The image is a false-color mosaic of the seasonal values of the NDVI* (Normalized Difference Vegetation Index) calculated starting from the collection of images acquired over Piedmont by the pair of Sentinel 2A-2B satellites of the European Copernicus programme, relating to the autumn period 2020 - summer 2021. The mosaic was generated by composing in a single image, according to the RGB color model, the seasonal summary values of the NDVI index: the red (R) channel was associated with autumn 2020, that of green (G) in spring 2021, to blue (B) in summer 2021. The composition of the seasonal NDVIs of this kind makes it possible to differentiate the areas for which there are one or more vegetative cycles or in any case variations in the land cover (areas variously coloured) from those in which the soil is completely devoid of vegetation or with permanent water (shades of gray up to black). For the calculation of the three seasonal synthesis images of the NDVI index, the procedure was as follows:1) From seasonal multitemporal stack, for each of the bands that contributes to the calculation of the NDVI, the median reflectance value of each pixel was calculated. Thus two images were obtained: the synthesis image of the red band and that of the near infrared band. 2) From the synthesis images of the individual bands produced in the previous point, the seasonal synthesis image of the NDVI index was finally calculated. The processing was carried out by Arpa Piemonte as part of the activities connected to the national consumption monitoring project of soil 2020 conducted by the National System for Environmental Protection (SNPA) through the coordination of ISPRA and the involvement of various regional agencies. The project aims to monitor the transformations of the territory due to urban, infrastructural, commercial expansions, etc. with the consequent loss of natural, agricultural and semi-natural soil, understood as an essential and fundamentally non-renewable environmental resource. The analysis methodology uses, for the first time on a national scale in a unitary and homogeneous way, the new Sentinel 2A/B images which, given their level of detail and the frequency of revisiting guaranteed by the Sentinel mission, allow to obtain visions of whole of the national territory in a periodic and constant manner (multi-temporal analysis). The comparison between these allows us to highlight the main transformations of the territory and the related phenomena of land consumption (expansion of urban settlements, new roads, shipbuilding for new works, etc. ).* The NDVI is a vegetation index based on reflectance measurements acquired in the red and near infrared spectral regions and is strongly correlated to the chlorophyll content and, if measured over time, to the phenological cycle of plants. Before flow into the stack the individual images have been appropriately masked to eliminate the cloud cover.
