EFFICIENT SWATH MAPPING LASER ALTIMETRY DEMONSTRATION INSTRUMENT INCUBATOR PROGRAM Anthony W. Yu, Michael A. Krainak, David J. Harding, James B. Abshire, Xiaoli Sun, John Cavanaugh, Susan Valett NASA Goddard Space Flight Center, Greenbelt, MD 20771 ABSTRACT In this paper we will discuss our eighteen-month progress of a three-year Instrument Incubator Program (IIP) funded by NASA Earth Science Technology Office (ESTO) on swath mapping laser altimetry system. This paper will discuss the system approach, enabling technologies and instrument concept for the swath mapping laser altimetry. 1. INTRODUCTION NASA Goddard Space Flight Center (GSFC) is developing an airborne instrument under the Swath Mapping IIP with the objectives to advance the key technologies and mitigate some of the risks associated with the LIdar Surface Topography (LIST) mission. The key attributes of the LIST mission, as described in the NRC Earth Science Decadal Survey report, are: (1) a medium cost mission to be launched by NASA between 2016-2020; (2) a single-instrument payload carrying an imaging lidar at low Earth orbit; (3) one-time global mapping of land, ice sheet and glacier topography and vegetation structure through the duration of the mission; (4) observe topography and vegetation structure change through time in selected areas; and (5) achieve 5 m horizontal resolution, 0.1 m vertical precision, and absolute vertical accuracy for ground surface topography including where covered by vegetation. LIST is recommended as a third tiered mission with launch date no earlier than 2018 [1]. As pointed out by the LIST study findings, the instrument required to meet the LIST objectives far exceed those of existing space laser altimeter technologies. In simple terms, an instrument needs to be able to generate a swath width of 5 km, image this swath onto a detector array and produce an image that describes the topography of the sampled area, including through foliage if covered by vegetation, and the 3-D structure of the vegetation cover. An advanced mission concept study for LIST was conducted at GSFC in mid-2007 by the LIST Science Working Group (SWG) which links science objectives and measurement requirements for land topography, vegetation structure, ice sheets and glaciers, and inland water bodies. The results of the study highlight key challenges that are driving factors for any laser altimeter instrument approach used to achieve the mission objectives. The instrument must be capable of: (1) mapping a swath with a width of at least 5 km to acquire global coverage in a reasonable amount of time; (2) ranging accurately to the surface through thin to moderate cloud cover in order to acquire complete coverage in regions that are frequently cloudy; (3) operate with solar background noise to accomplish mapping during both day and night conditions (even for a dawn-dusk sun-synchronous orbit the solar zenith angle is large during parts of the year); (4) large dynamic range to accommodate highly varying apparent reflectance conditions due to changes in surface reflectance, atmospheric transmission and canopy cover; (5) high sensitivity in order to detect returns from the ground through dense vegetation cover; (6) an effective pulse rates of 10 kHz or less for atmospheric profiling and unambiguous surface ranging through clouds; and most importantly (7) highest efficiency in order to minimize required power, mass, size, complexity and cost.