When updating the dataset to the version of 2020, the entire procedure of recording vegetation heights was switched from object-based sectioning (aerial photography flights in 2009/ 2010) to grid-based sectioning. Key advantages include the size and completeness of the dataset and therefore its suitability for further processing. Using this method, the 2010 dataset could also be reclassified and recalculated. The two periods could therefore be compared without methodological discrepancies while also minimising potential errors (cf. project report, only in German, SenStadtWohn 2021).
In the following, the two different datasets from 2010, from the old and new survey will be compared (cf. Table 1). First of all, it is clear that the old survey underestimated the green volume in all use groups. The largest discrepancy here occurs for the built-up area types. The new survey recorded an additional 148.3 km³ of green volume for these groups. This is due to the fact that the green structures in built-up areas are rather fragmented and were eliminated in the course of the segmentation process of the old mapping in which areas were combined. By switching to a grid-based segmentation for the new survey, these smaller green structure fragments could be recorded in more detail.
The old mapping of the forest areas also omits a green volume of 88.4 km³. For other green and open spaces and road areas, the green volume difference is smaller, amounting to about 21 km³.
Overall, the total green volume for 2010 that is recorded in the new mapping is therefore 5,157 km³, exceeding that of the old survey by 279.8 km³.