Readout Techniques for Drift and Low Frequency Noise Rejection in Infrared Arrays

Three different methods are presented to subtract thermal drifts and low-frequency noise from the signal of infrared array. The first is dead pixels with open Indium bumps, the second is reference output as implemented on the Hawaii2 multiplexer, and the third is dark pixels to emulate reference cells having a capacity connected to the gate of the unit cell field-effect transistor (FET). The third method is the most effective and yields a reduction in readout noise from15.4–9.4 erms. A novel method will be described to extend this readout technique to the Aladdin 1 K × 1 K InSb array. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tritium profiles in the Weddell Sea

Tritium data were collected between 1985 and 1987 on several cruises of the German research icebreaker “Polarstern” to the Weddell Sea. Maximum tritium concentrations in the surface waters are of the order of 200 mTU. The minimum values observed in the Weddell Sea Deep Water at about 1000 m depth are about 15–40 mTU. The bottom waters show tritium concentrations of about 70–100 mTU in the central gyre, increasing to about 120 mTU in the northwestern corner of the Weddell Sea. The overflowing Ice Shelf Water observed on the continental slope west of the Filchner Depression has tritium concentrations close to those of the surface waters, indicating rapid renewal of this water mass. The data reflect the rapid renewal of the bottom waters in the northwestern corner of the Weddell Sea and the mixing of bottom water from this boundary current into the bottom waters of the central Weddell Gyre.     

The distribution of tritium and CFCs in the Weddell Sea during the mid-1980s

Transient tracer data (tritium, CFC11 and CFC12) from the southern, central and northwestern Weddell Sea collected during Polarstern cruises ANT III-3, ANT V-2/3/4 and during Andenes cruise NARE 85 are presented and discussed in the context of hydrographic observations. A kinematic, time-dependent, multi-box model is used to estimate mean residence times and formation rates of several water masses observed in the Weddell Sea.Ice Shelf Water is marked by higher tritium and lower CFC concentrations compared to surface waters. The tracer signature of Ice Shelf Water can only be explained by assuming that its source water mass, Western Shelf Water, has characteristics different from those of surface waters. Using the transient nature of tritium and the CFCs, the mean residence time of Western Shelf Water on the shelf is estimated to be approximately 5 years. Ice Shelf Water is renewed on a time scale of about 14 years from Western Shelf Water by interaction of this water mass with glacial ice underneath the Filchner-Ronne Ice shelf. The Ice Shelf Water signature can be traced across the sill of the Filchner Depression and down the continental slope of the southern Weddell Sea. On the continental slope, new Weddell Sea Bottom Water is formed by entrainment of Weddell Deep Water and Weddell Sea Deep Water into the Ice Shelf Water plume. In the northwestern Weddell Sea, new Weddell Sea Bottom Water is observed in two narrow, deep boundary currents flowing along the base of the continental slope. Classically defined Weddell Sea Bottom Water (θ ≤ −0.7°C) and Weddell Sea Deep Water (−0.7°C ≤ θ ≤ 0°C) are ventilated from the deeper of these boundary currents by lateral spreading and mixing. Model-based estimates yield a total formation rate of 3.5Sv for new Weddell Sea Bottom Water (θ = −1.0°C) and a formation rate of at least 11Sv for Antarctic Bottom Water (θ = −0.5°C).     

Benthic Metabolism and Standing Stock in the Central and Northern Deep Red Sea

Abstract. Benthic metabolism and standing stocks were investigated in the deep Red Sea between 21^o and 27^oN, Activity was assessed by the determination of respiration rates with a shipboard method and by calculating oxygen consumption from the activity in the electron transport system. We attempted to compare results from different latitudes within the warm Red Sea and with data from cold Atlantic environments. Our investigations were part of an environmental risk assessment to evaluate future mining of metalliferous sediments from the Atlantis II Deep.     

