Optical and radar temporal signatures of sunflower using synchronous satellite images — Multi-frequencies and multi-polarizations analyses

This paper aims to establish and to analyze the temporal reflectance signatures of sunflower according to optical and radar satellite images. The study is performed in the south west of France, and takes advantage of the MCM´10 experiment (Multispectral Crop Monitoring), conducted in 2010 by the CESBIO laboratory. Images are provided by 6 satellites sensors (Formosat-2, Spot-4 and -5, TerraSAR-X, Radarsat-2 and Alos). The proposed method consists in correcting the angular effect of radar signal, and in analyzing the different temporal signatures depending on the phenological cycle of the sunflower (at parcel and landscape scales). Results highlight the importance of the radar angular normalization and show the importance of multi-frequency approaches in the context of Sentinel-1, TerraSAR-X and Alos-2 missions. Among the wide range of tested radar signal combinations, the C- and L-bands appear more adapted to monitor sunflower, and further estimate its biophysical parameters.