Remote sensing for petroleum exploration, Part 1: Overview of imaging systems

his paper, the first of two that summarize remote sensing as applied to petroleum exploration, provides an overview of the science and the computer techniques used to process the data. The second (to be published in TLE’s May issue) will describe successful oil-exploration projects that employed remote-sensing technology. The examples are from projects by colleagues and myself at Chevron, from which I retired in 1992. Remote sensing has several applications to geophysical exploration of onshore regions. Images are interpreted to produce geologic maps that show structural trends and potential prospects which are, in turn, used to plan an efficient seismic program. Furthermore, if an area lacks a reliable base map, one can be readily generated from remote-sensing data, as can maps showing access and trafficability which can also improve the efficiency of field operations. (When Lee Lawyer, a former SEG President, was chief geophysicist of Chevron Overseas Petroleum, he insisted that any onshore seismic survey be preceded by a remotesensing interpretation.) Landsat images have also been employed in shallow offshore areas to identify uncharted reefs and other hazards to seismic surveys. Remote sensing is defined as the science of acquiring, processing, and interpreting images from satellites and aircraft that record the interaction between matter and electromagnetic energy. Remote-sensing images of the earth are acquired in three wavelength intervals, or regions, of the electromagnetic spectrum. The visible region ranges from 0.4 to 0.7 μm and is divided into the blue, green, and red bands. The infrared (IR) region ranges from 0.7 to 30 μm and is divided into the reflected IR and thermal IR portions. The reflected IR portion ranges from 0.7 to 3.0 μm; the energy is predominantly reflected sunlight at wavelengths longer than visible light. The Landsat and SPOT satellite systems acquire valuable images in the visible and reflected IR regions. The thermal IR portion ranges from 3.0 to 15.0 μm; the energy is radiant, or heat, energy. Thermal IR images have considerable potential for exploration in arid and semiarid terrains; however, the method has been underutilized in recent years largely owing to the lack of suitable images. Images in the visible, reflected IR and thermal IR are acquired in the passive mode by systems that simply record the available energy that is reflected or radiated from the earth. The microwave region ranges from 0.1 to 30 cm; images for exploration are primarily acquired in the active mode called radar. This paper focuses on three systems: Landsat Thematic Mapper and SPOT panchromatic images in the visible and reflected IR regions, and aircraft radar images.