High resolution layer HRL, forest - tree cover density

Abstract

A national coverage exercise was carried out to analyse the Forest Tree Cover using in-situ imagery data and the HRL TRC_2015 provided for verification. The TRC 2015 HRL data layer was superimposed onto the in-situ data namely; Orthoimagery1 (2012), OrthoImagery 2016, the CLC layers (2012, 2018) and the national biotope map database layer (updated as of 2011).

In Malta’s case it was deemed best to apply a complete coverage methodology rather than verifying specific area samples. As defined by the Copernicus HRL Forest defines Tree Cover Density as the “vertical projection of tree crowns to a horizontal earth’s surface” and provides information on the proportional crown coverage per pixel.

In Malta’s case it was deemed best to apply a complete coverage methodology rather than verifying specific area samples. Hence each area marked as “Tree Cover” was individually verified with in-situ Orthoimagery (2012 and 2016), the CLC databases (reference years 2012 and 2018) and the national Biotope 2011 database. All the major errors identified are categorised as “Commission” or “Omission” error types as per guidelines provided for the verification process. When considering the physical area of the Maltese Islands, applying this method of photo interpretation, resulted in a more adequate verification of the HRL layer rendering a more detailed result.

Overall HRL layer provides a generalized overview when compared to the level of detail that is normally utilized locally (1:1000). However the detail provided in the TRC 2015 layer can still be deemed acceptable for the parameters/requirements of this verification exercise. The majority of the errors were of the ‘Commission’ type with 357 cases and 57 cases identified as ‘Omission’ errors.