PR Aerial imagery sources

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  • For the inventory and MEA-assessment of pro rata grasslands, aerial imagery is a commonly used source data set. It can be complemented or substituted with VHR satellite imagery that meets the same specifications. We should prescribe what is needed as described below.
  • All imagery should have spatial resolution compliant with cartographic scale of 1:5.000 or better. - This translates into a positional accuracy requirement lower than 1,25 m RMSExy and a GSD/pixel size below 50-70cm depending on the sensor. Viewing angles should be appropriate for the landscape.
  • The objective is to quantify the proportion of eligible land cover (grass including its forage shrubs and eligible landscape features) by excluding both the ineligible vegetation (trees, gorse,…) and non-vegetative land cover elements (rocks, water, substrate,…) that are scattered throughout the grassland. The local conditions will dictate whether panchromatic, multispectral, SAR or even thermal or SAR imagery is most suitable and it is essential to adhere to that choice. See the chapter on processes for further criteria for the selection of image radiometry.
  • Similar considerations about the suitability of the source images apply to their acquisition date of the source image, as it is essential in LPIS-terms that PG can be unambiguously delineated. The phenology differences between the grass and the ineligible features may peak outside the agricultural growing season allowing best identification and delineation at such times. In such cases, if there is a different image for the on-the-spot check (remote sensing), particular attention should be paid. The differences between the images should be carefully assessed and there should be a rapid field visit to visually confirm the recorded extent of the pro rata land cover (in LPIS) rather than delineating new polygons..
  • LPIS deals with spatial features that are stable in time. The use of multiannual series of imagery is essential to reliably distinguish the pro rata PG that represents a stable agricultural land from grassland where the scattered ineligible features are a fast-growing encroachment after abandonment. Whereas the former PG is in the scope of this specification, the latter “grassland” is deprived of agricultural activity and therefore not in scope. Ensure historic images are at hand to make the distinction where necessary.
  • Ancillary data and image sources from different dates and with different specifications may be required to perform and confirm the RC assessment on a sample of the grasslands.

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