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  • 1
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    A Simulation Study of Multi-Beam Altimetry for Lunar Reconnaissance Orbiter and Other Planetary Missions (2009)
    In:  Other Sources
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    Publication Date: 2018-06-06
    Description: The combined use of altimetry, Earth-based Doppler and Earth-based range measurements in the lunar reconnaissance orbiter (LRO) mission (Chin et al. in Space Sci Rev 129:391-419, 2007) has been examined in a simulation study. It is found that in the initial phases of the mission orbit and altimeter geolocation accuracies should be better than 10m in the radial component and 60m overall. It is demonstrated that LRO's precise 1-way laser range measurement from Earth-based stations (Smith et al. in Proceedings of the 15th International Laser Ranging Workshop, Canberra, Australia, October 15-20, 2006) will be useful for gravity recovery. The advantages of multiple laser beams are demonstrated for altimeter calibration, orbit determination and gravity recovery in general planetary settings as well as for LRO.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Journal of Geodesy; Volume 83; No. 8; 709-721
    Format: text
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  • 2
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    The Use of Mascons to Resolve Time-Variable Gravity from GRACE (2005)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: We have analyzed GRACE Level 1B data to resolve time-variable gravity using a local mascon approach. The spherical harmonic solutions released to date resolve the signal from surface hydrology over land areas at spatial scales of 750 to 1000 km over one month intervals [Wahr et al., 2004; Tapley et al., 2004]. In our local approach, we solve explicitly for the mass of water in surface blocks using only the KBRR data collected as GRACE overflies the region of interest. The local representation of gravity minimizes leakage of errors from other areas due to aliasing or mismodelling. In this paper, we report on the analysis of GRACE data from January 2003 through August 2004 over three regions: the Amazon, the Indian subcontinent, and the continental United States. We solve for mass change at 10-day intervals using 4 deg x 4 deg blocks. We give an overview of our latest results, and we present the results of error analyses, and comparisons to both hydrology models and in-situ data.
    Keywords: Numerical Analysis
    Type: IAG Joint Assembly; Aug 22, 2005 - Aug 26, 2005; Cairns; Australia
    Format: text
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  • 3
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    Lunar Gravity Field Determination Using SELENE Same-Beam Differential VLBI Tracking Data (2010)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A lunar gravity field model up to degree and order 100 in spherical harmonics, named SGM 100i, has been determined from SELENE and historical tracking data, with an emphasis on using same-beam S-band differential VLBI data obtained in the SELENE mission between January 2008 and February 2009. Orbit consistency throughout the entire mission period of SELENE as determined from orbit overlaps for the two sub-satellites of SELENE involved in the VLBI tracking improved consistently from several hundreds of metres to several tens of metres by including differential VLBI data. Through orbits that are better determined, the gravity field model is also improved by including these data. Orbit determination performance for the new model shows improvements over earlier 100th degree and order models, especially for edge-on orbits over the deep far side. Lunar Prospector orbit determination shows an improvement of orbit consistency from I-day predictions for 2-day arcs of 6 m in a total sense, with most improvement in the along and cross-track directions. Data fit for the types and satellites involved is also improved. Formal errors for the lower degrees are smaller, and the new model also shows increased correlations with topography over the far side. The estimated value for the lunar GM for this model equals 4902.80080 +/- 0.0009 cu km/sq s (10 sigma). The lunar degree 2 potential Love number k2 was also estimated, and has a value of 0.0255 +/- 0.0016 (10 sigma as well).
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC.JA.5447.2011 , Journal of Geodesy; 85; 4; 205-228
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  • 4
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    Unique Approaches to Analysis of Time-Variable Gravity from GRACE (2004)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: We have developed an innovative analysis strategy for analysis of GRACE data. We have developed a capability to recover local/regional gravity changes using non-global functional representations (Le. surface anomalies vs. global spherical harmonics) h m the GRACE data. Our approach can take regularly or irregularly shaped regions, populate them with surface anomaly blocks of suitable area and solve for the resulting mass flux with respect to a mean field. The surface mass or gravity anomalies benefit from the application of spatial and temporal constraints to add stability to the solution. In this paper we discuss the analysis of four months of GRACE Level 1B data (accelerometry, intersatellite data, attitude information and precise orbits) from July to October 2003, recently released to the GRACE Science Team. We compare and contrast this local approach to gravity recovery, with the more conventional approach using global spherical harmonics. We review simulations of this technique which allow us to pinpoint optimum strategies for applications of this local gravity recovery approach.
    Keywords: Numerical Analysis
    Type: Joint CHAMP/GRACE Science Meeting; Jul 06, 2004 - Jul 08, 2004; Potsdam; Germany
    Format: text
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