Wu Yonghua, Gan Chuen Meei, Cordero Lina, Gross Barry, Moshary Fred, Ahmed Sam
Optical Remote Sensing Laboratory, City College of New York, New York, New York 10031, USA.
Appl Opt. 2011 Jul 20;50(21):3987-99. doi: 10.1364/AO.50.003987.
Calibration is essential to derive aerosol backscatter coefficients from elastic scattering lidar. Unlike the visible UV wavelengths where calibration is based on a molecular reference, calibration of the 1064 nm lidar channel requires other approaches, which depend on various assumptions. In this paper, we analyze two independent calibration methods which use (i) low-altitude water phase clouds and (ii) high cirrus clouds. In particular, we show that to achieve optimal performance, aerosol attenuation below the cloud base and cloud multiple scattering must be accounted for. When all important processes are considered, we find that these two independent methods can provide a consistent calibration constant with relative differences less than 15%. We apply these calibration techniques to demonstrate the stability of our lidar on a monthly scale, along with a natural reduction of the lidar efficiency on an annual scale. Furthermore, our calibration procedure allows us to derive consistent aerosol backscatter coefficients and angstrom coefficient profiles (532-1064 nm) along with column extinction-to-backscatter ratios which are in good agreement with sky radiometer inversions.
校准对于从弹性散射激光雷达推导气溶胶后向散射系数至关重要。与基于分子参考进行校准的可见紫外波长不同，1064 nm激光雷达通道的校准需要其他方法，这些方法依赖于各种假设。在本文中，我们分析了两种独立的校准方法，它们分别使用（i）低空水相云以及（ii）高卷云。特别地，我们表明，为实现最佳性能，必须考虑云底以下的气溶胶衰减和云的多次散射。当考虑所有重要过程时，我们发现这两种独立方法能够提供相对差异小于15%的一致校准常数。我们应用这些校准技术来证明我们激光雷达在月度尺度上的稳定性，以及在年度尺度上激光雷达效率的自然下降。此外，我们的校准程序使我们能够得出一致的气溶胶后向散射系数和埃斯特朗系数剖面（532 - 1064 nm），以及与天空辐射计反演结果高度吻合的柱消光与后向散射比。
