The application and potential of remote sensing in the Great Barrier Reef

The availability of multispectral data from the satellite-borne ASTER (Advanced Space borne Thermal Emission Reflection Radiometer) sensor with 14 spectral bands, launched on 18 December 1999, ushers in a new dimension in large-scale mineral exploration. The ASTER bands are strategically positioned to map distinctive absorptive features for mapping alteration mineralogy, which has increased the potential to map hydrothermal alteration zones as compared to the conventional Landsat TM satellite and aerial photographs. This research tests the ability of ASTER to map hydrothermal alteration zones by applying various image enhancement techniques and comparing them. The study area is the Haib copper prospect in Namibia. The Crosta technique, standard colour composites, spectral band ratioing, the software defoliant technique, log residuals and spectral linear unmixing were applied and compared against results from the previous detailed geophysical and geochemical exploration. The results from all the techniques corresponded with published geological maps from previous work and indicated ASTER's ability to detect alteration zonations. Comparison of the methods applied showed that choice of technique is usually dependent of the level of detail which one seeks to achieve. Standard colour composite and log residuals are more useful for a generalized overview of the alteration mineralogy, whilst uniquely defining mineral end members is achieved by application of the Crosta technique, ratioing and spectral linear unmixing. Application of the software defoliant techniques involved ratioing results, which are affected by spectral interferences from other minerals. The presence of a highly fractured system has been established by application of Sobel filtering. A spatial association of the extracted fracture system with alteration areas suggest mineralization at the Haib is fracture controlled. The results support the presence of argillicphyllic and prophylitic alteration zones on a regional scale, a scenario which can be equated to the Lowell-Guilbert model. The potassic-phyllic zone boundary could not be spectrally detected which also supports previous studies which suggest the potassic zone is nondefinitive and is over-printed by the phyllic zone. The results demonstrate that ASTER is an effective tool to map hydrothermal alteration systems in arid areas. Stellenbosch University http://scholar.sun.ac.za

Testing the ability of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) to map hydrothermal alteration zones : a case study of the Haib Porphyry Copper-Molybdenum Deposit, Namibia

This study explores the role that satellite imaging systems might play in obtaining information needed in the management of natural and manmade disasters. Information requirements which might conceivably be met by satellite were identified for over twenty disasters. These requirements covered pre-disaster mitigation and preparedness activities, disaster response activities, and post-disaster recovery activities. The essential imaging satellite characteristics needed to meet most of the information requirements are 30 meter (or finer) spatial resolution, frequency of observations of one week or less, data delivery times of one day or less, and stereo, synoptic all-weather coverage of large areas in the visible, near infrared, thermal infrared and microwave bands. Of the current and planned satellite systems investigated for possible application to disaster management, Landsat-D and SPOT appear to have the greatest potential during disaster mitigation and preparedness activities, but all satellites studied have serious deficiencies during response and recovery activities. Several strawman concepts are presented for a satellite system optimized to support all disaster management activities.

P. B. Richards

Papers

Recommended satellite imagery capabilities for disaster management