good resolution are too large. Above 90 GHz, the sensitivity of the system is so low and the cost so great that all-weather capabilities cannot be fully utilized.
Frequency bands at 10 GHz and 35 GHz are a good compromise ~ because they are within a window frequency. ', 3 15 A preferred system 201, utilizing a 10 GHz radiometer 'I is shown in Fig.3. This system is also designed to distinguish , types of vehicles as will be described. The system has an '~
antenna 203 of a size and beamwidth commensurate with the , height of the system and the vehicle size to be detected. A
horn antenna with a beamwidth of 32 at the 3db points can be ' used for example. The traffic system is suspended over the highway 205 at a distance which allows a truck 207 to fill the area 209 on the highway illuminated by the beam 211 when ' `'I passing under the sensor. This is the area encompassed on the ' 25 highway by the 3db beamwidth of the antenna. When the traffic I sensor is observing the highway 205 in the absence of a vehicle, it views the radiometric temperature of the highway which is ~! Tr = Tke ~ '' Where Tr ~ radiometry temperature '~
Tk = kinetic temperature e - emissivity of the highway . ~ . . . ... . .
~57 ~ ~
This temperature on a warm summer day is approxi-mately 200~ Kelvin. When a truck 207 enters the beam 211, the truck 207 reflects the sky temperature which is approximately 10K. This gives rise to a temperature signal oF 190K. This signal (centered at the band around 10 GHz in the present system~ is collected by the antenna 203 and is ct~upled to a pin diode switch 213, toggled by a square wave of plus and minus one volt at a rate of 1 KHz. In the closed position it has an attenuation of 2db and in the open position its attenuation is 60db. In one position of the switch 213 it connects the antenna 203 to the isolator 215. In the other position it connects a reference load 217, which it is at ambient temperature, to the isolator 215. Appearing at the isoiator 215 is a square wave signal of an amplitude pro-1 15 portional to the difference between the antenna signal (antennabrightness temperature) and the reference load. The isolator 215 couples the signal to the mixer-preamplifier 219. The isolator has a forward attenuation of 0.3db and la reverse attenuation (isolation) of 20db, resulting in a low attenuation for a signal passing from the antenna to the mixler-preamplifier.
..
1 However, a s;gnal passing from the mixer to the ,~ntenna is ~ ;~
attenuated heavily. Since the receiver is a supler-heterodyne l type, the local oscillator 221 supplies energy at or near the -l incoming signal frequency. Some of this energy used to down-convert the incoming signal is coupled through the mixer to the antenna. If there is a mismatch between the antenna and mixer, energy is reflected back to the mixer and is down converted as a signal. By placing the isolator 215 between the switch 213 and mixer 219, the energy coupled out of the mixer is absorbed by the isolator preventing the energy from getting to the mismatch and re~lecting back to the mixer as ~,' .,.
.~ ...... . . ., ~
~(35~3~
a signal. The attenuator 223 reduces the local qscillator signal to the proper power level for the mixer. It also provides isolation between the mixer 219 and local oscillator 221 and prevents local oscillator pulling with s1gnal amplitude.
The down converted signal (10 MHz to 4~0 MHz) is amplified by the preamplifier 219, having an overall gain of 23db. This signal is coupled to a main IF amplifier 225, with a gain of 43db and a bandwidth of over 500 MHz. The output of the IF amplifier 225 is coupled to second detect~r 227 which j10 envelope detects the double side band IF signal, producing DC
and a noisy 1 KHz square wave. The second detector 227 has a tangential sensitivity of -52 dbm when coupled t~ an amplifier with a noise figure (NF) of 2db and a bandwidth of 2 MHz. The output is AC coupled to a low noise (NF 2db) witb a bandwidth ¦15 of 30 KHz. Its output feeds a synchronous detector and JI integrating amplifier. The overall gain of this amplifier chain 229 is 60db. After synchronous detection and integration, I the output signal is DC with an AC signal (noise). The AC
; signal represents an rms variation about the DC signal.
¦ 20 The output of the synchronous detector and integrator 229 is coupled to a dual threshold circuit block 231. As a car or a truck enters the beam, the resulting temperature seen by ~' the antenna is the average of the ground and sky temperatures weighed by the rdtlo of the surface of the vehicle to the total area. Total temperature is given by the expression Ttot - Te Av ~Tv - Te) Where Te = temperature of earth or highway v ~ temperature of vehicle or sky temperature Av = area of vehicle Atot = area of beam on highway . . .
