GLORIA image processing: The state of the art     

R. C. Searle  T. P. Le Bas  N. C. Mitchell  M. L. Somers  L. M. Parson  PH. Patriat 《Marine Geophysical Researches》1990,12(1-2):21-39

This chapter presents a summary of the image-processing techniques being used at present in the Institute of Oceanographic Sciences Deacon Laboratory's GLORIA long-range sidescan sonar system. It begins with a brief review of the development of GLORIA, and then describes in outline the present shipboard data acquisition, recording and replay system, including simple image-processing techniques that can be used on-board ship. Next, a detailed form of the sonar equation is developed, and this is evaluated factor-by-factor, to demonstrate the effects of beam directivity, refraction and water depth on the form of intensity variation to be expected in the final image. Finally, we discuss recent developments in shore-based image-processing. These include the development of improved radiometric corrections to normalize range-dependent intensity variations, recovery of true backscattering levels and estimation of backscattering coefficients, and combination of GLORIA with other data sets into single, colour digital images. As an example of the last process we show a digital mosaic of sonar data from the Southwest Indian Ridge, coloured as a function of depth derived from Sea Beam data in the same area.  相似文献   

Discussion on ‘The effect of fresh water flow on siltation in the Humber estuary, Northeast UK’ by Pontee NI, Whitehead PA and Hayes CM (ECSS vol. 60, 241–249)     

Steven B. Mitchell 《Estuarine, Coastal and Shelf Science》2005,62(4):725-729

This discussion identifies and presents recent data which show that suspended sediment concentrations in the macrotidal Humber–Trent–Ouse system are much higher, and extend further upstream, than originally presented. The importance of a link between tidal range, fresh water flow and recorded suspended sediment concentrations, is illustrated by reference to data collected under the UK Natural Environment Research Council (NERC) Land–Ocean Interaction Study (LOIS) initiative (1992–1998). Data recorded at Burringham, on the River Trent upstream of Trent Falls show a clear link between tidal range and suspended sediment concentrations which is strongly influenced by the downstream flushing effects of high fresh water flow events. While the arguments presented in this discussion do not contradict the main findings in the original paper it is proposed that a better understanding of siltation in the Humber system may be promoted by understanding the behaviour of the turbidity maximum in this system and its related mobile sediment population. It is suggested that the rapid reduction in suspended sediment concentration brought about by sudden increases in fresh water flow is probably indicative of the highly canalised nature of the tidal reaches of the Trent and Ouse.  相似文献   

Cloning and analysis of the CYP1A promoter from the atlantic killifish (Fundulus heteroclitus)     

Powell WH  Morrison HG  Weil EJ  Karchner SI  Sogin ML  Stegeman JJ  Hahn ME 《Marine environmental research》2004,58(2-5):119-124

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Evidence That Sea State Bias is Different for Ascending and Descending Tracks     

D. A. Mitchell  W. J. Teague  K. R. Whitmer 《Marine Geodesy》2004,27(3):483-494

Jason-1 and TOPEX/Poseidon (T/P) measured sea-surface heights (SSHs) are compared for five regions during the verification tandem phase. The five regions are of similar latitude and spatial extent and include the Gulf of Mexico, Arabian Sea, Bay of Bengal, and locations in the Pacific and Atlantic Oceans away from land. In all five regions, a bias, defined as Jason SSH—TOPEX-B SSH, exists that is different for ascending and descending tracks. For example, in the Gulf of Mexico the bias for ascending tracks was -0.13 cm and the bias for descending tracks was 2.19 cm. In the Arabian Sea the bias for ascending tracks was -2.45 cm and the bias for descending tracks was -1.31 cm. The bias was found to depend on track orientation and significant wave height (SWH), indicating an error in the sea state bias (SSB) model for one or both altimeters. The bias in all five regions can be significantly reduced by calculating separate corrections for ascending and descending tracks in each region as a function of SWH. The correction is calculated by fitting a second-order polynomial to the bias as a function of SWH separately for ascending and descending tracks. An additional constraint is required to properly apply the correction, and we chose to minimize the sum of the TOPEX-B and Jason-1 root-mean-square (rms) crossover differences to be consistent with present SSB models. Application of this constraint shows that the correction, though consistent within each region, is different for each region and that each satellite contributes to the bias. One potential source that may account for a portion of the difference in bias is the leakage in the wave forms in TOPEX-B due to differing altitude rates for ascending and descending tracks. Global SSB models could be improved by separating the tracks into ascenders and descenders and calculating a separate SSB model for each track.  相似文献   

