Data enhancement from a 500-channel streamer

Seismic reflection data obtained with a 500-channel digital streamer cable can be processed by array-forming techniques such as optimal weighting of individual channels and beam-steering. Such processing can improve the resolution of horizons at early and intermediate times as well as enhance the continuity and clarity of later reflections. The data may also be processed to simulate results obtainable with a wide variety of conventional streamers. To demonstrate data enhancement obtained by these processing techniques, a selected line was surveyed in the Gulf of Mexico, first with the 500-channel digital system and then with a conventional 48-channel streamer. Comparison of stacked sections shows that: 1) long steered arrays can enhance deeper events while retaining the high-frequency content of shallow data, and 2) short arrays at small group intervals allow finer vertical resolution of shallow events, as well as finer lateral resolution at all depths. When the digital streamer data were processed to duplicate the 48-channel conventional data, the digital system yielded somewhat better results; this improvement may be attributed in part to inherent advantages of digital telemetry over analog telemetry.     

Coral recruitment onto an experimental pulverised fuel ash-concrete artificial reef

An experimental artificial reef was deployed in December 1993 at Hoi Ha Wan Marine Park, Hong Kong. This is the first study documenting natural scleractinian coral recruitment onto a stabilised pulverised fuel ash (PFA)-concrete artificial reef. Visible recruits were first recorded 9-10 months after the placement of reef blocks, i.e., in the autumn of 1994. Two scleractinians, Oulastrea crispata and Culicia japonica, were recruited. The recruit density of the former was much greater than the latter. The spatial recruitment pattern of the corals was observed to be affected by the orientation of the attaching surface. O. crispata settled predominantly on the undersides of the reef blocks. There was an edge effect on O. crispata recruitment. C. japonica, however, had a preference for exposed surfaces. O. crispata did not show a preference for block composition whereas C. japonica favoured blocks with high (75% by volume) PFA levels. This shows that PFA-concrete is a potential substratum for artificial reef construction, especially when such reefs aim at rehabilitating corals.     

Viking's Experiments and Hypothesis that Fe(VI) Is a Possible Candidate as a Martian Oxidant

In this rebuttal to G. Levin's critique of our previous publication, we claim again that iron(VI) is a very good candidate as a martian oxidant. Our experiments cannot be explained as a result of microbial activities, as we showed that Fe(VI) could be used as a sterilizing agent for destroying microorganisms, nucleic acids, and proteins.     

The ‘Stained Glass Procedure’, a new method to compare classification performance of images acquired with different pixel sizes

Objective comparison of classification performance of earth observation images, acquired at different spatial resolutions (e.g. NOAA-AVHRR, IRS-MOS, IRS-WiFS, Landsat-TM, IRS-LISS), is complicated because both class definition and training site selection are hampered by the inherent scale differences. This paper presents a new, generic method to compare the information content of such a set of images, the “Stained Glass Procedure”. It overcomes the stated problems by computing the scale-dependent, internal spectral variation in an image and by using this as an indicator for land cover information. The Stained Glass Procedure creates segments in the images and calculates the internal spectral variation in a high-spatial-resolution image for each segment. For each image from the set the average variance, weighted to area, is calculated. The Stained Glass Procedure can be used to predict the performance of sensors that are not available, yet, or to roughly determine the optimal spatial resolution for the classification of a specific area.The procedure was applied to images with pixel sizes ranging from 23 to 1100 m. Classification detail of Envisat-MERIS (300 m pixel size), not included in the image set, could be predicted accurately using the Stained Glass Procedure.The Stained Glass Procedure applies one procedure to all images, without any subjective decision during the analysis, thus offering a method to compare images with different pixel sizes in terms of classification detail that is truly objective.     

Shifts in the synoptic systems influencing southwest Western Australia

A self-organising map is used to classify the winter circulation affecting southwest Western Australia (SWWA) into 20 different synoptic types. The changes in the frequency of these types and their links to observed rainfall are analysed to further understand the significant, prolonged, rainfall drop observed in this region since 1975. The temporal variability of the different synoptic types link well with the observed rainfall changes. The frequency of the troughs associated with wet conditions across SWWA has declined markedly since 1975 while the frequency of the synoptic types with high pressure over the continent, associated with dry conditions, has increased. Combining the frequency of the synoptic systems with the amount of observed rainfall allows a quantitative analysis of the rainfall decline. The decreased frequency of the troughs associated with very wet conditions accounts for half of the decline. Reductions in the amount of rainfall precipitating from each system also contribute to the decline. Large-scale circulation changes, including increases in the mean sea-level pressure and a decrease in the general baroclinicity of the region have been associated with the rainfall decline. These changes are suggested to be linked to increasing levels of greenhouse gases. Due to the strong link between the number of trough types and the rainfall over SWWA, the shifts in the frequency of these synoptic types could be used as a tool to assess simulated rainfall changes, particularly into the future.     

Variations of the snow cover regime in the second half of the 20th century in Georgia

Possible relationships are studied between changes in major climate parameters (air and soil surface temperature, precipitation, and specific and relative humidity) and in regime characteristics of snow cover (duration of occurrence of snow cover and of stable snow cover, dates of their appearance and disappearance), with emphasis on Georgia.