Rainfall Drop Size Distribution Research Articles

Measurements of Rainfall Properties Using Long Optical Path Imaging

Abstract Measurements of long-path optical attenuation of visible light due to rainfall are described, from which rainfall parameters are derived. Novel aspects of the method are the use of a distant uncontrolled and broadband spotlight source, and analysis of image characteristics to obtain the distribution of drop radius a. A theory is developed that uses the image attenuation and spatial resolution to retrieve the two parameters, n0 and Λ, of the distribution n(a) = n0e−Λa. In particular, n0 is obtained to within about 20%; this error is relatively small compared to n0 jumps of more than 100% commonly observed in rainfall data. The method holds promise as an inexpensive path-averaged remotely sensed method for obtaining rainfall intensity and drop size distributions. Its validity is confirmed by a Monte Carlo model for photon scatter and imaging.

Acoustical Rainfall Analysis: Rainfall Drop Size Distribution Using the Underwater Sound Field

Abstract Rainfall estimation is difficult, especially in oceanic regions where land-based techniques are unavailable. Fortunately, rain produces a loud and unique sound underwater that can be used to detect and quantify rainfall. Laboratory studies of the sound generated by individual raindrops have provided the basis for a formal inversion of the naturally generated underwater ambient sound field. Field measurements of subtropical rainfall at the Atlantic Oceanographic and Meteorological Lab Rain Gauge Facility are used to demonstrate the forward (predicting the sound field given the rainfall drop size distribution) and the inverse problem (estimating the drop size distribution given the sound field). This acoustical rainfall analysis (ARA) algorithm was tested for several dozen rainfall events spanning six months and was found to provide excellent estimates of rainfall rate, rainfall accumulation, and rainfall reflectivity (the quantity sensed by radars). High temporal resolution (order 5–10 s) variatio...

Measurements of passive and active microbubbles in the sea

Around 1960 an oceanographer at the Navy Electronics Laboratory dared to question physics laboratory measurements when he wrote an internal memo titled ‘‘Do Invisible Microbubbles Exist at Sea?.’’ Indeed they do! From 1964 to 1974 a series of M.S. students at the Naval Postgraduate School published the first microbubble density distributions at sea. These were measured by several in-situ ocean techniques including: change of transducer impedance; photography; excess attenuation, backscatter and sound-speed dispersion in a small pulse-echo system: Fourier transform of a sawtooth signal propagating between two separated hydrophones. An ‘‘unbelievable’’ immense number of coastal bubbles of radius 15 to 300 μm were found. The 1990s have seen a renaissance in the field. The spatial and temporal variation of bubble numbers have been studied, and acoustical oceanographers now use bubbles as tracers to determine ocean processes near the ocean surface. Sea state noise and rain noise have both been definitively ascribed to the radiation from huge numbers of infant microbubbles. Indeed, the ‘‘noises’’ have now become ‘‘signals.’’ The underwater sound of breaking waves has been inverted to yield the spectrum of ocean wave height and recently the underwater sound of rainfall has been inverted to reveal the real-time rainfall drop size distribution. The distinctive spectrum of underwater sound during rainfall even allows one to describe the clouds from which the rain has fallen. [Work supported by ONR.]

Simulation of the size distribution and erosivity of raindrops and throughfall drops

AbstractThis paper presents a model that simulates the size distribution and erosivity of raindrops and throughfall drops. It utilizes existing models of rainfall drop size distribution and fall velocity and combines them with newly collated evidence of throughfall drop size distributions. A sensitivity analysis reveals that the model is sensitive to parameters that are easily measured or estimated: rainfall intensity, the mean volume drop diameter of the intercepted throughfall, canopy cover, and canopy height.The results of the model may be used at two levels. Firstly, to calculate specifically the size and fall velocity of individual drops, parameters that are needed in studies examining the response of soil surfaces to forces applied by rainfall. Secondly, to produce erosivity indices, based on rainfall intensity but which take account of the effects of a vegetation canopy. The paper shows that while the kinetic energy of rainfall (E(0), J mm−1 m−2) may be calculated from an equation of the familiar form: the kinetic energy of throughfall under any canopy may be calculated by combining this equation with another that relates the energy of drops under a 100 per cent canopy cover (E(100)) and the canopy height: .

Transformations of Rainfall by Plant Canopy

ABSTRACT IT is shown by measurement and analysis that plant canopy transforms rainfall characteristics of drop size, spatial distribution of volume and spatial distribution of drop size. Transformed rainfall drop size distributions are presented for four species. Spatially redistributed rainfall characteristics under corn and soybean are also shown. Implications of rainfall transformations for splash detachment of soil particles are explored.

Field measurements of rainfall drop‐size distribution, and the relationships between rainfall parameters and soil movement by rainsplash

AbstractRainfall drop‐size distributions were measured at a site in northern England using the ‘oflour‐pellet’ technique. A relationship between intensity and kinetic energy is presented. Even at the low rainfall intensities observed (< 5 mm h−1 average over an hour) measureable amounts of rainsplash movement took place, and these movements have been related to rainfall parameters.