A system is for sensing a property of a material mat from a construction vehicle. The system includes a sensor for sensing the material property and a positioning mechanism connected with the vehicle and with the sensor. The mechanism displaces the sensor between first and second positions with respect to the vehicle as the vehicle displaces with respect to the material mat. The first sensor position is spaced a substantial distance above the mat upper surface. The second sensor position is located proximal to or on the mat surface such that the sensor is able to sense the material property in the second position. A controller operates the mechanism to sequentially displace the sensor from the first to second positions, permit the sensor to remain disposed at the second position for a period of time, and displace the sensor from the second to first positions after the period of time.