Using image-based modelling (SfM–MVS) to produce a 1935 ortho-mosaic of the Ethiopian highlands

Abstract

Approximately 34,000 aerial photographs covering large parts of Ethiopia and dating back to 1935-41 have been recently recovered. These allow investigating environmental dynamics for a past period that until now was only accessible from terrestrial photographs or narratives. As the archive consists of both oblique and vertical aerial photographs that cover rather small areas, methods of image-based modelling were used to orthorectify the images. In this study, 9 vertical and 18 low oblique aerial photographs were processed as an ortho-mosaic, covering an area of 25 km², west of Wukro town in northern Ethiopia. Using 15 control points (derived from Google Earth), a RMSE of 28.5 m in X, 35.4 m in Y was achieved. These values can be viewed as optimal, given the relatively low resolution and poor quality of the imagery, the lack of metadata, the geometric quality of the Google Earth imagery and the recording characteristics. Land use remained largely similar since 1936, with large parts of the land being used as cropland or extensive grazing areas. Most remarkable changes are the strong expansion of the settlements as well as land management improvements. In a larger effort, ortho-mosaics covering large parts of Ethiopia in 1935-41 will be produced.

Changes in land use/cover mapped over 80 years in the Highlands of Northern Ethiopia

“…Despite its obvious importance for the study of land use, the 1930s photography, which represent the oldest APs of Ethiopia remain underutilized in Ethiopia (Frankl et al, 2015;Nyssen et al, 2016), mainly due to their recent rediscovery. The Italian Military Geographical Institute (IGM) took these black and white APs with a scale ranging from 1:11,500 (nearly vertical photograph) to 1:13,000-1:18,000 (oblique photographs) during the Italian occupation of Ethiopia (1930s-1940s) and the sets were recovered by Nyssen et al (2016).…”

“…Although the 1930s Aerial Photographs (APs), which are the oldest aerial photographs of the region taken during the Italian occupation of Ethiopia (1935)(1936)(1937)(1938)(1939)(1940)(1941) (Nyssen et al, 2016), are available, they have rarely been used to compare the historical LUC with the current situation. An exception to that is the local study by Frankl et al (2015). These Italian aerial photographs are important historical datasets for spatio-temporal analyses of land use, cover and management (Nyssen et al, 2016).…”

Land Management in the Northern Ethiopian Highlands: Local and Global Perspectives; Past, Present and Future

“…Recently, the interpretation of over 350 historical photographs of Ethiopian landscapes and their recent repeats allowed mapping land use and cover since the late 19th century and the development of timelines of vegetation cover and soil and water conservation (SWC) (Meire et al, 2013;Nyssen et al, 2014). The latest methodological development is the recovery of Italian aerial photographs of Ethiopia realised in 1935-1941, the reconstruction of the photogrammetry used at that time, and the fusion with current remotely sensed imagery for retrospective geomorphological analysis (Frankl et al, 2015b;Nyssen et al, 2015).…”

Historical Aerial Surveys Map Long-Term Changes of Forest Cover and Structure in the Central Congo Basin

“…Survey data across the African continent is less common, inaccessible, or both. Some studies do exist; Buitenwerf et al [24] and Hudak and Wessman [25] used aerial survey images to map vegetation changes in South African savannas whilst Frankl et al [26] and Nyssen et al [27] mapped the Ethiopian highlands of the 1930s.…”