RADARSAT-2 Imagery Research Articles

Methods for Remote Engineering Geology Terrain Analysis in Boreal Forest Regions of Ontario, Canada

Research Article| March 01, 2004 Methods for Remote Engineering Geology Terrain Analysis in Boreal Forest Regions of Ontario, Canada PETER J. BARNETT; PETER J. BARNETT 1Ontario Geological Survey, Ministry of Northern Development and Mines, 933 Ramsey Lake Road, Sudbury, ON P3E 4V6 Search for other works by this author on: GSW Google Scholar VERNON H. SINGHROY; VERNON H. SINGHROY 2Canada Centre for Remote Sensing, Natural Resources Canada, 588 Booth Street, Ottawa, ON K1A 0Y7 Search for other works by this author on: GSW Google Scholar JIRO SHIROTA; JIRO SHIROTA 3Ontario Geological Survey, Ministry of Northern Development and Mines, 933 Ramsey Lake Road, Sudbury, ON P3E 4V6 Search for other works by this author on: GSW Google Scholar STEPHEN J. LENEY STEPHEN J. LENEY 4Geomatic Service Centre, Ontario Ministry of Natural Resources, 300 Water Street, Peterborough, ON K9J8M5 Search for other works by this author on: GSW Google Scholar Author and Article Information PETER J. BARNETT 1Ontario Geological Survey, Ministry of Northern Development and Mines, 933 Ramsey Lake Road, Sudbury, ON P3E 4V6 VERNON H. SINGHROY 2Canada Centre for Remote Sensing, Natural Resources Canada, 588 Booth Street, Ottawa, ON K1A 0Y7 JIRO SHIROTA 3Ontario Geological Survey, Ministry of Northern Development and Mines, 933 Ramsey Lake Road, Sudbury, ON P3E 4V6 STEPHEN J. LENEY 4Geomatic Service Centre, Ontario Ministry of Natural Resources, 300 Water Street, Peterborough, ON K9J8M5 Publisher: Association of Environmental & Engineering Geologists First Online: 02 Mar 2017 Online ISSN: 1558-9161 Print ISSN: 1078-7275 Copyright © 2004 Geological Society of America Environmental & Engineering Geoscience (2004) 10 (3): 229–241. https://doi.org/10.2113/10.3.229 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation PETER J. BARNETT, VERNON H. SINGHROY, JIRO SHIROTA, STEPHEN J. LENEY; Methods for Remote Engineering Geology Terrain Analysis in Boreal Forest Regions of Ontario, Canada. Environmental & Engineering Geoscience 2004;; 10 (3): 229–241. doi: https://doi.org/10.2113/10.3.229 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract The Ontario Geological Survey and Canada Centre for Remote Sensing have developed methods for engineering geology terrain analysis using digital elevation models (DEMs) and remotely sensed imagery for remote areas within the boreal forest region of the Canadian Shield. Traditional methods of terrain analysis would be expensive because of the limited access and the vast area involved. Four main components of the terrain are considered: material, landform, relief, and regional drainage conditions. Landform (roughness) and relief are derived automatically from an analysis of a detailed hydrological-conditioned DEM. Regional drainage conditions are estimated from RADARSAT imagery with a mask based on the use of aspect and slope to limit the effects of topography on backscatter. Various types of analysis of LANDSAT imagery are then combined with all the above digital data layers to interpret material type. An automated method that first determines the relationships of the various layers of digital information in areas of known terrain conditions and then predicts terrain conditions in adjacent unmapped areas, is discussed. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

ICESat observations of Arctic sea ice: A first look

Analysis of near‐coincident ICESat and RADARSAT imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings (containing thin ice or open water) in the sea ice cover as well as to surface relief of old and first‐year ice. The precision of the elevation estimates, measured over relatively flat sea ice, is ∼2 cm. Using the thickness of thin‐ice in recent openings to estimate sea level references, we obtain the sea‐ice freeboard along the altimeter tracks. This step is necessitated by the large uncertainties in the sea surface topography compared to that required for accurate determination of freeboard. Unknown snow depth introduces the largest uncertainty in the conversion of freeboard to ice thickness. Surface roughness is also derived, for the first time, from the variability of successive elevation estimates along the altimeter track. Overall, these ICESat measurements provide an unprecedented view of the Arctic Ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint of ∼70 m.

