Non-contact sensors for distance measurement from ground surface

Optical and ultrasonic sensors were designed and fabricated for non-contact detection of ground height. Indoor and outdoor experiments were conducted to evaluate the detection performance of both sensors under the following test conditions: moisture content and type of soil; ambient temperature and sunlight intensity; configuration of the ground surface; distance of the sensor from the ground surface; and moving speed of the sensor. The type of soil, the sunlight intensity and the moving speed had little effect on the detection performance of both sensors. The optical sensor could detect the distance from the ground surface accurately in spite of irregularity of the ground surface configuration. High moisture content (40% D.B.) of the soil greatly affected the detection performance of the optical sensor due to the refraction of the light at the water film on the soil surface. On the other hand, the detection performance of the ultrasonic sensor was not affected by moisture content, but was largely influenced by temperature. The detection accuracy of the ultrasonic sensor on an irregular ground surface was greatly affected by the measuring distance due to its wide beam width. Copyright (C) 1996 ISTVS.