Measurement and modeling of soil moisture basedon dual-sensor data fusion

In order to overcome soil hardness influence on the measured soil moisture data using TDR-3 soil humidity sensor, and to obtain an objective soil moisture, a soil humidity measurement device was designed and developed based on the TDR-3 soil humidity sensor and a soil hardness tester. The device was calibrated by three-factor orthogonal test with factors as the soil moisture, soil hardness and TDR-3 sensor output voltage was carried out through the reverse drying precise calculation of water and soil mass percentage. The mathematical relationship among the three factors was constructed with Matlab software by dualistic curve fitting. Experimental results indicated that the developed device can directly measure mass percentage of soil moisture after fusing output voltage from the TDR-3 sensor with the hardness data from the soil hardness tester. Test result indicated that, after fusing the TDR-sensor output voltage with the soil hardness data, the soil moisture can be measured directly by the device. The error between measured and theoretical values was less than 4.75% and the measurement accuracy could be significantly improved comparing to that only using the TDR-3 sensor. The maximum repeatability error for the same soil was 0.83%, indicating that the model has a certain reliability and robustness. The research can provide a reference for the development of accurate soil moisture sensors.