Determination of Minimum Sun Angle for Digital Aerial Image Acquisition



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Tomasz Zakiewicz, PLATO, South Africa,
Sibonelo Zulu, PLATO, South Africa,

Zulu, S


The Chief Directorate: National Geo-spatial Information (CD: NGI), Department of Rural Development and Land Reform, is responsible, amongst other duties, for the programme of the acquisition of the national aerial imagery. Since 2008, all imagery is acquired digitally with multispectral large format digital sensor systems. The acquisition of aerial photography is influenced by several factors. In order to obtain quality output from the imagery, images must be captured in accordance with the Standard set by CD: NGI.

The Standard specifies clearly the flying times for capturing of the images. The norms, however, were adapted from analogue aerial photography, without any scientific basis, and were not verified for digital imagery. The low sun angle, especially during winter, has historically presented the aerial mapping community with significant imagery acquisition constraints. For decades, the accepted practice urges on obtaining imagery with the sun angle exceeding 30 degrees above the horizon.

The authors will endeavour to provide answers to the questions of whether flying at lower solar elevations is relevant to the CD: NGI and what impact it would have on its various Divisions. For this reason, two pilot areas were flown in the morning and the afternoon, in both urban and mountainous areas.

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