Don’t See the Dwellings for the Trees: Quantifying the Effect of Tree Growth on Multi-temporal Dwelling Extraction in a Refugee Camp. GI_Forum|GI_Forum 2015 – Geospatial Minds for Society|

Automated and visual approaches for the monitoring of refugee or IDP camps based on satellite data are very important as independent information sources, especially for insecure and remote areas. Nevertheless, monitoring based on satellite data always has a certain degree of uncertainty, e.g. due to data quality, complexity of the area of investigation, seasonal pheonological problems, or algorithmic limitations. Within this paper, we aim to quantify one of these limiting aspects: the factor of vegetation (i.e. tree) growth and its effect on multi-temporal dwelling monitoring, hampering the identification of dwellings on the ground. For the refugee camp Djabal, Chad, we found that 2506 dwellings (25 %) of 2010 are at least partly affected by tree growth three years later (2013), which is influencing automated extraction methods, as well as visual interpretations. 395 of these dwellings were completely covered by vegetation and vegetation shadow, and were therefore not detectable anymore. Taking this factor into account, the decrease of dwellings between 2010 and 2013 is potentially lowered from 10 % to 5 %