METHOD AND APPARATUS FOR DETERMINING THE SPEED AND LOCATION OF A VEHICLE

Abstract: The invention relates to a method for measuring the speed of a vehicle by transmitting a wave beam directed at the vehicle, receiving a part of the wave beam reflected by the vehicle, comparing the reflected beam part with the transmitted wave beam and deriving from this comparison the speed of the vehicle, wherein during the speed measurement the position of the vehicle is also determined. A vehicle committing an offence can thus be identified unambiguously in a recording which is made after detection of the speeding offence. The speed of the vehicle can be determined from a difference in wavelength detected during the comparison between the reflected beam part and the transmitted wave beam, while the position of the vehicle is determined from a time lag detected during the comparison between the moment of transmitting and the moment of receiving the reflected beam part. The invention also relates to an apparatus for performing this method.

Description: Method and apparatus for determining the speed and location of a vehicle The invention relates to a method for measuring the speed of a vehicle by transmitting a wave beam directed at the vehicle, receiving a part of the wave beam re¬ flected by the vehicle, comparing the reflected beam part with the transmitted wave beam and deriving from this comparison the speed of the vehicle. Such a method is generally known and is frequently used by police in the form of radar speed measurements. In the known method a radar beam is transmitted at an acute angle to a road axis from a fixed, generally concealed position along the road. When a vehicle passes through the beam a part of the beam is reflected. This reflected part is received at the measuring point and the frequency of the reflected beam is compared with the (exact) frequency of the transmitted beam. Because the beam is reflected by a moving vehicle it will undergo, as a result of the Doppler effect, a frequency change which is a measure for both the speed of movement and the direction of movement of the vehicle. When it is found from the comparison of the transmitted and received frequency that the speed of the vehicle exceeds the maximum allowed speed at that location a warning signal is generated. This signal is generally used to activate a camera whereby a recording is made of the vehicle commit- ting the speeding offence. This recording then also shows the relevant data such as date and time of the recording and the measured speed. Problems occur in the known method when it is ap¬ plied on roads with a number of traffic lanes, such as motorways. Here several vehicles may pass through the measuring beam simultaneously. If one of these vehicles commits a speeding offence it is often not possible to determine indisputably which vehicle this was. When the speed measurement is combined with making a recording, complicated and time-consuming processing of the recording is required in order to determine the offender therefrom on the basis of secondary indications. The invention now has for its object to provide a method of the above described type, wherein this drawback does not occur. This is achieved according to the inven¬ tion in that during the speed measurement the position of the vehicle is determined. By determining not only the speed but simultaneously also the position of the vehi- cle, it is still possible to identify with certainty the vehicle which committed the offence, also when a number of vehicles passes through the beam. An efficient manner of position determination is achieved when the position of the vehicle, as well as the speed thereof, is determined by comparing the reflected beam part with the transmitted wave beam. The speed of the vehicle can advantageously be determined from a difference in wavelength detected during the comparison between the reflected beam part and the trans- mitted wave beam, and the position of the vehicle can be determined from a time lag detected during the comparison between the moment of transmitting and the moment of receiving the reflected beam part. Both the speed and the position of the vehicle are thus determined with a single measurement. It will further be apparent that instead of the difference in wavelength the frequency change which after all is associated therewith could also be measured. The wave beam is preferably transmitted in pulse form. By using separate wave pulses the time which has lapsed between the moment of transmission and the moment of reception can be determined unequivocally. When during the speed measurement the direc¬ tion of travel of the vehicle is also determined, even more certainty is obtained concerning the identity of the offending vehicle. The wave beam is preferably transmitted at an acute angle to the direction of movement of the vehicle. A reliable measurement is thus obtained which can be per¬ formed from a concealed position. The invention also relates to an apparatus for performing the above described method. According to the invention such an apparatus, which is provided with means for generating and transmitting a directed wave beam, means for receiving a part of the wave beam reflected by a vehicle and means for comparing the reflected beam part with the transmitted beam and deriving the speed of the vehicle from this comparison, is characterized by means for determining the position of the vehicle during the speed measurement. Preferred embodiments of the apparatus according to the invention form the subject-matter of the dependent claims 8 to 12. The invention is now elucidated on the basis of an embodiment, wherein reference is made to the annexed drawing, wherein: fig. 