Water distribution measurement in soil using sound vibration

Abstract

Now in agriculture, it tends to save the agricultural water as much as possible. Therefore, the irrigation method using the minus pressure difference of soil water attracts attention. This method has the nature keeping the water content inside the ground. In other words, when there are crops, it is the mechanism which supplies the water content which is same quantity with the water content that it absorbed. However, effective saving water is not able to be performed, because the water distribution in soil is difficult to grasp. Therefore, we propose a method of monitoring and imaging of the water content in the rooting zone using a sound vibration and the scanning laser Doppler vibrometer (SLDV). The plastic container (40×50×30 cm) which is made from acrylic in the laboratory that had been filled with sand of uniform particle size (200 to 300 μm) was used for this experiment. In this experiment, it measures the status of the water distribution by the change of the vibration propagation. The making method of the moisture distribution is shown below. First, the plastic container is filled with the sand into the plastic container. The water of the fixed quantity is pour into the container. A plastic container is removed after having put it in the sand tank upside down. The size of the water distribution is 14×11×10 cm. This time, the water-content of the reviewed water distribution is 200 ml, 250 ml, and 300 ml. Experiment method is shown as follows. First, there are nine holes to set up the sound source which was covered with the rubber in the sand tank base. It sends vibration with the giant magnetostriction vibrator to have installed in the hole of the sand tank base. SLDV measures the vibration of ground surface excited by sound wave caused from vibratory source. The output waveform uses the burst wave of doing 2 kHz of sine wave, 300 mVpp, 3 cycles. The scan area of SLDV is 17×23 points, the point interval is about 1.8cm. As a result, we can confirm that the distribution of the propagation velocity was a very effective method to the water distribution which is in the shallow position near the ground surface. Also, we can see that the difference of the propagation velocity distribution reflected the difference of the water distribution. We plan to measure when changing the depth of the water distribution position and the implication water ratio in the future.