GLAS/ICESat L1A Global Laser Pointing Data, Version 33

NOTE ON GLAS BINARY DATA: Access to all ICESat/GLAS binary data products at NSIDC DAAC was removed 01 August 2017.The Binary Data Subsetter also has been decommissioned.ICESat/GLAS data remain available in HDF5 format.

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.

ICESat/GLAS二进制数据说明：NSIDC DAAC提供的所有ICESat/GLAS二进制数据产品的访问权限已于2017年8月1日移除，二进制数据子集器也已停用。目前ICESat/GLAS数据仍以HDF5格式开放获取。

搭载于冰、云与陆地高程卫星（Ice, Cloud, and Land Elevation Satellite, ICESat）上的地球科学激光测高系统（Geoscience Laser Altimeter System, GLAS）可开展极地冰盖高程的全球测量，以追踪冰体体积（物质平衡）随时间的变化。GLAS的次要科学目标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、海洋表面地形以及地表反射率。

GLAS配备1064纳米激光信道，用于地表测高与厚云高度探测；同时搭载532纳米激光雷达信道，用于获取云与气溶胶的垂直分布信息。

1A级全球激光指向数据（GLA04）包含航天器星敏感器、仪器星敏感器、陀螺仪与激光参考系统的两轨姿态数据，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，字节序为大端（Unix）格式。