The GRECOS operating system of the GCT

The computer operating system of the Gregory Coudé Telescope (GCT) at Observatorio del Teide is described. The GRECOS command language provides the user with a flexible means of operating both telescope and spectrograph, to execute complex measuring sequences, and to handle and display his observational data.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Verteilung und Wanderung von Neunaugen im Elbeästuar (Deutschland)

From March 1989 until May 1995 overall 675 hauls were performed using a commercial stow net vessel to get information concerning spatial and seasonal distribution, length frequency distribution, stock situation and migration patterns of lampreys in the Elbe estuary in northern Germany.2217 river lampreys (Lampetra fluviatilis) and 10 sea lampreys (Petromyzon marinus) were caught during the whole study period. The river lamprey occurred in 40.3% of the performed stow net hauls. The catch success was highest in the western main channel, whereas the frequency of occurrence of river lampreys was only about 10.9% at the most upstream site in the southern marginal area. In 1989 and 1990 significantly more than 50% of the hauls contained river lampreys. In contrast, from 1991 to 1995 their frequency of occurrence was lower than 40%, in 1991 even lower than 20%. Sea lampreys occurred only at 6 from 9 sampled sites and were only observed in 1990 and 1992-1994.Total lengths of river lampreys varied between 7 and 46 cm. Based on the length frequency distribution, the following three size classes of river lampreys were separated: LF I (7 to 16 cm), LF II (17-26 cm) and LF III (27-46 cm). The majority of the caught individuals could be grouped in size class LF III. Total lengths of sea lampreys ranged between 69 and 85 cm and were restricted to only one size class (PM III).70% of all sea lampreys were caught in April and May. Most of the sea lampreys were observed in the eastern main channel. The maximum average abundance of river lampreys was observed with 6.75 Ind · m⁻³ · 10⁻⁶ in the same area in 1992. However, in 1993 and 1994 the highest average abundances of river lampreys occurred in the western main channel.Based on redundance analysis, a significant correlation between the abundances of lampreys and the environmental variables autumn, spring, summer, salinity, water temperature, grain size, new moon and first moon quarter was found. The downstream migrating river lampreys of size class LF I und the sea lampreys during their anadromous spawning migration showed highest abundances mainly in spring, whereas high abundances of river lampreys of size class LF II in the feeding phase occurred in summer. The presence of both size classes LF I and LF II confirms the successful reproduction of river lampreys in the catchment area of the Elbe. The observation of river lampreys of size class LF III during their anadromous spawning migration was closely correlated with the variable autumn. A spring spawning migration of river lampreys was not observed.     

Large-scale dune erosion tests to study the influence of wave periods

Large-scale physical model tests were performed to quantify the effects of the wave period on dune erosion. Attention was focussed on 2D cross-shore effects in a situation with sandy dunes and extreme water levels and wave conditions. Besides profile measurements, detailed measurements in time and space of water pressure, flow velocities and sediment concentrations were performed in the near near-shore area. It was concluded that a longer wave period leads to a larger dune erosion volume and to a larger landward retreat of the dune face. Tests with double-peaked wave spectra showed that the influence of the spectral shape on dune erosion was best represented by the T_m − 1,0 spectral mean wave period, better than the peak wave period, T_p. The effect of the wave period on dune erosion was implemented in a dune erosion prediction method that estimates erosion volumes during normative storm conditions for the Dutch coast. More details of the measurements and additional analyses of physical processes are described in an accompanying paper by Van Thiel de Vries et al. [Van Thiel de Vries, J.S.M., van Gent, M.R.A., Reniers, A.J.H.M. and Walstra, D.J.R., submitted for publication. Analysis of dune erosion processes in large scale flume experiments, In this volume of Coastal Engineering.].     

Resistance of a soil layer to horizontal vibration of a pile

The resistance of a soil to horizontal harmonic vibration of a vertical, end bearing pile with circular cross-section is theoretically investigated. The soil is considered to be a continuum with material damping of the hysteretic type. The motions of the soil and pile are expressed as series, and a resistance coefficient on each term in the series of the pile motion is found. The resistance is found to depend on the excitation frequency, the pile slenderness and on the material properties of the soil. Finally a study of the influence of the parameters is carried out.     

Das luftelektrische Erscheinungsbild des Südföhns in den Nordalpen nach synoptisch-klimatologischen Untersuchungen im Wettersteingebirge 1955 bis 1959

