GLAS/ICESat L1A Global Altimetry Data, Version 18

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 altimetry data (GLA01) include the transmitted and received waveform from the altimeter. Each data granule has an associated browse product that users can quickly view to determine the general quality of the data in the granule. Browse products consist of image plots of key parameters and statistics. 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）可开展极地冰盖高程的全球测量，以辨识冰体体积（物质平衡）随时间的变化。GLAS的次要观测目标包括海冰粗糙度与厚度、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纳米激光通道，用于地表测高与稠密云体高度测量；同时搭载532纳米激光雷达（lidar）通道，用于探测云与气溶胶的垂直分布。 Level-1A级测高数据（GLA01）包含测高仪的发射与接收波形。 每个数据颗粒（data granule）均配有配套的浏览产品，用户可通过该产品快速查看并判断该数据颗粒的整体质量。浏览产品由关键参数与统计量的图像绘图构成。数据采用缩放整数二进制格式，以大端（Unix）字节序存储，可通过文件传输协议（FTP）获取。