Rayleigh waves (or surface waves) are commonly used for vibration-based nondestructive testing. Two examples are Spectral Analysis of Surface Waves (SASW) and Multichannel Analysis of Surface Waves (MASW), which are both used to detect subsurface properties for geologic inspections. Recently, efforts have been made to scale down these subsurface detection approaches to see how they perform on small-scale structures such as concrete slabs and pavement. Additional efforts have been made to replace the traditional surface-mounted transducers with non-contact acoustic transducers. Though some success has been achieved, most of these new approaches are inefficient because they require point-to-point measurements and off-line signal analysis. This poster introduces the MASS (Mobile Acoustic Subsurface Sensing) system, which is an improved surface wave-based approach for measuring the subsurface profile of pavement structures. The compact MASS system is a 3-wheeled cart outfitted with an electromagnetic hammer (impact source), non-contact acoustic sensors, and data acquisition and processing equipment. A key advantage of the MASS system is that it can collect measurements continuously at walking speed. This is due to the non-contact sensors and a fast inversion analysis algorithm that estimates shear velocity profile and elastic modulus instantaneously. The theory behind the MASS system, hardware/ software integration, and field test results are presented in this poster.