Intercomparison of clumping index estimates from POLDER, MODIS, and MISR satellite data over reference sites

• Published in: ISPRS journal of photogrammetry and remote sensing Vol. 101; pp. 47 - 56
• Main Authors: Pisek, Jan, Govind, Ajit, Arndt, Stefan K., Hocking, Darren, Wardlaw, Timothy J., Fang, Hongliang, Matteucci, Giorgio, Longdoz, Bernard
• Format: Journal Article Web Resource
• Language: English
• Published: Elsevier B.V 01.03.2015; Elsevier
• Subjects: Distribution functions; Earth sciences & physical geography; Hot spot; Hotspot; Image reconstruction; Life Sciences; MISR; MODIS; Multi-angle remote sensing; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; POLDER; Radiometers; Reflection; Remote sensing; Satellite imagery; Sciences de la terre & géographie physique; Space optics; Spectrometers; Vegetation; Vegetation clumping index; Vegetation clumping index; Multi-angle remote sensing; POLDER; Hotspot; MODIS; MISR; vegetation clumping index; multi-angle remote sensing; hotspot
• ISSN: 0924-2716; 1872-8235
• DOI: 10.1016/j.isprsjprs.2014.11.004

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 ∼6km resolution and the Bidirectional Reflectance Distribution Function (BRDF) product from Moderate Resolution Imaging Spectroradiometer (MODIS) at 500m resolution. Most recently the algorithm was also applied with Multi-angle Imaging SpectroRadiometer (MISR) data at 275m 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 275m in particular, can provide good quality clumping index estimates at spatial scales pertinent for modeling local carbon and energy fluxes.