Radiometer Datasets Research Articles

Gravity, magnetic and radiometric evidence for the geological setting of the Lady Loretta Pb-Zn-Ag deposit; a qualitative appraisal

Semi-regional gravity, magnetic and radiometric data sets, augmented by a prospect-scale gravity survey, have been used to qualitatively assess the geological setting of the Lady Loretta Pb-Zn-Ag deposit. Regional gravity and magnetic fields are influenced chiefly by the Eastern Creek Volcanics and are sensitive to the thicknesses of overlying clastic and dolomitic sedimentary sequences, including the McNamara Group which hosts the mineralization. These are primarily controlled by Isan orogeny deformation, but a number of earlier structures are discernible. The most important of these postulated syndepositional structures are a west-northwest-oriented bounding fault extending from Lady Loretta to the Mount Gordon fault along the Redie Creek fault, and a possible sub-basin or zone of alteration beneath the Lady Loretta orebody, which manifests as a magnetic low.Prospect-scale gravity data contain anomalies clearly associated with the mineralized strata at Lady Loretta. Contrasts between McNamara Group formations as well as older units are also apparent, reflecting differences in lithology or weathering characteristics. Higher Bouguer gravity signatures tend to be associated with the more dolomitic units.The radiometric data set allows for the mapping of surface geochemical signatures that are sensitive to a number of geological parameters. These include sedimentological factors such as provenance, maturity, and proportion of argillaceous material, as well as chemical alteration. This variation occurs within as well as between mapped stratigraphic units, and is itself variable across the region. Potassium-channel signatures are an example of this, implying a general westerly decrease in argillaceous or feldspathic content within some formations. Some radiometrically distinct layers visible within sedimentary units appear to be absent at the equivalent stratigraphic level elsewhere. These observations may have implications for attempts to erect a regional sequence stratigraphic framework based on gamma ray logs from relatively few locations.

Structure of Florida Thunderstorms Using High-Altitude Aircraft Radiometer and Radar Observations

Abstract This paper presents an analysis of a unique radar and radiometer dataset from the National Aeronautics and Space Administration (NASA) ER-2 high-altitude aircraft overlying Florida thunderstorms on 5 October 1993 during the Convection and Moisture Experiment (CAMEX). The observations represent the first ER-2 Doppler radar (EDOP) measurements and perhaps the most comprehensive multispectral precipitation measurements collected from a single aircraft. The objectives of this paper are to 1) examine the relation of the vertical radar reflectivity structure to the radiometric responses over a wide range of remote sensing frequencies, 2) examine the limitations of rain estimation schemes over land and ocean backgrounds based on the observed vertical reflectivity structures and brightness temperatures, and 3) assess the usefulness of scattering-based microwave frequencies (86 GHz and above) to provide information on vertical structure in the ice region. Analysis focused on two types of convection: a sma...

Compression of the Global Land 1-km AVHRR dataset

Abstract Large datasets, such as the Global Land 1-km Advanced Very High Resolution Radiometer (AVHRR) Data Set (Eidenshink and Faundeen 1994), require compression methods that provide efficient storage and quick access to portions of the data. A method of lossless compression is described that provides multiresolution decompression within geographic subwindows of multi-spectral, global, 1-km, AVHRR images. The compression algorithm segments each image into blocks and compresses each block in a hierarchical format. Users can access the data by specifying either a geographic subwindow or the whole image and a resolution (1,2,4, 8, or 16 km). The Global Land 1-km AVHRR data are presented in the Interrupted Goode's Homolosine map projection. These images contain masked regions for non-land areas which comprise 80 per cent of the image. A quadtree algorithm is used to compress the masked regions. The compressed region data are stored separately from the compressed land data. Results show that the masked regio...

