South Alligator River

The SAR instrument onboard ERS-1 uncovers the beauties of Kakadu National Park in the Northern Territories of Australia.
The area imaged is about 100 by 100 km wide. It shows the South Alligator River in the center, the smaller West Alligator river to the left and East Alligator River top right. The shape of the estuaries and the meandering river courses suggest a consistent influence of the tides. In fact, brackish water can be found in the rivers up to 80 km inland. The area is well known for being not only the ideal habitat of several migrating bird species, but also for hosting alligators!
The image appears colorful because of the seasonal changes occurring in the area
A composite of 3 acquisition dates is presented here, namely: 24 Aug. 1993 ( red), 2 Nov. 1992 (green) and 5 July 1993 (blue). One of the dates (November) falls at the beginning of the wet season; the two other dates correspond to the dry season.
Areas with no changes are diifies mux. There, poorly vegetated, deeply cut cliffs can be found.
Grass and shrub land areas, periodically burnt by the aborigines, are displayed in grey. The dark zones near the lower river courses correspond to tidal mud flats. 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 burst into many cracks, thus making the microwave backscatter very strong.
The green color represents the contribution of the November acquisition, which most likely took place during or soon after a rainfall occurred over the area to the West (left part of the image).
The areas in bright along the coastline reveal the presence of dense mangrove forests, whilst the close-by greenish or bluish indicate degraded woodlands and sand dunes.
This is a national park area, therefore little man-made features can be observed. Roads are visible only partially, either in dark, or from north to south bright lines. This is due to the road cut into the landscape including facets facing the microwave illumination which result in high reflection. There are also the airstrips of Jabiru (mid-right) and Yellow Water (near the image centre) that can be spotted clearly.
ERS-1 SAR time series of data are particularly suitable to monitor large ecosystems. They can contribute to a more efficient management of the National Park, through an early detection of the level of degradation of the single landscape elements.
Technical information:
Acquisition dates and orbit reference :
24 Aug.1992 (red) - orbit no.05787 frame no.3861
2 Nov.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

ERS Data Utilization Section, ESA/ESRIN

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry