HRL verification report : water and wetness 2015

Abstract

A national coverage exercise was carried out to analyse the water and wetness using in-situ imagery data and the HRL WAW_2015 provided for verification. The WAW 2015 HRL data layer was superimposed onto the in-situ data namely; Orthoimagery1 (2012), OrthoImagery 2016, the CLC layers (2012, 2018) and the national inland water bodies database layer (updated as of 2014).

In Malta’s case it was deemed best to apply a complete coverage methodology rather than verifying specific area samples. As highlighted in the HRLs 2015 verification guidelines the nature of the 2015 WAW product is fundamentally based on time-series and frequency of occurrence data sources. As such a quantitative verification was not feasible except for the permanent water class.

In this respect the focus of the verification was on the areas marked as permanent water bodies utilising in-situ Orthoimagery (2012 and 2016), the CLC database (for the reference years 2012 and 2018), and the local inland water bodies layer. All the major errors identified were categorized 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 giving us 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 WAW 2015 layer can still be deemed acceptable for the parameters/requirements of this verification exercise. All in all eight (8) errors were identified, five (5) Commission cases and the remaining three (3) being Omission cases.