scholarly journals Solar tracker with optical feedback and continuous rotation

2020 ◽  
Vol 13 (11) ◽  
pp. 5855-5871
Author(s):  
John Robinson ◽  
Dan Smale ◽  
David Pollard ◽  
Hisako Shiona
Keyword(s):  
Optical Feedback ◽  
Power Transformer ◽  
Polar Regions ◽  
Tracking Accuracy ◽  
Good Reliability ◽  
Continuous Rotation ◽  
Polar Day ◽  
History Of ◽  
Control Electronics ◽  
Solar Tracker

Abstract. Solar trackers are often used by spectrometers to measure atmospheric trace gas concentrations using direct sun spectroscopy. The ideal solar tracker should be sufficiently accurate, highly reliable, and with a longevity that exceeds the lifetime of the spectrometer that it serves. It should also be affordable, easy to use, and not too complex should maintenance be required. In this paper we present a design that fulfils these requirements using some simple innovations. Our altitude–azimuth design features a custom coaxial power transformer, enabling continuous 360∘ azimuth rotation. This increases reliability and avoids the need to reverse the tracker each day. In polar regions, measurements can continue uninterrupted through the summer polar day. Tracking accuracy is enhanced using a simple optical feedback technique that adjusts error offset variables while monitoring the edges of a focused solar image with four photodiodes. Control electronics are modular, and our software is written in Python, running as a web server on a recycled laptop with a Linux operating system. Over a period of 11 years we have assembled four such trackers. These are in use at Lauder (45∘ S), New Zealand, and Arrival Heights (78∘ S), Antarctica, achieving a history of good reliability even in polar conditions. Tracker accuracy is analysed regularly and can routinely produce a pointing accuracy of 0.02∘.

scholarly journals Solar tracker with optical feedback and continuous rotation

2020 ◽  
Author(s):  
John Robinson ◽  
Dan Smale ◽  
David Pollard ◽  
Hisako Shiona
Keyword(s):  
Optical Feedback ◽  
Power Transformer ◽  
Polar Regions ◽  
Tracking Accuracy ◽  
Good Reliability ◽  
Continuous Rotation ◽  
History Of ◽  
Control Electronics ◽  
Pointing Accuracy ◽  
Solar Tracker

Abstract. Solar trackers are often used by spectrometers to measure atmospheric trace gas concentrations using direct-sun spectroscopy. The ideal solar tracker should be sufficiently accurate, highly reliable and with a longevity that exceeds the lifetime of the spectrometer which it serves. It should also be affordable, easy to use and not too complex should maintenance be required. In this paper we present a design that fulfils these requirements using some simple innovations. Our altitude-azimuth design features a custom coaxial power transformer, enabling continuous 360° azimuth rotation. This increases reliability and avoids the need to reverse the tracker each day. In polar regions, measurements can continue uninterrupted through the summer polar night. Tracking accuracy is enhanced using a simple optical feedback technique which adjusts error offset variables while monitoring the edges of a focused solar image with just four photodiodes. Control electronics are modular, and our software is written in Python, running as a webserver on a recycled laptop with a Linux operating system. Over a period of 11 years we have assembled four such trackers. These are in use at Lauder (45° S), New Zealand and Arrival Heights (78° S), Antarctica, achieving a history of good reliability even in polar conditions. Tracker accuracy is analysed regularly and can routinely produce a pointing accuracy of 0.02°.

scholarly journals A synthesis of atmospheric mercury depletion event chemistry linking atmosphere, snow and water

2007 ◽  
Vol 7 (4) ◽  
pp. 10837-10931 ◽  
Author(s):  
A. Steffen ◽  
T. Douglas ◽  
M. Amyot ◽  
P. Ariya ◽  
K. Aspmo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Current Knowledge ◽  
Kinetic Studies ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Polar Regions ◽  
Environmental Media ◽  
Gaseous Elemental Mercury ◽  
History Of

