Radiometric Normalization of Spot - 5 Scenes : 6

Description: The 6S code provides a significantly lower radiometric variation (2.8%) than the use of pseudo-invariant features (4.1%), which remains a valid approach with only a few carefully selected invariant sectors. Abstract We compared the efficiency and robustness of two radiometric correction techniques applied to six SPOT-5 scenes used for assessing environmental changes of Camargue wetlands: the 6S atmospheric model and 86 pseudo-invariant features (PIFs) found in deep water, pine trees, roofs and sand. The few PIFs were selected subjectively following the low number of potentially invariant sectors available on the scenes. Both approaches provided a similar radiometric variation (6S =4.3%; PIFs = 4.0%). The latter increased from water to pine trees, to roofs and sand, with five reference points per feature being identified as cost effective. The withdrawing of variant features among the PIFs across dates or points caused a significant decrease in radiometric variation, especially with 6S (6S = 2.8%, PIFs = 3.4%). As many as 31 point per type of PIFs would be necessary to provide a radiometric variation that is not significantly different from that obtained with 6S, whereas nearly 300 and 4000 points per feature would be required to provide similar or better results than the 6S code, respectively. Use of a few PIFs remains a valid approach, as long as the invariant sectors cover a wide range of 2 2 brightness and are represented by objects of which the radiometric variation has preliminarily been tested.