Terrestrial Coordinates Research Articles

The New Archangel (Sitka) Magnetic Observatory: Archival Materials of Mid-19th Century

The article is based on archival materials on the activity of the New Archangel (Sitka) Magnetic Observatory, which are being introduced into scientific use. The sources (materials of official correspondence, registers of scientific instruments, texts of contracts, observation dairies) have been identified in the Russian State Archive of the Navy (RGA VMF) and in the Russian State Historical Archive. The observatory was established as a part of the worldwide net of observation stations created in the 1840s. It was a logical continuation of A. von Humboldt’s experiments in syntonical registration of angle and force elements of geomagnetism. The main initiator of Russian participation in this international project was academic A. Kupfer strongly supported by the minister of finance E. F. Kankrin and other high-level officials, mining engineers, businessmen, representatives of army and Navy commanders. The New Archangel Magnetic Observatory faced all the difficulties common for Russian America: stuff shortage, problems with supply of food, scientific instruments, books, journals, and correspondence. Nevertheless, it worked over twenty years. The most Eastern observation station of the Russian Empire played an important role in the development of sciences in Russia and worldwide. Systematic observations form different points of the planet paved way to solving one of the most important navigation problems of the period: determination of terrestrial coordinates in open sea using magnetic instruments, without astronomical methods and devices. Revealed and analyzed documents contain valuable data on the details of the observatory organization, its instruments and devices, its stuff members. Original project was modest in its terms and research objects. First two navigators sent from St. Petersburg to New Archangel spent there seven years instead of the planned three. Besides magnetic, they took systematic meteorological observations, made conclusions on local climate and perspectives of agriculture development. Permanent observatory stuff included director, two assistants from lower ranks; periodically, they had help from mechanic and clock-master sent there from St. Petersburg by the Russian-American Company. Collected data became a valuable contribution to the development not only of geomagnetism, but also of meteorology, climatology, geography, and astronomy.

Potential and limitations of LiDAR altimetry in archaeological survey. Copper Age and Bronze Age settlements in southern Iberia

Potential and limitations of LiDAR altimetry in archaeological survey. Copper Age and Bronze Age settlements in southern Iberia

Preserving Location Privacy in UASN through Collaboration and Semantic Encapsulation

UASN has gained much attention during the past decades. Based on fruitful research and development, UASN could be a compelling component of the global IoT in the future. From the view of location privacy preservation, state-of-the-art investigations mainly concentrate on UASN infrastructures and focus on the location privacy preserving of the source location privacy of the infrastructures, such as anchor nodes, positioning nodes, and communication channel security. However, in the IoT scenario, the underwater positioning service provided by UASN becomes pervasive, and the location privacy of the end-user of this service will come into sight. On the other hand, the presentation model of underwater semantic location is still in use of traditional terrestrial coordinates and geometric points, the concept of underwater semantic location could be further adopted to improve the location privacy. In this article, both these two location privacy issues are concerned. From the view of a UASN positioning service user, we discuss location privacy-related problems and propos a UASN nodes collaboration method to prevent the adversary from learning the precise location of the user when they intercept the communication or hack the central node. Then a concept of "semantic envelope" is designed to encapsulate the location information, which could further strengthen the location privacy.

Mediterranean blues: archives, repertoires and the black holes of modernity

The Mediterranean is often evoked as the metaphor for the various faces of modernity: from its presumed roots in classical Greece to the intertwining of Africa, Asia and Europe in its waters, emerging and insisting in today’s immigration ‘crisis’. Attempting to take methodological certainties and the universalizing history of Western modernity ‘offshore’, we propose to confront the sea not only in terms of a barrier or a bridge, but also as an ontological challenge. Thinking with the Mediterranean allows us to trace a history that questions and interrupts the institutional organisation of events and knowledge. Other scales of interpretation bring into play the potential of dissonance and a reworking of the inherited world into unexpected interpretations. Here, repertoires more than archives emerge as sites of constant re-elaboration and re-assemblage. If the Mediterranean exposes us to a ‘crisis’ – migrant, environmental – then it is a crisis of modernity itself, of its narrative, and its seemingly firm terrestrial coordinates.

