Methods and systems for detecting road surface conditions

1. A method for detecting road surface conditions, the method comprising:

transmitting one or more radio frequency (RF) beams at a road surface;

receiving RF reflections of the one or more transmitted RF beams at two or more receive channels;

determining a road surface condition based on a doppler signature of the received RF reflections;

performing Frequency Fourier Transform (FFT) processing of the RF reflections on each of the two or more receive channels;

determining range, doppler, phase difference and magnitude based on the FFT processing;

determining angle and azimuth of the RF reflections based on the phase difference;

filtering the received RF reflections to remove those RF reflections that originate outside the FoV;

determining a doppler speed from the filtered RF reflections;

generating a normalized doppler signal that is a function of the doppler speed and a vehicle speed; and

generating first and second histograms of the normalized doppler signal;

wherein the first histogram comprises data received from the RF reflections originating from a near region of the road surface and the second histogram comprising data from the RF reflections originating from a far region of the road surface, and

determining the road surface condition based a quality factor (Q-factor) of each histogram.

2. The method of claim 1 further comprising transmitting the one or more RF beams using one or more sensors.

3. The method of claim 2 further comprising directing the one or more RF beams in front of and/or behind a vehicle traveling on a road surface.

4. The method of claim 1 controlling the transmission of the one or more beams such that each beam has a field of view (FoV) selected to limit a spread of normalized doppler and provide a statistical amount of data sufficient for an accurate determination of a road surface condition.

5. The method of claim 4 further comprising generating an RF waveform for transmission via the one or more RF beams, the RF waveform comprising a plurality of chirps with each chirp having a transmit duration.

6. The method of claim 5 further comprising generating each chirp to have a slope that is a function frequency change over the transmit duration.

7. The method of claim 5 wherein a single data cycle count comprises 64 chirps.

8. A road surface condition detector comprising:

a transmitter configured to transmit one or more radio frequency (RF) beams at a road surface;

a receiver configured to receive RF reflections of the one or more transmitted RF beams at two or more receive channels;

one or more processors configured to:

determine a road surface condition based on a doppler signature of the received RF reflections,

perform Frequency Fourier Transform (FFT) processing of the RF reflections on each of the two or more receive channels;

determine range, doppler, phase difference and magnitude based on the FFT processing;

determine angle and azimuth of the RF reflections based on the phase difference;

filter the received RF reflections to move those RF reflections that originate outside the FoV;

determine a doppler speed from the filtered RF reflections;

generate a normalized doppler signal that is a function of the doppler speed and a vehicle speed;

generate first and second histograms of the normalized doppler signal;

wherein the first histogram comprises data received from the RF reflections originating from a near region of the road surface and the second histogram originating from a far region of the road surface; and

determine the road surface condition based a quality (O) factor of each histogram.

9. The detector of claim 8 wherein the transmitter comprises one or more spaced apart sensors configured to transmit the one or more RF beams.

10. The detector of claim 8 wherein the transmitter is further configured to direct the one or more RF beams in front of and/or behind a vehicle traveling on a road surface.

11. The detector of claim 10 wherein the transmitter is further configured to control the transmission of the one or more beams such that each beam has a field of view (FoV) selected to limit a spread of normalized doppler and provide a statistical amount of data sufficient for an accurate determination of a road surface condition.

12. The detector of claim 11 wherein the transmitter generates an RF waveform for transmission via the one or more RF beams, the RF waveform comprising a plurality of chirps with each chirp having a transmit duration.

13. The detector of claim 12 wherein each chirp has a slope that is a function frequency change over the transmit duration.

14. The detector of claim 13 wherein a single data cycle count comprises 64 chirps.