Abstract
The Advanced Topographic Laser Altimeter System (ATLAS) was launched
aboard the Ice Cloud and land-Elevation Satellite-2 (ICESat-2) satellite
in September 2018. ATLAS is a single wavelength (532 nm) lidar system
designed to acquire high resolution measurements of the earth’s surface
while also obtaining atmospheric backscatter from molecules, clouds, and
aerosols. Because ATLAS is optimized for altimetry, the atmospheric data
acquired is unique in many respects and requires non-standard analysis
techniques. For example, the high repetition rate laser limits the
vertical extent of the profiles to just 14 km and causes atmospheric
scattering from above 15 km to be added to the scattering in the lower 0
-14 km profile. In addition, the limited vertical range of the acquired
profiles renders it difficult to compute the magnitude of the solar
background and hinders the application of standard calibration
techniques. Despite these limitations, techniques have been developed to
successfully produce data products that have value to the atmospheric
community for cloud and aerosol research and are currently available at
the National Snow and Ice Data Center (NSIDC). In this paper we describe
the ICESat-2 atmospheric channel and the methods used to process the
ATLAS raw photon count data to obtain calibrated backscatter and higher
level products such as layer heights and type, blowing snow, column
optical depth and apparent surface reflectance.