Book reviews     

Margaret Brock  David Rich  P.B. Mitchell  Roger Epps 《The Australian geographer》1995,26(1):97-100

WETLANDS: a threatened landscape (Institute of British Geographers Special Publication Series No.25) edited by M. Williams. 17 × 24 cm, x + 419 pp. Blackwell, Oxford 1993 (first published 1990) (ISBN 0 631 19199 2) $65.00 (soft).

GUIDE TO MAPS IN SOUTH AUSTRALIAN PARLIAMENTARY PAPERS 1852–1971 (Historical Geography Monograph No.7) edited by J. McQuilton. 21 × 29 cm, 178 pp. Australian Reference Publications, Melbourne 1994 (ISBN 0 9587876 4 6).

THE EMERGENCE OF BIOREGIONALISM IN THE MURRAY‐DARLING BASIN by J.M. Powell. 21 × 30 cm, 105 pp. Murray‐Darling Basin Commission, Canberra 1993. (ISBN 1 875209 212) $20.00 (soft).  相似文献   

Product formation from the gas-phase reactions of OH radicals and O3 with a series of monoterpenes     

Hannele Hakola  Janet Arey  Sara M. Aschmann  Roger Atkinson 《Journal of Atmospheric Chemistry》1994,18(1):75-102

The formation yields of nine carbonyl products are reported from the gas-phase OH radical-initiated reactions (in the presence of NO _x ) and the O₃ reactions with seven monoterpenes. The products were identified using GC/MS and GC-FTIR and quantified by GC-FID analyses of samples collected on Tenax solid adsorbent cartridges. The identities of products from camphene, limonene and -pinene were confirmed by comparison with authentic standards. Sufficient quantities of products from the 3-carene, limonene, -pinene, sabinene and terpinolene reactions were isolated to allow structural confirmation by proton NMR spectroscopy. The measured total carbonyl formation yields ranged from non-detectable for the OH radical reaction with camphene and the O₃ reactions with 3-carene and limonene to 0.5 for the OH radical reaction with limonene and the O₃ reaction with sabinene.  相似文献   

Meridional motions of magnetic features in the solar photosphere     

Herschel B. Snodgrass  Sara B. Dailey 《Solar physics》1996,163(1):21-42

We cross-correlate pairs of Mt. Wilson magnetograms spaced at intervals of 24–38 days to investigate the meridional motions of small magnetic features in the photosphere. Our study spans the 26-yr period July 1967–August 1993, and the correlations determine longitude averages of these motions, as functions of latitude and time. The time-average of our results over the entire 26-yr period is, as expected, antisymmetric about the equator. It is poleward between 10° and 60°, with a maximum rate of 13 m s^–1, but for latitudes below ±10° it is markedly equatorward, and it is weakly equatorward for latitudes above 60°. A running 1-yr average shows that this complex latitude dependence of the long-term time average comes from a pattern of motions that changes dramatically during the course of the activity cycle. At low latitudes the motion is equatorward during the active phase of the cycle. It tends to increase as the zones of activity move toward the equator, but it reverses briefly to become poleward at solar minimum. On the poleward sides of the activity zones the motion is most strongly poleward when the activity is greatest. At high latitudes, where the results are more uncertain, the motion seems to be equatorward except around the times of polar field reversal. The difference-from-average meridional motions pattern is remarkably similar to the pattern of the magnetic rotation torsional oscillations. The correspondence is such that the zones in which the difference-from-average motion is poleward are the zones where the magnetic rotation is slower than average, and the zones in which it is equatorward are the zones where the rotation is faster.Our results suggest the following characterization: there is a constant and generally prevailing motion which is perhaps everywhere poleward and varies smoothly with latitude. On this is superimposed a cycle-dependent pattern of similar amplitude in which the meridional motions of the small magnetic features are directed away from regions of magnetic flux concentration. This is suggestive of simple diffusion, and of the models of Leighton (1964) and Sheeley, Nash, and Wang (1987). The correspondence between the meridional motions pattern and the torsional oscillations pattern in the magnetic rotation suggests that the latter may be an artifact of the combination of meridional motion and differential rotation.  相似文献   

