Application of remote sensing techniques

Surface structures are changing rapdily during the initial ecosystem development at the Chicken Creek catchment. Very soon erosion processes led to a fast evolution of an ersoion gully network which altered the surface of the site significantly. In addition, plants are invading the site forming vegetation patterns. In order to monitor these structures at the surface of the catchment and their changes remote sensing methods using aerial photographs are applied.

First aerial photos were taken from a helicopter on September 22nd, 2006, June 14th, 2007, and July 10th, 2008. Since spring 2008 a microdrone equipped with a digital camera that allows terrain resolution of less than 1cm/pixel depending on flying height is in use for taking aerial photographs. Starting in 2009 aerial photographs of the whole catchment are taken regularly in spring (April), summer (July) and autumn (September). In addition to these microdrone based aerial photographs Vattenfall Europe Mining AGprovides aerial pictures taken during routine flights at the opencast mine. These pictures are taken monthly and are also used for photogrammetry in order to obtain digital elevation models of the site. These pictures with a lower spatial resolution compared to the microdrone based photographs are available as from 2004.

The MD4-200 microdrone is constructed by microdrones GmbH, Kreuztal, Germany. It is built from carbon fiber reinforced plastics. The payload capacity is about 200 g and the take-off weight is abouty 900 g including the camera system. The the size of the microdrone is 0.912 x 0.912 m including its four rotors. The drone has a maximum operating distance of about 2000 m depending on the flight velocity, wind force and the charging level of the batteries. A characteristic feature of the microdrone is the built-in GPS receiver that facilitates its use. By means of the GPS receiver the microdrone can hold its position. The programming of the microdrone is realised by the software developed by microdrones GmbH. The navigation by GPS allows way point navigation and enables to define flight plans beforehand. Due to the limited payload capacity of the microdrone the commercial, relatively high resolution digital camera Pentax Optio A40 is in use. The camera offers an absolute solution of 4000 x 3000 pixels. The specified camera settings in combination with the defined flight plan resulted in a maximum terrain resolution of about 0.02 m per pixel depending on the defined operating altitude of 80 m. The complete aerial photo of the total catchment is obtained from single pictures as a mosaic. WGEO BASIS is used to rectify the original pictures by means of at least four ground control points at each aerial photo (trapezoid rectification tool of WGEO). The creation of an aerial image mosaic is carried out by means of ArcGIS 9.3 (ESRI).

An overview of the microdrone based aerial photographs of the catchment is available here.

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