Compressive shear faults within arctic sea ice: Fracture on scales large and small

We examined fracture features within arctic sea ice as revealed by Landsat‐7 and RADARSAT imagery, by an aerial survey, and through observations in the laboratory of specimens loaded to brittle failure under biaxial compression. Regardless of scale, which spans the range from kilometers to millimeters, the features look alike. They consist mainly of narrow lineaments that traverse the field of view, plus wing‐like and comb‐like secondary cracks. The lineaments occasionally intersect and generally exhibit either right‐lateral or left‐lateral relative movement, like strike‐slip faults within Earth's crust. We term them brittle compressive shear faults. They form through the linking of en echelon arrays of deformation‐induced secondary cracks. From an application of wing‐crack and comb‐crack mechanics, we estimated the maximum compressive stress near the onset of faulting and found that our estimates compare favorably with in situ measurements by earlier investigators of ice sheet failure stresses. To account for the brittle behavior of the sea ice cover, we applied a recent model of the ductile‐to‐brittle transition in which the key idea is the competition between stress buildup and stress relaxation at stress concentrators. In identifying the nature of sea ice fracture features, we advance the view that failure occurs on many scales through highly localized as opposed to uniformly distributed deformation, via the operation of scale‐independent mechanisms.

Use of SAR satellites for mapping zonation of vegetation communities in the Amazon floodplain

Radarsat and JERS-1 imagery were used for mapping zonation of vegetation communities in the Amazon floodplain. Imagery analysis indicates that at periods of minimum water level the backscattering values of both C and L bands are the lowest and as the water level rises, so do the backscattering values. JERS-1 imagery exhibits a larger dynamic range of backscattering in response to the ground cover for the two extremes of water level (10 dB) compared to Radarsat imagery. The backscattering differences from different ground cover allowed the use of a region-based classification that produced seasonal maps with accuracies higher than 95% for vegetated areas of the floodplain. These seasonal maps were used to estimate the spatial distribution and time of inundation and the vegetation cover of the floodplain. It was possible to determine that semi-aquatic vegetation, tree-like aquatic plants, and shrub-like trees colonize regions flooded for at least 300 days year−1. Secondary colonizers, such as tall well-developed floodplain forest, cover regions flooded for approximately 150 days year−1, and floodplain climax forest colonize regions inundated for approximately 60 days year−1.

Subglacial bedrock structure in the Transantarctic Mountains and its influence on ice sheet flow: insights from RADARSAT SAR imagery

The Transantarctic Mountains represent a major Cenozoic rift-flank uplift that crosses the interior of Antarctica. On one side of the mountains lies the Ross embayment, a submarine portion of the West Antarctic rift system. The East Antarctic Ice Sheet overlies the cratonic margin of the mountains. The Transantarctic Mountains restrict flow of the ice sheet to lower elevations within the Ross embayment. Using RADARSAT imagery, radio-echo sounding data and field-based structural data, we demonstrate that RADARSAT imagery can be used for regional structural mapping of the Transantarctic Mountains and, in particular, that bedrock structures can be traced subglacially beneath the ice-covered mountain flanks. Our analysis shows that regional structures in the mountains have provided preferred pathways for ice flow from the East Antarctic Ice Sheet across the Transantarctic Mountains barrier to the Ross embayment in West Antarctica. Further regional mapping using RADARSAT imagery has the potential to delineate the regional structural architecture of the Transantarctic Mountains and to establish the degree of spatial coupling between structures associated with mountain uplift and regional drainage patterns of the Antarctic ice sheets.

