Publications (9)0 Total impact
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Conference Proceeding: Calibration, Parameterization and Application of MERIS Water Constituent Algorithms for Perialpine Lakes.
IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2009, July 12-17, 2009, University of Cape Town, Cape Town, South Africa, Proceedings; 01/2009 -
Conference Proceeding: Coupling Imaging Spectroscopy and Ecosystem Process Modelling - The Importance of Spatially Distributed Foliar Biochemical Concentration Estimates for Modelling NPP of Grassland Habitats.
IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2008, July 8-11, 2008, Boston, Massachusetts, USA, Proceedings; 01/2008 -
Conference Proceeding: HYPER-I-NET: European research network on hyperspectral imaging.
IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2007, July 23-28, 2007, Barcelona, Spain, Proceedings; 01/2007 -
Conference Proceeding: Inversion of Combined Radiative Transfer Models for Imaging Spectrometer and LIDAR Data.
IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2006, July 31 - August 4, 2006, Denver, Colorado, USA, Proceedings; 01/2006 -
Article: Toward a direct comparison of field and laboratory goniometer measurements.
IEEE T. Geoscience and Remote Sensing. 01/2005; 43:2666-2675. -
Article: Spectrodirectional remote sensing for the improved estimation of biophysical and -chemical variables: two case studies
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ABSTRACT: Over the past few years, significant advancements are made in the acquisition, processing, analysis and interpretation of quantitative directional and high spectral resolution data. In particular, the broader availability of air- and spaceborne directional imaging spectrometer data supports the estimation of biophysical and -chemical variables with unprecedented accuracy and in calibrated physical units. We describe in this paper two experiments that we carried out to demonstrate regional performance of spectral and directional-based retrieval approaches in vegetated areas. In the first case study, we focus on a mountain forest located in South-Eastern Switzerland representing a boreal forest like ecosystem. DAIS7915 imaging spectrometer data have been acquired with simultaneous ground measurements. We describe the soil–vegetation–atmosphere radiative transfer using a combination of the PROSPECT, GeoSAIL, and ATCOR models. In the second case study, we acquired spectrodirectional data on ground using a field goniometer in parallel with several HyMap imaging spectrometer overflights. Both cases demonstrate conditions for the estimation of biophysical and -chemical canopy properties with reduced uncertainties by respecting the full spectral coverage and directionality of the data. We conclude that the derived canopy variables represent the actual spatial distribution of properties as they occur in the landscape.International Journal of Applied Earth Observation and Geoinformation. -
Article: Intercomparison of field and laboratory goniometer measurements
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ABSTRACT: Field and laboratory goniometers are widely used in the remote sensing community to assess spectrodirectional reflectance properties of selected targets. Even when the same target and goniometer system are used, field and laboratory results cannot directly be compared due to inherent differences, mainly in the illumination conditions: typically goniometers measure a hemispherical-conical reflectance in the field and a biconical reflectance in the laboratory. Yet, the ability to compare and combine measurements from different instrumental designs is critical to ensure sensor cross-calibration. It is also critical for all applications that rely on measurements obtained with both types of instruments. One solution is to retrieve the BRDF of the targets of interest for each experimental setup individually and to compare those, since theoretically they are independent from the particular conditions of illumination and observation. This involves a correction for diffuse incoming radiation in the case of field measurements, and a correction for the conicality and inhomogeneity of illumination in the case of laboratory measurements. We present a BRDF retrieval scheme for typical laboratory goniometers as well as results of measurements and BRDF retrievals using the field and laboratory goniometer systems (FIGOS/LAGOS) of the University of Zurich and the same artificial target for both goniometer setups. -
Article: Comparison of field and laboratory spectro-directional measurements using a standard artificial target
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ABSTRACT: Spectro-directional surface measurements can either be performed in the field or within a laboratory setup. Laboratory measurements have the advantage of constant illumination and neglectable atmospheric disturbances. On the other hand, artificial light sources are usually less parallel and less homogeneous than the clear sky solar illumination. To account for these differences and for determining for which targets a replacement of field by laboratory experiments is indeed feasible, a quantitative comparison is a prerequisite. Currently, there exists no systematic comparison of field and laboratory measurements using the same targets. In this study we concentrate on the difference in spectro-directional field and laboratory data of the same target due to diffuse illumination. The field data were corrected for diffuse illumination following the proposed procedure by Martonchik 1 . Spectro-directional data were obtained with a GER3700 spectroradiometer. In the field, a MFR sun photometer directly observed the total incoming diffuse irradiance. In the laboratory, a 1000W brightness-stabilized quartz tungsten halogen lamp was used. For the first direct comparison of field and laboratory measurements, we used an artificial and inert target with high angular anisotropy. Analysis shows that the diffuse illumination in the field is leading to a higher total reflectance and less pronounced angular anisotropy. -
Article: LIDAR-based geometric reconstruction of boreal type forest stands at single tree level for forest and wildland fire management
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ABSTRACT: Vegetation structure is an important parameter in fire risk assessment and fire behavior modeling. We present a new approach deriving the structure of the upper canopy by segmenting single trees from small footprint LIDAR data and deducing their geometric properties. The accuracy of the LIDAR data is evaluated using six geometric reference targets, with the standard deviation of the LIDAR returns on the targets being as low as 0.06 m. The segmentation is carried out by using cluster analysis on the LIDAR raw data in all three coordinate dimensions. From the segmented clusters, tree position, tree height, and crown diameter are derived and compared with field measurements. A robust linear regression of 917 tree height measurements yields a slope of 0.96 with an offset of 1 m and the adjusted R2 resulting at 0.92. However, crown diameter is not well matched by the field measurements, with R2 being as low as 0.2, which is most certainly due to random errors in the field measurements. Finally, a geometric reconstruction of the forest scene using a paraboloid model is carried out using values of tree position, tree height, crown diameter, and crown base height.Remote Sensing of Environment.
