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See detailIntercomparison of clumping index estimates from POLDER, MODIS, and MISR satellite data over reference sites
Pisek, J.; Govind, A.; Arndt, S. K. et al

in ISPRS Journal of Photogrammetry & Remote Sensing (2015), 101

Clumping index is the measure of foliage grouping relative to a random distribution of leaves in space. It is a key structural parameter of plant canopies that influences canopy radiation regimes and ... [more ▼]

Clumping index is the measure of foliage grouping relative to a random distribution of leaves in space. It is a key structural parameter of plant canopies that influences canopy radiation regimes and controls canopy photosynthesis and other land-atmosphere interactions. The Normalized Difference between Hotspot and Darkspot (NDHD) index has been previously used to retrieve global clumping index maps from POLarization and Directionality of the Earth's Reflectances (POLDER) data at ~6. km resolution and the Bidirectional Reflectance Distribution Function (BRDF) product from Moderate Resolution Imaging Spectroradiometer (MODIS) at 500. m resolution. Most recently the algorithm was also applied with Multi-angle Imaging SpectroRadiometer (MISR) data at 275. m resolution over selected areas. In this study for the first time we characterized and compared the three products over a set of sites representing diverse biomes and different canopy structures. The products were also directly validated with both in-situ vertical profiles and available seasonal trajectories of clumping index over several sites. We demonstrated that the vertical distribution of foliage and especially the effect of understory need to be taken into account while validating foliage clumping products from remote sensing products with values measured in the field. Satellite measurements responded to the structural effects near the top of canopies, while ground measurements may be biased by the lower vegetation layers. Additionally, caution should be taken regarding the misclassification in land cover maps as their errors can propagate into the foliage clumping maps. Our results indicate that MODIS data and MISR data, with 275. m in particular, can provide good quality clumping index estimates at spatial scales pertinent for modeling local carbon and energy fluxes. © 2014 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS). [less ▲]

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See detailA proof of concept of Iterative DSM improvement through SAR scene simulation
De Rauw, Dominique ULg

in ISPRS Journal of Photogrammetry & Remote Sensing (2009), XXXVIII(3/W4), 121-126

In Very High Resolution (VHR) Synthesis Aperture Radar (SAR) context, very fine and accurate georeferencing and geoprojection processes are required. Both operations are only applicable if accurate local ... [more ▼]

In Very High Resolution (VHR) Synthesis Aperture Radar (SAR) context, very fine and accurate georeferencing and geoprojection processes are required. Both operations are only applicable if accurate local heights are known. 3D information may be derived from SAR interferometry (InSAR), But in VHR context, InSAR reveals to be inaccurate mostly due to phase unwrapping problems and to phase/height noise. Generated InSAR Digital Surface Models (DSM) can only be considered as a first good approximation of the observed surface. Therefore, we proposed to start from the InSAR DSM, to project it on ground range on a given datum, to model the observed scene using this projected DSM, then to simulate in slant range the intensity image issued from this structure model. Comparison between simulated and observed intensity image can then be used as a criterion to modify and improve the considered underlying DSM. In this paper, we present the different steps of the proposed approach and results obtained so far, showing that the proposed process can be run iteratively to modify the DSM and reach a stable solution. [less ▲]

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