Quantifying Surface Reflectivity for Spaceborne Lidar via Two Independent Methods
Quantifying Surface Reflectivity for Spaceborne Lidar via Two Independent Methods
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DOI：
10.1109/tgrs.2009.2019268
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发表时间：
2009-06
影响因子：
8.2
通讯作者：
M. Disney;Philip Lewis;M. Bouvet;A. Prieto-Blanco;S. Hancock
中科院分区：
文献类型：
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作者：
M. Disney;Philip Lewis;M. Bouvet;A. Prieto-Blanco;S. Hancock
星载差分吸收激光雷达已被提议用于精确测量大气CO2（和表面特性）。激光雷达仪器通常观察到最高可能的表面反射率，因为在反向反射方向（所谓的ldquohotspotrdquo）观察到的阴影最小。观测到的反射率范围将决定仪器的尺寸和信噪比，但很难在全局范围内先验地预测这个范围。提出了两种互补的方法来估计在一系列植被表面类型上的激光雷达反射率。第一种方法是从多角度多光谱反射数据模拟激光雷达仪器的预期响应。第二种方法是利用详细的三维植被结构模型和蒙特卡罗射线追踪来模拟激光雷达信号。模拟用于验证第一种方法，并评估可能的仪器配置的影响。两种方法的一致性都很好，并且对观测误差都很稳健，预测的激光雷达反射率（此处为1570和2050 nm）通常比非最低点反射率高10%到33%，范围在0.02到~ 0.7之间。我们使用三维模拟表明，移位的激光雷达开关脉冲对检索CO2的准确性的影响不大，并且我们证明了三维模拟方法是一种灵活而强大的方式原型未来的星载激光雷达任务。
Spaceborne differential absorption lidar has been proposed for accurate measurements of atmospheric CO2 (and surface properties). Lidar instruments typically observe the highest possible surface reflectance due to observing in the retroreflection direction (the so-called ldquohotspotrdquo) where viewed shadow is minimized. The range of observed reflectance will determine instrument dimensions and signal-to-noise ratio, but it is difficult to predict this range globally a priori. Two complementary methods are presented for estimating lidar reflectivity over a range of vegetated surface types. The first method simulates the expected response of a lidar instrument from multiangle multispectral reflectance data. The second method uses detailed 3-D vegetation structural models and Monte Carlo ray tracing to simulate the lidar signal. The simulations are used to validate the first method and assess the impact of possible instrument configurations. Both methods agree well and are robust to error in observations, with predicted lidar reflectivity (at 1570 and 2050 nm here) typically between 10% and 33% higher relative to off-nadir reflectance and ranging from 0.02 to ~ 0.7. We use the 3-D simulations to show that the impact of shifted on-off lidar pulses is not likely to be significant for accuracy of retrieved CO2, and we demonstrate that the 3-D simulation method is a flexible and powerful way of prototyping future spaceborne lidar missions.