Knowledge Transfer - Formalising an Interpretation Key

The paper deals with the transformation of an interpretation key, established for a visual interpretation, into a rule base applied for automated image analysis. An object-based approach is used for that purpose. The methodology is demonstrated for the detection of coca fields on medium resolution satellite imagery. The monitoring of illicit coca cultivation in Colombia is currently based on a visual interpretation of various types of satellite images. Medium resolution satellite imagery is used due to economical restrictions. The detection of relatively small coca fields (average field size: 1.8 ha) on medium resolution satellite imagery as Landsat makes a per-pixel classification difficult. Thus a visual interpretation is applied. An interpretation key is being developed together with experts in order to conduct a rigorous interpretation and to document the experience of the interpreters. Beside spectral characteristics of the image data, contextual information and results from previous surveys or classifications of previous images are used for the interpretation. The interpretation key is used to establish a rule base that can be applied for an automated interpretation of coca fields. The tools of the commercial software package eCognition are used for this purpose. An advantage of automation is the improvement of the transparency of the interpretation process.