Вклад системы DORIS в построение общеземной системы координат (ITRF2013)

Abstract: A practical utilization of the DORIS system started in February 1990 with launching of the SPOT 2 satellite. During the last decades the role of DORIS system for geodetic measurements and for improvement of the Terrestrial coordinate frame increased significantly. Positioning accuracy of the DORIS system is in the limits of 8.2–12.7 mm for coordinates and 2.7–3.8 mm/y for velocities. Such a high accuracy permits to include DORIS data for the general solution of the new version of the ITRF 2013. Now DORIS is considered as a part of the Global Geodetic Observing System (GGOS) program, initiated by the International Association of Geodesy.

Levantamento planialtimétrico no plano topográfico local: estudo comparativo dos resultados obtidos a partir de métodos geodésicos e topográficos

The appearance of geodesy through satellites revolutionized the geodesic survey. However, the transformation of the results obtained in surveys of local topographic planes, using the traditional methodology, presents operational problems. A method, in which Earth rotation movements are applied to the Tridimensional Orthogonal Cartesian System in order to transform it into a system of local geodesic terrestrial coordinates, can be used, giving precise results and accuracy compatible to the application. The objective of this study was to obtain a terrain digital model (TDM), based on point coordinates gathered via GPS set on the rapid static method, and to transform them in local coordinates, comparing this model to the one gained from the coordinates determined through electronics tacheometry. To do so, a double frequency GPS receiver and a total station were the equipments used in this survey. The comparative study was done in an area of the city of Santa Maria (RS, Brazil), and the results of local coordinates acquired from the GPS coordinates were compatible with plans of classes B and C, in a scale of 1:1000 or less, as well as with level curves with equidistance of one meter, according to the established by the 89.817/84 decree, or in a scale of 1:2500, with level curves spaced out at one meter and a half, when these refer to specifications of NSSDA. Key words: geodetic coordinates, local terrestrial coordinates, local geodetic system.

Precession-nutation procedures consistent with IAU 2006 resolutions

Context. The General Assembly has adopted the P03 model of Capitaine et al. (2003a) recommended by the WG on precession and the ecliptic (Hilton et al. 2006) to replace the 2000 model, which comprised the Lieske et al. (1977) model with adjusted rates. Practical implementations of this new IAU 2006 model are therefore required, involving choices of procedures and algorithms. Aims. The purpose of this paper is to recommend based precession-nutation computing procedures, suitable for different classes of application and achieving high standards of consistency. Methods. We discuss based procedures and algorithms for generating the rotation matrices that transform celestial to terrestrial coordinates, taking into account frame bias (B), P03 precession (P), P03-adjusted 2000A nutation (N) and Earth rotation. The NPB portion can refer either to the equinox or to the celestial intermediate origin (CIO), requiring either the Greenwich sidereal lime (GST) or the Earth rotation angle (ERA) as the measure of Earth rotation. Where GST is used, it is derived from ERA and the equation of the origins (EO) rather than through an explicit formula as in the past, and the EO itself is derived from the CIO locator. Results. We provide precession-nutation procedures for two different classes of full-accuracy application, namely (i) the construction of algorithm collections such as the Standards Of Fundamental Astronomy (SOFA) library and (ii) IERS Conventions, and in addition some concise procedures for applications where the highest accuracy is not a requirement. The appendix contains a fully worked numerical example, to aid implementors and to illustrate the consistency of the two full-accuracy procedures which, for the test date, agree to better than 1 μas. Conclusions. The paper recommends, for case (i), procedures based on angles to represent the PB and N components and, for case (ii), procedures based on series for the CIP X, Y. The two methods are of similar efficiency, and both support equinox based as well as CIO based applications.

