Modelling in Very - High - Energy γ - ray Astronomy

Context. Ground based Cherenkov telescope systems measure astrophysical γ-ray emission against a background of cosmic-ray induced air showers. The subtraction of this background is a major challenge for the extraction of spectra and morphology of γ-ray sources. Aims. The unprecedented sensitivity of the new generation of ground based very-high-energy γ-ray experiments such as H.E.S.S. has lead to the discovery of many previously unknown extended sources. The analysis of such sources requires a range of different background modelling techniques. Here we describe some of the techniques that have been applied to data from the H.E.S.S. instrument and compare their