GB2358269A - Vehicle detection - Google Patents

Abstract

Described herein is a vehicle detection system which operates to detect the presence of vehicles in a zone using radiometry. The system comprises an antenna (100) arranged to monitor a zone (105) which provides signals indicative of the presence of objects in that zone to processing apparatus (120, 140, 160, 180) for evaluation. If the processing apparatus (120, 140, 160, 180) detects a change in the signals due to the presence of a vehicle in the zone (105), it passes a control signal to a traffic signal controller (200) to change traffic lights under its control.

Description

i IMPROVEMENTS IN OR RELATING TO VEHICLE DETECTION The present invention

relates to improvements in or relating to vehicle detection, and is more particularly concerned with a radiometric 5 system for effecting such detection.

In some traffic light systems, the presence of one or more vehicles is detected using sensors which are either mounted on a traffic light unit or in the road. The sensors having detected the presence of one or more vehicles provide signals indicative of the presence of the vehicle(s) to a traffic light controller unit which determines whether the traffic lights need to be changed in response to the presence of the vehicle(s). For example, if the traffic lights are at red in one direction and no traffic is passing through the junction in the other direction where the traffic lights are green, the sensing of a vehicle in the one direction may be used to activate the traffic lights so that the ones that were red turn to green and the ones which were green turn to red allowing the vehicle to pass through the junction without having to stop for the red light in its direction.

It is known to use radiometry to detect thermal radiation which depends on the temperature and emissivity of an object. However, reflections from other sources may also be significant. Radiometry is typically used at frequencies close to 35GHz or 94Gl-1z because there are local minima in atmospheric attenuation centred on these frequencies. Frequencies between these two values tend to have very high attenuation and therefore cannot provide the high resolution required to produce photographic-like quality images of an object. However, components suitable for use at these frequencies are highly specialised, very expensive i and difficult to obtain.

It is therefore an object of the present invention to provide a low-cost, reliable, passive vehicle detection system which can be used in traffic control or monitoring.

In accordance with one aspect of the present invention, there is provided a vehicle detection system comprising:- an antenna for monitoring a zone in which the presence of a vehicle is to be detected; and processing means for receiving signals from said antenna and for providing an output signal indicative of characteristics of said zone, said output signal changing in response to the presence of a vehicle in said zone.

Advantageously, the vehicle detection system in accordance with the present invention does not require the use of a transmitter in order to detect the presence of a vehicle within the zone. It detects energy radiated from the vehicle within a predetermined frequency band of between 8 and 12GHz, preferably, between 10 and 12GHz. However, other suitable frequencies could also be used depending on the particular application.

Furthermore, the detection system of the present invention can also be used for detecting the presence of objects other than vehicles.

For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which:Figure I is a schematic diagram of one embodiment of a vehicle detection system in accordance with the present invention; and Figure 2 illustrates a block diagram of a simple radiometer for use in a vehicle detection system of Figure 1.

Although the present invention is described with reference to vehicle detection, it will be appreciated that it can have other applications where the presence of an object is to be detected by means of its temperature and/or emissivity differs significantly from that of its background.

Figure 1 illustrates a road junction 10 which is controlled by four sets of traffic lights 20, 30, 40, 50. Each set of traffic lights 20, 30, 40, 50 has an antenna 22, 32, 42, 52 mounted on it for monitoring respective zones 24, 34, 44, 54 as shown. These zones 24, 34, 44, 54 are monitored all the time with the antennas 22, 325 425 52 sending signals to a traffic signal controller (not ishown). The traffic signal controller uses the signals received from the antennas 22, 325 425 52 to control the operation of the sets of traffic lights 20, 30, 40,50 in a predetermined sequence, for example, sets 20, 40 and 30,50 could operate together as pairs changing colour at the same time as is conventional. The traffic signal controller may also operate to control each set of traffic lights 20, 30, 40, 50 so that they change to green in turn allowing traffic from each direction to flow through the junction 10 in turn.

As shown in Figure 1, the junction 10 is clear with no cars waiting at the lights with traffic lights 30, 50 on red and traffic lights 20, 40 on green.

Alternatively, sets 20, 30, 40 could be on red with set 50 on green. As a vehicle 60 approaches the junction 10 in the direction indicated by the arrow, it passes into monitored zone 34 and its presence in that area is detected by antenna 32. Antenna 32 sends a signal to the traffic signal controller indicating the presence of the vehicle 60. As vehicle 60 tends to be generally made of metal, the signal sent to the traffic signal controller from antenna 32 comprises a drop in the signal prior to the detection of the vehicle 60.

Simultaneously, antennas 20, 40, 50 also send signals to the traffic signal controller indicating that no traffic is present in the zones 24, 44, 54 which they are monitoring. The traffic signal controller processes the received signals to control operation of the sets of traffic lights 20, 30, 40, 50 by changing sets 20, 40 to red and sets 30, 50 to green to allow vehicle 60 to pass through the junction 10.

In accordance with the present invention, each of the antennas 22, 32, 42, 52 form part of a radiometer as will be described with reference to Figure. 5 2.

