Answer 1: Hyperspectral scanners have very high spectral resolution because of their narrow bandwidths. By measuring radiation over several small wavelength ranges, we are able to
5.4 Geology
Geology involves the study of landforms, structures, and the subsurface, to understand physical processes creating and modifying the earth's crust. It is most commonly understood as the exploration and exploitation of mineral and hydrocarbon resources, generally to improve the conditions and standard of living in society. Petroleum provides gas and oil for vehicle transportation, aggregate and limestone quarrying (sand and gravel) provides
ingredients for concrete for paving and construction, potash mines contribute to fertilizer, coal to energy production, precious metals and gems for jewelry, diamonds for drill bits, and copper, zinc and assorted minerals for a variety of uses. Geology also includes the study of potential hazards such as volcanoes, landslides, and earth quakes, and is thus a critical factor for geotechnical studies relating to construction and engineering. Geological studies are not limited to Earth - remote sensing has been used to examine the composition and structure of other planets and moons.
Remote sensing is used as a tool to extract information about the land surface structure, composition or subsurface, but is often combined with other data sources providing
complementary measurements. Multispectral data can provide information on lithology or rock composition based on spectral reflectance. Radar provides an expression of surface
topography and roughness, and thus is extremely valuable, especially when integrated with another data source to provide detailed relief.
Remote sensing is not limited to direct geology applications - it is also used to support logistics, such as route planning for access into a mining area, reclamation monitoring, and generating basemaps upon which geological data can be referenced or superimposed.
Geological applications of remote sensing include the following:
surficial deposit / bedrock mapping
lithological mapping
structural mapping
sand and gravel (aggregate) exploration/ exploitation
mineral exploration
hydrocarbon exploration
environmental geology
geobotany
baseline infrastructure
Page 196 Section 5.4 Geology
sedimentation mapping and monitoring
event mapping and monitoring
geo-hazard mapping
planetary mapping
Page 197 Section 5.4 Geology
5.4.1 Structural Mapping & Terrain Analysis
Syncline structures (in Pennsylvania) on SAR imagery Background
Structural geology plays an important role in mineral and hydrocarbon exploration, and potential hazard identification and monitoring.
Structural mapping is the identification and characterization of structural expression. Structures include faults, folds, synclines and anticlines and lineaments. Understanding structures is the key to interpreting crustal movements that have shaped the present terrain. Structures can indicate potential locations of oil and gas reserves by characterizing both the underlying subsurface geometry of rock units and the amount of crustal deformation and stress experienced in a certain locale. Detailed examination of structure can be obtained by geophysical techniques such as seismic surveying.
Structures are also examined for clues to crustal movement and potential hazards, such as earthquakes, landslides, and volcanic activity. Identification of fault lines can facilitate land use planning by limiting construction over potentially dangerous zones of seismic activity.
Why remote sensing?
A synoptic view of regional scale is a much different perspective than point ground observations when trying to map structural elements. Remote sensing offers this perspective and allows a geologist to examine other reference ancillary data simultaneously and synergistically, such as geo-magnetic information.
Certain remote sensing devices offer unique information regarding structures, such as in the relief expression offered by radar sensors.
Comparing surface expression to other geological information may also allow patterns of association to be recognized. For instance, a rock unit may be characterized by a particular radar texture which may also correlate with a high magnetic intensity or geochemical anomaly. Remote sensing is most useful in combination, or in synergy, with complementary datasets.
A benefit of side looking radar is that the illumination conditions can be controlled, and the most Page 198 Section 5.4.1 Structural Mapping & Terrain Analysis
appropriate geometry used for type of terrain being examined. Uniform illumination conditions provided by the sun, especially at equatorial latitudes, are usually not conducive to highlighting relief features. An extra benefit of airborne SAR sensors is that acquisition missions can be customized to orient the flightline parallel to the target orientation, to maximize the illumination and shadow effect.
Data requirements
In areas where vegetation cover is dense, it is very difficult to detect structural features. A heavy canopy will visually blanket the underlying formation, limiting the use of optical sensors for this application. Radar however, is sensitive enough to topographic variation that it is able to discern the structural expression reflected or mirrored in the tree top canopy, and therefore the structure may be clearly defined on the radar imagery.
Structural analyses are conducted on regional scales, to provide a comprehensive look at the extent of faults, lineaments and other structural features. Geologic features are typically large (kilometre scale) and applications therefore require small-scale imagery to cover the extent of the element of interest. Aerial photos can be used in temperate areas where large-scale imagery is required, particularly to map potential geohazards (e.g. landslides).
Structural mapping applications generally are not time sensitive (other than for project deadlines!) and so a fast turnaround is not required. Unless a time series analysis of crustal deformation is being conducted, frequency of imaging is not a critical issue either. The key factor for remotely sensed data are that they provide some information on the spatial distribution and surficial relief of the structural elements. Radar is well suited to these requirements with its side-looking configuration. Imaging with shallow incidence angles enhances surficial relief and structure.
Shadows can be used to help define the structure height and shape, and thus increasing the shadow effect, while shallow incidence angles may benefit structural analysis.
Canadian vs. International requirements
Requirements for remote sensing parameters of structural features are fairly constant throughout the world. Those areas of persistent cloud cover will benefit from radar imaging, while areas at very high or low latitudes can benefit from low sun angles to highlight subtle relief for optical imaging.
Page 199 Section 5.4.1 Structural Mapping & Terrain Analysis