Enhanced classification of prairie landscapes using simulated RADARSAT-2 imagery

For the past decade, we have been using Landsat TM imagery to monitor changes in the area and distribution of ecosystems in a relatively undisturbed natural region in southwestern Manitoba, Canada. The 40 000 ha of Canadian Forces Base Shilo are protected from urbanization, commercialization, and agriculture, and are disturbed only by modest and controlled amounts of military training. A significant problem with the use of TM imagery for this study is that some of the more sensitive indicators of environmental change, such as the infestation of disturbed grassland by leafy spurge (Euphorbia esula), are very difficult to identify and delineate in the visible and near-IR bands. A fully polarized synthetic aperture radar that is sensitive to vegetation morphology may not have the same difficulty. C-band radars, such as that being constructed for RADARSAT-2, are known to have difficulty differentiating vegetation types in regions of dense foliage, but, in a prairie ecosystem such as the one under study here, even the densest foliage should be sparse enough to yield a unique polarization signature. To test this hypothesis, we have simulated RADARSAT-2 HH, HV, and VV images, using TM images of the area, polarization ratios extracted from the literature for vegetation types similar to those found in the area, and a RADARSAT-1 HH image of the area collected almost simultaneously with one of the TM images. Estimation of class separation by Bhattacharyya distance, first using only HH information and then using the full HH, HV, VV imagery, shows an increase of statistically separable classes and class groups when the fully polarized class characterization is used. Visual comparison of synthesized imagery from different years shows sufficient differences to imply that RADARSAT-2 imagery will likely be a useful tool to augment our continuing monitoring and assessment of this prairie ecosystem.

Integration of RADARSAT and GIS modelling for estimating future Red River flood risk

A new geomatics-based approach for flood prediction was developed and used to model the magnitude and spatial extent of a future Red River flood in southern Manitoba. This approach combines the statistical modelling capabilities of Markov (non-spatial) analysis and logistic regression (spatial) within a geographic information system (GIS) environment, utilizing modelling inputs derived from remotely sensed RADARSAT imagery and other digital geographic data. The 1997 Red River flood was the second largest in recorded history, and the largest for which accurate data are available. The results indicate: (i) a flood “one time interval-in terms of 3 days time unit measurement- larger in area” than the 1997 flood is expected to affect 17.6% more land (an additional 47.6 km2) within the study area compared to 1997 levels based on Markovian probability derived from observations from the 1997 event; and (ii) the majority of this excess flooding will take place on agricultural land; no additional communities are expected to be at risk. Quantitative assessment verified the capability of this modelling approach for producing statistically significant results. The methodology used in this research would be easily transferable to other areas, and may provide the basis for a viable alternative to conventional hydrologic-based flood prediction approaches

Break‐up of the largest Arctic ice shelf and associated loss of an epishelf lake

Field observations and RADARSAT imagery of the Ward Hunt Ice Shelf (lat. 83°N, long. 74°W), Nunavut, Canada, show that it broke in two over the period 2000 to 2002, with additional fissuring and further ice island calving. The fracturing caused the drainage of an ice‐dammed epishelf lake (Disraeli Fiord), a rare ecosystem type. Reductions in the freshwater volume of Disraeli Fiord occurred from 1967 to the present and accompanied a significant rise in mean annual air temperature over the same period in this far northern region. The recent collapse of ice shelves in West Antarctica has been interpreted as evidence of accelerated climate change in that region. Similarly, the inferred thinning and observed fragmentation of the ice shelf, plus the drainage of the epishelf lake, are additional evidence for climate change in the High Arctic.

Contribution of the synergy of RADARSAT-1 and seismic imagery interpretation in the structural geology of the Central Alberta Foothills, Canada, as an aid for oil and gas exploration

The synergy of RADARSAT-1 and seismic imagery interpretation has been applied in the Blackstone area of the Central Alberta Foothills in the Canadian Cordillera thrust and fold belt to map the continuity of geological structures, which are of importance for oil and gas exploration. The surface features located in the radar images have been confirmed through seismic imaging, which helped in the definition of the deep expression of thrusts and related fold structures. RADARSAT-1 imaging provided important information for the connection along strike of geological structures with subtle surface expression. The reconstruction of the continuity of thrust‐fold related major structures known in the area has been successful. Moreover, transverse faults and lineaments with east-northeast‐west-southwest, northeast‐southwest, and north-northeast‐south-southwest trends have been delineated in the radar images. The east-northeast‐west-southwest transverse faults have an extensional character, cut across the inner and outer Foothills, and are persistent at the regional scale. The northeast‐southwest and north-northeast‐south-southwest transverse faults are wrench-type faults, which are mainly localized in the inner Foothills. These structures have been identified for the first time in the area and are possibly a third-generation fault-play type for oil and gas exploration. The results of this work show that satellite radar imagery can greatly contribute to the structural and geological mapping of the Foothills terrain and is therefore a valuable aid for oil and gas exploration in analogous tectonic environments.

