Requirements for a Global Lidar System: Spaceborne lidar with wall-to-wall coverage

Lidar is the optimum technology for measuring bare Earth elevation beneath, and the structure of, vegetation. Consequently airborne laser scanning (ALS) is widely employed for use in a wide range of applications. However, ALS is not available globally nor frequently updated due to its high cost per unit area. Spaceborne lidar can map globally, but energy requirements limit existing spaceborne lidars to sparse sampling missions unsuitable for many common ALS applications.This paper derives the equations to calculate the coverage a lidar satellite could achieve for a given set of characteristics (and released open-source), then uses a cloud map to determine the number of satellites needed to achieve continuous, global coverage within a certain time-frame. Using the characteristics of existing in-orbit technology, a single lidar satellite could have a continuous swath width of 300 m when producing a 30 m resolution map. Consequently 12 satellites would be needed to produce a continuous map every five years, increasing to 418 satellites for 5 m resolution.Building twelve of the currently in-orbit lidar systems is likely to be prohibitively expensive and so the potential of technological developments to lower the cost of a GLS are discussed. Once these technologies achieve a sufficient readiness level, a Global Lidar System could be cost-effectively realised.