Day 6 - GIS and Remote Sensing

By: Lwazi and Malusi

“Everything is related to everything else, but near things are more related than distant things” First law of Geography

Introduction to GIS and Remote Sensing

After a long drive from Knysna we finally arrive in Bellville, where we had our final pit stop for our South African geology tour. Bright and early we departed for the CGS offices in Bellville, where we attended lectures on basics of GIS, remote sensing and marine, given by one of the best scientists in the CGS. Firstly Chiedza Musekiwa took us for an introduction of GIS, with emphasis on the Arc GIS software, showing us the different tools within it:Arc Catalog and Arc Map and their capabilities for mapping purposes. She also touched on the most crucial issue of map projections and datum which normally confuses young GIS users, explaining to us the difference between the two and lastly she showed us how to georeferencing images in Arc Map.

GIS and Remote sensing course in Bellville

Following her presentation it was Paul Macey, whom took us for modern geological techniques and how to conduct and manage geological mapping projects. With his vast amount of experience in the geological mapping and the forever evolving technologies, he reiterates that a good geologist still needs to write down field notes, rather than relying on modern technologies.    One of the popular technologies which is being utilized for geological mapping is remote sensing, where we are able to retrieve the vital information without being in contact with them. With different mathematical manipulations embedded within it,  such as band combination, Principal Component Analysis (PCA), band ratios and Normalized Difference Vegetation Index,etc embedded a user is able to extract useful information in the desktop stage of a mapping project. Various satellite data sets which are being used for geology are ASTER, LANDSAT, SPOT, etc. Showing us a glimpse of some of the work that he has done through the years it is evident that experience must be earned.

To cap off the long and knowledgeable day, we had Mac (Michael Machutchon), who’s a senior scientist in the marine geoscience unit (MGU). As expected, concentration spans were at a low, considering it was Friday afternoon. However, we had to pull ourselves together and brace ourselves for the last session of the day. The presentation kicked off with an intro into the various geophysical techniques utilized within the unit. These include single-beam, multi-beam surveys (for bathymetry), seismics (boomer and pinger) and side-scan sonar, to mention a few. This was followed by a series of videos and photos meant to demonstrate what the marines get up to on a typical day out to sea.

2014 Diary: Day 5 - Remote Sensing

Remote Sensing 

Today the team spent the day with Dr Paul Macey from Mapping Geosciences (Western Cape) learning all about remote sensing techniques and how these are used to do preliminary investigations of their mapping areas. Dr Macey has substantial experience in geological mapping throughout Africa and the applications and uses of advanced remote sensing techniques to aid in the geological investigations.

Example of remote sensed ASTER imagery using various band ratio combinations to highlight possible variations in the geology. Typically different colours relate to different rock/soil chemistry

Remote Sensing stems from the manipulation of band ratio combinations of aerial imagery to delineate various geological units. The imagery is obtained from passive sources such as satellites or airborne photographic sensors, or active sensors such as radar or lasers. The material (e.g. rocks, soil, forestry, oceans) being captured by the sensors will absorb certain amount of light and reflect according to several factors, most notably, the chemistry of the material. Through the use of various band ration combinations, rocks high in certain chemistries will reflect a specific colour. Remote Sensing techniques can make estimations of what the chemistry of these different colours are and further relate that to possibly geological units. Through this mechanism, a preliminary geological polygon map can be created and be cross checked while performing field work. This is particularly useful once all different colour-coded polygon have been cross checked and can aid in the production of an accurate geological map if 100 % field coverage is not possible during the mapping.