Atmospheric densities derived from CHAMP/STAR accelerometer observations

The satellite CHAMP carries the accelerometer STAR in its payload and thanks to the GPS and SLR tracking systems accurate orbit positions can be computed. Total atmospheric density values can be retrieved from the STAR measurements, with an absolute uncertainty of 10–15%, under the condition that an accurate radiative force model, satellite macro-model, and STAR instrumental calibration parameters are applied, and that the upper-atmosphere winds are less than 150 m/ s . The STAR calibration parameters (i.e. a bias and a scale factor) of the tangential acceleration were accurately determined using an iterative method, which required the estimation of the gravity field coefficients in several iterations, the first result of which was the EIGEN-1S (Geophys. Res. Lett. 29 (14) (2002) 10.1029) gravity field solution. The procedure to derive atmospheric density values is as follows: (1) a reduced-dynamic CHAMP orbit is computed, the positions of which are used as pseudo-observations, for reference purposes; (2) a dynamic CHAMP orbit is fitted to the pseudo-observations using calibrated STAR measurements, which are saved in a data file containing all necessary information to derive density values; (3) the data file is used to compute density values at each orbit integration step, for which accurate terrestrial coordinates are available. This procedure was applied to 415 days of data over a total period of 21 months, yielding 1.2 million useful observations. The model predictions of DTM-2000 (EGS XXV General Assembly, Nice, France), DTM-94 (J. Geod. 72 (1998) 161) and MSIS-86 (J. Geophys. Res. 92 (1987) 4649) were evaluated by analysing the density ratios (i.e. “observed” to “computed” ratio) globally, and as functions of solar activity, geographical position and season. The global mean of the density ratios showed that the models underestimate density by 10–20%, with an rms of 16–20%. The binning as a function of local time revealed that the diurnal and semi-diurnal components are too strong in the DTM models, while all three models model the latitudinal gradient inaccurately. Using DTM-2000 as a priori, certain model coefficients were re-estimated using the STAR-derived densities, yielding the DTM-STAR test model. The mean and rms of the global density ratios of this preliminary model are 1.00 and 15%, respectively, while the tidal and latitudinal modelling errors become small. This test model is only representative of high solar activity conditions, while the seasonal effect is probably not estimated accurately due to correlation with the solar activity effect. At least one more year of data is required to separate the seasonal effect from the solar activity effect, and data taken under low solar activity conditions must also be assimilated to construct a model representative under all circumstances.

New Definition for the Celestial Pole and the Celestial Origin in the ICRS

AbstractTwo Resolutions have been submitted to the 24thGeneral Assembly of the IAU concerning the definition and use of the celestial pole of reference and the celestial origin. The aim of both resolutions is to provide new parameters for Earth rotation which are consistent with the properties of the International Celestial Reference System (ICRS), adopted from 1 January 1998 as the IAU celestial reference system. The definition of the parameters have also to be consistent with the precision and the temporal resolution of the current Earth rotation measurements as well as with the theory for nutation and polar motion at the microarcsecond level. This paper explains the basis of the resolutions as well as their practical application. One of the resolutions defines the “Celestial Intermediate Pole” (CIP) in order to replace the “Celestial Ephemeris Pole” (CEP) for the new IAU precession-nutation model; its specifies the way for taking into account the constant offset from the ICRS and the high frequency terms in polar motion and nutation. The other resolution recommends the use of the “non-rotating origin” (Guinot 1979) on the moving equator, for defining Earth rotation and UT1; it also recommends the use of the celestial and terrestrial coordinates of the CIP in the transformation from the celestial to the terrestrial systems.

Effects of the Earth’s Curvature on the Dynamics of Isolated Objects. Part I: The Disk

Abstract A disk over the frictionless surface of the earth shows an interaction between the center of mass and internal motions. At low energies, the former is an “inertial oscillation” superimposed to a uniform zonal drift c and the latter is a rotation with variable vertical angular velocity ω (as measured by a terrestrial observer). The dynamics is understood best in a stereographic frame following the secular drift. The center of mass has a circular but not uniform motion; its meridional displacement induces the variations of the orbital and internal rotation rates. On the other hand, the temporal mean of the Coriolis forces due to both rotations produces the secular drift. In spherical terrestrial coordinates geometric distortion complicates the description. For instance, the zonal velocity of the center of mass U is not equal to the average zonal component of the particle velocities 〈u〉, as a result of the earth’s curvature. The drift c and the temporal means U and 〈u〉 are all three different. In ad...

Comparison between Astronomical and Geodetic Coordinates

A requirement for solving Earth rotation problems is the definition of a terrestrial reference system (or systems) and the determination of a terrestrial coordinate frame (or frames). In this context it is important to determine the positions of the observing sites and their temporal variations and establish the dependence of the observations on local conditions and observing methods.In situ concurrent observations are therefore important. In this paper we report the results of a comparison between astronomical and geodetic coordinates derived from different observations at the Cagliari Observatory and the Carloforte latitude station.

