1. A method for determining a distance of a vehicle passing a radio beacon of a road toll system, from said radio beacon, wherein the vehicle is equipped with an onboard unit, which emits a signal with a known curve of a signal frequency over time, the method comprising:
receiving the signal in the radio beacon and recording a frequency curve of the signal frequency over time, in relation to the known frequency curve;
detecting a change in the recorded frequency curve exceeding a first predetermined threshold value;
determining two far regions in the recorded frequency curve, wherein the far regions lie before and after the detected change in the recorded frequency curve and indicate a frequency change below a second predetermined threshold value;
scaling the recorded frequency curve in such a manner that the far regions assume predetermined values; and
determining the distance from a gradient of the scaled frequency curve in an inflection point thereof.
2. The method according to claim 1, wherein a lane of a multi-lane road, on which the vehicle is moving, is determined from the distance.
3. The method according to claim 1, wherein the inflection point is determined by determining a point in the frequency curve, at which the recorded frequency has a predetermined value.
4. The method according to claim 1, wherein the inflection point is determined by determining a point in the recorded frequency curve, which corresponds to a frequency mean value of the far regions.
5. The method according to claim 1, wherein the signal is emitted by the onboard unit as at least one carrier frequency modulated with a modulation frequency, wherein the signal frequency is the modulation frequency.
6. The method according to claim 1, wherein a dedicated short-range communication (DSRC) or a wireless access in a vehicle environment (WAVE) transmitter in the onboard unit is used to emit the signal.
7. A radio beacon for a road toll system for determining a distance of a vehicle passing the radio beacon, wherein the vehicle is equipped with an onboard unit which emits a signal with a known frequency curve of a signal frequency over time, comprising:
a receiver configured to receive the signal of the vehicle;
a memory coupled to the receiver configured to record a curve of the frequency of the received signal over time in relation to the known frequency curve over time;
a detector coupled to the memory and configured to detect a change in the recorded frequency curve exceeding a first predetermined threshold value;
an evaluation device coupled to the detector and the memory and configured to determine two far regions in the frequency curve lying before and after the detected change in the recorded frequency curve, the two far regions showing a frequency change below a second threshold value;
a scaling device coupled to the memory and the evaluation device and configured to scale the recorded frequency curve in such a manner that the far regions assume predetermined values; and
a differentiator coupled to the scaling device configured to determine a gradient of the scaled frequency curve in an inflection point thereof and to determine the distance therefrom.
8. The radio beacon according to claim 7, wherein the radio beacon is installed on a multi-lane road and the differentiator is configured to determine a lane, on which the vehicle is passing, from the distance.
9. The radio beacon according to claim 7, wherein the differentiator determines the inflection point by determining a point in the frequency curve, at which the frequency has a predetermined value in the frequency curve.
10. The radio beacon according to claim 7, wherein the differentiator determines the inflection point by determining a point in the frequency curve, at which the frequency corresponds to a frequency mean value of the far regions.
11. The radio beacon according to claim 7, wherein the received signal has at least one carrier frequency modulated with a modulation frequency, and the signal frequency is the modulation frequency, which is obtained in the receiver by demodulation.
12. The radio beacon according to claim 7, wherein the receiver is a dedicated short-range communication (DSRC) or a wireless access in a vehicle environment (WAVE) transceiver.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
It is claimed:
1. An apparatus for detecting hydrogenous materials, comprising:
a. a time-tagged neutron source that provides a stream of fast neutrons directed toward a target;
b. at least one sensing head comprising a neutron sensor and a neutron shield, wherein a portion of said stream of fast neutrons is backscattered from said target to said neutron sensor that produces a neutron count signal dependent on the amount of hydrogenous material present in said target; and
c. a control system comprising a timing circuit, wherein said timing circuit disables said neutron sensor during a time delay beginning at the time said stream of fast neutrons is emitted from said neutron source and enables said neutron sensor after said time delay.
2. The apparatus as recited in claim 1, wherein said timing circuit enables said neutron sensor after said time delay during a window and disables said neutron sensor after said window.
3. The apparatus as recited in claim 1, wherein said control system further comprises a pulse-height analyzer with at least one pulse-height discriminator setting.
4. The apparatus as recited in claim 3, wherein said at least one pulse-height discriminator setting is an upper level discriminator setting.
5. The apparatus as recited in claim 1, wherein said neutron sensor is capable of spatially resolving said neutron count signal so that the location of said target can be determined.
6. The apparatus as recited in claim 5, wherein said neutron sensor comprises a collimating material.
7. The apparatus as recited in claim 5, wherein said neutron sensor comprises a coded-array aperture.
8. The apparatus as recited in claim 1, wherein said neutron source is selected from the group consisting of a fission source, an (alpha, n) source, a (gamma, n) source, and combinations thereof.
9. The apparatus as recited in claim 8, wherein said fission source comprises 252Cf.
10. The apparatus as recited in claim 1, wherein said neutron source is a neutron generator that is capable of being operated in pulse mode.
11. The apparatus as recited in claim 1, wherein said neutron sensor comprises a material selected from the group consisting of 3He, 10B, 6Li, and combinations thereof.
12. The apparatus as recited in claim 1, wherein said neutron sensor is selected from the group consisting of a 3He gas-proportional counter, a 10BF3 gas-proportional counter, a scintillating glass containing 6Li, a scintillating glass containing 10B, a scintillating plastic containing 6Li, a scintillating plastic containing 10B, a scintillating crystal containing 6Li, a scintillating crystal containing 10B, and combinations thereof.
13. The apparatus as recited in claim 1, wherein said neutron shield comprises a material selected from the group consisting of 10B, 6Li, and combinations thereof.
14. The apparatus as recited in claim 1, further comprising an extension arm, one end of said extension arm connected to said sensing head and the other end of said extension arm connected to said control system.
15. The apparatus as recited in claim 1, further comprising a user interface wherein said user interface comprises a means for communicating said neutron count signal to a user.
16. A method for detecting hydrogenous materials comprising the steps of:
a. directing a stream of fast neutrons from a neutron source toward a target;
b. detecting the time when said stream of fast neutrons is emitted from said neutron source;
c. measuring a portion of said stream of fast neutrons that is backscattered from said target after a time delay beginning when said stream of fast neutrons is emitted from said source; and
d. communicating said measurement to a user.
17. The method as recited in claim 16, wherein said measuring occurs after said time delay and only during a window.
18. The method as recited in claim 16, further comprising the step of pulse-height discriminating said measurement.
19. The method as recited in claim 18, wherein said discriminating is performed using an upper level discriminator setting.
20. The method as recited in claim 16, wherein said target comprises an explosive.
21. The method as recited in claim 16, wherein said explosive is a land mine.
22. The method as recited in claim 16, wherein said explosive is unexploded ordinance.
23. The method as recited in claim 16, wherein said target is contraband narcotics.
24. The method as recited in claim 16, wherein said target is biological tissue.