Any object emits electromagnetic radiation in the form of random noise. The level of this noise depends on the physical temperature of the object and the material ftom which it is made. If the object were a perfect 'black body' radiator, that is, all radiation incident on the object was absorbed, then the noise power obtained from this object at an antenna, P, , can be expressed as:- PN= kTB where k is Boltzmann's constant (1.38 x 10-2'JK-1) T is the physical temperature of the object (in Kelvin) and B is the bandwidth of the receiving antenna.

At a given frequency, all materials have a characteristic emissivity, F-, reflectivity, p, and transmiSSiVity, T. The emissivity, s, of a 'black body' is equal to 1. However, most objects do not absorb perfectly, and these are called 'grey bodies'. For a 'grey body':

8 + p +T = 1 (2) If, as in most cases, the body is homogeneous and is several skin depths thick, the effects of transmission can be ignored and equation (2) can be reduced to:

8 + p (3) If a 'grey body' reflects the sky, its noise brightness temperature is related to the emissivity and reflectivity of its material:- TO =cT+PTsky(O) (4) w,here TO is the object brightness temperature (in Kelvin) F- is the emissivity of the object p is the reflectivity of the object nd Tk,(o) is the brightness temperature of the sky and is dependent on angle of incidence, 0.

The noise temperature of an antenna can be calculated using the f1 ollowing relationship:

1 (5) TA -: fT, (u)G(u)dQ 4n4x where TAis the antenna noise temperature TO is the object noise temperature and Q is the solid angle.

If the object fills the antenna beam width, then equation (5) becomes.

TA -" TO (6) Substituting equation (6) into equation (1) to find the total noise power from the antenna gives:

P1v = kTOB (7) The power from the antenna, PN, will be very small and requires amplification.

Figure 2 illustrates a block diagram of a simple radiometer. It will be understood that each antenna 22, 32, 42, 52 forms part of such a radiometer.

A radiometer is an instrument or sensor devised for the detection and measurement of radio or microwave energy.

As shown in Figure 2, the radiometer comprises an antenna 100, which corresponds to antennas 22, 32, 42, 52, for monitoring zone 105, which corresponds to zones 24, 34, 44, 54 as described above with reference to Figure 1. Antenna 100 receives random noise relating to the physical characteristics of the object it is monitoring. In the example described in Figure 1, each zone 23, 34, 44, 54 comprises a portion of road surface of a particular material which will have a given physical temperature at any one time. Therefore, antenna 100 will receive random noise indicative of the object or objects which are being monitored in zone 105. The antenna 100 converts the random noise into a received signal 110 which is passed to an amplifier 120 as the power level of the random noise received at the antenna 100 is very low. The amplifier 120 amplifies the received signal 110 and forms an amplified signal 130 which is passed to rectifier 140. The received signal 110 comprises a high frequency a.c. signal which need to be rectified for further processing. Rectifier 140 converts the amplified high frequency a.c. signal to a d.c. signal 150 which is then passed to an averaging unit 160. In averaging unit 160, the high frequency variations are removed from the d.c. signal 150 to form an average signal 170. Average signal 170 is then passed to a processor unit 180 for processing and the processed signal 190 is output to a controller 200, for example, a traffic signal controller as described with reference to Figure 1 above. As described above, the processor unit 180 effectively determines when the signals it receives falls due to the presence of a vehicle in its proximity.

The antenna 100 operates on fTequencies between 8GHz and 12GI-1z and components for such systems are readily available as they are used in commercial applications, such as satellite television systems. It will be possible for the antenna 100 to operate on any other suitable ftequency, but it will be appreciated that the lower the frequency, the longer the wavelength and hence less resolution available to the system. Moreover, larger antennas would be required to give the same performance.

In a specific example, a radiometer was constructed which operated on a frequency range of between 1 OGHz and 12GHz. It was used to detect vehicles in a system in accordance with the present invention, and it was found that vehicles could be detected reliably at a range of approximately 7m.

Advantageously, lower frequencies are attenuated much less by rain and fog.

Although the present invention has been described as being used for intelligent' traffic signal control, it will readily be appreciated that it is not limited to such an application. For example, the present invention could also be used to monitor traffic movement around a site or to monitor entry of vehicles into a car park.

The principles of the vehicle detection system as described above can readily be applied to detect other metal objects and not just vehicles.

Moreover,. the system of the present invention could also be used to detect the presence of non-metallic objects by detecting suitable frequencies.

i 8-

Claims (6)

CLAIMS:

1 A vehicle detection system comprisingan antenna for monitoring a zone in which the presence of a vehicle is to be detected; and processing means for receiving signals from said antenna and for providing an output signal indicative of characteristics of said zone, said output signal changing in response to the presence of a vehicle in said zone.

2. A system according to claim 1, wherein said antenna operates on a frequency in the range of 8 to 12GHz.

3. A system according to claim 2, wherein said frequency range is between 10 and 12GHz.

4. A system according to any one of the preceding claims, wherein said antenna forms part of a radiometer and detects temperature and/or emissivity of objects within said zone.

5. A traffic signal control system including at least one vehicle detection system according to any one of the preceding claims.

6. A vehicle detection system substantially as hereinbefore described with reference to the accompanying drawings.