The daytime F layer trough and its relation to ionospheric‐magnetospheric convection

The daytime F layer trough is studied by means of an extensive network of ground‐based ionospheric sounders in the northern hemisphere under conditions of solar maximum near winter solstice. The trough is observed to be a continuous band having an instantaneous extent of thousands of kilometers consisting of depletions in the daytime electron density, often by an order of magnitude. It lies in regions of sunward ionospheric‐magnetospheric convection, an afternoon sector corresponding to the dusk cell, a morning sector corresponding to the dawn cell, and morphology and activity dependence consistent with convection. As detected in the diurnal distributions of f0F2, the trough is a persistent feature at high latitudes, appearing on each day of a 31‐day period of continuous observation, and, although highly variable from day to day, is apparent in the monthly medians. The afternoon trough, which is detected independently by at least five and as many as 17 stations on each day, is generally continuous and stationary for a duration of many hours in magnetic latitude/magnetic local time coordinates. The trough contracts during quiet conditions so as to lie above 70° magnetic latitude but expands during disturbed conditions so as to extend from 75° to 52° magnetic latitude. The trough has a pronounced dependence on longitude, appearing principally in the afternoon in eastern magnetic longitudes but in the morning in western magnetic longitudes, an effect so prevalent that it produces large east‐west local time asymmetries in the diurnal distributions of median daytime F layer electron densities throughout a wide range of latitudes. The longitudinal dependence is found to result from the relation between the two principal coordinate systems of the ionosphere‐magnetosphere interaction: solar geomagnetic coordinates in which the convection pattern and the resultant daytime trough reside, and solar terrestrial coordinates in which solar ion production and the undisturbed daytime F layer in general reside; as a consequence of the fact that these coordinate systems vary with respect to one another with longitude, the trough varies within the daytime F layer with longitude.

IRIS‐S: Extending geodetic Very Long Baseline Interferometry observations to the southern hemisphere

High‐accuracy geodetic very long baseline interferometry measurements between the African, Eurasian, and North American plates have been analyzed to determine the terrestrial coordinates of the Hartebeesthoek observatory to better than 10 cm, to determine the celestial coordinates of eight southern hemisphere radio sources with milliarc second (mas) accuracy, and to derive quasi‐independent polar motion, UTl, and nutation time series. Comparison of the Earth orientation time series with ongoing International Radio interferometric Surveying project values shows agreement at about the 1 mas of arc level in polar motion and nutation and 0.1 ms of time in UTl. Given the independence of the observing sessions and the unlikeliness of common systematic error sources, this level of agreement serves to bound the total errors in both measurement series.

Toward a unified terrestrial coordinate system

In order to obtain coordinate transformations between our CDP-VLBI terrestrial coordinate frame and the corresponding frames used by the Goddard Space Flight Center SLR group, the University of Texas Center for Space Research SLR group, and Deep Space Network, we obtained geocentric, Cartesian coordinates and formal errors of five locations in our system and those of the two SLR groups, and of three locations in our system and that of the Deep Space Network. After transformation we found that both SLR coordinate sets agree at the 20 to 30 mm level with our values. The Deep Space Network values, with higher formal errors than the other sets, agree at the half meter level.

Determining coordinates of the rotational pole using satellite data from four sites

This study investigates how precisely the terrestrial coordinates of the rotational pole can be determined from satellite data from four sites in the United States. The five satellites used are those of the Navy Navigation Satellite System (Transit). Tracking data for these satellites are Doppler observations from sites in Maine, Minnesota, California, and Hawaii. The data used in the study are intermediate data products of the near‐real‐time orbit determination procedure, which is an integral part of the navigation system operations. Six 5‐day intervals were selected for study, one every other month during 1976. Coordinates were determined daily from five satellites. Five‐day averages were used as final estimates. Comparisons were made with extrapolated and final coordinates from the Bureau International de l'Heure (BIH) and final coordinates from the Doppler Polar Motion Service (DPMS). The final coordinates determined in the study agree as well with the final values of BIH as do the results of DPMS. The study implies that low‐cost and near‐real‐time estimates of the terrestrial coordinates of the pole can be made available daily as a by‐product of the routine support needed for the Navy Navigation Satellite System.

