The electronically steerable flash lidar (ESFL) is a waveform lidar sensor that incorporates two advances relevant to the design of future spaceborne lidar sensors. The first is a nonmechanical scanner that splits a single incoming beam into a variable number of output beams that can be aligned independently across track; the transmitted beam pattern can be changed up to 60 Hz. The second is a flash focal plane array (FFPA) capable of recording waveforms simultaneously from a 128 × 128 pixel grid with individual footprints spread over multiple pixels. In this paper, the incoming beam was used to illuminate eight 8.4-m footprints which were imaged simultaneously on 12 × 12 pixel subsets of the FFPA. The FFPA digitizes waveforms at a vertical resolution of 75 cm over 41 vertical bins to create waveforms of 30.75-m depth. Multiple waveforms obtained using range-gating were combined for these analyses. ESFL data were collected at Manitou Experimental Forest (MEF), located in the Pikes Peak National Forest, Colorado, USA and the Stephen F. Austin Experimental Forest (AEF), located in the Angelina Forest, Nacogdoches, TX. We evaluated the use of individual pixel-level and aggregated footprint-level waveforms and alternate approaches to define the extent of each footprint in the focal plane array. Using discrete return lidar data as a reference, we evaluated the ability of ESFL lidar to estimate canopy height and compared the two sensors' rates of penetration to the terrain surface. We found the footprint-level waveforms were better suited for use with existing waveform processing techniques, although techniques for processing at the pixel-level appear feasible. Relationships between height estimates from each lidar data set were most closely related when footprint-level ESFL waveforms were calculated after removing pixels that had less than 50% of the maximum energy within that footprint. Regressions between ESFL and reference lidar data estimates of height explained 84% (AEF) and 85% (MEF) of variance; this study could not say definitively which method yielded the more accurate estimate of height.

Satellite and aircraft observations have revealed that remarkable changes in the Earth's polar ice cover have occurred in the last decade. The impacts of these changes, which include dramatic ice loss from ice sheets and rapid declines in Arctic sea ice, could be quite large in terms of sea level rise and global climate. NASA's Ice, Cloud and Land Elevation Satellite-2 (ICESat-2), currently planned for launch in 2015, is specifically intended to quantify the amount of change in ice sheets and sea ice and provide key insights into their behavior. It will achieve these objectives through the use of precise laser measurements of surface elevation, building on the groundbreaking capabilities of its predecessor, the Ice Cloud and Land Elevation Satellite (ICESat). In particular, ICESat-2 will measure the temporal and spatial character of ice sheet elevation change to enable assessment of ice sheet mass balance and examination of the underlying mechanisms that control it. The precision of ICESat-2's elevation measurement will also allow for accurate measurements of sea ice freeboard height, from which sea ice thickness and its temporal changes can be estimated. ICESat-2 will provide important information on other components of the Earth System as well, most notably large-scale vegetation biomass estimates through the measurement of vegetation canopy height. When combined with the original ICESat observations, ICESat-2 will provide ice change measurements across more than a 15-year time span. Its significantly improved laser system will also provide observations with much greater spatial resolution, temporal resolution, and accuracy than has ever been possible before.