Images from remote sensing satellites have been used for geological and environmental mapping since the launch of Landsat 1 in 1972. Today, imagery from sensors covering the visible, infrared, thermal and microwave sections of the electromagnetic spectrum are being used to support exploration and production activities.

Multispectral imaging systems provide a picture of the earth’s surface, filling in the white space in vector mapping at different spatial resolutions and scales, while synthetic aperture radar (SAR) can provide millimetric scale measurements of ground movements.

Until recently, however, the value of satellite imagery and the potential of remote sensing

Figure 1. Landsat image. This image, part of the Friesian Islands and the Netherlands, reveals surface processes and modern analogs of reservoirs.
(Images courtesy of Shell)
was only known by the technical specialists within Shell and had limited application despite some noteworthy projects.

Nevertheless, the advent of Google Earth (http://earth.google.com), following in the footsteps of World Wind from NASA (http://worldwind.arc.nasa.gov), has changed the world’s perception of remote sensing and raised expectations across the industry. It also has raised questions about data quality, the accuracy of geo-coding and the role of satellite imagery in decision making.

The purpose of this short article is to illustrate some of the E&P applications of remote sensing technology used in Shell and also to highlight the value of the considerable archive of satellite imagery available within the organization. Some of these applications may be considered very low-tech, providing alternatives to traditional surveying and mapping techniques; however, the advantages of using satellite imagery can be considerable. Images can be obtained from anywhere in the world, regardless of the location or political situation and with no exposure to personnel.

Image interpretation
Image interpretation is the oldest and most established use of satellite imagery. Depending
Figure 2. Geological analysis of Landsat imagery. Light reflected at different wavelengths is combined to highlight different lithologies. The surface expression of folds and faults can also be seen.
on the spectral properties and spatial scale of an image, uses can include geological and land surface mapping at a regional scale or mapping and planning of buildings and facilities. Satellite imagery is also used to complement existing mapping, providing information about areas for which no conventional mapping exists. Other applications include geological interpretation and structural mapping, base mapping for seismic and well planning, asset inventory and integrity, environmental baselines and studies, and due diligence work for new opportunities.

Through comparison of images acquired on different dates, it is possible to track changes in the earth’s environment and identify potential causes of change, both natural or man-made. Global Landsat coverage (Figure 1) is available within Shell, together with considerable volumes of Aster and SPOT imagery that can be accessed across the company intranet. This imagery is identical to that used in some earth viewers; the advantages of the Shell data, are the extensive coverage, the application of in-house processing algorithms and the availability throughout the company to ArcGIS and other exploration applications.

A number of high-resolution images with a spatial resolution of one meter or less from
Figure 3. Doha, Qatar, as captured from the Landsat 5 satellite c. 1990 (top) and from the Landsat 7 c. 2000 (bottom). Each image combines three spectral channels of visible and infrared light. The sensors on the two satellites have comparable spectral resolution and an effective spatial resolution of 93.5 ft and 50 ft (28.5 m and 15 m), respectively. These images clearly demonstrate the rapid development of the city during the 1990s.
Quickbird and Ikonos satellites are also available for areas relating to previous projects images also can be obtained from commercial vendors. During 2007, these satellites have been joined by World View 1, with a spatial resolution of half a meter. The new satellite also significantly increases the acquisition capacity available to the commercial market, although the success of acquisition requests depends heavily on the weather conditions in the target area. This problem can also be overcome now, following the launch of a new radar satellite, TerraSAR-X, which has a high-resolution imaging capability.

All imagery acquired by Shell is archived with appropriate metadata, ensuring that it is available for re-analysis and for future work. Image processing can add further value to satellite imagery through the enhancement of lithology and geological structures (Figure 2) and the identification of vegetation based on differences in spectral properties. This approach has been employed, for example, to map vegetation across the Niger Delta in successive epochs of satellite imagery acquired between the 1970s and the 1990s. Automated spectral classification, identifying areas with similar reflectance properties, was controlled and checked using helicopter-based reconnaissance.

Surface mapping
The value of satellite imagery in mapping surface changes is illustrated in Figure 3. The increased spectral resolution of the Aster sensor, which images 14 bands at visible and near infrared, shortwave and thermal wavelengths with a maximum spatial resolution of 50 ft (15 m), can be used to map different lithologies and structures and also to examine the variations in the conditions of vegetation. As new hyperspectral satellite missions are launched, it may be possible to directly map individual vegetation species and identify stress caused by the presence of hydrocarbons at or near the surface, but it will probably be at least five years before commercial hyperspectral satellite imagery is available. Shell is actively exploring new developments in remote sensing and is active in research.

Elevation mapping
The need for height maps, usually referred to as digital elevation models (DEMs), for
Figure 4. The Space Shuttle Radar Topographic Mapping mission is available within Shell.
geological analysis, route planning and other applications requiring data on surface elevation can now be met using a number of space-based instruments. The Space Shuttle Radar Topographic Mapping mission (SRTM – Figure 4) generated a DEM with a spatial resolution of 295 ft (90 m) between latitudes 60N and 54S and is available within Shell. For some areas, overlapping, cloud-free satellite images acquired from different positions have been processed photogrammetrically to generate DEMs. Sources of this type of DEM include SPOT, Aster, Quickbird and Ikonos. In cases where surface elevation data are required or there is a need to monitor ground movement continuously but no cloud-free images can be obtained, synthetic aperture radar interferometry (InSAR) can be employed. Examples where this technique has been used include structural mapping in equatorial regions and the monitoring of the surface expression of reservoir movement at the millimeter scale.

Although the success of optical image acquisition depends on the weather and climate of the target area, remote sensing satellites offer an unparalleled opportunity to explore even the remotest areas from the Shell desktop.