Showing papers on "Disdrometer published in 1998"
TL;DR: In this paper, a long-term temporal model governed by a renewal process whose survival law is a Bi-Pareto law of the third kind is presented and analyzed to derive a long term temporal model for predicting the total fallen-water height and the conversion between various rain gauge integration times.
Abstract: A disdrometer simultaneously measuring time of arrival and size of raindrops was set up in the Paris, France, area. Data collected over a period of 25 months (May 1992 to May 1994) are presented and analyzed to derive a long-term temporal model governed by a renewal process whose survival law is a Bi-Pareto law of the third kind. The model thus found allows nearly nine orders of magnitude of the time intervals between raindrops to be mathematically represented at the same time using only six parameters. The analysis presented here does not consider rainfall intensity and the nature of rain (convective, stratiform, etc.) as classification parameters. This approach, which may at first sight seem objectionable, is justified by the quality of the statistical inferences that can be made from the model. Two such applications are described—namely, the prediction of the total fallen-water height and the conversion between various rain gauge integration times, which are often necessary for telecommunicati...
98 citations
TL;DR: In this article, a new optical disdrometer was developed that is optimized for use in high wind speeds, for example, on board ships, where each drop is measured separately with regard to its size and residence time within the sensitive volume.
Abstract: A new optical disdrometer has been developed that is optimized for use in high wind speeds, for example, on board ships. The minimal detectable size of droplets is 0.35 mm. Each drop is measured separately with regard to its size and residence time within the sensitive volume. From the available information, the drop size distribution can be calculated with a resolution of 0.05 mm in diameter either by evaluation of the residence time of drops or by drop counting knowing the local wind. Experience shows that using the residence time leads to better results. Rain rates can be determined from the droplet spectra by assuming terminal fall velocity of the drops according to their size. Numerical modeling of disdrometer measurements has been performed, allowing the study of the effect of multiple occupancy of the sensitive volume and grazing incidences on disdrometer measurements. Based on these studies an iterative procedure has been developed to eliminate the impact of these effects on the calculated drop size distributions. This technique may also be applied to any other kind of disdrometer. Long-term simultaneous measurements of the disdrometer and a conventional rain gauge have been used to validate this procedure.
52 citations
TL;DR: In this article, the erosive effect produced by direct raindrop impact on the soil surface may be quantified in terms of the raindrop kinetic energy (KE), which is usually calculated from the rainfall rate even though a precise description of raindrop size distribution is required.
Abstract: The erosive effect produced by direct raindrop impact on the soil surface may be quantified in terms of the raindrop kinetic energy (KE). This variable is usually calculated from the rainfall rate even though a precise description of the raindrop size distribution is required. In this study, raindrop size and fall velocities were measured for 2 yr in Barcelona, Spain, with an optical disdrometer. Fitted drop-size distributions were used to obtain relationships between raindrop KE and rainfall rate. A comparison between KE calculated from experimental distributions indicated that the lognormal distribution model was most suitable to provide a KE-rainfall rate relation. Predicted KE values from this relationship had better agreement with observations (differences of 7%) than predicted values from other models based on different rainfall conditions.
46 citations
TL;DR: In this article, it is shown that drop counts at different sizes are correlated rather than independent, and it is argued that it is more appropriate to characterize rain statistically as a doubly stochastic Poisson process (Poisson mixture) among a collection of correlated random variables (fluxes) each having its own probability distribution of unpredictable (random) mean values and its own coherence time, τM.
Abstract: For M drop size categories, rain is frequently viewed simply as the superposition of M, statistically independent Poisson-distributed drop fluxes each described by its own mean concentration. Implicit in such a Poissonian model is the assumption of uncorrelated counts among the drops. However, it is well known that drop size distributions are the result of the processes of collision, coalescence, and breakup, which should lead to correlations. This inconsistency is resolved in this work. Using 1-min disdrometer measurements, two-point cross-correlation functions are used to show that drop counts at different sizes are correlated rather than independent. Moreover, it is argued that it is more appropriate to characterize rain statistically as a doubly stochastic Poisson process (Poisson mixture) among a collection of M correlated random variables (fluxes) each having its own probability distribution of unpredictable (random) mean values and its own coherence time, τM. It is also shown that a drop s...
44 citations
TL;DR: In this article, the authors present results of computational fluid dynamics calculations of the measurement error of the video disdrometer based on the high resolution observations of drop size distribution and wind velocity.