On the Establishment of Terrestrial Coordinate System by Classical Techniques

AbstractThe definition and practical realization of the astronomical system of terrestrial coordinates are discussed. In particular, the separation of secular polar motion and nonpolar drift of observatories are touched upon as far as those phenomena are crucially intertwined with the realization of a terrestrial coordinate system.

The Definition of the Terrestrial Coordinate Frame by Long Baseline Interferometry

AbstractThis paper examines the question of the definition of the celestial and terrestrial coordinate frames by the technique of long baseline interferometry. It demonstrates how the celestial coordinate frame may be usefully defined in terms of basis 1-forms associated with the advancing phase fronts of the radiation fields from compact radio sources using only interferometer observables. The paper then proceeds to show how the terrestrial coordinate frame could be usefully defined, incorporating fully the effects of plate tectonics and secular motion of the observatories, by an application of the theory of continuum mechanics to interferometer observations.

Spherical projections in teaching astronomy

Two of the calculations with which many students involved with position-finding have difficulty are the interconversions between sidereal and solar times and between celestial and terrestrial coordinates. The author describes how these calculations are aided by the use of spherical polar and stereographic projections. The methods have limited accuracy but are quick and simple and reinforce understanding of the concepts involved.

The Zenith Indicator Position Instrument

The Zenith Indicator Position navigation instrument is a device for instantaneously determining the latitude and longitude of a position on the surface of the earth with respect to the celestial sphere. The instrument operates on the fundamental principle that if the celestial coordinates of a position on the zenith are known, the corresponding terrestrial coordinates can be calculated by:

Plastic boats turned out at the pugget sound naval shipyard

The satellite CHAMP carries the accelerometer STAR in its payload and thanks to the GPS and SLR tracking systems accurate orbit positions can be computed. Total atmospheric density values can be retrieved from the STAR measurements, with an absolute uncertainty of 10–15%, under the condition that an accurate radiative force model, satellite macro-model, and STAR instrumental calibration parameters are applied, and that the upper-atmosphere winds are less than 150m/s. The STAR calibration parameters (i.e. a bias and a scale factor) of the tangential acceleration were accurately determined using an iterative method, which required the estimation of the gravity field coefficients in several iterations, the first result of which was the EIGEN-1S (Geophys. Res. Lett. 29 (14) (2002) 10.1029) gravity field solution. The procedure to derive atmospheric density values is as follows: (1) a reduced-dynamic CHAMP orbit is computed, the positions of which are used as pseudo-observations, for reference purposes; (2) a dynamic CHAMP orbit is fitted to the pseudo-observations using calibrated STAR measurements, which are saved in a data file containing all necessary information to derive density values; (3) the data file is used to compute density values at each orbit integration step, for which accurate terrestrial coordinates are available. This procedure was applied to 415 days of data over a total period of 21 months, yielding 1.2 million useful observations. The model predictions of DTM-2000 (EGS XXV General Assembly, Nice, France), DTM-94 (J. Geod. 72 (1998) 161) and MSIS-86 (J. Geophys. Res. 92 (1987) 4649) were evaluated by analysing the density ratios (i.e. “observed” to “computed” ratio) globally, and as functions of solar activity, geographical position and season. The global mean of the density ratios showed that the models underestimate density by 10–20%, with an rms of 16–20%. The binning as a function of local time revealed that the diurnal and semi-diurnal components are too strong in the DTM models, while all three models model the latitudinal gradient inaccurately. Using DTM-2000 as a priori, certain model coefficients were re-estimated using the STAR-derived densities, yielding the DTM-STAR test model. The mean and rms of the global density ratios of this preliminary model are 1.00 and 15%, respectively, while the tidal and latitudinal modelling errors become small. This test model is only representative of high solar activity conditions, while the seasonal effect is probably not estimated accurately due to correlation with the solar activity effect. At least one more year of data is required to separate the seasonal effect from the solar activity effect, and data taken under low solar activity conditions must also be assimilated to construct a model representative under all circumstances.