For any given time Te can be considered a constant and Ttot changes by the ratio Av Since a truck and a car have tot different areas, the amplitude of the s-igna1 is proportional to the areas.
~ 5 This amplitude difference is detected by the dual ; threshold circuits 231 which consist of parallel comparators having their thresholds set for car and truck amplitude respectively. The output of each comparator is ooupled to their respective counter. Since a car has a smaller area than a truck~ its signal will only exceed the first threshold and one counter 233 will count. A truck whose signal is larger than a car will exceed both thresholds and will cause both counters 233, 235 to count. The low threshold counter counts total vehicles and the high threshold counter only trucks.
By subtracting the count for trucks from total v,ehicle count, the total car count can be obtained.
~, The counter outputs are fed to seven segment decoders :;! which drive seven-segment pin lights for a visual display 237.
A clock circuit drives a seven segment pin light to show elapsed time as well in the display 237.
A multivibrator 239 generates a square wave signal, used to toggle the switch 213 and the synchronous detector 229.
Fig. 4 illustrates the type of signals received by `~
the system 201 just described when sensing vehicles in a time . i interval. The signals illustrate graphically, small vehicles, ~ small trucks and large trucks and trailers. The amplitude of j the signals are proportional to the size of the vehicles.
If it is desired to measure the velocity of each vehicle sensed3 the system shown in Fig. 3 can be modified to do so. The system can include an operational amplifier in a differentiating mode to measure the slope of the vehicle signal .. . . . . . . . .
, ~ ; . . ..
~ 7~
received. The slope in the signal is due to the fact that the signal varies in amplitude at a rate proportionall to the velocity at which a vehicle enters the antenna beam. In addition, means are provided for measuring t-he amplitude of the signal since the slope is also prop~rtional to this amplitude. The combination of these two measurements gives the velocity of the vehicle sensed.
The system of Fig. 3 can be used as we`ll to identify emergency vehicles. This is useful if the system is controlling traffic lights so that upon sensing an emergency vehicle, the system will set the traffic lights to give the vehicle a non-stop route. To identify emergency vehicles the ~ystem is frequency multiplexed and equipped with a PCM demodulator.
Approximately four megahertz of the system bandwidth IS will be used to receive radiated PCM signals transmitted by an emergency vehicle or vehicle to be identified. The PCM
demodulator will decode the PCM signal and operate the traffic light or interrogate a control computer. To interrogate an emergency vehicle the local oscillator can be coupled to the ;
antenna through a power split~er and perform as a low power PCM transmitter.
It should be noted that the vehicle count operation observes "cold" signals about an average background. The e~ergency signal is a "hot" radiated signal which is easily separated and distinguished ~rom the cold vehicle signal.
Conversely, the hot signal does not interfere with or cause a count in ~he vehicle count mode.
The systems have been described as sensing vehicles in one lane of traffic. The antenna could however be used to ` 30 sense traffic in two or more lanes simultaneously. As shown in Fig. 5 the antenna 401 has a beam width to cover three :: - 1 0 -: ~.
~ 57~3~
traffic lanes 403, 405 and 407. A vehicle in any lane is sensed by signal processing means 409 and counted by a counter 411. This system gives an average vehicle count for each lane (by dividing the total counter by the number of lanes).
I~ a traffic count for each lane is desired, the system shown in Fig. 6 can be used. Here an antenna 501, 503, - 505 is provided for each lane 507, 509, 511 respectively. A
counter 513~ 515, 517 is also provided for each lane S07, 509, 511 respectively. A single processing means 519 is provided connected by switches 521, 523 to the antenna and counters respectively. The switches are operated in a time-sharing mode to connect each antenna to its reSpeCtiYe counter.
Hence, a microwave radiometric traffic sensor made in accordance with the present invention is a simple passive all weather device. It does not radiate energy to generate a signal. It also operates day or night and in every type of weather. It does not require modification to the road bed ~;
nor does it require surface sensors. It has the capability to distinguish various catagories of vehicles by the amplitude and shape of the signal. It can measure velocity. Road wetness can be determined by monitoring the road temperature.