Zusammenfassung Die Arbeit bringt alle Erfahrungen über Föhn in luftelektrischer Hinsicht, die im Laufe von fünf Jahren durch Registrierungen, Messungen und Beobachtungen vor allem im Raum des Wettersteingebirges bei Garmisch-Partenkirchen gewonnen wurden. Es stand hierfür ein Netz von sieben ständig betriebenen Stationen zur Verfügung, zwei weitere Stationen wurden 1958 während einer zweimonatigen Exkursion auf dem Zugspitzplatt (2600 m NN) unterhalten. Diese neun Stationen lagen in einigermaßen gleichmäßiger Höhenstaffelung zwischen 675 und 2963 m NN. Ihre Basisentfernungen waren relativ gering. Alle neun Stationen registrierten den luftelektrischen Potentialgradienten, vier der sieben ständigen sowie eine der beiden vorübergehenden Stationen registrierten zusätzlich den luftelektrischen Leitungsstrom. Als weitere Elemente des Komplexes Luftelektrizität und Aerosol wurden registriert bzw. gemessen: positive und negative Kleinionen, positive und negative Luftleitfähigkeit, natürliche und künstliche Radioaktivität der Luft, Kondensationskerne (Aitkenkerne), Luftverunreinigung, Spitzenstrom und Atmospherics. Ein tragendes Grundprinzip der Arbeit ist die synoptische Verwertung der Daten des relativ dichten und auch in die Vertikale reichenden Stationsnetzes, mit dessen Hilfe ein dreidimensionaler Ausschnitt der Atmosphäre überschaubar wird. Die Einheitlichkeit der verwendeten Methoden sowohl in der räumlichen als auch in der über Jahre gehenden zeitlichen Erstreckung trägt zur Festigung der Ergebnisse und Schlüsse bei.Aus dem Beobachtungsmaterial wird abgeleitet, daß Föhnlagen sich nicht dadurch auszeichnen, daß sich bestimmte luftelektrische Einzelgrößen dabei besonders oder außergewöhnlich verhalten würden. Typisch für den Föhn ist vielmehr ein ganz bestimmter Akkord der luftelektrischen (und meteorologischen) Elemente, wobei sich innerhalb des Stationsnetzes wiederum typische Variationen bemerkbar machen.Luftelektrisch gesehen, konnten zwei Föhntypen unterschieden werden: Bei Typ I sind die Kurven des Potentialgradienten und des Leitungsstromes sehr glatt, der Potentialgradient ist anhaltend erniedrigt, die Werte des Leitungsstromes und der Kleinionendichte sind erhöht. Kennzeichnend für Föhntyp II ist ein extrem unruhiger Verlauf der Potentialgradient- und Leitungsstromkurven bei stark erhöhten Werten an den Talstationen; er ist immer mit dem Vorkommen von Schneefegen an den Gebirgskämmen mehr oder weniger weit südlich der Registrierstationen gekoppelt. Häufig besteht bei Föhntyp II eine Bodeninversion.Für beide Föhntypen werden repräsentative Einzelbeispiele gebracht. Außerdem wurde das gesamte Beobachtungsmaterial der Jahre 1955 bis 1958 statistisch verarbeitet, um für die sieben Stationen, d. i. im Schnitt durch die Atmosphäre bis rund 3000 m NN, das luftelektrische und meteorologische Bild eines mittleren Föhntages für beide Typen abzuleiten. Die bei Föhn gesammelten Ergebnisse sind übrigens nicht nur zur Erweiterung unserer Vorstellungen über den Föhn an sich von Bedeutung, sondern geben auch Hinweise zu anderen geophysikalischen Problemen, so etwa auf dem Gebiet der Wolkenphysik (z. B. durch die Erfahrungen hinsichtlich der Ladungstrennung beim Zusammenprall und Zerbrechen von Eiskristallen), zur Frage der atmosphärischen elektrischen und elektromagnetischen Wellenvorgänge (durch Registrierungen von Stationen, die sich gerade in der Grenzschicht zwischen Föhn und positiv geladener, schwingender Inversionsoberseite befinden) sowie zur Frage des Ionisationsgleichgewichtes und der Beziehungen zwischen Kleinionen- und Kondensationskerndichte, denn in der Föhnströmung sind ja die Kondensationskerndichten besonders niedrig und außerdem ist—in den Nordalpen—die natürliche Luftradioaktivität während des Föhns erhöht.Bioklimatische Gesichtspunkte werden lediglich angedeutet.

