Thematic Mapper Scenes Research Articles

New constraints on Red Sea rifting from correlations of Arabian and Nubian Neoproterozoic outcrops

New constraints on the mechanics of Red Sea opening were obtained by correlating Neoproterozoic outcrops of the Arabian and Nubian Shields along two thirds of the Red Sea coastlines. Using a mosaic of 23 Landsat thematic mapper scenes (5×105 km²) together with field, geochemical, and geochronological data, we identified and mapped lithologic units, mobile belts, and terranes within the Arabian and Nubian Shields. Features best align if Arabia is rotated by 6.7° around a pole at latitude 34.6°N, longitude 18.1°E. Implications of our reconstruction include (1) the amount of continental crust underlying the Red Sea is small because the restored Red Sea coasts are typically juxtaposed, (2) only a single pole is needed, implying that the Arabian and Nubian Shields were rigid plates during Red Sea rifting, (3) coastlines reorient to align with preexisting structures, suggesting the rift propagated in part along pre‐existing zones of weakness, (4) large sinistral displacements of up to 350 km along the Red Sea are not supported, (5) the pole is inconsistent with the Pliocene‐Pleistocene motion along the Dead Sea transform (pole: 32.8°N, 22.6°E +/− 0.5° [Joffe and Garfunkel, 1987]), indicating that more than one phase of motion is required to account for the Red Sea opening. However, our pole is similar to that for the total motion along the Dead Sea transform (pole: 32.7°N, 19.8°E +/− 2° [Joffe and Garfunkel, 1987]), suggesting that the motion between Arabia and Nubia was parallel to the total motion along the Dead Sea transform.

Coastal environmental sensitivity mapping for oil spills in the United Arab Emirates using remote sensing and GIS technology

Abstract Accidental or intentional oil spills may impact ecologically sensitive areas such as the shoreline of the United Arab Emirates (UAE). The environmental consequences can be compounded if there are no effective clean‐up plans. An environmental sensitivity index (ESI) database developed with the aid of remote sensing and geographic information systems (GIS) is an effective tool in clean‐up operations. Three Landsat Thematic Mapper (TM) scenes were used to classify the shoreline sensitivity of the Abu Dhabi Emirate. The TM data were also used to produce an accurate planimentric basemap. These data were then merged with in situ information of the coastine and placed in a GIS. The GIS can be interrogated by oil spill response personnel to optimize the allocation of finite oil spill mitigation resources.

Studies of snow surface characteristics by Landsat TM in Dronning Maud Land, Antarctica

Large scale melting phenomena like meltwater drainage channels and meltwater accumulation basins or frozen “lakes” have been surveyed on the land ice mass in Dronning Maud Land, Antarctica. These melting features were also detected in a Landsat Thematic Mapper (TM) image recorded on 12 February 1990. Image processing techniques such as principal component (PC) analysis, band ratioing and histogram-equalizing are carried out to emphasize the melting phenomena. Interestingly, a histogram-equalized single TM Band 5 image appears to be a good discriminator, leaving the melting phenomena as bright areas in the TM scene. The largest frozen “lake” is close to 1km wide while some of the drainage channels stretch more than 5 km. There is also a comparison of satellite-derived and in situ reflectance and temperature. The atmospheric corrected satellite data underestimate surface snow albedo by about 16% while TM measurements of surface temperature are 2° to 6°C lower than that measured on the ground.

Studies of snow surface characteristics by Landsat TM in Dronning Maud Land, Antarctica

Large scale melting phenomena like meltwater drainage channels and meltwater accumulation basins or frozen “lakes” have been surveyed on the land ice mass in Dronning Maud Land, Antarctica. These melting features were also detected in a Landsat Thematic Mapper (TM) image recorded on 12 February 1990. Image processing techniques such as principal component (PC) analysis, band ratioing and histogram-equalizing are carried out to emphasize the melting phenomena. Interestingly, a histogram-equalized single TM Band 5 image appears to be a good discriminator, leaving the melting phenomena as bright areas in the TM scene. The largest frozen “lake” is close to 1km wide while some of the drainage channels stretch more than 5 km. There is also a comparison of satellite-derived and in situ reflectance and temperature. The atmospheric corrected satellite data underestimate surface snow albedo by about 16% while TM measurements of surface temperature are 2° to 6°C lower than that measured on the ground.

