Abstract
ESA’s upcoming satellite Sentinel-2 will provide Earth images of high spatial, spectral and temporal resolution and aims to ensure continuity for Landsat and SPOT observations. In comparison to the latter sensors, Sentinel-2 incorporates three new spectral bands in the red-edge region, which are centered at 705, 740 and 783 nm. This study addresses the importance of these new bands for the retrieval and monitoring of two important biophysical parameters: green leaf area index (LAI) and chlorophyll content (Ch). With data from several ESA field campaigns over agricultural sites (SPARC, AgriSAR, CEFLES2) we have evaluated the efficacy of two empirical methods that specifically make use of the new Sentinel-2 bands. First, it was shown that LAI can be derived from a generic normalized difference index (NDI) using hyperspectral data, with 674 nm with 712 nm as best performing bands. These bands are positioned closely to the Sentinel-2 B4 (665 nm) and the new red-edge B5 (705 nm) band. The method has been applied to simulated Sentinel-2 data. The resulting green LAI map was validated against field data of various crop types, thereby spanning a LAI between 0 and 6, and yielded a RMSE of 0.6. Second, the recently developed “Normalized Area Over reflectance Curve” (NAOC), an index that derives Ch from hyperspectral data, was studied on its compatibility with simulated Sentinel-2 data. This index integrates the reflectance curve between 643 and 795 nm, thereby including the new Sentinel-2 bands in the red-edge region. We found that these new bands significantly improve the accuracy of Ch estimation. Both methods emphasize the importance of red-edge bands for operational estimation of biophysical parameters from Sentinel-2.
Highlights
Global Monitoring for Environment and Security (GMES) is a joint initiative of the EuropeanCommission and the European Space Agency (ESA), designed to establish a European capacity for the provision and use of operational monitoring information for environment and security applications [1].Given the fact that the current services are based on data from Landsat and SPOT sensors, a satisfactory service could be expected by continuing these mission programmes as a minimum scenario
leaf area index (LAI) measurements from the Spectra Barrax Campaigns (SPARC) campaign were plotted against the normalized difference index (NDI) calculated with the
While the importance of red-edge bands has been addressed in earlier studies [49,66], in this work we found that the inclusion of these bands are important for S2 to enable the delivery of accurate green LAI and canopy chlorophyll products
Summary
Global Monitoring for Environment and Security (GMES) is a joint initiative of the EuropeanCommission and the European Space Agency (ESA), designed to establish a European capacity for the provision and use of operational monitoring information for environment and security applications [1].Given the fact that the current services are based on data from Landsat and SPOT sensors, a satisfactory service could be expected by continuing these mission programmes as a minimum scenario. Global Monitoring for Environment and Security (GMES) is a joint initiative of the European. Commission and the European Space Agency (ESA), designed to establish a European capacity for the provision and use of operational monitoring information for environment and security applications [1]. Given the fact that the current services are based on data from Landsat and SPOT sensors, a satisfactory service could be expected by continuing these mission programmes as a minimum scenario. With a view to demanded service improvements in the near future, an enhanced land surface monitoring system in terms of spectral, temporal and spatial coverage is required. The upcoming Sentinel-2 (S2) mission intends to provide such continuity to services, but with improved features compared to the later sensors [1]. S2 is a polar-orbiting, superspectral high-resolution imaging mission designed for GMES land monitoring. The mission is envisaged to fly a pair of satellites, with the first planned to be launched in
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