GLAS/ICESat L1A Global Laser Pointing Data V018

The Geoscience Laser Altimeter System (GLAS) instrument on the Ice, Cloud, and Land Elevation Satellite (ICESat) provides global measurements of polar ice sheet elevation to discern changes in ice volume (mass balance) over time. Secondary objectives of GLAS are to measure sea ice roughness and thickness, cloud and atmospheric properties, land topography, vegetation canopy heights, ocean surface topography, and surface reflectivity.

GLAS has a 1064 nm laser channel for surface altimetry and dense cloud heights, and a 532 nm lidar channel for the vertical distribution of clouds and aerosols.

Level-1A global laser pointing data (GLA04) contain two orbits of attitude data from the spacecraft star tracker, instrument star tracker, gyro, and laser reference system, and other spacecraft attitude data required to calculate precise laser pointing. Data are in scaled integer binary format, big-endian (Unix) byte order, and are available via FTP.

冰、云与陆地高程卫星（Ice, Cloud, and Land Elevation Satellite, ICESat）搭载的地球科学激光测高系统（Geoscience Laser Altimeter System, GLAS）可获取极地冰盖高程的全球观测数据，以辨识冰体体积（物质平衡）随时间的变化。GLAS的次要科学目标还包括测量海冰粗糙度与厚度、云与大气特性、陆地地形、植被冠层高度、海洋表面地形及地表反射率。

GLAS配备1064纳米激光通道，用于地表测高与浓密云体高度探测；同时搭载532纳米激光雷达（lidar）通道，用于获取云与气溶胶的垂直分布信息。

Level-1A 全球激光指向数据（GLA04）包含来自航天器星跟踪器、仪器星跟踪器、陀螺仪与激光参考系统的两条轨道姿态数据，以及计算精确激光指向所需的其他航天器姿态数据。该数据采用缩放整数二进制格式，遵循大端（Unix）字节序，可通过FTP获取。