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Continuous time-series spectral data are important for inversion of crop or soil information. UAV remote sensing is usually selected under clear and windless weather conditions, but it is not possible to have such weather every day, which results in the UAV not collecting continuous daily spectral information. To explore this issue, we focused on summer maize with four irrigation levels as the research subject. A UAV platform with a multispectral sensor was used to acquire measured spectra of the maize canopy. The solar zenith angle was calculated and substituted into the Ambrals kernel-driven model to obtain simulated spectral data for the maize canopy, and the time-series UAV spectral data were complemented. Then, four vegetation indices (VIs) were established using simulated and measured spectral data, respectively, and the accuracy of the simulated VIs was evaluated. Finally, the simulated and measured VIs were used to monitor and evaluate variations in soil surface moisture content, respectively, and provide irrigation warning. The results demonstrated that Ambrals kernel-driven model can be used to simulate the reflectance of maize canopy collected by UAV. The simulated reflectance can complement time-series UAV spectral data and be used to establish VIs, among which Structure Intensive Pigment Index (SIPI) was established with the highest accuracy (R = 0.729). The VIs established by simulated reflectance can be used to monitor soil surface moisture content, and the monitoring effect is similar to the measured data (R2 = 0.642, RMSE = 0.42). It can evaluate the soil moisture a few days after irrigation and ensure the continuity and timeliness of soil moisture data, so as to improve the crop irrigation system and carry out irrigation warning. These results have certain reference for the supplementation of time-series spectral data and farmland irrigation using UAV multispectral remote sensing. [ABSTRACT FROM AUTHOR]

Pure CCl[sub 3]F (Freon-11) vapor, initially below its room-temperature saturated vapor pressure, was compressed behind weak incident shock waves. The initial pressure was varied from 26 to 747 mm Hg, and the shock speed was varied from 141 to 321 m/s. The equilibrium cluster-size distribution was thus perturbed to varying degrees. Under the present experimental conditions cluster-forming processes en route to homonuclear condensation were set into motion. The exothermic redistribution of cluster sizes at the new temperature and pressure was monitored using the laser-schlieren technique over a time period of 10–300 μs. A characteristic redistribution time scale was measured as a function of temperature and pressure. The measured temperature and pressure dependence of the redistribution times are different than the classical temperature and pressure dependence of lag times in supersaturated vapors. A negative activation energy is observed, indicative of a strong competition between cluster formation, redissociation, and stabilization. A stability analysis of the nonlinear kinetic mechanism leads to a criterion for the onset of oscillations, and provides a basis for extracting elementary rate constants from the observations. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]