Effectiveness of the river environment classification in the Auckland Region     

Liza Inglis  Ian K. G. Boothroyd  Gary Brierley 《New Zealand geographer》2008,64(3):181-193

Abstract: The River Environment Classification (REC) provides a GIS‐based tool to differentiate between biophysical attributes of river systems. This study tests the effectiveness of the REC as a tool to differentiate physical habitat and macroinvertebrate assemblages between four classes of stream in the Auckland region. Results indicate significant within‐class variability in physical habitat and macroinvertebrate assemblages, with considerable overlap among the four classes. Biophysically meaningful stream classes cannot be identified from GIS‐derived data applied in this research. Field analyses of physical habitat (i.e. geomorphic river condition) are required as a supplementary tool to interpret ecological relationships for differing stream types.  相似文献   

Elementary forms for land surface segmentation: The theoretical basis of terrain analysis and geomorphological mapping   总被引：10，自引：0，他引：10  

Jozef Minr  Ian S. Evans 《Geomorphology》2008,95(3-4):236-259

Land surface morphology is fundamental to geomorphological mapping and many GIS applications. Review and comparison of various approaches to segmentation of the land surface reveals common features, and permits development of a broad theoretical basis for segmentation and for characterization of segments and their boundaries. Within the context of defining landform units that maximise internal homogeneity and external differences, this paper introduces the concept of elementary forms (segments, units) defined by constant values of fundamental morphometric properties and limited by discontinuities of the properties. The basic system of form-defining properties represents altitude and its derivatives, constant values of which provide elementary forms with various types of homogeneity. Every geometric type of elementary form can be characterized by a defining function, which is a specific case of the general polynomial fitted function. Various types of boundary discontinuity and their connections and transformations into other types of morphological unit boundaries are analysed.The wealth of types of elementary forms and their boundaries is potentially unbounded and thus is sufficient to cover the real variety of landforms. Elementary forms in the basic set proposed here have clear potential for genetic and dynamic interpretation. A brief worked example documents the possibility of analytical computation of various models of ideal elementary forms for particular segments of landform. Ideal elementary forms can be considered as attractors, to which the affinity of surface segments can be measured by multivariate statistical methods. The use of the concept of elementary forms in landscape segmentation is promising and it could be adapted for elementary segmentation of various other spatial fields.  相似文献   

积雪对南极冰盖自动气象站气温观测影响的研究          下载免费PDF全文

马永锋  卞林根  效存德  Ian Allison 《极地研究》2008,20(4):299-309

随着冰盖表面雪的累积或消融,自动气象站(AWS)传感器相对地表的高度随之发生变化,故所记录的观测资料不能直接反映相对地表固定高度上的气象参数。为了使南极冰盖上AWS所获取的气象资料具有可靠性,在积累率对AWS观测气温影响的基础上,将东南极冰盖上中山站至DomeA断面3个AWS的连续观测气温修正到相对于雪表面的某一真实高度上。结果表明:(1)DomeA,Eagle和LGB69年平均1m气温分别为-53.19℃,-41.33℃和-26.29℃,年平均积累率分别为0.11m、0.30m和0.49m,对应的1m气温年平均修正量分别为0.34℃、0.29℃和0.35℃,2m和4m气温的年平均修正量均小于0.1℃;(2)积累率变化对离地表最近层次上的气温影响最大,越往上层影响越小;(3)气温的修正量大小与积累率并非成简单的正比关系,它与气温本身的季节变化特征以及局地近地表逆温强度有很大的关系。气温的平均修正量冬季为正,夏季修正量的正负由局地是否存在逆温决定,修正量值的大小主要由逆温强度和积累率决定。  相似文献   

The SCUBA HAlf Degree Extragalactic Survey – VI. 350-μm mapping of submillimetre galaxies     

Kristen Coppin  Mark Halpern  Douglas Scott  Colin Borys  James Dunlop  Loretta Dunne  Rob Ivison  Jeff Wagg  Itziar Aretxaga  Elia Battistelli  rew Benson  rew Blain  Scott Chapman  Dave Clements  Simon Dye  Duncan Farrah  David Hughes  Tim Jenness  Eelco van Kampen  Cedric Lacey  Angela Mortier  Alexandra Pope  Robert Priddey  Stephen Serjeant  Ian Smail  Jason Stevens  Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2008,384(4):1597-1610

A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 μm has been carried out to map the regions around several 850-μm-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared (IR) luminosities and hence star formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350-μm flux densities for 24 850-μm sources, seven of which are detected at ≥2.5σ within a 10 arcsec search radius of the 850-μm positions. When results from the literature are included the total number of 350-μm flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-IR (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich  ( M _dust≃ 9 × 10⁸ M_⊙)  , luminous  ( L _FIR≃ 2 × 10¹² L_⊙)  star-forming galaxies with intrinsic dust temperatures of ≃35 K and star formation rates of  ≃400 M_⊙ yr⁻¹  . We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350-μm source counts, N ₃₅₀(>25 mJy) ∼ 200–500 deg⁻².  相似文献   

Some laboratory experiments on shear wave propagation in unconsolidated sands     

Ian W. Horn 《Marine Georesources & Geotechnology》2013,31(1):31-54

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Distribution and abundance of the Weddell seal in the western Ross Sea,Antarctica     