Snow grain-size determination from Landsat imagery over Terre Adélie, Antarctica

A Landsat Thematic Mapper scene over Terre Adélie, Antarctica, is used to estimate the snow grain-size. New calibration coefficients are computed for the TM scene, using sea-water reflectance. Topographic effects are corrected with the visible band TM2. Atmospheric effects are taken into account. The snow theoretical reflectance is calculated with the Wiscombe and Warren (1980) model. Estimated snow grain-sizes are similar to those given in the literature.

Snow grain-size determination from Landsat imagery over Terre Adélie, Antarctica

A Landsat Thematic Mapper scene over Terre Adélie, Antarctica, is used to estimate the snow grain-size. New calibration coefficients are computed for the TM scene, using sea-water reflectance. Topographic effects are corrected with the visible band TM2. Atmospheric effects are taken into account. The snow theoretical reflectance is calculated with the Wiscombe and Warren (1980) model. Estimated snow grain-sizes are similar to those given in the literature.

Nature of the Red Sea crust: A controversy revisited

Whether the Red Sea floor is underlain mostly by oceanic or extended continental crustal material is a controversial topic. To test between the two hypotheses, we used a digital color mosaic of 23 Landsat thematic mapper (TM) scenes with field, geochemical, and geochronological data to identify and correlate crosscutting geologic features on the African and Arabian sides. Faults, shear zones, sutures, granitic complexes, volcano-sedimentary units, and dike swarms align if Arabia is rotated relative to Africa by 6.7° around a pole at lat 34.6°N, long 18.1°E. This solution implies that the amount of continental crust underlying the Red Sea is small because the restored Red Sea coasts are typically juxtaposed.

Geomorphology and reflectance patterns of vegetation-covered dunes at the Tsodilo Hills, north-west Botswana

Seasonal reflectance variations in semigrid environments provide a means of assessing vegetation health and density as well as monitoring landform processes. Multitemporal Landsat Thematic Mapper scenes with field measurements are used to map geomorphology and vegetation density in a stabilized dune environment and to measure seasonal reflectance changes for a series of ten geomorphological and vegetation units on the Kalahari-age linear dunes. Units were chosen based on differences in landform and proportion of trees, forbs and bare soil. Reflectance curves and normalized-difference vegetation indices (NDVI) show that dune crests have the strongest seasonal variability in color and brightness. The geomorphological link with reflectance and NDVI values are linked to biomass production and zoning of vegetation with slope, drainage and subtle soil differences.

Analysis of normalized difference and surface temperature observations over southeastern Australia

Abstract Relations between radiative surface temperature (TR) and visible and near-infrared reflectances expressed as the normalized difference (ND) from a Landsat Thematic Mapper scene were analysed to study the heat balance of agriculture and native evergreen forests in southeastern Australia. The scene was at 0922 h (local time) during late spring (15 October 1986) with phenology of winter annual species between flowering and grain filling. Factors determining the slope of, and residual scatter about, the TR)/ND relationships were analysed using a coupled two-layer soil-vegetation model of the surface heat balance. Inverse linear relationships were found between TR), and ND for agriculture, but not for forests. This was a result of a wide range of ND and TR) values in agricultural areas caused by wide variations in fractional vegetation cover. The relationships between ND and fractional vegetation cover was not general, thus, when forest and agricultural data were combined, the lower near-infrared reflectance of forests (16-9 per cent) compared with agricultural crops (29-0 per cent) resulted in forest data falling below the regression line for agriculture. From the agricultural relations, 60 to 70 per cent of the variation in TR) was explained by ND, indicating that fractional vegetation cover was the dominant factor determining TR). Residual variability of TR) was attributed to spatial variability in ambient temperature, rates of soil evaporation and variations in stage of phenological development affecting stoma-tal resistance. Energy-balance analysis of the effect of soil water availability on the slope of the R)‘ND relationship indicated opposite effects depending on whether the reduction in evaporation was from soil or from vegetation. Thus, the generality of using the slope of the TR)/ND relationship to predict surface resistance to evaporation may be limited. It was concluded that extraction of information contained in TR) and ND data for regional estimation of evaporation requires the separation of TR) into soil and vegetation temperatures and an alternative to ND that relates more generally to fractional vegetation cover.

