REMOTE SENSING OF RAINFALL PARAMETERS BY LASER SCINTILLATION CORRELATION--EXPERIMENT AND ANALYSIS

Remote sensing of rainfall parameters—rainfall rate and size distribution—by raindrop-induced laser bcam scintillation is a new kind of precipitation measurement technique. This paper presented the primary field experiment results based on the theory and numerical simulations by Wu and Lü (1984, 1985) and Lü and Wu (1984).Rainfall rate and size distribution were deduced from observations of laser beam scintillation and compared with those of the filter-paper sampling method. Qualitative analysis of the experiment error was also given here. All the work showed that the theory is applicable, and under proper experiment conditions, remote sensing of rainfall parameters by laser scintillation correlation is an advanced and accurate technique.

Turbulence and Rainfall Microphysical Parameters Retrieval and Their Relationship Analysis Based on Wind Profiler Radar Data

Rainfall is triggered and mainly dominated by atmospheric thermo-dynamics and rich water vapor.Nonetheless, turbulence is also considered as an important factor influencing the evolution of rainfall microphysical parameters. To study such an influence, the present study utilized boundary layer wind profiler radar measurements. The separation point of the radar power spectral density data was carefully selected to classify rainfall and turbulence signals;the turbulent dissipation rate ε and rainfall microphysical parameters can be retrieved to analyze the relationship betweenε and microphysical parameters. According to the retrievals of two rainfall periods in Beijing 2016, it was observed that(1) ε in the precipitation area ranged from 10^(-3.5) to 10^(-1) m^(2) s^(-3) and was positively correlated with the falling velocity spectrum width;(2) interactions between turbulence and raindrops showed that small raindrops got enlarge through collision and coalescence in weak turbulence, but large raindrops broke up into small drops under strong turbulence, and the separation value of ε being weak or strong varied with rainfall attributes;(3) the variation of rainfall microphysical parameters(characteristic diameters, number concentration, rainfall intensity, and water content) in the middle stage were stronger than those in the early and the later stages of rainfall event;(4) unlike the obvious impacts on raindrop size and number concentration, turbulence impacts on rain rate and LWC were not significant because turbulence did not cause too much water vapor and heat exchange.

Reasonable selection of yield criteria for quantitative analysis of unsaturated soil slope stability

The yield criterion parameters of the soil material change with different values of the cohesion and the angle of friction because of sustained rainfall infiltration. Based on the Mohr-Coulomb(M-C) and Drucker-Prager(D-P) yield criteria, some reasonable yield criteria selections were discussed for quantitative analysis of unsaturated soil slope stability. Moreover, a critical point was found at the effective angle of friction equaling to 16.5° by transformation of parameters related to unsaturated soil under sustained rainfall. When the effective angle of friction more than 16.5° through parameter transformation of different yield criteria under natural condition, the calculation result of the safety factor was such that: f(DP1) > f(M-C) > f(equivalent M-C) > f(DP2) > f(DP3). While the effective angle of friction less than 16.5°, through parameter transformation, the safety factors were in the following order: f(DP1) > f(M-C) > f(DP2) > f(equivalent M-C) > f(DP3). The calculated results from a case study showed that the equivalent M-C yield criterion should be the best at evaluating soil slope stability before rainfall; the DP2 yield criterion should be selected to calculate the soil slope stability at the effective angle of friction less than 16.5° under sustained rainfall. The yield criterion should be selected or adjusted reasonably to calculate the safety factor of unsaturated soil slopes before and during sustained rainfall.