Correction of aerosol effects on multi-temporal images acquired with constant viewing angles: application to Formosat-2 images

Olivier Hagolle (1, 2) , Gérard Dedieu (1) , Bernard Mougenot (1) , Vincent Debaecker (1) , Benoît Duchemin (1) , Aimé Meygret (2)

1 CESBIO - Centre d'études spatiales de la biosphère
2 CNES - Centre National d'Études Spatiales [Toulouse]

This paper presents a new method developed for the atmospheric correction of the images that will be acquired by the Venµs satellite after its launch expected in early 2010. Every two days, the Venµs mission will provide 10m resolution images of 50 sites, in 12 narrow spectral bands ranging from 415 nm to 910 nm. The sun synchronous Venµs orbit will have a 2 day repeat cycle, and the images of a given site will always be acquired from the same place, at the same local hour, with constant observation angles. Thanks to these characteristics, the directional effects will be considerably reduced since only the solar angles will slowly vary with time. The algorithm that will be implemented for the atmospheric correction of Venµs data is being developed using both radiative transfer simulations and the actual data acquired by the Formosat-2 satellite. Because of its one day sun synchronous repeat cycle, Formosat-2 acquires images with a sun-viewing geometry close to the one Venµs will offer. With this geometry, reflectance time series are free from directional effects on the short term, a feature which reduces the number of unknowns to retrieve. The atmospheric corrections algorithm exploits this feature and the two following assumptions: - aerosol optical properties vary quickly with time but slowly with location. - surface reflectances vary quickly with location but slowly with time. Consequently, the top of atmosphere reflectance short term variations (10 to 15 days) are mainly due to the variations of aerosol optical properties, and it is thus possible to use these variations to characterise the atmospheric aerosols and to retrieve surface reflectances. This paper first describes the aerosol inversion method we developed and its results when applied to simulations. In a second part, we show the first tests of the method against three data sets acquired by Formosat-2 images with constant observation angles. Aeronet sun photometers measurements were available on all sites. Formosat-2 estimates of optical thickness compare favourably with Aeronet in-situ measurements, leading to a noticeable improvement of the smoothness of time series of surface reflectances after atmospheric correction.

Mots clés: Atmospheric correction; Aerosols; Multi-temporal measurement; Venμs; Formosat-2; Constant viewing angle

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Interfaces continentales, environnement; Milieux et Changements globaux

Olivier Hagolle, Gérard Dedieu, Bernard Mougenot, Vincent Debaecker, Benoît Duchemin, et al.. Correction of aerosol effects on multi-temporal images acquired with constant viewing angles: application to Formosat-2 images. Remote Sensing of Environment, 2008, 112 (4), pp.1689-1701. ⟨10.1016/j.rse.2007.08.016⟩. ⟨hal-00265400⟩