Abstract. It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). This phenomenon is termed atmospheric mercury depletion events (AMDEs) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. Shortly after the discovery was made in Canada, AMDEs were confirmed to occur throughout the Arctic, sub-Artic and Antarctic coasts. It is now known that, through a series of photochemically initiated reactions involving halogens, GEM is converted to a more reactive species and is subsequently associated to particles in the air and/or deposited to the polar environment. AMDEs are a means by which Hg is transferred from the atmosphere to the environment that was previously unknown. In this article we review the history of Hg in Polar Regions, the methods used to collect Hg in different environmental media, research results of the current understanding of AMDEs from field, laboratory and modeling work, how Hg cycles around the environment after AMDEs, gaps in our current knowledge and the future impacts that AMDEs may have on polar environments. The research presented has shown that while considerable improvements in methodology to measure Hg have been made the main limitation remains knowing the speciation of Hg in the various media. The processes that drive AMDEs and how they occur are discussed. As well, the roles that the snow pack, oceans, fresh water and the sea ice play in the cycling of Hg are presented. It has been found that deposition of Hg from AMDEs occurs at marine coasts and not far inland and that a fraction of the deposited Hg does not remain in the same form in the snow. Kinetic studies undertaken have demonstrated that bromine is the major oxidant depleting Hg in the atmosphere. Modeling results demonstrate that there is a significant deposition of Hg to Polar Regions as a result of AMDEs. Models have also shown that Hg is readily transported to the Arctic from source regions, at times during springtime when this environment is actively transforming Hg from the atmosphere to the snow and ice surfaces. The presence of significant amounts of methyl Hg in snow in the Arctic surrounding AMDEs is important because this species is the link between the environment and impacts to wildlife and humans. Further, much work on methylation and demethylation processes have occurred but are not yet fully understood. Recent changes in the climate and sea ice cover in Polar Regions are likely to have strong effects on the cycling of Hg in this environment; however more research is needed to understand Hg processes in order to formulate meaningful predictions of these changes. Mercury, Atmospheric mercury depletion events (AMDE), Polar, Arctic, Antarctic, Ice

Effects of Continents and Supercontinents on Climate

2004 ◽  
Author(s):  
John J. W. Rogers ◽  
M. Santosh
Keyword(s):  
Global Climate ◽  
Climatic Conditions ◽  
Polar Regions ◽  
The North ◽  
Rock Types ◽  
Control Climate ◽  
The Earth ◽  
History Of ◽  
Earth’S Climate ◽  
Geologic Record

Continents affect the earth’s climate because they modify global wind patterns, control the paths of ocean currents, and absorb less heat than seawater. Throughout earth history the constant movement of continents and the episodic assembly of supercontinents has influenced both global climate and the climates of individual continents. In this chapter we discuss both present climate and the history of climate as far back in the geologic record as we can draw inferences. We concentrate on longterm changes that are affected by continental movements and omit discussion of processes with periodicities less than about 20,000 years. We refer readers to Clark et al. (1999) and Cronin (1999) if they are interested in such short-term processes as El Nino, periodic variations in solar irradiance, and Heinrich events. The chapter is divided into three sections. The first section describes the processes that control climate on the earth and includes a discussion of possible causes of glaciation that occurred over much of the earth at more than one time in the past. The second section investigates the types of evidence that geologists use to infer past climates. They include specific rock types that can form only under restricted climatic conditions, varieties of individual fossils, diversity of fossil populations, and information that the 18O/16O isotopic system can provide about temperatures of formation of ancient sediments. The third section recounts the history of the earth’s climate and relates changes to the growth and movement of continents. This history takes us from the Archean, when climates are virtually unknown, through various stages in the evolution of organic life, and ultimately to the causes of the present glaciation in both the north and the south polar regions. The earth’s climate is controlled both by processes that would operate even if continents did not exist and also by the positions and topographies of continents. We begin with the general controls, then discuss the specific effects of continents, and close with a brief discussion of processes that cause glaciation. The general climate of the earth is determined by the variation in the amount of sunshine received at different latitudes, by the earth’s rotation, and by the amount of arriving solar energy that is retained in the atmosphere.

Late Quaternary Geological History of the Dead Sea Area, Israel

1993 ◽  
Vol 39 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Y. Yechieli ◽  
M. Magaritz ◽  
Y. Levy ◽  
U. Weber ◽  
U. Kafri ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Thick Layer ◽  
Time Frame ◽  
Dead Sea ◽  
Polar Regions ◽  
Geological History ◽  
The Holocene ◽  
History Of ◽  
The Dead ◽  
Sea Area

