National aerial imagery quality improved

February 20th, 2018, Published in Articles: EE Publishers, Articles: PositionIT, Featured: PositionIT

The Chief Directorate: National Geo-spatial Information (NGI), under the Department of Rural Development and Land Reform (DRDLR), has improved its digital imagery acquisition by changing its resolution from 0,5 m to 0,25 m ground sample distance (GSD).

In 2005, NGI noticed a global trend towards digital image acquisition and decided to acquire its imagery using a large format digital sensor system. From 2008 to 2016, all imagery was captured digitally and supplied in 12-bit, full colour (RGB and CIR) format at 0,5 m GSD. Since July 2017 the imagery has been captured using a new generation large format digital sensor system to offer a better and clearer view.

Fig. 1: A comparative view of imagery acquired at 0,5 m and 0,25 m GSD.

Fig. 1: A comparative view of imagery acquired at 0,5 m and 0,25 m GSD.

This sensor offers superior image quality with the advantage of 16-bit density depth, although the calibrated imagery can still be supplied in an 8-bit format. There is also sufficient shadow to highlight details and facilitate accurate image interpretation. It also offers a true reflection of the terrain at exposure and is spectrally consistent.

Improving the utilisation of the aerial imagery also saves the public-sector money. By improving the GSD, the NGI will be broadening its user base, with many clients standing to benefit from the latest aerial imagery products. These include departments such as the Department of Defence, the Department of Mineral Resources, the Department of Transport, as well as municipalities which use the imagery for municipal property valuations. This is in addition to private and semi-private stakeholders who also use NGI’s aerial imagery in their operations.

NGI’s higher quality imagery will play an important role in supporting the Department of Defence in the planning, administration, evaluation, execution and monitoring of its projects. It will also assist the Department of Mineral Resources with easier identification of boundaries to prevent overlapping when granting mining licenses. The Department of Transport also uses the imagery with local maps for the location, planning and mapping of additional routes.

The Department of Water and Sanitation, which is involved in programmes such as the WESSA Eco-Schools Water Project, Sanitation Services Programme, and Water Infrastructure Programme, is another important beneficiary of the higher resolution imagery. The imagery will be particularly useful to the Water Infrastructure Programme, which sets out to develop, rehabilitate and refurbish raw water resources and water services infrastructure to meet the socio-economic and environmental needs of South Africa.

The Free State Province was the first area to be captured at the at this higher resolution after it was flown around July 2017, and the next area, which forms part of the Northern Cape, is currently being processed. The final product is processed to 16-bit RGBN tiff format. The imagery is stored as Tiff files with a JPEG compression of Q=3, along with tiles and a full set of overviews.

Contact Dr. Francis Owusu Twumasi, CD: NGI, Tel 082 969-4512, francis.twumasi@drdlr.gov.za