Ian Stirling 《新西兰海洋与淡水研究杂志》2013,47(2):191-200

The distribution and abundance of the Weddell seal (Leptonychotes weddelli Lesson) in the fast ice and pack ice of the western Ross Sea, Antarctica, were investigated during 1967 and 1968 from icebreakers and accompanying helicopters. It was estimated that there were about 50,000 Weddell seals in the western Ross Sea between Cape Adare and McMurdo Sound. Weddell seals appear to breed mainly in the fast ice along the Victoria Land coast and less frequently in some nearby areas of pack ice. Fast ice is preferred to pack ice. Most Weddell seals in the pack ice were adults. General observations on the distribution of crabeater, leopard, and Ross seals are included.  相似文献   

Global Snow Mass Measurements and the Effect of Stratigraphic Detail on Inversion of Microwave Brightness Temperatures     

Mark Richardson  Ian Davenport  Robert Gurney 《Surveys in Geophysics》2014,35(3):785-812

Snow provides large seasonal storage of freshwater, and information about the distribution of snow mass as snow water equivalent (SWE) is important for hydrological planning and detecting climate change impacts. Large regional disagreements remain between estimates from reanalyses, remote sensing and modelling. Assimilating passive microwave information improves SWE estimates in many regions, but the assimilation must account for how microwave scattering depends on snow stratigraphy. Physical snow models can estimate snow stratigraphy, but users must consider the computational expense of model complexity versus acceptable errors. Using data from the National Aeronautics and Space Administration Cold Land Processes Experiment and the Helsinki University of Technology microwave emission model of layered snowpacks, it is shown that simulations of the brightness temperature difference between 19 and 37 GHz vertically polarised microwaves are consistent with advanced microwave scanning radiometer-earth observing system and special sensor microwave imager retrievals once known stratigraphic information is used. Simulated brightness temperature differences for an individual snow profile depend on the provided stratigraphic detail. Relative to a profile defined at the 10-cm resolution of density and temperature measurements, the error introduced by simplification to a single layer of average properties increases approximately linearly with snow mass. If this brightness temperature error is converted into SWE using a traditional retrieval method, then it is equivalent to ±13 mm SWE (7 % of total) at a depth of 100 cm. This error is reduced to ±5.6 mm SWE (3 % of total) for a two-layer model.  相似文献   

The submillimetre revolution     

Ian Robson 《Experimental Astronomy》2009,26(1-3):65-78

Although this is a personal reflection of the rise of submillimetre and far-infrared astronomy I will attempt to cover all the major events and players. The review will be restricted to continuum techniques and will principally cover ground-based telescopes. Balloon-based platforms will also be discussed but airborne platforms will be covered by George Rieke. It is always important to remember that a telescope is only as good as the instrumentation it supports, and because there have been few true submillimetre telescopes constructed to date, this review will devote significant time to the instrumentation and technical developments that have been the underpinning of the submillimetre revolution.  相似文献   

RAT J1953+1859: a dwarf nova discovered through high amplitude QPOs in quiescence     

Gavin Ramsay  Pasi Hakala  Thomas Barclay  Peter Wheatley  George Marshall  Harry Lehto  Ralf Napiwotzki  Gijs Nelemans  Stephen Potter  Ian Todd 《Monthly notices of the Royal Astronomical Society》2009,398(3):1333-1338

We report the discovery of an accreting binary, RAT J1953+1859, made during the RApid Temporal Survey (RATS) on the Isaac Newton Telescope. It showed high amplitude (0.3 mag) quasi-periodic oscillations on a time-scale of ∼20 min. Further observations made using the Nordic Optical Telescope showed it to be ∼4 mag brighter than in the discovery images. These photometric observations, together with radial velocity data taken using the William Herschel Telescope, point to an orbital period of ∼90 min. These data suggest that RAT J1953+1859 is a dwarf novae of the SU UMa type. What makes RAT J1953+1859 unusual is that it is the first such system to be discovered as a result of high amplitude QPOs during quiescence. This suggests that high-cadence wide-field surveys could be another means to discover cataclysmic variables as a result of their short period variability.  相似文献   

Future cereal production in China: The interaction of climate change,water availability and socio-economic scenarios   总被引：4，自引：0，他引：4  

Xiong Wei  Conway Declan  Lin Erda  Xu Yinlong  Ju Hui  Jiang Jinhe  Holman Ian  Li Yan 《Global Environmental Change》2009,19(1):34-44

Food production in China is a fundamental component of the national economy and driver of agricultural policy. Sustaining and increasing output to meet growing demand faces significant challenges including climate change, increasing population, agricultural land loss and competing demands for water. Recent warming in China is projected to accelerate by climate models with associated changes in precipitation and frequency of extreme events. How changes in cereal production and water availability due to climate change will interact with other socio-economic pressures is poorly understood. By linking crop and water simulation models and two scenarios of climate (derived from the Regional Climate Model PRECIS) and socio-economic change (downscaled from IPCC SRES A2 and B2) we demonstrate that by the 2040s the absolute effects of climate change are relatively modest. The interactive effects of other drivers are negative, leading to decreases in total production of ?18% (A2) and ?9% (B2). Outcomes are highly dependent on climate scenario, socio-economic development pathway and the effects of CO₂ fertilization on crop yields which may almost totally offset the decreases in production. We find that water availability plays a significant limiting role on future cereal production, due to the combined effects of higher crop water requirements (due to climate change) and increasing demand for non-agricultural use of water (due to socio-economic development). Without adaptation, per capita cereal production falls in all cases, by up to 40% of the current baseline.By simulating the effects of three adaptation scenarios we show that for these future scenarios China is able to maintain per capita cereal production, given reasonable assumptions about policies on land and water management and progress in agricultural technology. Our results are optimistic because PRECIS simulates much wetter conditions than a multi-model average, the CO₂ crop yield response function is highly uncertain and the effects of extreme events on crop growth and water availability are likely to be underestimated.  相似文献