Browsing by Author "Luyssaert, Sebastiaan"

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Assimilating satellite-based canopy height within an ecosystem model to estimate aboveground forest biomass
(2017-07) Joetzjer, Emilie; Pillet, Michiel; Ciais, Philippe; Barbier, N.; Chave, Jerome; Schlund, M.; Maignan, F.; Barichivich, Jonathan; Luyssaert, Sebastiaan; Hérault, Bruno; Poncet, F.; Poulter, Benjamin
Despite advances in Earth observation and modeling, estimating tropical biomass remains a challenge. Recent work suggests that integrating satellite measurements of canopy height within ecosystem models is a promising approach to infer biomass. We tested the feasibility of this approach to retrieve aboveground biomass (AGB) at three tropical forest sites by assimilating remotely sensed canopy height derived from a texture analysis algorithm applied to the high-resolution Pleiades imager in the Organizing Carbon and Hydrology in Dynamic Ecosystems Canopy (ORCHIDEE-CAN) ecosystem model. While mean AGB could be estimated within 10% of AGB derived from census data in average across sites, canopy height derived from Pleiades product was spatially too smooth, thus unable to accurately resolve large height (and biomass) variations within the site considered. The error budget was evaluated in details, and systematic errors related to the ORCHIDEE-CAN structure contribute as a secondary source of error and could be overcome by using improved allometric equations.
Land management and land-cover change have impacts of similar magnitude on surface temperature
(2014-04-13) Luyssaert, Sebastiaan; Jammet, Mathilde; Stoy, Paul C.; Estel, Stephan; Pongratz, Julia; Ceschia, Eric; Churkina, Galina
Anthropogenic changes to land cover (LCC) remain common, but continuing land scarcity promotes the widespread intensification of land management changes (LMC) to better satisfy societal demand for food, fibre, fuel and shelter1. The biophysical effects of LCC on surface climate are largely understood2,3,4,5, particularly for the boreal6 and tropical zones7, but fewer studies have investigated the biophysical consequences of LMC; that is, anthropogenic modification without a change in land cover type. Harmonized analysis of ground measurements and remote sensing observations of both LCC and LMC revealed that, in the temperate zone, potential surface cooling from increased albedo is typically offset by warming from decreased sensible heat fluxes, with the net effect being a warming of the surface. Temperature changes from LMC and LCC were of the same magnitude, and averaged 2 K at the vegetation surface and were estimated at 1.7 K in the planetary boundary layer. Given the spatial extent of land management (42–58% of the land surface) this calls for increasing the efforts to integrate land management in Earth System Science to better take into account the human impact on the climate.
Land management and land-cover change have impacts of similar magnitude on surface temperature
(2014-04) Luyssaert, Sebastiaan; Jammet, Mathilde; Stoy, Paul C.; Estel, Stephan; Pongratz, Julia; Ceschia, Eric; Churkina, Galina; Don, A.; Erb, K.; Ferlicoq, M.; Gielen, Bert; Grünwald, Thomas; Houghton, Richard A.; Klumpp, K.; Knohl, A.; Kolb, T.; Kuemmerle, T.; Laurila, T.; Lohila, A.; Loustau, Denis; Meyfroidt, P.; Moors, Eddy J.; Novick, Kimberly A.; Otto, Juliane; Pilegaard, Kim; Pio, C. A.; Rambal, Serge; Rebmann, C.; Ryder, J.; Suyker, Andrew E.; Varlagin, Andrej B.; Wattenbach, M.; Dolman, A. J.
Anthropogenic changes to land cover (LCC) remain common, but continuing land scarcity promotes the widespread intensification of land management changes (LMC) to better satisfy societal demand for food, fibre, fuel and shelter1. The biophysical effects of LCC on surface climate are largely understood2,3,4,5, particularly for the boreal6 and tropical zones7, but fewer studies have investigated the biophysical consequences of LMC; that is, anthropogenic modification without a change in land cover type. Harmonized analysis of ground measurements and remote sensing observations of both LCC and LMC revealed that, in the temperate zone, potential surface cooling from increased albedo is typically offset by warming from decreased sensible heat fluxes, with the net effect being a warming of the surface. Temperature changes from LMC and LCC were of the same magnitude, and averaged 2 K at the vegetation surface and were estimated at 1.7 K in the planetary boundary layer. Given the spatial extent of land management (42–58% of the land surface) this calls for increasing the efforts to integrate land management in Earth System Science to better take into account the human impact on the climate8.