GEDI Footprint Geolocation and Gridded Topography Products Performance

The Global Ecosystem Dynamics Investigation (GEDI) instrument was launched on December 5th, 2018 and has been collecting operational science data from the International Space Station since April 18th, 2019. The mission has collected over 10 billion observations of the Earths surface elevation and structure. The GEDI mission is producing unprecedented sampling of bare earth topography at the footprint level and through Level-3 (L3) gridded products. The standard GEDI L3 grid products consist of one square kilometer cells, with each cell representing the best estimate of the mean and its error estimate within that cell computed from the GEDI footprint sampling. We first present the performance of the GEDI geolocation including positioning, pointing, ranging, and calibration, as well as the overall expected geolocation performance relevant to topography observations and the gridded L3 topography products. A comparison of gridding methods is discussed including block mean, kriging, and integral methods using thin plate spline radial basis functions for producing the L3 grid products from the irregularly spaced footprint data. Algorithms are developed to compute high resolution (100 square meter) continental-scale grids. An Interpolatory Tension Spline Gridding (ITSG) algorithm is developed to optimally and efficiently compute high resolution grids and their error estimates. To allow continental-scale and global grids to be computed on readily available hardware, we also develop a method to seamlessly stitch regional grids into continental and global grids. Satellite and airborne data, including data from the Land, Vegetation, and Ice Sensor (LVIS), are used to assess and characterize performance of the gridded topography products.