Satellite-derived reflectance of snow-covered surfaces in Northern Minnesota

Its high albedo and low thermal conductivity make snow a key component of the global energy balance. Snow depth and reflectance are crucial inputs to General Circulation Models (GCMs). Satellite data from the Landsat Thematic Mapper (TM) have been used to estimate the reflectance of snow and snow-covered surfaces integrated over part (0.45–0.90 μm) of the reflective range of the electromagnetic spectrum. The integrated reflectance, R 1, has been computed for snow-covered agricultural and forested areas, and a frozen lake in northern Minnesota using Landsat TM scenes acquired in November 1984 and January 1985. TM-derived reflectances, corrected for atmospheric effects, are mapped for subscenes within the Minnesota TM scenes and reflectances have been color coded. The average R 1 within the November 1984 subscene was 0.429 ± 0.176 whereas the average R 1 within the January 1985 subscene was 0.669 ± 0.236. Snow reflectance is known to increase with solar and sensor zenith angle. The solar zenith angle was 70° at the scene center of the 17 November 1984 scene, and 75° at the scene center of the 04 January 1985 scene. Both areas were predominately snow covered. Lowest reflectances (near 0%) were found in the non-snow-covered agricultural fields. Reflectances of lake ice in the January scene averaged 0.957 ± 0.0008. In the future, the Moderate Resolution Imaging Spectrometer (MODIS), as part of the Earth Observing System, will enable calculation of R 1 over most of the reflective part of the electromagnetic spectrum. R 1 may then be used, along with bidirectional reflectance data, to calculate snow albedo, an important input to GCMs and regional energy balance models.

Technical note GPS location data An aid to satellite image analyses of poorly mapped regions

Abstract In inaccessible and highly heterogeneous areas where aerial photography and accurate up-to-date topographic maps are unavailable and where suitable features for ground-based navigation by triangulation are absent, accurately locating ground truth sites and then integrating the field data with digital imagery is often extremely difficult. The advent of the satellite global positioning system (GPS) offers a solution to this problem. Over a 6 month period a battery powered, solar recharged, backpack mounted GPS was used to collect the precise location data essential to the ground truth component of a Landsat Thematic Mapper (TM) landcover classification of the Ituri rain forest of northeastern Zaire. Three-dimensional locations were readily obtained in forest openings > 0·125 ha where the angle to the horizon did not exceed 50° and canopy closure was less than 30 per cent. GPS location data are presently being used to reference a TM scene geographically and to assign pixels to appropriate landcover ...

External effects correction of Landsat Thematic Mapper data

A procedure has been developed to estimate and correct for external effects (haze level, solar zenith angle) in a Landsat Thematic Mapper scene. The procedure is based on the Dave model and uses a scatterplot-matching technique to estimate haze level directly from the scene data. A means for dealing with haze that spatially varies in density over a large scene is also included. The effectiveness of this procedure is demonstrated by showing that it permits a data screening algorithm with fixed thresholds to work on hazy areas as well as clear ones. An alternative formulation is proposed that would replace manual haze estimation with automated estimation based on a computed diagnostic feature.

