Mapping the fine-scale shallow water bathymetry of the Great Barrier Reef using ALOS AVNIR-2 data

Mapping the shallow water bathymetry of aquatic environments such as the Great Barrier Reef presents a number of challenges, due to both the large area which it occupies and the widely dispersed and variable shallow water reef areas which characterize it. The cost of implementing traditional methods, such as multibeam sonar, and, more recently, Laser Airborne Depth Sounding (LADS), can be prohibitive when dealing with large offshore areas. In addition, ship-based techniques are often restricted to surveys in water no shallower than ~10-15 m. Spaceborne remote sensing can be used for shallow water bathymetry estimation, potentially as a cost-effective tool to complement these other survey methods. A number of techniques have been developed in this field, using a combination of various sensors and methodologies. However, restrictions to the implementation of a broader scale approach still exist due to the requirement of existing calibration depth data, high imagery data costs and small spatial coverage. In this study we propose the application of a physics-based methodology to multi-spectral data from the AVNIR-2 sensor onboard the Japanese Advanced Land Observing Satellite (ALOS). The use of a physics-based approach enables bathymetry to be derived without the need for existing depth knowledge in the study area to calibrate the algorithm. This, combined with the large (70 km²) spatial coverage and high resolution (10 m) of AVNIR-2 data, enables the potential for high resolution mapping of the entire reef with approximately 25-30 scenes. Initial results show depths can be derived to approximately 15-20 m, with an accuracy of 10-20% of existing LADS data in the study area. Further work is outlined to potentially move to a more operational, broad-scale context, and to further understand the limitations and possibilities of working with AVNIR-2 for bathymetry applications.