Raindrop massage 600011/25/2023 The data were accumulated for 1 min, and recorded each minute. Drops are counted into 20 drop size bins, ranging from 0.3-mm to over 5-mm diameter. The sensor head has a surface area of 50 cm 2. This instrument measures the drop size of individual drops as they strike the sensor head. Of greatest interest in this study are the data from the disdrometer. The relative performance of these automatic rain gauges is reported in Nystuen (1999). Young capacitance rain gauge (CAP), a Belfort 382 tipping-bucket rain gauge, and a custom-built weighing rain gauge. Various rain gauges were deployed nearby, including a Joss–Waldvogel (JW) disdrometer, an Scientific Technology Inc. This sound spectrum was recorded every second. Spectral analysis (filter, FFT, and averaging) were applied to reduce the output to a single 128-point acoustic spectrum (0–50 kHz, 390-Hz resolution, 43 degrees of freedom). A three-stage amplifier was used to increase the dynamic range. Each second a 4096 point time series was recorded at 100 kHz (40.96 ms). The signal was cabled to shore and recorded on a 50-MHz 486 PC computer equipped with a Microstar Laboratories DAP 2400/6 12-bit A/D board. The mangrove trees averaged 5–7 m in height producing a “sheltered” situation with relatively low wind speeds. An ITC-4123 hydrophone was mounted 1.5 m below the surface in a mangrove-lined pond approximately 30 m from the nearest edge. The data for this study are from a 17-month field experiment in Miami, Florida ( Nystuen et al. Finally, the relatively large spatial coverage (catchment area) associated with the underwater sound field allows high temporal analysis of the rain. By using the sound field as a disdrometer, additional descriptors of rain are available to extend this classification potential. Rainfall classification has been attempted acoustically ( Black et al. The relationship between equivalent reflectivity and rainfall rate, the Z– R diagram, can be partitioned acoustically and shows that parts of this diagram are occupied by rain containing specific raindrop populations. The Miami data are used to examine three rainfall research issues. 1996).Īs with any tool to measure rain, one would like to use it to learn about rain. This study extends the Nystuen (1996) result to refine the inversion algorithm, demonstrate its success, and to identify limitations associated with actual measured drop size distributions using an extensive dataset collected in Miami, Florida ( Nystuen et al. Because different raindrop sizes produce distinctive sound underwater, the sound field can be decomposed to measure the drop size distribution in the rain ( Nystuen 1996). 1992 Nystuen and Medwin, 1995) and field studies ( Nystuen 1986 Nystuen et al. 1978) has been developed through laboratory studies on individual drop splashes ( Pumphrey et al. The idea that underwater sound can be used as a signal to detect and quantify rainfall at sea ( Shaw et al. Rain is also one of the principal natural sources of underwater sound. Data are needed to identify occurrence of rain, type of rainfall, and to quantify rainfall amounts. Furthermore, instrumentation to measure rain, especially in oceanic regions, is limited. This is because of its inherent inhomogeneity in both time and space. Rain is one of the most important components of climate, and one of the most difficult to measure. This technique has inherent application in remote oceanic regions where measurements of rainfall are needed to help establish knowledge of the global distribution and intensity of rainfall. And because of its relatively large catchment area, high temporal resolution analysis of rainfall is possible. Rainfall type can be classified acoustically. The relationship between equivalent reflectivity and rainfall rate, the Z– R diagram, is partitioned acoustically showing that parts of this diagram are occupied by rainfall containing specific drop populations. Various measures of rainfall, including rainfall rate, equivalent radar reflectivity, median drop size, and other integrated moments of the drop size distribution are measured acoustically and used to examine rainfall research issues. Limitations to the inversion include problems associated with the relative loudness of the largest drops (diameter over 3.5 mm), the relative quietness of the medium drops (diameter 1.2–2.0 mm), and the influence of wind to suppress the signal from the otherwise remarkably loud small drops (diameter 0.8–1.2 mm). An inversion of the underwater sound to measure the drop size distribution in the rain is described and demonstrated. Five acoustically significant raindrop sizes are described. Different sized raindrops splashing on a water surface produce sound underwater that is distinctive and can be used to measure the drop size distribution in the rain.
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