GOLD: Geophysical Setting of BIF-Hosted Gold Deposits at Tuckabianna, Western Australia

Tuckabianna Gold Mine is located about 25 km east of Cue, on the Mount Magnet-Meekatharra Shear Zone. The mine sequence consists largely of basalt, dolerite to gabbro, mafic schists, banded iron-formation (BIF), and intrusive quartz-feldspar porphyry dykes and sills. Gold mineralisation is hosted by the NE-striking, E-dipping BlFs with shears localising the ore zones. Laterite derived from the weathering of these BlFs may contain a significant gold resource. Downhole logging has shown that the BlFs typically have lower relative gamma activity and higher densities, resistivities and susceptibilities compared with the mafic units and porphyry. Petrophysical measurements of magnetic susceptibility, anisotropy of magnetic susceptibility and natural remanent magnetisation have characterised two BIF types, although no relationship between gold mineralisation and the BIF types has been conclusively demonstrated. Tuckabianna's regional geophysical dataset consists of Bureau of Mineral Resources (BMR) aeromagnetic and gravity data and high-resolution aeromagnetic and radiometric data. Of these, the most useful have been the high-resolution aeromagnetic data, because they clearly define the BlFs and structures which can localise gold mineralisation. Such lithological and structural detail cannot be recognised in either the BMR regional magnetic and gravity datasets or the high-resolution radiometric dataset. The Geoscan remote-sensing system has been flown over Tuckabianna. However, the laterite cover (1-21 m thick) has blanketed much of the geology and only some rock types and major lineaments can be identified from the data. Ground geophysical surveys have been dominated by the magnetic method, which has been extremely useful in delineating the BlFs and structural features, as has the gravity method. Electrical surveys, including magnetometric resistivity, induced polarisation (frequency and time-domain) and electromagnetic methods have also been used. These electrical techniques have not been completely successful in the direct detection of mineralised zones. However, the resistive nature of the BIF is such that these methods may be successfully used to locate the BIF and porphyry, in addition to delineating some structures.

Spatial patterns of increases and decreases in the length of the sea ice season in the north polar region, 1979–1986

Recently it was reported that sea ice extents in the northern hemisphere showed a very slight but statistically significant decrease over the 8.8‐year period of the Nimbus 7 scanning multichannel microwave radiometer (SMMR) data set. In this paper the same SMMR data are used to reveal spatial patterns in increasing and decreasing sea ice coverage. Specifically, the length of the ice season is mapped for each full year of the SMMR data set (1979–1986), and the trends over the 8 years in these ice season lengths are also mapped. These trends show considerable spatial coherence, with a shortening in the sea ice season apparent in much of the eastern hemisphere of the north polar ice cover, particularly in the Sea of Okhotsk, the Barents Sea, and the Kara Sea, and a lengthening of the sea ice season apparent in much of the western hemisphere of the north polar ice cover, particularly in Davis Strait, the Labrador Sea, and the Beaufort Sea.

A strategy to study regional hydrology and terrestrial ecosystem processes using satellite remote sensing, ground-based data and computer modeling

This paper describes a multidisciplinary research project which seeks to characterize the terrestrial water cycle and use this characterization to derive simulations of carbon dioxide and methane flux. The water cycle work links interpolated climate fields, macrohydrologic models and Scanning Multichannel Microwave Radiometer datasets. The aim of the analysis is to use output from calibrated water balance models to develop relationships with SMMR datasets. SMMR estimates of surface hydrology can then be evaluated. Both modeled and SMMR datasets will be tested as inputs to regional biogeochemical models. All determinations will be made under climatically-averaged conditions and for 1979–1985, the years for which SMMR data is available.

Electromagnetic remote sensing of the temperature profile in a stratified medium of biological tissues by stochastic inversion of radiometric data

Some results are presented from investigations studying the process of inversion of multispectral microwave radiometric data to determine the subcutaneous temperature distribution in biological tissues. A transmission line concept is used to model a three‐layer planar configuration as typical for the tissue composition of a human upper arm (skin‐fat‐muscle). Computer‐simulated data are generated at 3, 5, and 10 GHz using the Rayleigh‐Jeans approximation and the radiative transfer approach. Starting from a characteristic temperature profile, the radiometric data set is inverted to yield reconstructed values of the profile. Using the process of stochastic inversion, it is shown how to compromise between penetration depths, temperature resolution, and confidence level of the temperature values retrieved.