RADARSAT backscatter characteristics of ice growing on shallow sub‐Arctic lakes, Churchill, Manitoba, Canada

AbstractResults from an investigation on the evaluation of RADARSAT (C‐HH) imagery for monitoring ice growth and decay, and related processes of shallow sub‐Arctic (tundra and forest) lakes in northern Manitoba, Canada, are presented. Field observations on the structural and stratigraphic characteristics of snow and ice from four lake sites are used in support of the interpretation of changes in synthetic aperture radar backscatter intensity as a function of time and incidence angle (20–49°). Results show that bubble inclusions, most of which are tubular and oriented in the direction of growth, strongly influence backscatter intensity from floating ice in RADARSAT Standard beam mode imagery. It is shown that radar return can vary considerably as a function of incidence angle. Differences of as much as 6·5 dB were observed for the same ice cover when observed at steeper (20–35°) compared with shallower (35–49°) incidence angles. During the early stages of ice growth and/or when the ice volume contains a small amount of tubular bubbles, backscatter intensity from the floating ice measured at shallower incidence angles (35–49°) is similar to that observed from the grounded ice at any incidence angle (−17 to −11 dB). A strong decrease in backscatter was observed at all sites during spring thaw and was explained by the microwave signal being absorbed by the wet snow cover and by specular reflection from the standing water (ponds) on the lake ice surface. With its multiple beam mode configurations, RADARSAT offers an improved temporal coverage over ERS‐1/2, thus making it possible to determine more precisely freeze‐up and break‐up dates, and timing of bottom freezing from shallow Arctic and sub‐Arctic lakes. Copyright © 2002 John Wiley & Sons, Ltd.

A multi‐sensor approach to wetland flood monitoring

AbstractThe Peace–Athabasca Delta, Canada, is a 3900 km2 freshwater wetland complex, characterized by numerous river channels, lakes and wetland basins. Periodic flooding of the wetland basins is necessary to maintain the productivity in the delta. The delta experienced a 22 year drying trend between 1974 and 1996, resulting in considerable changes in water boundaries. Availability of water is the dominant mechanism driving the ecosystem response. As such, accurate and frequently updated maps of floodwater extent and vegetation types are necessary for proper wetland management. Owing to the large size, remoteness, and dynamic nature of the delta, flood mapping is only feasible using remote sensing.This paper evaluates the use of radar and visible/infrared satellite imagery for mapping the extent of flooded wetland areas. The extent of standing water in the delta during May 1996 and May 1998 was mapped using RADARSAT and SPOT imagery. The RADARSAT scenes, the SPOT scenes, and a combination of the two were, for each year, classified into open water, flooded vegetation, and non‐flooded land using a Mahalanobis distance classifier. When the 1996 RADARSAT scene and the 1996 SPOT scene were classified separately, they resulted in Kappa coefficients of 70% and 66% respectively. The accuracy increased to 92% when the RADARSAT and the SPOT scenes were combined and classified together. Classification of the 1998 RADARSAT scene and the 1998 SPOT scene resulted in accuracies of 76% and 80% respectively, whereas a combination of the two scenes resulted in an accuracy of 92%. The results from this study indicate that the information from radar and visible/infrared satellite imagery is complementary and that flood mapping in wetland areas can be achieved with higher accuracy if the two image types are used in combination. Copyright © 2002 John Wiley & Sons, Ltd.