Use of error probabilities to improve area estimates based on maximum likelihood classifications

Maximum likelihood classification of multispectral remotely sensed data has been demonstrated to be extremely powerful and efficient in a great number of investigations; but it shows marked limitations when applied to highly heterogeneous surfaces, mainly because of distribution anomalies of the cover categories. In these cases, the extent of some cover classes tends to be overestimated with respect to that of other classes, so that the general utility of the entire process can be seriously decreased. In the present paper a method is presented for correcting this kind of misclassification based on the estimation of error probabilities from a preliminary classification and on the insertion of this information in a subsequent processing. The evaluation of error rates is performed by means of confusion matrices referring to the original training pixels, and the information obtained is then inserted in another discrimination process according to the theory of the insertion of prior probabilities in maximum likelihood classifiers. The whole procedure was tested in a semiarid environment with extremely heterogeneous cover types using Landsat-5 Thematic Mapper scenes and relying on representative ground references. The results show a marked improvement in classification performances mainly in terms of symmetry between the extension of the ground references and that of the surfaces obtained by the interpretation technique.

Registering Landsat images by point matching

Image registration of Landsat Thematic Mapper scenes with translational and rotational differences is studied. Two major steps of image registration, control-point selection and control-point matching, are emphasized. In control-point selection, the properties that a good control point should satisfy are defined. Several potential control-point candidates are suggested, and methods are discussed for extracting them from the input image. In control-point matching, a relaxation algorithm proposed in the literature is improved by reducing its time complexity from O(n/sup 4/) to O(n/sup 3/), where n is the number of control points. The matching algorithm also uses a two-way matching concept which utilizes the inherent symmetry property of the point-matching problem. The robustness of the proposed algorithm was demonstrated through simulation experiments by evaluating a matching index. Experimental results on Landsat images show that the proposed method produces results comparable to those obtained by an experienced photointerpreter. >

Radiometric calibration of Landsat Thematic Mapper thermal band

Radiometric calibration of satellite-acquired data is essential for quantitative scientific studies, as well as for a variety of image-processing applications. This paper describes a multilayer, on-orbit radiometric calibration of the Landsat Thematic Mapper (TM) Band 6 conducted at DOE's Pacific Northwest Laboratory (PNL). Numerous Landsat TM scenes acquired and analyzed included day and night coverage at several geographical locations over several seasons. Concurrent with Landsat overpasses, thermal field and local meteorological (surface and radiosonde) measurements were collected. At-satellite (uncorrected) radiances and temperatures for water and nonwater land cover were compared to ground truth (GT) measurements after making adjustments for atmospheric (using LOWTRAN), mixed-pixel, and emissivity effects. Results indicated that, for both water and nonwater features, TM band 6 average corrected temperature determinations using local radiosonde data to adjust for atmospheric effects, and using appropriate emissivities, are within ⩽1.0°C of GT temperature values. Temperatures of water pixels derived from uncorrected TM Band 6 data varied roughly between 1 and 3°C of ground truth values for water temperatures ranging between 4 and 24°C. Moreover, corrections using nonlocal and noncoincident radiosonde data resulted in errors as large as 12°C. Corrections using the U.S. Standard Atmosphere gave temperature values within 1–2°C of GT. The average uncertainty for field instruments was ± 0.2°C; average uncertainty for Landsat TM corrected temperature determinations was ± 0.4°C.

The effects of a complex environment on crop separability with landsat TM

Studies in the midwestern United States have shown that crop variations associated with regionally varying environmental factors can be important to crop inventory design using Landsat multispectral scanner data. This study examined the consequences of a more complex environment and a higher resolution sensor. Unsupervised classification accuracy and divergence of crop spectra were determined for six crop classes from early season Landsat Thematic Mapper (TM) scenes for 31 sites across New York State. These indicators of crop separability were related to 12 environmental variables. Although statistically significant models were found for individual crops, no significant relationship was found to characterize general crop separability. Regional variation is too large to be ignored in an early season TM-based inventory of areas as complex as New York; however, stratification based on readily obtainable environmental data is of only moderate value in describing the variation.

