Use of an L-band radiometer for proximal moisture measurement in road construction

The moisture content level during compaction plays a crucial role in the performance of road pavements. Current state-of-the-art methods involve manually taking small samples from a few isolated locations, making it difficult to monitor the spatial variation in moisture content along the entire construction corridor during compaction in an economically feasible manner. Therefore, finding an easy and effective method to measure soil moisture is a matter of importance. In agricultural applications, L-band passive microwave has proven to be the most accurate method for measuring soil moisture, with current satellites having a spatial resolution of approximately 40 km, which however is too coarse for road construction. Nevertheless, this technology can be deployed closer to the ground, to the point that a spatial resolution of less than 10 m is possible to achieve. Consequently, this study demonstrates the effectiveness of an L-band passive microwave radiometer for measuring soil moisture in the context of optimum compaction for road construction materials. An L-band radiometer called ELBARA-III was used to measure near-surface soil moisture in a 4.5 m × 7.5 m × 0.3 m test-bed having a sand subgrade and then an unbound granular material (UGM) sub base/base. The moisture content of the material was measured using traditional techniques such as taking thermogravimetric physical samples at targeted locations at 50 mm depth to validate the results. The results demonstrated that the L-band microwave radiometer can provide an accuracy of 5 % volumetric moisture content (VMC) or 3 % gravimetric moisture content (GMC) for sand subgrade and 2 % VMC or 1 % GMC for UGM sub base/base. An incidence angle of 0° using dual or single (horizontal or vertical) polarization was found to be the most effective configuration since it is less affected by surface roughness and is recommended for use in further field testing.