The effect of dew on the use of RADARSAT-1 for crop monitoring: Choosing between ascending and descending orbits

Radar sensors, like RADARSAT-1, can be a valuable tool for monitoring agricultural crops. RADARSAT-1 imagery can be acquired regardless of cloud cover, and the satellite can be programmed to collect imagery in a wide range of beam modes and incidence angles. This flexibility significantly increases the revisit schedule, thereby ensuring that images can be acquired during key crop growth stages. Users also have the flexibility of choosing acquisitions during either ascending or descending orbits. However, the condition of agricultural targets can change diurnally, and consequently, care must be taken in choosing between RADARSAT-1's dawn and dusk orbits. In temperate regions, early morning dew is often present on the crop canopy at the time of the satellite overpass. Consequently, this study used fine mode dawn/dusk image pairs acquired over western Canada to examine the potential effect of dew on operational crop mapping. The data consistently demonstrated that backscatter increased when dew was present on the canopy. However, overall crop separability did not appear to be affected by the presence of dew. These results indicate that although choice of orbit is less important for crop classification, the probability of dew on the canopy must be carefully considered when users are extracting quantitative crop information from radar imagery.

Providing crop information using RADARSAT-1 and satellite optical imagery

In 1997, the Canada Centre for Remote Sensing acquired RADARSAT-1, SPOT and IRS-1C imagery over an agricultural site in western Canada. These data were used to address the information content of RADARSAT-1 imagery for mapping crop type and for providing information on crop condition, and to explore the implications of crop growth stage on crop monitoring with radar imagery. The use of radar for crop mapping is particularly attractive because of its all weather capability and the sensitivity of microwaves to canopy structure and moisture. Results from this study indicated that multi-date RADARSAT-1 imagery, with or without satellite optical imagery, can provide accurate information about crop types, although timing of image acquisition was important. Regression analysis established that some indicators of crop vigour - in particular leaf area index and crop height - were correlated with backscatter. The highest correlations were for wheat and potatoes. However, backscatter was insensitive to variations in corn growth and only moderately sensitive to differences in indicators of canola crop condition. Nevertheless, this study clearly demonstrates that multi-temporal RADARSAT-1 imagery can be used to provide useful crop information.

Iceberg calving from the Amery Ice Shelf, East Antarctica

AbstractWe investigate the iceberg-calving cycle of the Amery Ice Shelf (AIS), East Antarctica, using evidence acquired between 1936 and 2000. The most recent major iceberg-calving event occurred between late 1963 and early 1964, when a large berg totalling about 10 000 km2 in area broke from the ice front. The rate of forward advance of the ice front is presently 1300–1400ma–1. At this rate of advance, based on the present ice-front position from recent RADARSAT imagery, it would take 20–25 years to attain the 1963 (pre-calve) position, suggesting that the AIS calving cycle has a period of approximately 60–70 years. Two longitudinal (parallel-to-flow) rifts, approximately 25 km apart at the AIS front, are observed in satellite imagery acquired over the last 14+years. These rifts have formed at suture zones in the ice shelf, where neighbouring flow-bands have separated in association with transverse spreading. The rifts were 15 km (rift A) and 26 km (rift B) in length in September 2000, and will probably become the sides of a large tabular iceberg (25 km 625 km). Atransverse (perpendicular-to-flow) fracture, visible at the upstream end of rift A in 1996, had propagated 6 km towards rift B by September 2000; when it meets rift B the iceberg will calve. A satellite image acquired in 1962 shows an embayment of this size in the AIS front, hence we deduce that this calving pattern also occurred during the last calving cycle, and therefore that the calving behaviour of the AIS apparently follows a regular pattern.

An Integration of RADARSAT and Landsat Imagery to Identify Areas of Urban Poverty in Rosario, Argentina

RÉSUMÉLes villes dans les pays en voie de développement font face à de sérieux problèmes quant à leur capacité de rester au fait des changements dans l'utilisation du sol et à fournir les infrastructures nécessaires suite à l'accroissement rapide de la population. Les images satellitales constituent une source d'information fiable, à jour, facile d'accès et à coût relativement faible. Ces données sont essentielles pour les planificateurs urbains travaillant dans les pays en voie de développement s'ils veulent assurer la mise en place des infrastructures appropriées pour les populations urbaines. L'existence de zones de pauvreté urbaine dans les grandes zones urbaines constitue un intérêt particulier. L'objectif de cet article est d'identifier et de localiser ces différentes zones de pauvreté à l'aide d'images satellitales. La procédure implique la classification d'images RADARSAT en mode fin conjointement avec l'utilisation d'une image Landsat dans une tentative de localiser des couverts spécifiques. Pour mener cette analyse, deux sous-secteurs de la ville de Rosario, en Argentine, sont utilisés dans une étude de cas. Les caractéristiques de ces secteurs et les résultats de la classification des images suggèrent que l'approche est utile pour la localisation de zones probables de pauvreté urbaine dans les pays en voie de développement.