1 shows a top view of the use of the apparatus according to the invention in a speed measure¬ ment, fig. 2A to 2C show a schematic view of the measuring method according to the invention, fig. 3 shows a front view of the beam generating and transmitting means of the apparatus shown in fig. 1, and fig. 4 shows a cross section along the line IV-IV in fig. 3. In order to measure the speed of vehicles 2 travel- ling on a multi-lane highway 1 (fig. 1) a speed measuring apparatus 3 according to the present invention is dis¬ posed along the road. The apparatus 3 can herein be incorporated in a vehicle 9, for instance an inconspicu¬ ous police patrol car. The apparatus 3 transmits a wave beam 4, for instance a radar beam, over the road 1 at an acute angle a of for instance 20° to the direction of movement of vehicles 2. When a vehicle 5A or 5B passes through the beam 4, a part of beam 4 is reflected. By comparing the frequency of the reflected part of the beam with the transmission frequency, the speed of vehicle 5A or 5B can be determined using the Doppler effect. Because the road 1 has a number of traffic lanes 6 it is conceivable that, as shown, a number of vehicles 5A and 5B pass through the beam virtually simultaneously. In order to still be able to determine indisputably in these cases which of vehicles 5A or 5B is committing a speeding offence, the position of the vehicle, in this case its distance from measuring apparatus 3, is determined simul¬ taneously with its speed. For this purpose the wave beam is transmitted in pulse form and the time is measured between the moment that such a wave pulse 11 is transmitted by the beam generating and transmitting means 7 (fig. 2A) and the moment that a part 12 of this wave pulse, which is re¬ flected by a passing vehicle (fig. 2B) , is received again by receiving means 8 (fig. 2C) . Because use is made of separate wave pulses, of which the moment of transmission is known in each case and which are therefore as it were "recognized" by the receiving means, the distance from the measuring apparatus 3 of the vehicle by which the wave pulse is reflected can be determined without diffi- culty. Transmitting means 7 and receiving means 8 herein make use, with interposing of a selector switch 15, of a collective antenna 10, which is shown here schematically. Transmitting means 7 and receiving means 8 are each further connected to a central control unit 13, in which are arranged the means for comparing the frequency or wavelength of the transmitted and reflected beam and for measuring the time which has lapsed between transmitting and receiving. The central control unit 13 also contains the means for determining from this comparison the speed and direction of travel of the vehicle as well as its dis¬ tance from measuring apparatus 3. The starting point for determining the speed and travel direction of the vehicle are per se known relations between the fre¬ quency change and the speed of the reflecting vehicle resulting from the Doppler effect. The distance of the vehicle from the measuring apparatus is simply determined by multiplying the measured time by the known propagation velocity of the wave beam. When a speeding offence is determined, a warning signal is generated. Herein is indicated how great the measured speed is and what is the distance of the vehicle from the apparatus. The detected direction of travel can also be indicated. This warning signal can be used to activate a camera, whereby a recording is made. The speed and distance can be shown in the recording. From the distance can also be directly determined in which lane the offender is travelling. The comparing means can further be programmed such that they ignore reflected beams which are received within a determined time of the moment of transmitting. To this end the measured time is compared with an adjustable lower threshold value. The speed measurement can thus be limited for instance to the left-hand lane, which is after all the furthest removed from measuring apparatus 3 and in which the highest speeds will generally be reached. By also comparing the measured time with an upper threshold value, a measuring window can be adjusted whereby the measurement can be limited to one of the middle lanes. When the measurement is limited to the left-hand lane, reflections from oncom¬ ing traffic in the other lanes can also be filtered out in this manner. This same effect can be achieved by determining the travel direction of the vehicle, which follows simply from the nature of the measured frequency change (frequency increase or decrease) . In order to direct wave beam 4 at an acute angle over the road 1 without having to rotate the entire measuring apparatus 3 through this angle, use is made of an antenna 10 with a large plurality of slots 14, 14 ' , ..., I4n (fig. 3), a so-called slotted array antenna. Integrated in antenna 10 are the transmitting means 7 which take the form of an oscillator 15, which is connected over a mixing block 16 to an elongate wave guide 17, in which are arranged the slot-like transmit- ting apertures 14, 14', ..., 14n. The wave guide 17 is arranged in a dish 18 of horn-shaped cross section which forms the actual antenna (fig. 4) . The distribution of the slots 14, 14', ..., 14n over the length of wave guide 17 and their specific orientation, in the shown example at an angle of approximately 60 degrees to the longitudinal axis of the wave guide, allows the wave beam to be transmitted at an angle α relative to the normal of antenna 10 (fig. 1) . This is of particu¬ lar importance when, as in the shown example, measuring apparatus 3 is incorporated in a vehicle 9, since the required installation space is considerably limited thereby.

