Spectral rules and geostatistic features for characterizing olive groves in QuickBird images

The variogram image extracted from the panchromatic band of a QuickBird image has been analyzed to discriminate between similar spectral vegetated land use classes, such as forest and dense olive groves, once spectral features have been exploited. Such images seem to reproduce the direction and inter-row spacing of oriented texton-based textures present in the original input image. The variogram based texture algorithm (VBTA), recently proposed in literature for analyzing aerial images, tries to determine if texture in a region is not oriented, as in the case of forested and grassland areas or is oriented in one or two main directions, as in the case of vineyards and olive groves, respectively. If texture is oriented, the number of orientations, the orientation angle and periods (i.e. the distance between textons in each direction) are extracted, the latter depending on agricultural practices. This paper concentrates on: 1) the experimental selection of some variables useful for variogram analysis: i) the size of the input image moving window for variogram calculation; ii) some threshold values to be used for variogram normalization and for testing the presence/absence of any directionality in the variogram image; 2) The methodology for orientation and period estimation from the cumulative variance of the variogram image. The results obtained for a Southern Italy area characterized by intensive olive trees cultivation reveals the effectiveness of VBTA for QuickBird images.