IITB_TDR: A portable TDR system with DWT based denoising for soil moisture measurement

In this paper, we have discussed design and development of Time domain reflectometery (TDR) system called as IITB_TDR and also explained the novel TDR signal analysis method with wavelet based denoising technique in order to determine the soil moisture. Among the reported soil measurement techniques, the TDR is known for the accuracy, robustness and ease of use for in-situ measurement. Even-though TDR is an established technique, high cost and complex design restrict its penetration into the agricultural practices. The complexity of the TDR system is mainly due to the need of time synchronization between the pulse generator which generates the EM wave and sampler which samples the pulse with few hundreds of pico seconds resolution. In IITB_TDR, the pulse generator and sampler run independent of each other without requiring the time synchronization. The proposed design uses the equivalent time sampling with an adaptive delta modulation and the sampling resolution of 100 ps has been achieved. To analyze the captured TDR signal, a novel time extraction method with wavelet transform based denoising is also proposed in this paper. The IITB_TDR system and signal analysis technique have been tested with 5 different standard materials and three different types of soil for various levels of moisture. The maximum difference of ±2% and ±3% has been observed with the IITB_TDR system when compared with the standard oven drying technique and commercial TDR.