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Hyperspectral imagery originating from airborne sensors is nowadays widely used for the detailed characterization of land surface. The correct mapping of the pixel positions to ground locations largely contributes to the success of the applications. Accurate geometric correction, also referred to as 'orthorectification', is thus an important prerequisite which must be performed prior to using airborne imagery for evaluations like change detection, or mapping or overlaying the imagery with existing data sets or maps. A so-called 'ortho-image' provides an accurate representation of the earth's surface, having been adjusted for lens distortions, camera tilt and topographic relief. In this paper, we describe the different steps in the geometric correction process of APEX hyperspectral data, as applied in the Central Data Processing Center (CDPC) at the Flemish Institute for Technological Research (VITO, Mol, Belgium). APEX ortho-images are generated through direct georeferencing of the raw images, thereby making use of sensor interior and exterior orientation data, boresight calibration data and elevation data. They can be referenced to any userspecified output projection system and can be resampled to any output pixel size. [ABSTRACT FROM AUTHOR]

Atmospheric correction plays a crucial role among the processing steps applied to remotely sensed hyperspectral data. Atmospheric correction comprises a group of procedures needed to remove atmospheric effects from observed spectra, i.e. the transformation from at-sensor radiances to at-surface radiances or reflectances. In this paper we present the different steps in the atmospheric correction process for APEX hyperspectral data as applied by the Central Data Processing Center (CDPC) at the Flemish Institute for Technological Research (VITO, Mol, Belgium). The MODerate resolution atmospheric TRANsmission program (MODTRAN) is used to determine the source of radiation and for applying the actual atmospheric correction. As part of the overall correction process, supporting algorithms are provided in order to derive MODTRAN configuration parameters and to account for specific effects, e.g. correction for adjacency effects, haze and shadow correction, and topographic BRDF correction. The methods and theory underlying these corrections and an example of an application are presented. [ABSTRACT FROM AUTHOR]

APEX (Airborne Prism EXperiment) is a high spectral and spatial resolution hyperspectral sensor developed by a Swiss-Belgian consortium on behalf of the European Space Agency. Since the acceptance of the instrument in 2010, it has been operated jointly by the Flemish Institute for Technological Research (VITO, Mol, Belgium) and the Remote Sensing Laboratories (RSL, Zurich, Switzerland). During this period, several flight campaigns have been performed across Europe, gathering over 4 Terabytes of raw data. Following radiometric, geometric and atmospheric processing, this data has been provided to a multitude of Belgian and European researchers, institutes and agencies, including the European Space Agency (ESA), the European Facility for Airborne Research (EUFAR) and the Belgian Science Policy Office (BelSPO). The applications of APEX data span a wide range of research topics, e.g. landcover mapping (mountainous, coastal, countryside and urban regions), the assessment of important structural and (bio)physical characteristics of vegetative and non-vegetative species, the tracing of atmospheric gases, and water content analysis (chlorophyll, suspended matter). Recurrent instrument calibration, accurate flight planning and preparation, and experienced pilots and instrument operators are crucial to successful data acquisition campaigns. In this paper, we highlight in detail these practical aspects of a typical APEX data acquisition campaign. [ABSTRACT FROM AUTHOR]

Information about vegetation condition is needed for the effective management of natural resources and the estimation of the effectiveness of nature conservation. The aim of the study was to analyse the condition of non-forest mountain communities: synanthropic communities and natural grasslands. UNESCO's M&B Karkonosze Transboundary Biosphere Reserve was selected as the research area. The analysis was based on 40 field test polygons and APEX hyperspectral images. The field measurements allowed the collection of biophysical parameters - Leaf Area Index (LAI), fraction of Absorbed Photosynthetically Active Radiation (fAPAR) and chlorophyll content - which were correlated with vegetation indices calculated using the APEX images. Correlations were observed between the vegetation indices (general condition, plant structure) and total area of leaves (LAI), as well as fraction of Absorbed Photosynthetically Active Radiation (fAPAR). The outcomes show that the non-forest communities in the Karkonosze are in good condition, with the synanthropic communities characterised by better condition compared to the natural communities. [ABSTRACT FROM AUTHOR]