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| Titel |
The evolution of OPUS: A set of web-based GPS processing tools offered by the National Geodetic Survey |
| VerfasserIn |
Weston, Gerald Mader, Schenewerk |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061067
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| Zusammenfassung |
| The Online Positioning User Service (OPUS) is a suite of web-based GPS processing tools
that were initially developed by the National Geodetic Survey approximately eleven years
ago. The first version, known as OPUS static (OPUS-S), processes L1 and L2 carrier-phase
data in native receiver and RINEX formats. Datasets submitted to OPUS-S must be between
two and 48 hours in duration and pass several quality control steps before being passed onto
the positioning algorithm. OPUS-S was designed to select five nearby CORS to form
baselines that are processed independently. The best three solutions are averaged to produce a
final set of coordinates. The current version of OPUS-S has been optimized to accept and
process GPS data from any location in the continental United States, Alaska, Hawaii and the
Caribbean.
OPUS Networks (OPUS-Net), one of the most recently developed versions and currently
in beta testing, has many of the same processing characteristics and dataset requirements
as OPUS-S but with one significant difference. OPUS-Net selects up to 10 IGS
reference sites and three regional CORS to perform a simultaneous least squares
adjustment with the user-submitted data. The CORS stations are primarily used to
better estimate the troposphere while the position of the unknown station and the
three CORS reference stations are determined from the more precisely known and
monitored IGS reference stations. Additional enhancements to OPUS-Net are the
implementation of absolute antenna patterns and ocean tides (FES2004), using
reference station coordinates in IGS08 reference frame, as well as using improved
phase ambiguity integer fixing and troposphere modeling (GPT and GMF a priori
models).
OPUS Projects, the final version of OPUS to be reviewed in this paper, is a complete
web-based, GPS data processing and analysis environment. The main idea behind OPUS
Projects is that one or more managers can define numerous, independent GPS projects. Each
newly defined project is assigned a unique ID which is shared amongst field personel
assigned to the project. A typical GPS project may include simultaneous occupations that
span one or more days, often referred to as a session, as well as having numerous
sessions which can occur for projects that span several days, weeks or months. After
individual GPS data files have been collected in the field, they are submitted to
OPUS-S (OPUS-Net in the future) with the project-specific ID. OPUS-S is used as a
pre-processor at this stage, to determine if the results for each data file surpass a set of
pre-defined tolerances and is acceptable for further analysis. After all the data files for a
project have been successfully submitted to OPUS-S, an OPUS Projects manager
can begin to process each of the sessions in a least squares adjustment. Multiple
session adjustments are combined using GPSCOM, a Helmert blocking normal
equation processor, to estimate a single set of coordinates for each station in the
project.
To evaluate the accuracy and performance of OPUS, approximately 861 data files
collected at 227 stations in central Texas, during the summer of 2011, were submitted to each
version of OPUS (OPUS-S, OPUS-Net and OPUS Projects). An initial analysis using IGS08
coordinates from OPUS-S solutions show that the mean RMS double difference phase
residuals to be approximately 3.9 mm. The network approach from OPUS-Net shows very
low scatter and indicates homogeneous solution quality even when data quality
from some reference stations were poor. At the time this abstract was written and
submitted, the OPUS Projects session processing and combination using Helmert blocks
was incomplete, but a quick review of the completed sessions showed excellent
agreement between coordinates derived for individual stations using OPUS-Net and
OPUS Projects. The final set of analyses will compare coordinates derived using
individual baselines as well as from the network and Helmert blocking approaches. |
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