Temporal impact of selected GPS errors on point positioning

This paper is aimed at investigating the stability of point positions over time in support of applications that require high position stability when differential GPS is not feasible. One such application is the use of a P3-Orion aircraft offshore for magnetic measurement in support of submarine detection. Temporal changes in several GPS errors lead to variability in the computed positions, so it is not the absolute errors, but rather their temporal variations that are of importance. Furthermore, the temporal variability of the different error sources may dictate a certain algorithm approach and processing strategy. This paper analyzes the temporal variations of the broadcast satellite clock model and orbit parameters, as well as ionospheric errors, because these will typically be the dominant errors for real-time point positioning. These three errors are analyzed independently. A tropospheric correction is applied when computing all of the position results, so the tropospheric error itself is not investigated. Satellite clock and orbit errors are analyzed by comparing broadcast and precise post-mission SV clock corrections and orbits. For the ionosphere, the effect is separated using dual-frequency data. The analysis comprises primarily of assessing error behaviors and magnitudes through time and frequency analyses. In this way, the differences in variability of the errors are easily determined. The effect of each error in the position domain is also investigated in addition to the combined effect. Results show that, on a typical day when single frequency data are processed with broadcast orbit and clock data, the root mean square (RMS) of the changes in the position errors over a 50-s interval is about 5.8 cm in northing, 4.0 in easting, and 11.0 cm in height. When using precise orbits and clocks, in addition to dual frequency data, these values improve by 46–56% to 2.7 cm in northing, 2.2 cm in easting, and 4.9 cm in height. Under severe ionospheric activity, the RMS of the errors decrease from 8.1 to 3.3 cm in northing, 5.7 to 2.6 cm in easting, and 17.0 to 4.9 cm in height, which are improvements of 54–71%. Electronic Publication     

The 2dF Galaxy Redshift Survey: luminosity dependence of galaxy clustering

We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range     . The clustering of     galaxies in real space is well-fitted by a correlation length     and power-law slope     . The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M *, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between     and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.     

Stable carbon isotopes (δ<Superscript>13</Superscript>C) of total organic carbon and long-chain <Emphasis Type="Italic">n</Emphasis>-alkanes as proxies for climate and environmental change in a sediment core from Lake Petén-Itzá, Guatemala

Sediment core PI-6 from Lake Petén Itzá, Guatemala, possesses an ~85-ka record of climate and environmental change from lowland Central America. Variations in sediment lithology suggest large and abrupt changes in precipitation during the last glacial and deglacial periods, and into the early Holocene. We measured stable carbon isotope ratios of total organic carbon and long-chain n-alkanes from the core, the latter representing a largely allochthonous (terrestrial) source of organic matter, to reveal past shifts in the relative proportion of C₃–C₄ terrestrial biomass. We sought to test whether stable carbon isotope results were consistent with other paleoclimate proxies measured in the PI-6 core, and if extraction and isotope analysis of n-alkanes is warranted. The largest δ¹³C variations are associated with Heinrich Events. Carbon isotope values in sediments deposited during the last glacial maximum indicate moderate precipitation with little fluctuation. The deglacial was a period of pronounced climate variability, e.g. a relatively warm and moist Bølling–Allerød, but a cool and dry Younger Dryas. Arid periods of the deglacial were inferred from samples with high δ¹³C values in total organic carbon, which reflect times of greater proportions of C₄ plants. These inferences are supported by stable isotope measurements on ostracod shells and relative abundance of grass pollen from the same depths in core PI-6. Similar trends in carbon stable isotopes measured on bulk organic carbon and n-alkanes suggest that carbon isotope measures on bulk organic carbon in sediments from this lake are sufficient to infer past climate-driven shifts in local vegetation.     

Spatiotemporal analysis of residential flood exposure in the Atlanta,Georgia metropolitan area

Natural Hazards - This research examines changes in residential built-environment flood exposure within the current boundaries of the Atlanta, Georgia metropolitan statistical area, by estimating...     

The Meteoritical Bulletin,No. 100, 2014 June

Meteoritical Bulletin 100 contains 1943 meteorites including 8 falls (Boumdeid [2011], Huaxi, Ko?ice, Silistra, So?tmany, Sutter's Mill, Thika, Tissint), with 1575 ordinary chondrites, 139 carbonaceous chondrites, 96 HED achondrites, 25 ureilites, 18 primitive achondrites, 17 iron meteorites, 15 enstatite chondrites, 11 lunar meteorites, 10 mesosiderites, 10 ungrouped achondrites, 8 pallasites, 8 Martian meteorites, 6 Rumuruti chondrites, 3 enstatite achondrites, and 2 angrites, and with 937 from Antarctica, 592 from Africa, 230 from Asia, 95 from South America, 44 from North America, 36 from Oceania, 6 from Europe, and 1 from an unknown location. This will be the last Bulletin published in the current format. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available online at http://www.lpi.usra.edu/meteor/     

Critical error effects and analysis in carrier phase-based airborne GPS positioning over large areas

For high accuracy airborne differential GPS positioning over large areas, i.e. a monitor-remote separation over 50 km, residual errors from the atmosphere and orbit, as well as multipath effects are the main error sources which limit the potential positioning accuracy. The effects of these critical errors are quantified and analyzed using test data collected during an airborne positioning campaign. Four Trimble 4000 SSE receivers were used, with two serving as monitors and the other two as remote receivers installed in the aircraft. Monitor-aircraft separations of up to 200 km were experienced during the test. A formula is derived for analytical estimation of orbital error effects. Results and discussions relevant to the critical error analysis are presented with emphasis on their effects on the positioning results.