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A novel low-cost low-complexity design based on Radar technology operating at millimeter wave is presented for
the characterization of road surface conditions in real-time. At frequencies of 24-77 GHz the wavelength is long
enough to obtain slight penetration in the top 1-2" of asphalt or concrete surface, but is also short enough to
resolve details such as crack or pothole depth/etc. The Radar system operates by continuously outputting
radiation and sampling the roadway-reflected radiation through a receiver-downconverter-sampler system.
In initial laboratory testing, the received signal strength was observed to obey the inverse distance 1/R2
relationship. The received signal is further dependent on the incidence angle between the plane of the sensor and
the plane of the roadway. One observation from this is the need of auxiliary sensors for determining the distance
above the road surface as well as providing incident angle data.
The sensor was further mounted on a movable cart used to measure the reflected signal on a variety of road
surfaces (smooth, rough, surface defects, and environment factors such as various levels of moisture). By
comparing measurements of the material after soaking to measurements in the dry state, there is substantial
differentiation in measurements, which indicates the ability to measure the porosity of various materials.
Lastly the sensor bandwidth provides the capability to measure surface roughness illustrated in the standard
deviation of measurement data. On a macroscopic level, the aggregate in a roadway acts as a series of random
scatterers and rough roadways or roadways with surface voids show a large variance between measurements of
nearby points.
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