RADARSAT‐1 Imagery and GIS Modeling for Mineral Exploration in Nova Scotia, Canada

Radarsat's Application Development and Research Opportunity (ADRO) Project 656, with the Canadian Space Agency, has provided a wealth of Radarsat imagery for the Centre of Geographic Sciences. The focus has been on the validation of Radarsat data pertaining to geological investigations and base metal minerals exploration modeling. Two adjacent, descending Radarsat orbital tracks, comprising four Standard Beam Mode (S2) scenes, were ortho‐rectified, histogram matched, filtered and mosaicked. The imagery encompasses a substantial portion of central Nova Scotia, Canada. The S2 mode Radarsat imagery has been integrated with digital geological, geophysical and stream sediment mineral data layers utilising GIS and image analysis software packages. Within the broader framework of ADRO Project 656, mineral potential models have been constructed for a selected sub‐area in north‐central Nova Scotia. These models, which consist of value‐added Radarsat S2, geological, geophysical and stream sediment mineral concentration data layers, have contributed to a better understanding of the geological nature of central Nova Scotia and facilitated potential identification of mineral emplacement targets.

Multisensor Hydrologic Assessment of a Freshwater Wetland

This article evaluates the use of synthetic aperture radar (SAR) and visible/infrared (VIR) satellite imagery for mapping the extent of standing water in the Peace-Athabasca Delta during spring and summer of 1998. SAR images contain data about the geometric and electrical characteristics of the objects, while VIR images contain information about the reflectivity of objects. Radar pulses can also penetrate vegetation to some degree depending on the wavelength and vegetation thickness. It is hypothesized that since Radarsat and SPOT images contain complementary information, flood mapping will be more efficient when the two image types are used in combination. Radarsat SAR and SPOT multispectral imagery from May 1998 and July 1998 were used for the flood mapping. A Radarsat S2 image (27.5° incidence angle) was obtained for May 1998. To evaluate the incidence angle effect on flood mapping, a Radarsat S1 image (27.5° incidence angle) and a Radarsat S7 image (47.0° incidence angle) were obtained for July 1998. The Radarsat scenes were calibrated and filtered, and all imagery were orthorectified to minimize geometric distortion. A Mahalanobis distance algorithm was used to classify the SPOT scenes, the Radarsat scenes, and a combination of the two into open water, flooded vegetation, and nonflooded land. The results indicate that flood mapping in both spring and summer conditions has significantly higher accuracy when Radarsat and SPOT imagery are used in combination, rather than separately. However, it is important to use Radarsat imagery acquired at low incidence angles. Classification of the SPOT scene combined with the Radarsat S1 scene achieved significantly better results than those obtained when the SPOT scene was classified in combination with the Radarsat S7 scene.

Imaging Radar and Archaeological Survey: An Example from the Gobi Desert of Southern Mongolia

The application of spaceborne imaging radar data to archaeological survey in arid regions was investigated at a study area in the Gobi Desert of southern Mongolia. A repertoire of computer enhancement regimens specific to archaeological applications was applied to RADARSAT imagery of the study area to reduce noise, detect lineaments, or otherwise enhance the data. The imagery was then georectified and integrated into a large area mosaic, creating detailed multi-layered image-maps that were used to direct ground exploration. During two field seasons with the Joint Mongolian-Russian-American Archaeological Expedition (JMRAAE) in 1997 and 1998, precise latitude/longitude information was obtained with Global Positioning Satellite (GPS) devices, establishing Ground Control Points with which to further georectify the image-maps. Both navigation and archaeological site selection were enhanced by hydrologic and topographic information in these satellite image-maps. The JMRAAE field team successfully located Palaeolithic cultural artifacts showing little or no surface expression, most often in association with ancient watercourses. The team was able to navigate accurately through the extreme desert terrain using the image-maps and GPS in this otherwise only minimally mapped area, thereby facilitating detailed archaeological reconnaissance and survey.

