Topography, Cryosphere and Biomass

Chair: Toshiyoshi Kimura

Altimeter measurements of the elevation of the Earth’s ice sheets, glaciers, water bodies and land surface along with the height and vertical structure of vegetation and thickness of sea ice provide foundation data for science and applied purposes. The data is fundamental to understanding, modeling and predicting interactions within and between the solid Earth, hydrosphere, biosphere, cryosphere and atmosphere. The Ice Cloud and land Elevation Satellite (ICESat) mission began comprehensive, global lidar observations of these features, improving significantly upon the resolution and accuracy of spaceflight radar altimeters. Operating during the period 2003 to 2009, ICESat employed a single-beam approach using a low pulse rate, high pulse energy laser transmitter at 1064 nm and digitization of the analog output from a silicon avalanche photodiode detector. Major accomplishments included monitoring the changing elevation of the Greenland and Antarctic ice sheets and arctic sea ice thickness in response to climate change and providing a global map of biomass stored in forests. The ICESat-2 mission, launching in 2017, will continue this time-series using a more efficient measurement approach in order to increase the number of beams to six. It will employ a high pulse rate, low pulse energy micropulse laser transmitter at 532 nm and single photon detection using a photomultiplier tube. The increased number of beams will improve spatial and temporal coverage and the accuracy of change measurements. Beyond ICESat-2 the goal is to achieve wide swath lidar mapping, rather than a few profiling beams, with spatial resolution of a few meters thereby greatly expanding the scope of science questions that can be addressed. This will require a dramatic improvement in measurement efficiency, instrument performance and on-orbit data processing. This session will examine how spaceflight lidar technology has evolved to meet increasingly challenging requirements, in what ways science has been limited by available technology and mission implementations and where critical advances are needed to make the step to next-generation mapping instruments. The needs include: transmitter arrays with 10’s to 100’s of individual beams and/or high rate beam scanning; NIR, high-bandwidth, low-noise, many-element detector arrays capable of simultaneous detection of single photons; signal processing electronics integrated with the detector arrays; and high-speed computing for acquisition and handling large data volumes.