Quality assurance
A detailed description of the quality assurance tools can be found in the Guide to the Forest Condition Survey (Thünen Working Paper 84.2, German language).
Photo comparison tests: Thünen Working Paper 243 (in German) presents the results of the first online photo comparison test and demonstrates the extent to which a web-based procedure can serve as an effective quality assurance measure for the WZE.
The results of the nationwide calibration courses on crown condition assessment since 1992 can be found here: https://wo-apps.thuenen.de/apps/wze_ilk/ (in German).
Quality assurance tools
Instrument | Short description |
|---|---|
Guidelines and Documentation for the National Forest Condition Survey | Are based on the ICP Forests Manual and outline the regulations governing the data collection process that apply in Germany. |
Training programs by the federal states | These are mandatory for all data collection teams and take place annually before the start of the survey period. |
Nationwide Referendum Course | Takes place annually before the start of the survey period, with the mandatory participation of inventory managers. |
International Comparison Courses | These have been held separately for Central, Northern, and Southern Europe since 1987. The goal is, on the one hand, to determine the relative standing of the national reference teams in an international context and, on the other hand, to monitor consistency among teams over time. |
Photography Classes | Serve as another means of comparing the assessments made by inventory teams, but also offer a time- and cost-effective alternative to international comparison surveys. Repeated use of the photos ensures greater reproducibility of the results. A drawback is that not all details relevant to the assessment can be discerned in the photos. |
Independent field inspections | In Germany, these are recommended for 15–20% of the total sample in the 16×16 km grid. At least 70% of the two crown cover surveys must differ by less than ±10% from one another. |
Photography Guide | The image series by MEINING ET AL. (2007) is used by survey teams as a standardized benchmark for assessing crown thinning. |
Validity limits and checks | This occurs both during data collection (for which the federal states are responsible) and during data transmission to the Thünen Institute (an automated process in the federal database). |