Global clumping index map derived from modis BRDF products

In this study, we show for the first time a global Clumping Index (CI) map at 500 m resolution derived using the Bidirectional Reflectance Distribution Function (BRDF) product from Moderate Resolution Imaging Spectroradiometer (MODIS). We found that the hotspot calculated from the MODIS BRDF product is underestimated in comparison with POLarization and Directionality of the Earth´s Reflectances (POLDER) measurements very near the hotspot, so the MODIS-derived CI could be overestimated without correcting the bias. We developed an approach to correct the MODIS hotspot magnitude against synchronous co-registered POLDER-3 data. Field measured CIs by the Tracing Radiation and Architecture of Canopies instrument from 38 sites were used to evaluate the global CI map. Validation indicates that a strong correlation between MODIS-derived NDHD and CI indeed exists, and red band is better than near infrared band in effectively capturing the structural differences among cover types.