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Summary In this paper the author summarizes data, results of evaluations, and experiences in the field of atmospheric electricity, as far as connected with foehn situations. The observations were mainly made in the region of Garmisch-Partenkirchen (Wetterstein Mountains, Northern Alps) and cover a period of five years. Seven recording stations with heights between 675 and 2963 m above sea-level were operated permanently, two further stations were operated on the Zugspitzplatt (2600 m) during two months in 1958. All the nine stations have relatively small distances from each other. At each of the nine stations the atmospheric electrical potential gradient was recorded, at four of the permanent stations and at one of the temporary stations the air-earth current was recorded, too. Further there were recorded or measured positive and negative small ions, positive and negative conductivity, natural and artificial radioactivity of the air, condensation nuclei, air pollution, point discharge current, and sferics. A characteristic of this investigation is that a dense network of stations extending also in the vertical direction yields a synopsis of a small three-dimensional portion of the atmosphere, and that uniformly without interruptions through years.It is pointed out that a foehn situation is not distinguished by a special or extraordinary behaviour of single atmospheric electrical elements, but by a typical accord of the atmospheric electrical and meteorological elements, with typical spatial variations of them within the network.From the point of view of atmospheric electricity two main types of foehn were found: Type I shows lowered and smooth potential gradient curves at all stations, further increased and smooth curves of conduction current, increased concentrations of small ions, etc. Foehn of Type II, amongst other characteristics, shows increased and extremely agitated curves of potential gradient and conduction current at the valley stations. Type II is observed when there is drifting snow at the mountain ridges south of the recording stations and mainly in cases where the foehn current does not reach the bottom of the valley.Both types are illustrated here by examples. Beyond this, the data obtained at the seven permanent stations during four years were reduced to average foehn days of both types. The observations made during foehn, however, have interest not only for our knowledge of this weather situation itself but give results which are also important for studies on cloud physics (experience on charge separations caused by breaking and impact in drifting snow), on atmospheric electric and electromagnetic waves (records of stations just being in the boundary layer between foehn current and positively charged upper surface of an inversion), for the investigation of the ionization equilibrium and of the relations between the concentrations of small ions and condensation nuclei (there are special conditions because of the low concentrations of condensation nuclei in the foehn current and because of the increased natural radioactivity of air during foehn in our region), etc.Bioclimatological points of view are mentioned, only.

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Résumé La présente étude groupe les résultats obtenus depuis cinq ans au sujet de l'aspect électrique du foehn grâce à des mesures faites dans la région du Wetterstein près de Garmisch-Partenkirchen où se trouvait un réseau de 7 stations fixes ainsi que 2 stations installées pendant une excursion de deux mois au Zugspitzplatt (2600 m.). Ces 9 postes étaient répartis entre 675 et 2693 m. et se trouvaient peu éloignés les uns des autres; tous enregistraient le gradient de potentiel, 5 le courant de conductibilité en sus. En outre on enregistrait ou mesurait: les petits ions positifs et négatifs, la conductibilité positive et négative, la radioactivité naturelle et artificielle de l'air, les noyaux de condensation, la pollution et les parasites. Le principe de base est l'utilisation des données du point de vue synoptique. L'uniformité des méthodes et leur application à longue échéance donne du poids aux résultats.On constate que les situations de foehn ne se distinguent pas par des valeurs extraordinaires des différentes grandeurs de l'électricité de l'air. Les éléments électriques et météorologiques présentent entre eux, par foehn, un accord caractéristique, tandis qu'à l'intérieur du réseau il y a des variations typiques. On peut distinguer deux types de foehn. Type I avec courbe lisse du gradient de potentiel et du courant de conductibilité; le gradient de potentiel est anormalement faible, le courant de conductibilité est accru ainsi que la densité des petits ions. Type II avec marche très agitée du gradient de potentiel et du courant (valeurs accrues aux stations basses); le foehn de type II est toujours accompagné de chasse-neige sur les crêtes au Sud; il y a souvent inversion au sol.Exemples des deux types de foehn. En outre tout le matériel d'observation des années 1955 à 1958 a été traité de façon à obtenir une image de l'état moyen de l'atmosphère jusqu'à 3000 m. pour les deux types. Les résultats trouvent également leur application à d'autres problèmes tels que la rupture de charge par heurts et bris de cristaux, les phénomènes concernant les ondes électromagnétiques, l'équilibre d'ionisation, la relation entre les petits ions et la densité des noyaux de condensation. Les points de vue biologiques ne sont qu'esquissés.

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The research reported in this document has been sponsored in part by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, United States Air Force, under Contract AF 61 (514)-732-C, AF 61 (514)-949 and AF 61 (052)-55, through the European Office, ARDC.Die Auswertungen der Schönwetter-Registrierungen wurden durch Sachbeihilfen seitens der Deutschen Forschungsgemeinschaft möglich gemacht.Die Luftradioaktivitätsmessungen wurden aus Zuschüssen des Bundesministeriums für Atomkernenergie und Wasserwirtschaft an das Institut für Gesteinskunde der Universität München bestritten.