Road pavement reflectance is usually assumed to be invariant in short periods of time in some quantitative remote sensing applications. To examine its variability, reflectance sequences of concrete and asphalt pavement are measured in field for half a day in visible and near-infarecd (VNIR) spectral range using dual-beam method. As much as 20.7% and 3.52% of relative changes are found in asphalt and concrete reflectance data at 550 nm, and all VNIR bands demonstrate similar variations found to correlate with both illumination geometry and the relative portion of diffuse irradiance. In this letter, this effect is interpreted from a mathematic view. Further studies are needed to model the dynamics of reflectance physically.

利用PPG-Ⅰ脉冲功率装置(500 kV,400 kA,100 ns)驱动X箍缩负载,得到了μm量级的亚纳秒脉冲X射线辐射点源。在阴阳极轴线和回流柱上同时安装X箍缩负载,前者可作为背光照相的X射线点源;后者可作为被拍照的目标X箍缩。获得了X箍缩发展过程不同时刻的时间序列图像,在背光照相的图像中可以清晰观察到X箍缩交叉点处等离子体的外爆、箍缩以及最终的崩溃阶段。将阴阳极轴线上的X箍缩负载用Z箍缩丝阵负载代替,实现了对丝阵负载Z箍缩放电起始阶段的X射线背光照相,观察到了最初的各单丝电爆炸、等离子体膨胀及融合过程,同时观察到了双丝Z箍缩发展过程中的等离子体不稳定性。实验结果有助于深入理解Z箍缩发展的物理过程,同时可为有效的模拟建模分析提供基本的实验数据。