600 research outputs found
A demonstration of centimeter-level monitoring of polar motion with the Global Positioning System
Daily estimates of the Earth's pole position were obtained with the Global Positioning System (GPS) by using measurements obtained during the GPS IERS (International Earth Rotation Service) and Geodynamics (GIG'91) experiment from 22 Jan. to 13 Feb. 1991. Data from a globally distributed network consisting of 21 Rogue GPS receivers were chosen for the analysis. A comparison of the GPS polar motion series with nine 24-hour very long baseline interferometry (VLBI) estimates yielded agreement in the day-to-day pole position of about 1.5 cm for both X and Y polar motion. A similar comparison of GPS and satellite laser ranging (SLR) data showed agreement to about 1.0 cm. These preliminary results indicate that polar motion can be determined by GPS independent of, and at a level comparable to, that which is obtained from either VLBI or SLR. Furthermore, GPS can provide these data with a daily frequency that neither alternative technique can readily achieve. Thus, GPS promises to be a powerful tool for determining high-frequency platform parameter variation, essential for the ultraprecise spacecraft-tracking requirements of the coming years
A study of atmospheric neutrinos with the IMB detector
A sample of 401 contained neutrino interactions collected in the 3300 metric ton fiducial mass IMB detector was used to study neutrino oscillations, geomagnetic modulation of the flux and to search for point sources. The majority of these events are attributed to neutrino interactions. For the most part, these neutrinos are believed to originate as tertiary products of cosmic ray interactions in the atmosphere. The neutrinos are a mixture of v sub e and v sub micron
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Sources contributing to background surface ozone in the US Intermountain West
We quantify the sources contributing to background surface ozone
concentrations in the US Intermountain West by using the GEOS-Chem chemical
transport model with 1 / 2° × 2 / 3° horizontal
resolution to interpret the Clean Air Status and Trends Network (CASTNet) ozone monitoring data for 2006–2008. We
isolate contributions from lightning, wildfires, the stratosphere, and
California pollution. Lightning emissions are constrained by observations and
wildfire emissions are estimated from daily fire reports. We find that
lightning increases mean surface ozone in summer by 10 ppbv in the
Intermountain West, with moderate variability. Wildfire plumes generate
high-ozone events in excess of 80 ppbv in GEOS-Chem, but CASTNet ozone
observations in the Intermountain West show no enhancements during these
events nor do they show evidence of regional fire influence. Models may
overestimate ozone production in fresh fire plumes because of inadequate
chemistry and grid-scale resolution. The highest ozone concentrations
observed in the Intermountain West (> 75 ppbv) in spring are
associated with stratospheric intrusions. The model captures the timing of
these intrusions but not their magnitude, reflecting numerical diffusion
intrinsic to Eulerian models. This can be corrected statistically through a
relationship between model bias and the model-diagnosed magnitude of
stratospheric influence; with this correction, models may still be useful to
forecast and interpret high-ozone events from stratospheric intrusions. We
show that discrepancy between models in diagnosing stratospheric influence is
due in part to differences in definition, i.e., whether stratospheric ozone
is diagnosed as produced in the stratosphere (GEOS-Chem definition) or as
transported from above the tropopause. The latter definition can double the
diagnosed stratospheric influence in surface air by labeling as
"stratospheric" any ozone produced in the troposphere and temporarily
transported to the stratosphere. California pollution influence in the
Intermountain West frequently exceeds 10 ppbv but is generally not
correlated with the highest ozone events
Exploring the use of new school buildings through post-occupancy evaluation and participatory action research
This paper presents the results of the development and testing of an integrated post-occupancy evaluation (POE) approach for teachers, staff, pupils and community members using newly constructed school buildings. It focusses on three cases of UK secondary schools, demonstrating how users can be inspired to engage with the problems of school design and energy use awareness. The cases provided new insights into the engagement of school teachers, staff and young people regarding issues of sustainability, management, functional performance and comfort. The integrative approach adopted in these cases provided a more holistic understanding of these buildings’ performance than could have been achieved by either observational or more traditional questionnaire-based methods. Moreover, the whole-school approach, involving children in POE, provided researchers with highly contextualised information about how a school is used, how to improve the quality of school experiences (both socially and educationally) and how the school community is contributing to the building's energy performance. These POE methods also provided unique opportunities for children to examine the social and cultural factors impeding the adoption of energy-conscious and sustainable behaviours
The Spring 1985 high precision baseline test of the JPL GPS-based geodetic system
The Spring 1985 High Precision Baseline Test (HPBT) was conducted. The HPBT was designed to meet a number of objectives. Foremost among these was the demonstration of a level of accuracy of 1 to 2:10 to the 7th power, or better, for baselines ranging in length up to several hundred kilometers. These objectives were all met with a high degree of success, with respect to the demonstration of system accuracy in particular. The results from six baselines ranging in length from 70 to 729 km were examined for repeatability and, in the case of three baselines, were compared to results from colocated VLBI systems. Repeatability was found to be 5:10 to the 8th power (RMS) for the north baseline coordinate, independent of baseline length, while for the east coordinate RMS repeatability was found to be larger than this by factors of 2 to 4. The GPS-based results were found to be in agreement with those from colocated VLBI measurements, when corrected for the physical separations of the VLBI and CPG antennas, at the level of 1 to 2:10 to the 7th power in all coordinates, independent of baseline length. The results for baseline repeatability are consistent with the current GPA error budget, but the GPS-VLBI intercomparisons disagree at a somewhat larger level than expected. It is hypothesized that these differences may result from errors in the local survey measurements used to correct for the separations of the GPS and VLBI antenna reference centers
Improved treatment of global positioning system force parameters in precise orbit determination applications
Data collected from a worldwide 1992 experiment were processed at JPL to determine precise orbits for the satellites of the Global Positioning System (GPS). A filtering technique was tested to improve modeling of solar-radiation pressure force parameters for GPS satellites. The new approach improves orbit quality for eclipsing satellites by a factor of two, with typical results in the 25- to 50-cm range. The resultant GPS-based estimates for geocentric coordinates of the tracking sites, which include the three DSN sites, are accurate to 2 to 8 cm, roughly equivalent to 3 to 10 nrad of angular measure
Techniques for monitoring and controlling yaw attitude of a GPS satellite
Techniques for monitoring and controlling yawing of a GPS satellite in an orbit that has an eclipsing portion out of the sunlight based on the orbital conditions of the GPS satellite. In one embodiment, a constant yaw bias is generated in the attitude control system of the GPS satellite to control the yawing of the GPS satellite when it is in the shadow of the earth
An assessment of static Precise Point Positioning using GPS only, GLONASS only, and GPS plus GLONASS
The aim of this paper is to look into the achievable repeatability and accuracy from Precise Point Positioning (PPP) daily solutions when using GPS only (PPP GPS), GLONASS only (PPP GLO), and GPS plus GLONASS (PPP GPS+GLO) for static positioning. As part of the assessment, a comparison with global double difference (DD) GPS daily solutions is presented. It is shown, therefore, that all of the PPP daily solutions can achieve millimetric level repeatability, similar to the global DD GPS solutions. Furthermore, the mean of the biases between the PPP daily solutions and the global DD GPS daily solutions are constellation type dependent, while an improvement is found in the vertical component for PPP GPS+GLO over PPP GLO, as the latter may be more affected by any imperfections in the models for GLONASS antenna phase centre variations. It is concluded that PPP GLO daily solutions have the ability to be used as independent solutions to PPP GPS daily solutions for static positioning, and as an alternative to PPP GPS+GLO or global DD GPS daily solutions
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