Claims: Claims 1. Method for measuring the speed of a vehicle by transmitting a wave beam directed at the vehicle, receiv¬ ing a part of the wave beam reflected by the vehicle, comparing the reflected beam part with the transmitted wave beam and deriving from this comparison the speed of the vehicle, characterized in that during the speed measurement the position of the vehicle is determined. 2. Method as claimed in claim 1, characterized in that the position of the vehicle is likewise determined by comparing the reflected beam part with the transmitted wave beam. 3. Method as claimed in claim 2, characterized in that the speed of the vehicle is determined from a dif¬ ference in wavelength detected during the comparison between the reflected beam part and the transmitted wave beam, and the position of the vehicle is determined from a time lag detected during the comparison between the moment of transmitting and the moment of receiving the reflected beam part. 4. Method as claimed in any of the foregoing claims, characterized in that the wave beam is transmitted in pulse form. 5. Method as claimed in any of the foregoing claims, characterized in that during the speed measurement the direction of travel of the vehicle is also determined. 6. Method as claimed in any of the foregoing claims, characterized in that the wave beam is transmitted at an acute angle to the direction of movement of the vehicle. 7. Apparatus for measuring the speed of a vehicle provided with means for generating and transmitting a directed wave beam, means for receiving a part of the wave beam reflected by a vehicle and means for comparing the reflected beam part with the transmitted beam and deriving the speed of the vehicle from this comparison, characterized by means for determining the position of the vehicle during the speed measurement. 8. Speed measuring apparatus as claimed in claim 7, characterized in that the position determining means are connected to the comparing means and adapted to derive the position of the vehicle from the comparison of the reflected beam part with the transmitted beam. 9. Speed measuring apparatus as claimed in claim 8, characterized in that the comparing means are adapted to compare the wavelength of the reflected beam part with that of the transmitted beam, to measure the time lag between the moment of transmitting and the moment of receiving the reflected part of the beam and to derive the speed of the vehicle from a detected difference in wavelength, and the position determining means are adapt- ed to derive the position of the vehicle from a measured time lag. 10. Speed measuring apparatus as claimed in any of the claims 7-9, characterized in that the beam generating and transmitting means are adapted to generate and trans- mit a wave beam in the form of a pulse. 11. Speed measuring apparatus as claimed in claim 9 or 10, characterized in that the comparing means are adapted to derive the direction of travel of the vehicle from the detected difference in wavelength. 12. Speed measuring apparatus as claimed in any of the claims 7-11, characterized in that the beam generat¬ ing and transmitting means comprise an antenna provided with slots for transmitting the wave beam at an acute angle to the direction of movement of the vehicle.

Inventors: GATSONIDES TOM, GATSONIDES, TOM
Applicants: GATSOMETER B V, GATSONIDES TOM, GATSOMETER B.V., GATSONIDES, TOM
Application year: 1997
Main classification: G01S13
IPC codes: G01S13, G08G1