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Heflin, M. B.

Publications and source records attributed to Heflin, M. B..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)

A celestial reference frame at X/Ka-band (8.4/32 GHz) has been constructed using fifty-one 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec in a cos delta and 290 micro-arcsec in delta. There is evidence for zonal errors at the 100 micro-arcsec level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.

reference systems catalog↗
NASA NTRS2010

Rotational Alignment Altered by Source Position Correlations

In the construction of modern Celestial Reference Frames (CRFs) the overall rotational alignment is only weakly constrained by the data. Therefore, common practice has been to apply a 3-dimensional No-Net-Rotation (NNR) constraint in order to align an under-construction frame to the ICRF. We present evidence that correlations amongst source position parameters must be accounted for in order to properly align a CRF at the 5-10 (mu)as level of uncertainty found in current work. Failure to do so creates errors at the 10-40 (mu)as level.

Jacobs, Chris S.↗
NASA NTRS2010

The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)

A celestial reference frame at X/Kaband (8.4/32 GHz) has been constructed using fiftyone 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec ( mu as) in alpha cos delta and 290 mu as in delta. There is evidence for zonal errors at the 100 mu as level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.

interferometry↗
NASA NTRS2004

JPL IGS Analysis Center Report, 2001-2003

Three GPS orbit and clock products are currently provided by JPL for consideration by the IGS. Each differs in its latency and quality, with later results being more accurate. Results are typically available in both IGS and GIPSY formats via anonymous ftp. Current performance based on comparisons with the IGS final products is summarized. Orbit performance was determined by computing the 3D RMS difference between each JPL product and the IGS final orbits based on 15 minute estimates from the sp3 files. Clock performance was computed as the RMS difference after subtracting a linear trend based on 15 minute estimates from the sp3 files.

Heflin, M. B.↗
NASA NTRS1998

Modern Uplift of the Transantarctic Mountains: Preliminary Results of an Autonomous GPS Array

An autonomous GPS array is being implemented in the Transantarctic Mountains, sponsored by NSF and NASA, for the purpose of measuring uplift resulting from post-glacial rebound (PGR). The rebound of the solid earth due to unloading of ice since the Last Glacial Maximum is expected to dominate the measured uplift for most of West Antarctica, dwarfing the signals due to present-day ice sheet mass balance changes and tectonic motion, as long as mantle viscosity is greater than about 10(exp 20) Pa-s. Predicted uplift patterns have been calculated for a range of model scenarios, which illustrate how the uplift pattern might distinguish between different-sized ice sheets and deglaciation histories as represented by the competing models. The scenarios considered by James and Ivins (1998) include ICE-3G, CLIMAP and a variation of the CLIMAP model by Denton et al. For these models, peak uplift rates occur in the Transantarctic Mountains, and differences between models is often large there. Thus, the Transantarctic Mountains are an ideal place to obtain uplift measurements to constrain deglaciation models.

Raymond, C. A.↗
NASA NTRS1997

Precise Point Positioning for the Efficient and Robust Analysis of GPS Data From Large Networks

Networks of dozens to hundreds of permanently operating precision Global Positioning System (GPS) receivers are emerging at spatial scales that range from 10(exp 0) to 10(exp 3) km. To keep the computational burden associated with the analysis of such data economically feasible, one approach is to first determine precise GPS satellite positions and clock corrections from a globally distributed network of GPS receivers. Then, data from the local network are analyzed by estimating receiver specific parameters with receiver-specific data; satellite parameters are held fixed at their values determined in the global solution. This "precise point positioning" allows analysis of data from hundreds to thousands of sites every day with 40 Mflop computers, with results comparable in quality to the simultaneous analysis of all data. The reference frames for the global and network solutions can be free of distortion imposed by erroneous fiducial constraints on any sites.

Zumberge, J. F.↗
NASA NTRS1997

Precise Point Positioning for the Efficient and Robust Analysis of GPS Data from Large Networks

Networks of dozens to hundreds of permanently operating precision Global Positioning System (GPS) receivers are emerging at spatial scales that range from 10(exp 0) to 10(exp 3) km. To keep the computational burden associated with the analysis of such data economically feasible, one approach is to first determine precise GPS satellite positions and clock corrections from a globally distributed network of GPS receivers. Their, data from the local network are analyzed by estimating receiver- specific parameters with receiver-specific data satellite parameters are held fixed at their values determined in the global solution. This "precise point positioning" allows analysis of data from hundreds to thousands of sites every (lay with 40-Mflop computers, with results comparable in quality to the simultaneous analysis of all data. The reference frames for the global and network solutions can be free of distortion imposed by erroneous fiducial constraints on any sites.

Zumberge, J. F.↗
NASA NTRS1995

The International GPS Network for Charting the Evolving Global Reference Frame

The Telecommunications and Engineering Division of Caltech's Jet Propulsion Laboratory is funded by the National Aeronautics and Space Administration to play a variety of roles in applying the Global Positioning System (GPS) to geodesy and geodynamics. Among these are the operation of dozens of globally-distributed, permanently-operating Earth fixed GPS stations. This, and other applications are described.

Geodynamics Geodesy Global Positioning System GPS↗
NASA NTRS1993

Global Positions and Velocities from One Year of GPS Data

A generalized no-fiducial approach has been developed to obtain global positions and velocities without fixing any individual position or velocity components. The method used can be applied to any global geodetic technique and proceeds in three general steps. First, daily solutions derived with weak constraints are combined to yield one global set of positions and velocities. Second, 14 minimal constraints are applied to remove uncertainties due to the loosely defined reference frame. Third, transformation from one reference frame to another is accomplished with a 14 parameter transformation. One year of daily FLINN solutions, each made with data from about 40 sites, have been combined to yield our best fit global model...

Heflin, M. B.↗
NASA NTRS1993

The Earth Viewed as a Deforming Polyhedron: Method and Results

GPS is quite unlike any other geodetic technique, because we can use it to look at the Earth with high spatial and temporal resolution. For example, the GPS global network provides us with a daily snapshot of the Earth, allowing us to look with high temporal resolution at the motion of sites before, during, and after a large earthquake.The main focus of this paper is to view the Earth as an evolving polyhedron, whose vertices are defined by the GPS sites.

GPS global network GPS GPS sites deforming polyhed↗