Abstract Laser altimetry offers the potential to monitor ice-sheet elevation changes with millimeter accuracy. While previous missions have used infrared lasers to make these measurements, NASA's upcoming ICESat (Ice, Cloud, and land Elevation Satellite)-2 mission will use a green laser. Because ice absorbs green light very weakly, in the absence of light-absorbing impurities, green photons can scatter off many snow grains before returning to the surface, delaying the return pulse and leading to an apparent downward shift in the snow surface. In this paper, we explore the effects of snow-grain size and impurity content on these measurements, and investigate strategies that might help minimize the biases they introduce. We find that an uninformed choice of measurement parameters (a windowed mean including a large range of photons around the surface) can result in >0.45 m of apparent surface-height variation between large and small grain sizes. Other choices of measurement parameters, such as a windowed median, can reduce this uncertainty by a factor of two to three. In addition, measurements of surface reflectance at green and infrared wavelengths, and interpretation of return-pulse shapes may be used to estimate and correct for these biases.

中文翻译：

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雪中​​绿光散射引起的激光测高测量偏差建模

摘要 激光高度计提供了以毫米精度监测冰盖高度变化的潜力。虽然之前的任务使用红外激光进行这些测量，但 NASA 即将进行的 ICESat（冰、云和陆地高程卫星）-2 任务将使用绿色激光。由于冰对绿光的吸收非常弱，在没有吸光杂质的情况下，绿光子可以在返回表面之前从许多雪粒上散射出来，延迟返回脉冲并导致雪表面明显向下移动。在本文中，我们探讨了雪粒大小和杂质含量对这些测量的影响，并研究了可能有助于最小化它们引入的偏差的策略。我们发现测量参数的不知情选择（包括表面周围大范围光子的窗口平均值）可能导致大晶粒和小晶粒之间的表面高度变化 >0.45 m。测量参数的其他选择，例如加窗中值，可以将这种不确定性降低两到三倍。此外，绿色和红外波长下的表面反射率测量以及返回脉冲形状的解释可用于估计和校正这些偏差。