On the dependence of climate sensitivity on convective parametrization     

W M Cunnington  J F B Mitchell 《Climate Dynamics》1990,4(2):85-93

Two sensitivity experiments, in which CO₂ is doubled and sea-surface temperatures are enhanced, were carried out using a general circulation model to determine the influence of the convective parametrization on simulated climate change. In the first experiment, a non-penetrative layer-swapping convection scheme is used; in the second, a penetrative scheme is used. It is found that the penetrative scheme gives the greater upper tropospheric warming (over 4.5 K compared to 4 K) and the greater reduction in upper tropospheric cloud, consistent with recent CO₂ sensitivity studies. However, there is a 0.7 Wm^–2 greater increase in net downward radiation at the top of the atmosphere in the experiment with the non-penetrative scheme, implying a larger tropical warming which is inconsistent with recent CO₂ studies. Other possible explanations for discrepancies between recent studies of the equilibrium climate response to increasing CO₂ are considered and discussed. The changes in the atmospheric fluxes of heat and moisture from the tropical continents in the model with the penetrative scheme differ from those found using the non-penetrative scheme, and those in an equilibrium experiment using the penetrative scheme. Thus, changes in circulation may explain the apparent discrepancy in the current experiments, but prescribed sea-surface temperature experiments may not provide a reliable indication of a model's equilibrium climate sensitivity. Offprint requests to: JFB Mitchell  相似文献   

Guarding the middle ground: the ethics of experiments on animals     

Mitchell G 《South African Journal of Science》1989,85(5):285-288

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Geo- and cosmochemistry of the twin elements yttrium and holmium     

Andreas Pack  Sara S. Russell  Mark van Zuilen 《Geochimica et cosmochimica acta》2007,71(18):4592-4608

We have analyzed the Y/Ho-ratios in bulk chondrites, chondrules and four Ca- and Al-rich inclusions (CAIs) from carbonaceous and unequilibrated ordinary and enstatite chondrites (EC) by laser ablation inductively coupled mass spectrometry (LA-ICPMS). We demonstrate that bulk rock sample preparation by containerless melting is a suitable method for preparation of bulk rock samples for high-precision LA-ICPMS. Bulk chondrites have variable Y/Ho-ratios. Carbonaceous chondrites (CI1, CM2, CV3, and CK4) have a common Y/Ho-ratio (25.94 ± 0.08, 2σ) that is regarded as the solar system Y/Ho-ratio. The Y/Ho-ratio increases from carbonaceous, through ordinary (LL, L, H) to enstatite chondrites (EL6), which show the highest Y/Ho-ratio of 27.25. We discuss the result with respect to the origin of fractionation of Re and Os between chondrite groups. Within analytical error, Y and Ho show a good correlation in OC and CV3 chondrules and define an Y/Ho-ratio of 26.22 ± 0.40 (2σ). Y/Ho-fractionation in Ca- and Al-rich inclusions is related to differences in volatility. The bulk silicate Earth is suggested to have a solar Y/Ho-ratio and links the Earth with carbonaceous chondrites. Y/Ho variations in primitive and differentiated terrestrial igneous rocks are discussed in framework of incompatibility of Y and Ho during partial melting. Applicability of Y/Ho as tracer for or against a sedimentary origin of the putative host rock of the Earth’s oldest traces of life from the island of Akilia is briefly discussed.  相似文献