AbstractA 34.5 m borehole, which was drilled near the Dead Sea coast (altitude -394 m) in the southern part of the fan delta of Wadi Zeelim, reveals the geological history of that area from the latest Pleistocene to present. The depositional time frame is based on six 14C dates and two U-Th dates. An erosional (or nondepositional) period is implied by the hiatus between 21,100 yr B.P. (U-Th age, depth 33 m) and 11,315 yr B.P. (14C age, depth 32 m). A subsequent arid phase is recorded by a 6.5-m-thick layer of halite; based on 14C dates this phase relates to the abrupt Younger Dryas cold period reported in temperate to polar regions. The fragility of the environment in this region is indicated by the fact that the region experienced such a severe, short aridification phase (less than 1000 yr), evidence of which is found widely in the desert fringes of the Middle East and North Africa. The aragonite found in most of the Holocene section indicates that the well site was covered by the lake for most of the Holocene. Exceptions are the intervals at 0-3 and 10-14 m depths which represent low stands of the lake.

scholarly journals Survey stories in the history of British polar exploration: museums, objects and people

2018 ◽  
Vol 73 (2) ◽  
pp. 259-274
Author(s):  
Charlotte Connelly ◽  
Claire Warrior
Keyword(s):  
Polar Regions ◽  
Polar Research Institute ◽  
History Of ◽  
The Uk ◽  
Maritime Museum ◽  
Research Institute

This essay considers the two institutions that, between them, contain the most significant collections relating to British polar exploration in the UK: the Scott Polar Research Institute and the National Maritime Museum. A discussion of the differences between the two institutions, from their foundations to the substance of their collections, is followed by an indication of their similarities—particularly relating to the interpretation of the objects of exploration in museums, including artefacts of science and surveying. Histories of exploration, particularly in the polar regions, have been dominated by stories of individual sacrifice and achievement. This is despite the origins of many of the expeditions being rooted in scientific goals. This paper considers the role of survey stories within narratives of exploration, and the challenges that curators face in presenting them to audiences who continue to be drawn in by stories of well-known figures such as Scott and Amundsen.

scholarly journals Electrical Resistivity of Ice from the Antarctic Peninsula, Antarctica

1984 ◽  
Vol 30 (106) ◽  
pp. 289-295 ◽  
Author(s):  
John M. Reynolds ◽  
J. G. Paren
Keyword(s):  
Antarctic Peninsula ◽  
Flow Line ◽  
Polar Regions ◽  
List Type ◽  
Electrical Measurements ◽  
Ice Shelf ◽  
Ice Shelves ◽  
History Of ◽  
Surface Ice ◽  
The Antarctic

AbstractGeoresistivity soundings have been carried out at four sites in the Antarctic Peninsula. The objective of the work was to investigate the electrical behaviour of ice from an area where substantial melting occurs in summer and from contrasting thermal regimes. Electrical measurements made at three sites along a flow line within George VI Ice Shelf reveal that:(a)the resistivity of deep ice is similar to that of other Antarctic ice shelves,(b)the resistivity of the ice-shelf surface, which is affected by the percolation and refreezing of melt water, is similar to that of deep ice and hence the ice is polar in character.A compilation of published resistivities of deep ice from polar regions shows that the range of resistivities is very narrow (0.4 –2.0) x 105Ω m between –2 and – 29°C, irrespective of the physical setting and history of the ice. Typically, resistivity is within a factor of two of 80 kΩ m at –20° C with an activation energy of 0.22 eV. In contrast, the resistivity of surface ice at Wormald Ice Piedmont, where the ice is at 0°C throughout, is two orders of magnitude higher and falls at the lower end of the range of resistivities for temperate ice.

The moss flora of the Auckland Islands, New Zealand, with a consideration of habitats, origins, and adaptations

1979 ◽  
Vol 57 (20) ◽  
pp. 2226-2263 ◽  
Author(s):  
Dale H. Vitt
Keyword(s):  
Species Richness ◽  
New Zealand ◽  
Polar Regions ◽  
Growth Forms ◽  
Common Pattern ◽  
Moss Species ◽  
Tussock Grassland ◽  
History Of

The moss flora of the Auckland Islands (50°40′ S latitude and 166°00′ E longitude) consists of 145 species and seven varieties in 75 genera. A detailed description of the habitat of each taxon is given. The vegetation, climate, and history of the islands, as they pertain to bryology, are reviewed. Four broad vegetational zones are recognized: forest, scrub, tussock grassland, and tundra as well as areas of herbfields and mires. Phytogeographically, the most common pattern of distribution is Australasian with 29% of the moss species found in both New Zealand and Australia. Other patterns are common as well. Discussion is orientated toward species richness variability in polar regions. The origins and adaptations of mosses in subantarctic landscapes are reviewed and correlations drawn between particular growth forms and individual moss floras and habitats.

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