Validation of an ICESat-2 simulator: Can ICESat-2 provide the necessary metrics for global vegetation radiative transfer modelling?

Abstract:

Modelling vegetation radiative transfer at global scale requires global measurements of forest structure. Here, we use an ICESat-2 simulator, based on the GEDI simulator presented by Hancock et al. 2019, to investigate the utility of ICESat-2 measurements for driving vegetation radiative transfer (RT) models. An accurate ICESat-2 simulator can generate ICESat-2 tracks from the same terrestrial and airborne lidar data sets used to build 3D RT model scenes, allowing for controlled testing of the ability of ICESat-2 to drive 3D RT models. Airborne laser scanning data is used to classify real ICESat-2 photons as ground, vegetation or noise, from which the key simulation parameters - pure vegetation and pure ground photon rates - are calculated. The stability of these photon rates along and between tracks and through the canopy is tested. ICESat-2 tracks simulated using these realistic photon rates are then generated. The accuracy of these simulations is tested against both real ICESat-2 measurements and ALS truth data, and the simulator is used to interrogate the limits of ICESat-2 retrieval of canopy height, canopy cover and foliage profile, all key metrics for vegetation radiative transfer. ICESat-2 provides useful data for global vegetation radiative transfer modelling, but accurate modelling requires the fusion of ICESat-2 data with other earth observation data sets.