Abstract
This white paper has been submitted to the NRC in view of the preparation of its next Decadal Survey.Importance:Knowledge of the vertical structure of the Earth’s surface and its change, at high accuracy (decimeter level) and resolution (meter level), is required for a diverse array of science and applications objectives. The Earth’s topography, the height and structure of vegetation and the height of water, snow and ice are foundation data of critical importance spanning disciplines from the solid Earth to the biosphere, hydrosphere and cryosphere.Utility:Ongoing international commitment to acquiring elevation data has led to large investments in numerous spaceflight missions. Comprehensive global elevation mapping has been accomplished at moderate resolution (tens of meters) and vertical accuracy (meters) by Interferometric SAR and stereoscopic optical spaceflight missions. However, in the presence of vegetation these elevation data are biased upward, by as much as tens of meters where the canopy is tall and dense, introducing substantial errors in the ground topography. Lidar altimeter missions, both completed and scheduled for launch in the next several years, acquire elevation data with very high absolute vertical accuracy (decimeters) including of the surface topography beneath dense vegetation. However, as profiling systems they do not provide comprehensive mapping. Recognizing the need for improved global elevation mapping to accomplish multi-disciplinary, high priority objectives, the science and applications communities called for the Lidar Surface Topography (LIST) mission in the first Earth Science Decadal Survey.Quality:LIST was required to globally map ground topography at 5 m resolution and decimeter vertical accuracy, as well as the height and vertical structure of vegetation, for all land areas. An Advanced Mission Concept study, commissioned by NASA, provided thorough documentation of the science and applications utility of the LIST mission and rigorous traceability to measurement quality requirements.Engineering readiness for the mission and areas requiring technical advance were addressed in detail. Because a lidar mapping mission has not been implemented, the importance, utility and quality requirements remain applicable.Affordability:Substantial progress addressing the technical challenges for a LIST-class mission has been made over the past ten years. Key remaining challenges are large detector arrays and high throughput electronics requiring continuing investments to ensure a successful mission can be accomplished in the coming decade. An international partnership merging an integrated set of measurements, acquired from airborne and satellite platforms with complimentary measurements best suited to specific landscape and atmospheric conditions, may provide a more affordable path than a single lidar spacecraft tasked with complete global mapping.