41 citations
TL;DR: In this paper, a ship rain gauge has been developed that can be used under high wind speeds such as those experienced by ships at sea, which can be calibrated at sea against a specially designed optical disdrometer.
Abstract: A ship rain gauge has been developed that can be used under high wind speeds such as those experienced by ships at sea. The instrument has an improved aerodynamic design and an additional lateral collecting surface, which is effective especially with high wind speeds. The ship rain gauge has been calibrated at sea against a specially designed optical disdrometer. An accuracy of 2%–3% has been obtained for 6-hourly sums. The ship rain gauge has also successfully been tested at a test site of the German Weather Service and presently is used on research vessels and voluntary observing ship.
39 citations
TL;DR: In this paper, an optical spectrometer within the melting layer of stratiform precipitation was used to measure the number flux density of snowflakes and raindrops, and strong evidence was found for aggregation of hydrometeors within the upper part of a melting layer and breakup within the lower part.
36 citations
TL;DR: In this paper, vertical profiles of drop size distribution (DSD) parameters were obtained from data collected with the National Oceanographic and Atmospheric Administration 915 and 50-MHz Doppler radars at Darwin, Australia, for the 1993-94 monsoon season.
Abstract: Vertical profiles of drop size distribution (DSD) parameters are produced from data collected with the National Oceanographic and Atmospheric Administration 915- and 50-MHz Doppler radars at Darwin, Australia, for the 1993–94 monsoon season. An existing algorithm is used to retrieve gamma size distribution parameters from the VHF and UHF Doppler radar spectra. The clear-air mean velocities and spectral widths obtained from the VHF radar are used to fit DSDs accurately to UHF spectra. Uncertainties in retrieved precipitation parameters are estimated from errors in both VHF and UHF spectra. The statistics of the retrieved profiles of DSD parameters are summarized and compared with surface disdrometer data from a site near Darwin. Retrieved vertical profiles of gamma DSDs are input to a microwave radiative transfer model to determine realistic variations in upwelling 10- and 19-GHz brightness temperatures due to uncertainties in drop size distribution. These brightness temperature variations are the...
12 citations
06 Jul 1998
TL;DR: In this paper, the development in both surface and spaceborne methods and algorithms for the improved use of radar and satellite data to measure rainfall are studied and analyzed, in an effort to study the best possible quality of satellite and radar rain estimates, several products have to be selected and developed from calibrated radar-and satellite data.
Abstract: Precipitation is an important environmental parameter which affects the hydrology of the land surface, coastal processes, climate and global heat circulation. Understanding of rainfall distribution and its intensity can improve protection of the environment and knowledge of geophysical process of land, ocean and atmosphere. The use of satellite-derived products to estimate precipitation over land is important for monitoring the spatial and temporal distributions of precipitation. In this study the development in both surface and spaceborne methods and algorithms for the improved use of radar and satellite data to measure rainfall are studied and analysed. In an effort to study the best possible quality of satellite and radar rain estimates, several products have to be selected and developed from calibrated radar and satellite data. These products are processed to get information on areal distribution of reflectivity, rain existence and analysis. Using measurements from disdrometer, ground-based radar and raingauges, raindrop size distribution will be studied and used in analysing TRMM satellite rain retrieval.
2 citations
06 Jul 1998
TL;DR: In this article, a comparison of multiparameter radar and in-situ microphysical observations in winter precipitation during two storm events of different characteristics is presented, including, investigation of radar signatures of these storms to study their microphysical evolution, generation of insitu particle size distribution using the 2D-video disdrometer at different integration times, as well as estimation of particle densities and shapes.
Abstract: Polarimetric radars are very useful for remote sensing of storm microphysics. Multiparameter radar signatures have been used for quantitative and qualitative interpretation of convective storms. However, the interpretation of these signatures for aggregating snow particles is complicated because of many unknowns, such as bulk densities, and shapes of snow particles. During the winter of 1996-1997, extensive data were collected in Colorado winter storms using the CSU-CKILL radar in conjunction with a 2D-video disdrometer located on ground. This paper presents a comparison of multiparameter radar and in-situ microphysical observations in winter precipitation during two storm events of different characteristics. The comparison includes, investigation of radar signatures of these storms to study their microphysical evolution, generation of in-situ particle size distribution using the 2D-video disdrometer at different integration times, as well as estimation of particle densities and shapes. A model for radar backscatter, considering particle types, shapes, sizes, orientations, and densities is used, providing a framework for microphysical interpretation and for comparing radar signatures and disdrometer observations.
1 citations