Surface reflectance factor retrieval from thematic mapper data

Based on the absolute radiometric calibration of the Thematic Mapper (TM) and the use of a radiative transfer program for atmospheric correction, ground reflectances were retrieved for several fields of crops and bare soil in TM Bands 1–4 for six TM scenes acquired over a 12-month period. These reflectances were compared to those measured using ground-based and low-altitude, aircraft-mounted radiometers. When, for four TM acquisitions, the comparison was made between areas that had been carefully selected for their high uniformity, the reflectance factors agreed to ±0.01 (1 σ RMS) over the reflectance range 0.02–0.55. When the comparison was made for two of the above acquisitions and two others on different dates, for larger areas not carefully selected to be of uniform reflectance, the reflectance factors agreed to ±0.02 (1 σ RMS), again over the reflectance range 0.02–0.55.

Extension of the Najd Shear System from Saudi Arabia to the central eastern desert of Egypt based on integrated field and LANDSAT observations

The Najd Shear System in Saudi Arabia extends over 1200 km in a NW‐SE direction and has a width of approximately 300 km. A digital color mosaic, compiled from seven Landsat thematic mapper scenes, was used to delineate characteristic structural features of the Najd System in the Midyan region of Saudi Arabia and to search for similar features in the Egyptian Eastern Desert. The digital mosaic was generated using ratios of Landsat thematic mapper bands (bands 5/4 × 3/4, 5/1, 5/7) that are sensitive to the rock content of Fe‐bearing aluminosilicates, spectrally opaque phases, and hydroxyl‐bearing or carbonate minerals, respectively. The mosaic covers approximately 130,000 km² of late Proterozoic exposures of the Arabian‐Nubian Shield and has the Eastern Desert and the Midyan region placed in their approximate pre‐Red Sea locations. The Ajjaj Shear Zone (AJZ) marks the termination of the Najd System against the eastern margin of the Red Sea in the Midyan region. The AJZ aligns with the central Eastern Desert, based on analysis of pre‐Red Sea locations. Analyses of Landsat data and field observations show that the Ajjaj Shear Zone and the central Eastern Desert exhibit the following features in common: (1) outcrops that are generally elongate in a NW‐SE direction as a result of folding, with fine‐scale lithologic heterogeneity at the outcrop scale related to deformation associated with faulting; (2) NW trending left‐lateral faults and ductile shear zones; (3) subhorizontal, NW trending mineral lineations, and variably dipping NW trending foliations, with local changes in attitude around large competent (e.g., granitic) bodies; and (4) lithologic contacts that are generally tectonic in nature and related to faulting. These features are less common to the north and south of both the Ajjaj Shear Zone and the central Eastern Desert. Results are consistent with the Najd Shear System extending into the Eastern Desert and dominating the structural patterns within the central part of the Eastern Desert.

Interpretation and geometrical aspects of Thematic Mapper data

Abstract For a visual analysis assisted by digital imageenhancement procedures of a Thematic Mapper scene of the German Bight, a combination of the spectral channels 1-4 is suitable. Because of the extremely high correlation between channels 2 and 3 a principal component transformation is performed. This procedure enhances the interpretation possibilities especially for the recognition of structures like surface material in water. Incorporation of digitized contour lines from a marine chart and a syntheticchannel derived from the linescan support the interpretation. For that reason it is necessary to rectify the scene to the Mercator projection of the marine chart. The rectification performed by a second dxegree polynomial produces subpixel accuracies.

The effective resolution element of Landsat Thematic Mapper

Abstract As part of the U.K.'s contribution to NASA's Landsat [mage Data Quality Analysis (LIDQA) programme the system performance of the Thematic Mapper (TM) scanner has been studied by the determination of the Effective Resolution Element (ERE), a measure of its spatial resolution. Two methods have been used, the first by a simulation of the TM's spatial responses in an analytical model and the second by measurements of water bodies on a selected Landsat-5 TM scene. Bands 1-4 of the Thematic Mappers of both Landsat-4 and Landsal-5 have an effective resolution element by the former method of 52 m. This compares with a value of 122 m for band 4, near-infrared, of the Multispectral Scanner (MSS) by the same method. An image-derived value, by the latter method, for band 4 of the Landsat-5 TM scene is approximately 75 m. This increase in the ERE over the sensor-only value is attributed to additional factors within the imagery such as the pixel sampling of the scene, ground segment processing and the contribu...