A microwave sensor for agricultural implements

For soil preparation, the concept of precision agriculture requires real time measurements of soil characteristics and cultivator behavior. The microwave sensor presented in this paper overcomes the limitations of sensors based on optical or ultrasound devices towards agricultural environment (dust, rain, etc.). The sensor uses the principle of frequency-modulated continuous wave (FM-CW) radar, low cost technology well intended for short range applications. First laboratory results of two major applications are presented. The first one is the distance measurement applied to the control of working depth. Soil-implement distances are computed with the measurement of a beat frequency: a maximum positioning error of ±5 mm is obtained for distances between 0.7 and 1 m. The second one is the evaluation of soil roughness in order to control seedbed quality. The backscattered coefficient, measured at normal incidence with samples of dry soil, is correlated with the rms height.