ISSN:0143-1161    

DOI:10.1080/01431168708954786

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The British Geological Survey has completed the conversion of both aeromagnetic and gravity survey records to a digital data base. This paper examines some of the uses of the aeromagnetic data base. Rendering digitized aeromagnetic data as a rectangular grid of interpolated anomaly values allows regional variations in subsurface magnetization to be displayed as images rather than contoured maps. Images of the magnetic field are more appropriate for visual interpretation and can be enhanced using standard methods of digital image processing. The optimum method is a combination of directional first-derivative filtering to impart the illusion of side illumination, with spectral colouring of the 8-bit range of DN, the former being used to modulate the brightness of the latter. As well as many of the known regional magnetic features of the Solway Basin, this method highlights several trends that were unsuspected.

ISSN:0143-1161    

DOI:10.1080/01431168708954787

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Lineaments of lengths equal to or greater than 5 km have been interpreted on each of the 30 Landsat frames required to cover the entire area of Nigeria north of 8° latitude. All the spectral bands 4, 5, 6 and 7 were used each at scale 1: 1 000 000. A mosaic of the interpretations from the various scenes was used to prepare a lineament map of Nigeria. Regional analysis of the lineaments based on the spatial and directional attributes of their assemblages suggests general northeast-southwest, northwest-southeast and north-south tectonic trends. The density of lineaments within each 1° × 1° block was determined using the conventional approach and a contour map of lineament densities produced. The lineament density map has been compared with the primary mineral occurrences map of Nigeria adapted from the mineral map of Nigeria. The result shows good correlation between the areas of high lineament density and the areas where the occurrences of most primary minerals such as iron, cassiterite, gold, lead-zinc and uranium have been reported; this correlation suggests that primary mineralization in Nigeria is tectonically controlled. The lineament density map therefore constitutes a useful base map which could aid exploration efforts for solid minerals in Nigeria.

ISSN:0143-1161    

DOI:10.1080/01431168708954788

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The potential of the Thematic Mapper (TM) on board Landsal-5 for marine applications has been investigated with reference to the well-known performance of the Coastal Zone Color Scanner of Nimbus-7. The study consisted of (a) a sensitivity analysis, considering such fundamental error sources as retrieval algorithm sensitivity, atmospheric correclion, instrument noise and signal digitization and (b) the interpretation of a TM scene by the procedure suggested in (a). The evidence provided by the experimental test validated the positive conclusions of the theoretical work, indicating that the analysis of TM bands 1 to 4 data should be capable of yielding quantitative information of satisfactory quality on fundamental water quality parameters, such as chlorophyll (i.e. phytoplankion) and suspended sediment concentrations.

ISSN:0143-1161    

DOI:10.1080/01431168708954789

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

An algorithm has been developed for estimating total ice concentration from spaceborne high-frequency passive microwave instrumentation. The algorithm is intended for use with the coming Special Sensor Microwave/Imager (SSM/I) data giving a spatial resolution of 12 km. It is based on radiation physics and detailed millimetre wave surface signature measurements and can therefore be applied to other similar data. However, due to large effects on the signals caused by time varying atmospheric conditions and radiation properties of the ice, the algorithm is made self-adjusting. The atmospheric effects are implicitly treated as a smooth function of the ice concentration with tie points over open ocean and 100 per cent ice for each orbit. This means that the main errors are due to patches of heavy clouds and ice floes with atypical radiation properties. An error analysis indicates possible errors of the order of 5 percent for concentrations representative for the Arctic Basin, increasing with decreasing concentration.

ISSN:0143-1161    

DOI:10.1080/01431168708954790

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The contribution of volume scattering from the subsurface stratum of soil or snow to the backscattered radar signal decreases rapidly with increasing moisture content as compared to the contribution by rough-surface scattering. In order to obtain an evaluation of the relative importance of volume scattering of moist strata, a heterogeneous two-component mixture of water inclusions in a dry background medium is assumed and the formulation of the distorted Born approximation according to Tsanget al.is applied. Computed permittivities and backscatter cross-sections are compared with experimental data of situations with modest moisture content. From there, conclusions on the relative portion of volume scattering and on shape and size of the effectively-scattering water inclusions can be drawn.

ISSN:0143-1161    

DOI:10.1080/01431168708954791

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The in-flight two-point calibration of the AVHRR-2 radiometer introduces an error in the brightness temperature derived from the 11 μm and 12 μm channels, due to the non-linearity of the sensor response. The NOAA Users' Guide recommends assuming a negative value for the open space radiance to reduce this error for the range 225-310 K. This range however is too large for typical sea surface temperature variations, and differences as great as 0.4 deg K are still present in the derived 11 μm brightness temperature. This error is further amplified in the sea surface temperature, when estimated with the split window technique, as can be shown by radiative transfer model calculations. For this reason, a new practical calibration scheme is proposed to minimize the error due to the non-linearity of the sensor response, over the range of radiances from the sea surface.

ISSN:0143-1161    

DOI:10.1080/01431168708954792

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The split-window method is successfully used to infer sea surface temperature from satellite radiances, principally because sea surface temperature is not very different from the air temperature near the surface and because the emissivity of the sea is constant over large areas and is not very different from one in the spectral channels of interest. This is not true for land surfaces and the split-window method has to be re-examined for such a case. This is the aim of this paper. In order to relate land surface temperature to the two brightness temperatures measured from space in the two channels of interest (namely, AVHRR 4 and AVHRR 5), several formulae are derived and their accuracies are discussed. Assuming that the emissivities ϵ1and ϵ2in the two channels considered, and therefore their average $ are unity, it is shown that the error ΔT generated on the land surface temperature by correcting atmospheric effects using the split-window method in most situations studied is of the order of

ISSN:0143-1161    

DOI:10.1080/01431168708954793

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The second Indian remote sensing satellite Bhaskara-II has three microwave radiometers operating at 19.35, 22.235 and 3l.4GHz. Brightness temperature (TB) data have been acquired by these radiometers during the period from December 1981 to July 1983 comprising 325 passes. The ground resolution of these radiometers is about 125 km circular diameter. These data have the highest potentially for the use in sea. land- and snow/ice-based studies. A considerable amount of work has been carried out by the Indian scientists using these data and a lot more will follow. In view of this, an attempt is made in this paper to summarize some of the useful observations regarding the reliability and nature of the data. These observations can be useful guidelines in the interpretation of TBdata.

ISSN:0143-1161    

DOI:10.1080/01431168708954794

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The analysis of brightness temperature data acquired from field and aircraft experiments demonstrates a linear relationship between soil moisture and brightness temperature. However, the analysis of brightness temperature data acquired by the Skylab radiometer demonstrates a non-linear relationship between soil moisture and brightness temperature. In view of the above and also because of recent theoretical developments for the calculation of the dielectric constant and brightness temperature under varying soil moisture profile conditions, an attempt is made to study the theoretical relationship between brightness temperature and soil moisture as a function of frequency. Through the above analysis, the appropriate microwave frequency range for soil moisture studies is recommended.

ISSN:0143-1161    

DOI:10.1080/01431168708954795

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor