In 2009, Department of Water Management (DWM) at TU Delft conceptualized the design of a low-cost disdrometer suitable for large scale, remote deployment. But, being a novel idea, its electrical characteristics were not well researched. Also, the system was not sensitive enough to measure the raindrops of diameter less than 0.9mm. Furthermore, it was found that the proposed disdrometer suffers from the edge effect i.e. when a raindrop hits on the edge of the disdrometer; the size of the raindrop is underestimated. All the aforementioned issues have been addressed in this research. The presented work discusses the electrical characteristics of the disdrometer. A readout circuit has been designed to improve the performance of the disdrometer and an innovative technique has been developed to solve the problem of edge effect. The impedance response of the disdrometer has been analyzed and an equivalent electrical model of the proposed disdrometer has been developed and characterized. Furthermore, an elaborative analysis of the edge effect has been presented. Based on this analysis, an innovative technique has been proposed for reducing the edge-effect. This technique uses the envelope of the transducer’s output to determine if the drop hit on edge. Also, a low-power (17.8mA@5V), low-noise (7.8µVrms) readout circuit has been designed. This readout circuit is able to measure the drops of size as low as 0.4mm. Because of the achieved results, this disdrometer is attracting a lot of attention of various groups from industry as well as from academia. A group of researchers from the DWM, TU Delft is looking forward to turn it in to a commercial product.

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An acoustic water tank disdrometer

Characterization and Design of a Readout Circuit for a Piezoelectric-based Acoustic Disdrometer

Several rain drop size distribution (DSD) point measurement technologies exist, but all are unable to sample either short timescales or the large drop tail of the DSD due to inherent instrumental limitations. The development of an acoustic water tank disdrometer (AWTD) is described, which improves the sampling statistics by increasing the catchment area. This is achieved by distinguishing individual drops, locating them on the surface of the tank then converting the impact pressure into a drop size. Wavelet decomposition is used to distinguish the broadband, short duration impact events and a fast multilateration method is used to position the drop. Issues relating to the different types of noise are also investigated and mitigated. Also, further work on inverting the measured acoustic intensity into a DSD, by fitting sampling distributions, is presented. Six months of data were collected in the Eastern UK. The AWTD then converted the data into DSDs and the results were compared to a commercially available co-located laser precipitation monitor. The sampling errors are far lower due to the increased catchment size, and hence the large drop sized tail of the DSD is greatly improved. DSD results compare favourably to other disdrometers for drop diameters greater than 1.8 mm. Below this size individual drops become increasingly difficult to detect and are underestimated.

http://iopscience.iop.org/article/10.1088/0957-0233/24/6/065801/pdf

An acoustic water tank disdrometer

Citations

Characterization and Design of a Readout Circuit for a Piezoelectric-based Acoustic Disdrometer

Direct and indirect measurement of rain drop size distributions using an acoustic water tank disdrometer

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