Hyperion, IKONOS, ALI, and ETM+ sensors in the study of African rainforests |
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Authors: | Prasad S Thenkabail Eden A Enclona Mark S Ashton Christopher Legg |
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Affiliation: | a International Water Management Institute (IWMI), P.O. Box 2075, Street 127, Sunil Mawatha, Pelawatte, Battaramulla, Colombo, Sri Lanka b Center for Earth Observation, Yale University, USA c School of Forestry and Environmental Studies, Yale University, USA d International Institute of Tropical Agriculture, Ibadan, Nigeria e ONADEF, Cameroon |
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Abstract: | The goal of this research was to compare narrowband hyperspectral Hyperion data with broadband hyperspatial IKONOS data and advanced multispectral Advanced Land Imager (ALI) and Landsat-7 Enhanced Thematic Mapper Plus (ETM+) data through modeling and classifying complex rainforest vegetation. For this purpose, Hyperion, ALI, IKONOS, and ETM+ data were acquired for southern Cameroon, a region considered to be a representative area for tropical moist evergreen and semi-deciduous forests. Field data, collected in near-real time to coincide with satellite sensor overpass, were used to (1) quantify and model the biomass of tree, shrub, and weed species; and (2) characterize forest land use/land cover (LULC) classes.The study established that even the most advanced broadband sensors (i.e., ETM+, IKONOS, and ALI) had serious limitations in modeling biomass and in classifying forest LULC classes. The broadband models explained only 13-60% of the variability in biomass across primary forests, secondary forests, and fallows. The overall accuracies were between 42% and 51% for classifying nine complex rainforest LULC classes using the broadband data of these sensors. Within individual vegetation types (e.g., primary or secondary forest), the overall accuracies increased slightly, but followed a similar trend. Among the broadband sensors, ALI sensor performed better than the IKONOS and ETM+ sensors.When compared to the three broadband sensors, Hyperion narrowband data produced (1) models that explained 36-83% more of the variability in rainforest biomass, and (2) LULC classifications with 45-52% higher overall accuracies. Twenty-three Hyperion narrowbands that were most sensitive in modeling forest biomass and in classifying forest LULC classes were identified and discussed. |
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Keywords: | African rainforests Biomass models Carbon flux Hyperion IKONOS ALI ETM+ Most sensitive Hyperion bands Accuracy assessments Broadbands Narrowbands Hyperion vegetation indices |
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