Rainfall intensity and intermittency over timescales of minutes: Measurement using low sampling-rate acoustic recording

The acoustic recording of rainfall is well established in marine research and monitoring, but less so for application on land. It has several advantages, including the capacity to record the arrival of rainfall at an acoustic sensor with zero latency, and to identify the start and end times of a period of rainfall with high temporal precision. Acoustic data can provide accurate raining time, and in combination with conventional TBRG data that provide rainfall amount, can allow intensity to be characterised significantly more accurately than can be done with a TBRG alone. Conventional acoustic recording generates very large data files (Gb per hour). The solution proposed here is to log the microphone signal much less often-say, only every 10 s. Including date and time stamping of each data point, the resulting files occupy only about 50 kb per hour, or 1.2 Mb per day. A logger equipped with a suitable SD card could thus store acoustic data covering many years, sufficient for long-term deployment. Using a 10 s sampling, the detection of short showers and brief periods of intermittency is also achieved at low cost. It is proposed here that an effective setup for data collection targeting the analysis of rainfall intensity and intermittency would consist of a standard TBRG (for rainfall amounts) co-located with an acoustic recording system as outlined here. Proof-of-concept data are presented.