Focus Earth

Northern Territories of Australia

ERS-1's Synthetic Aperture Radar (SAR) instrument here uncovers the beauty of Kakadu National Park in the Northern Territories of Australia. The area imaged covers about 100x100 square kilometers. It shows the South Alligator River in the centre, the smaller West Alligator river to the left, and the East Alligator River to the top right.

The shape of the estuaries and the meandering river courses suggest a constant tidal influence, and brackish water can indeed be found in the rivers up to 80 km inland. The area is very well known not only as an ideal habitat for several migrating bird species, but also for its alligators!

The image is especially colourful because of the pronounced seasonal changes occurring in the area. It is a composite of three separate images, acquired on: 24 August 1993 (red), 2 November 1992 (green) and 5 July 1993 (blue). One of these dates (November) corresponded with the beginning of the wet season; the other two correspond to the dry season. Areas exhibiting no changes between these dates are displayed in grey and white. The white colour to the right identifies mainly the Arnhem sandstone plateau, where poorly vegetated, deeply cut cliffs are to be found. Grass and shrubland areas, periodically burnt by the aborigines, are displayed in grey. The dark zones near the lower river courses correspond to tidal mudflats. The wide but short affluents, with dendrite delineation, imaged mostly in pink but sometimes also in white, are the so-called 'billabongs'. During the wet season they form huge lakes, but when the soil dries it contains many cracks, making the microwave backscatter very strong. The green colour represents the contribution of the November image, which was probably acquired during or soon after rainfall had occurred over the area to the west (left part of the image). The bright areas along the coastline reveal the presence of dense mangrove forests, whilst the adjacent greenish or bluish hues indicate degraded woodlands and sand dunes.

This is a national-park area and small man-made features can be also observed. Roads are only partially visible, either as dark lines, or as bright north south lines when the road is cut into the landscape so that the banks facing the microwave illumination result in strong reflections. The airstrips of Jabiru (centre right) and Yellow Water (near the centre of the image) are clearly visible.

ERS-1 SAR time series of data are particularly suitable for monitoring large ecosystems. They can contribute to more efficient management of the national park by facilitating early detection of any degradation in individual landscape elements.

Acquisition dates and orbit reference:

24 August 1992 (red)              - orbit no. 05787
                                  - frame no. 3861
2 November 1992 (green)           - orbit no. 06789
                                  - frame no. 3861
5 July 1993 (blue)                - orbit no. 10296
                                  - frame no. 3861.

Acquisition station: Alice Springs, Australia

Data processing: ESA/ESRIN, Frascati, Italy

Northern Territories of Australia