Satellite Derived Bathymetry and Digital Elevation Models (DEM)

In 2010, Qatar Shell Upstream International B.V. (QSUI) re-entered Exploration in Qatar focusing on the relatively deep conventional Pre-Khuff gas plays with a view to discover additional hydrocarbons in the State of Qatar. In order to support Qatar Shell with the execution of onshore and offshore seismic programs, satellite imagery was used extensively to derive added value products in terms of shallow water bathymetry, seabed classification and onshore digital elevation models (DEM). For the offshore bathymetry and seabed classification products, 2m resolution multispectral WorldView-2 satellite scenes were processed following a data processing chain including the correction of atmospheric adjacency (increased radiance over water due to reflection of photons by the nearby land and their further scattering in the atmosphere), water surface and water column effects. The resulting offshore products had a spatial resolution of 4m and covered an area of ~700 km2. For the onshore elevation product, a 50cm WorldView-1 stereo image pair was processed using a photogrammetric stereo vision algorithm to generate a 1m spatial resolution DEM over an area of ~450 km2. The accuracy and quality of these satellite image derived products depend largely on the optical conditions of the satellite scene, the sensitivity of the satellite sensor and the accuracy of the calibration. Three types of independent control datasets were used to assess the quality and accuracy of the bathymetry and DEM; airborne LiDAR sounding transects, multibeam echo sounding swaths (offshore) and seismic survey lines (onshore and offshore). After correction for any systematic bias, the correlation of both products with the control data was found to be very good with <1m vertical error in general. Satellite image products are recognized within QSUI as a key technology to aid the planning and preparation of seismic operations and site evaluation by improving hazard identification and reducing field risk exposure early on in the project life cycle. In addition, cost savings were realized compared to more costly traditional acquisition methods. The seismic field conditions were assessed relatively quickly compared to the time frame required for traditional methods. This allowed the data to be included in commercial tendering which in turn resulted in sharper bids. In conclusion, satellite imagery in combination with the right processing techniques has the potential to provide an integrated wide area bathymetry and DEM coverage at relatively high resolution and low cost.