Chapter 7 Summary, Conclusions, and Recommendations
7.2 Recommendations for future work
produce changes in geopotential coefficients with smaller error degree variances and more evident gravity change signatures than the ones given by the GRACE-only solutions.
(5) Time series of second, third and fourth zonal geopotential coefficients are determined from COSMIC and GRACE GPS data and they are consistent with the SLR results. The rates of ΔC20 from SLR, AOP, ACC, and CSR RL04 are
(
−0.94±045)
×10−10,(
−1.06±0.86)
×10−10,(
0.15±0.78)
×10−11 and(
−1.98±0.86)
×10−10 ,respectively. The rates of ΔC30 from CSR RL04, AOP and ACC solutions are
(
−1.58±6.07)
×10−11,(
−5.13±7.09)
×10−11, and(
−7.07±8.14)
×10−11, and the rates of C40Δ are
(
3.46±3.06)
×10−11 ,(
−0.20±2.91)
×10−11, and(
2.33±3.01)
×10−11 ,respectively.
7.2 Recommendations for future work
To further improve accuracies in orbit determination and gravity recovery, there are several topics that need to be investigated in future works.
(1) Improving COSMIC kinematic orbits
This can be achieved by (1) using ambiguity fixing, (2) combing GPS data from the two POD antennas (3) using improved attitude data (collaborating with NSPO) and (4) using improved PCV estimates (Hwang et al. 2009).
(2) Improving the COSMIC and the GRACE dynamic orbits
Compared to the method used in this study, an improved method is to use the
stations. But this will require a higher computational capacity.
(3) Improving the accuracy of acceleration derivation
In this study, we use the numerical differential method to derive the acceleration from positional data. There are at least two different variants of acceleration approaches such as the point-wise acceleration method and average acceleration method. These methods to derive observed acceleration should be investigated.
(4) Accuracy assessment of the COSMIC and combined solutions
More quantitative assessments of accuracy and spatial resolution of the COSMIC and combined gravity solutions are yet to carry out, for example, using terrestrial based gravity measurements at locations with major gravity changes.
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Appendix A: Acronyms ACC Residual acceleration approach
AOCS Attitude and Orbit Control System AOP Analytical orbital perturbation approach CES Coarse Earth and Sun Sensor
CHAMP CHAllenging Minisatellite Payload CMT Center of Mass Trim Assembly
CODE Center for Orbit Determination in Europe
COSMIC Constellation Observing System for Meteorology, Ionosphere and Climate CSR Center for Space Research
DORIS Doppler Orbitography and Radio positioning Integrated by satellite GOCE Gravity Field and Steady-State Ocean Circulation Explorer
GPS Global Positioning System
GRACE The Gravity Recovery and Climate Experiment GST Greenwich sidereal time
hl-SST high-low satellite-to-satellite tracking ILRS International Laser Ranging Service JPL Jet Propulsion Laboratory
KBR K-Band Ranging System LEO Low Earth orbiter
LEOM Lagrange’s equation of motion ll-SST low-low satellite-to-satellite tracking LRR Laser Retro-Reflector
NSPO National Space Organization POD Precise Orbit Determination
PRARE Precise Range and Range Rate Experiment PCV phase center variation
RTN radial, along-track and cross-track SAD solar arrays drive
SCA Star Camera Assembly
SGG Satellite Gravity Gradiometry SLR Satellite Laser Ranging
UCAR the University Corporation for Atmospheric Research USO Ultra Stable Oscillator
Curriculum Vitae
Position
Department of Civil Engineering National Chiao-Tung University 1001 University Road, Hsinchu 300 Taiwan, ROC
Phone: (886) 35712121#54990 Fax: (886) 35716257
Email: [email protected]
WWW: http://space.cv.nctu.edu.tw Date of Birth
August 9, 1977.
Place of Birth
Yunlin County, Taiwan.