It does not have the disadvantage of pressure sensors or treadles which become inoperative in snow or ice. It will not wear out by constant vehicle passage. Optical and infrared -;
devices become inoperative in fog since the attenuation of the radiation becomes quite high. Doppler radar devices are all-weather but exhibit problems in resolution both in distance and amplitude when se t-up for appropriate speed measurement and resolution.
While specific types of antennas and signal -'7831~ .
processing means have been described in this application, other suitable antennas and signal processing means ma\~ be used as well, without departing from the scope of the invent~on.
~.
... ~.~
- 12- ~ ;
Claims (10)
1. Vehicle sensing apparatus comprising: a directional microwave non-emitting antenna installed above a roadway area for collecting microwave temperature signals reflected from said roadway area; and means connected to said antenna for processing the collected signals to detect the presence of a vehicle in said roadway area, said presence being indicated by a change in microwave reflectivity from said area.
2. An apparatus as claimed in Claim 1, wherein said processing means includes means for detecting the amplitude of the collected signals to provide an indication of the size of the vehicle sensed.
3. An apparatus as claimed in Claim 2, wherein said processing means includes means providing a count of the total number of vehicles sensed.
4. An apparatus as claimed in Claim 2, wherein said processing means includes means for providing a first count of the total number of vehicles sensed and a second count of the total number of vehicles greater than one size sensed.
5. An apparatus as claimed in Claim 4, wherein said antenna is focused on a roadway area substantially equal in size to the area of each of the vehicles of one size.
6. An apparatus as claimed in Claims 1, 2 or 3, wherein said roadway area comprises one lane of vehicle traffic.
7. An apparatus as claimed in Claims 1, 2 or 3, wherein said roadway area comprises two or more lanes of vehi-cle traffic.
8. An apparatus as claimed in Claims 1, 2 or 3, wherein said roadway area comprises two or more lanes of vehicle traffic, providing a directional microwave antenna for each lane, and switching means for connecting each antenna to said processing means in a time-sharing mode.
9. An apparatus as claimed in Claims 1, 2 or 3, including means in said processing means for measuring the slope and amplitude of the signals to provide a measurement of the velocity of the vehicle sensed.
10. An apparatus as claimed in Claims 1, 2 or 3, including a PCM demodulator in said processing means to receive a signal transmitted from a specific vehicle.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA218,238A CA1057834A (en) | 1975-01-20 | 1975-01-20 | Vehicle sensing apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA218,238A CA1057834A (en) | 1975-01-20 | 1975-01-20 | Vehicle sensing apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1057834A true CA1057834A (en) | 1979-07-03 |
Family
ID=4102095
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA218,238A Expired CA1057834A (en) | 1975-01-20 | 1975-01-20 | Vehicle sensing apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1057834A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0286251A2 (en) * | 1987-03-18 | 1988-10-12 | Centre De Recherche Industrielle Du Quebec | Microwave size/speed vehicle detector |
| WO1997025633A1 (en) * | 1996-01-11 | 1997-07-17 | Lockheed Martin Corporation | Vehicle detection radiometer |
| GB2390209A (en) * | 2002-05-14 | 2003-12-31 | Roke Manor Research | Vehicle detection using emitted radiation |
| FR3057093A1 (en) * | 2016-10-04 | 2018-04-06 | Commissariat Energie Atomique | SYSTEM FOR DETECTING AT LEAST ONE VEHICLE WITHIN A DETECTION AREA LOCATED ON A PAVEMENT |
-
1975
- 1975-01-20 CA CA218,238A patent/CA1057834A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0286251A2 (en) * | 1987-03-18 | 1988-10-12 | Centre De Recherche Industrielle Du Quebec | Microwave size/speed vehicle detector |
| EP0286251A3 (en) * | 1987-03-18 | 1990-07-11 | Centre De Recherche Industrielle Du Quebec | Microwave size/speed vehicle detector |
| WO1997025633A1 (en) * | 1996-01-11 | 1997-07-17 | Lockheed Martin Corporation | Vehicle detection radiometer |
| GB2390209A (en) * | 2002-05-14 | 2003-12-31 | Roke Manor Research | Vehicle detection using emitted radiation |
| FR3057093A1 (en) * | 2016-10-04 | 2018-04-06 | Commissariat Energie Atomique | SYSTEM FOR DETECTING AT LEAST ONE VEHICLE WITHIN A DETECTION AREA LOCATED ON A PAVEMENT |
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