Radarsat investigation of a circular feature in east central Jordan

A typical ring-like feature, located in east central Jordan about 150km south-east of Amman, is very obvious on Radarsat images. Four concentric circles, but only two perfect ones, were discriminated, ranging in size from about 6km to about 1km in diameter. At first glance, this feature greatly resembles an ideal impact structure. Previous geological studies, geophysical investigations and recent field observation proved the presence of a domal structure that incorporates lower Cretaceous sandstone at the core; middle of the central ring, and successively surrounded by a highly fractured and steeply dipping sequence of Cretaceous and lower Tertiary carbonates and chert. The principal faults and lineaments in the region follow N-W, N-E and E-W trends, the intersection of which is believed to have acted as a preferable place for the emplacement of an igneous body, most probably in the post-Eocene, which causes the domal uplift and the associated ring faults at Jabal Waqf as Suwwan. Interpretation of 1:60 000 aerial photographs and the 1:50 000 topographic maps clearly showed two concentric rings of about 6km and 1km in diameter, coinciding with the presence of steep dissected ridges of Late Cretaceous to Eocene chert and carbonates. Tectonic interpretation of gravity data showed the presence of concentric ring-like faults that greatly coincide with Radarsat imagery interpretation and field evidence. Magnetic data suggested the presence of either a dense non-magnetic igneous intrusion, a carbonate body or an anhydrite dome. Seismic data, on the other hand, confirmed the presence of a highly fractured zone about 6km wide. Merging of Radarsat with Landsat Thematic Mapper (TM) data enables discrimination of surficial deposits, chert and chalk and illustrates certain geological structures and drainage segments. Replacement of Radarsat standard (S7) images for intensity and hue in the IHS transformation and the first principal component of TM bands 7, 4 and 1 enhances lithological and main structural features.

The Utilization of RADARSAT-1 Imagery for the Characterization of Terrestrial Impact Landforms

RÉSUMÉCinq grandes structures complexes d'impact ont été examinées afin de déterminer l'utilité des données RADARSAT-1 pour l'analyse des formes de relief. Toutes les formes d'impacts étudiées étaient très apparentes dans les données RADARSAT-1. En particulier, il a été possible de superposer les caractéristiques des patrons de fractures de ces structures d'impact sur les patrons régionaux, permettant ainsi la production d'un patron isotropique de fracturation à l'intérieur du plancher du cratère et d'un halo périphérique de fracturation radiale. Il est évident toutefois que la profondeur et l'importance de l'érosion de même que les variations lithologiques pour chacune des structures d'impact individuelles ont beaucoup d'influence sur l'apparence générale et la visibilité de la fracturation reliée aux impacts dans les données RADARSAT-1. Les dimensions du rebord et l'étendue de la fracturation visible dans les données sont comparables aux estimés antérieurs basés sur des études de terrain. Dans certains cas, les données RADARSAT-1 peuvent servir comme outil pour la cartographie lithologique. Par exemple, les roches issues de la fusion lors de l'impact sur le site de la structure de Manicouagan ont une apparence caractéristique sur les données radar, dû à l'homogénéité de leur structure et aux effets subséquents de la glaciation. Il est aussi possible d'utiliser les données RADARSAT-1 pour la cartographie des contacts lithologiques dans l'image de la structure Haughton sur l'Ile Devon, dans l'Arctique canadien, étant donné que les zones de réflectivité différentes correspondent aux cartes géologiques de la zone. En conclusion, les données RADARSAT-1 sont utiles pour caractériser les structures d'impact étudiées compte tenu toutefois des caractéristiques étudiées ou mises en relief et en tant qu'outil pour la cartographie synoptique. Dans tous les cas, dans le contexte de la cartographie structurale/lithologique afin d'assurer un niveau de confiance suffisant dans le processus d'interprétation des données radar, l'utilisation d'autres sources d'information généralement associées aux données terrain s'est avérée nécessaire.