Education
B.S., Civil Engineering, National Chiao-Tung University, June 1999 M.S., Civil Engineering, National Chiao-Tung University, June 2002
Major: Satellite Geodesy and GIS
Thesis: Georeference and GIS Systems for Image Acquisition of ROCSAT-2 Satellite Mission
Advisor: Dr. Cheinway Hwang and Dr. Tienyaun Shih
Major Field of Research
Satellite geodesy, Physical geodesy List of Publications
Referred Journal Articles
Hwang, C, YS Hsiao, and TJ Lin, A digital elevation model of Taiwan and accuracy assessment, Cadastre Survey, 22 (2), 1-19, 2003. (in Chinese)
Hwang, C, TP Tseng and TJ Lin, C.L. Fu, D. Svehla, Precise orbit determination for FORMOSAT-3/COSMIC and gravity application, Chinese Journal of Physics, 28(6), 924-933, 2006. (in Chinese)
Hwang, C, TJ Lin and TP Tseng, BF Chao, Modeling orbit dynamics of FORMOSAT-3/COSMIC satellites for recovery of temporal gravity, IEEE Transactions on Geoscience and Remote Sensing, 46(11), 3412-3423, 2008.
Hwang, C, TP Tseng, TJ Lin, D Svehla, and B Schreiner, Precise orbit determination for FORMOSAT-3/COSMIC, J. Geod, 83, 477-489, 2009.
Hwang, C, TP Tseng, TJ Lin, D Švehla, Hugentobler, and BF Chao, Quality assessment of FORMOSAT-3/COSMIC and GRACE GPS observables: analysis of multipath, ionospheric delay and phase residual in orbit determination, GPS Solut, 14 , 121-131, 2010.
Conference Paper/Presentation
Hwang, C and TJ Lin, Georeference and GIS systems for image acquisition of ROCSAT-2 satellite mission, Proceedings of the 21th Conference on Surveying, Hsinchu, 2002.
Hwang, C, CG Wang, LS Hwang, TJ Lin, LS Chang, YS Lee, and SC Hsu, Orbit and gravity determinations using ROCSAT3/COSMIC GPS data: status 2004. Fall Meeting, American Geophysical Union, San Francisco, December 13-17, 2004.
Hwang, C, TJ Lin, CG Wang, YS Lee and LS Chang, Force modeling for FORMOSAT-3/COSMIC satellites: application to time-varying gravity determination, Scientific Assembly of International Association of Geodesy, and Dynamic Planet 2005, Cairns, Australia, August 22-26, 2005.
Lin, TJ, C Hwang, TP Tseng, Temporal gravity field recovery using
Workshop 2006, Taipei, 2006.
Hwang, C, TP Tseng and TJ Lin, CL Fu, D. Svehla, Precise Orbit Determination For FORMOSAT-3/COSMIC And Gravity Application, Fall Meeting, American Geophysical Union, San Francisco, December 11-15, 2006. (invited)
Hwang, C, TJ Lin and TP Tseng, Recovery and analysis of Earth’s gravity field using FORMOSAT-3/COSMIC GPS data, IUGG XXIV General Assembly, Perugia, Italy, July 2-13, 2007.
Shen, YC, C. Hwang, TJ Lin and JH Geng, FORMOSAT-3/COSMIC baseline solution using GPS data, Proceedings of the 26th Conference on Surveying, Yilan, Taiwan, 2007.
Lin TJ and C. Hwang, Recovery of time-varying gravity using GPS data of COSMIC, GRACE and CHAMP, poster paper presented in GGEO 2008 meeting, Crete, Greece, June 23-27, 2008.
Lin TJ and C Hwang, Low-degree gravity change from the GPS data of FORMOSAT-3 and GRACE, WPGM 2010, Taipei, Taiwan, June 22- 25, 2010.
Technical Reports
Chen C.S. and TJ Lin, The gravity surveying work on the first level leveling points, Report of Ministry of the Interior Program, 2002. (in Chinese)
Hwang, C and TJ Lin, Determination and analysis of Earth’s gravity field using COSMIC GPS data, Report of National Space Organization 5-year Program, 2003-2007. (in Chinese)
Hwang, C, TJ Lin, TP Tseng, and N. Tangdamrongsub, Precise orbit determination and analysis of Earth’s gravity field using COSMIC GPS data, Report of GPS Science and Application Research Center 3-year Program, 2008-2010.