Radiometric Normalization of Landsat Etm+ Data for Multitemporal Analysis

The advantages of Remote Sensing for the knowledge of environmental dynamics are widely ascertained by scientific community. Spatial synchronization and temporal resolution of large areas have meaningfully improved quantity and quality of satellite imagery which have assumed an important role in the field of environmental monitoring. Nevertheless, preliminary processing problems of multitemporal satellite data, as basic information in the analysis of land cover transformations, persist because of errors due to noise, to environmental conditions and to geometric and radiometric distortions introduced during the acquisition and the transmission phases. The methods of radiometric normalization for multitemporal analysis of satellite imagery can be absolute and relative. The absolute methods are not always feasible because they need to measure the optical properties of the atmosphere acquired “in situ” and simultaneously with the moment of scene recording. The relative methods proceed under the assumption that the relationship between the at-sensor radiances recorded at two different times from regions of constant reflectance is spatially homogeneous and can be approximated by linear functions. The most difficult and time consuming aspect of all of these methods is the determination of suitable time-invariant features upon which to base the normalization. In this paper the radiometric normalization techniques of Landsat ETM+ were analysed. These data were referred to acquisitions times comprised in 1999-2001-2002 years on a test area of southern Lazio. A normalization algorithm, based on MAD (Multivariate Alteration Detection) transformation, was implemented for this aim, by executing a quantitative and qualitative comparison with the consolidated ELC (Empirical Line Calibration) method.