SELECTED LIST OF PUBLICATIONS:
Blaha, J., G. Born, N. Guinasso, J. Herring, G. Jacobs, F. Kelly, R. Leben, R. Martin, G. Mellor, P. Niiler, M. Parke, R. Patchen, K. Schaudt, W. Scheffner, C. Shum, C. Ohlmann, W. Sturges, G. Weatherly, D. Webb and H. White, Gulf of Mexico Ocean Monitoring System, Oceanography, 13(2), 2000.
Chao, B., E. Pavlis, C. Hwang, C. Liu, C. Shum, C. Tseng, and M. Yang, COSMIC: Geodetic applications in improving Earth’s Gravity Model, Terrestrial Atmospheric Oceanic Sciences (TAO), Vol. 11, No. 1, 365-378, March 2000.
Chen, J., C. Wilson, B. Chao, C. Shum, and B. Tapley, Hydrologic and oceanic excitations to polar motion and length-of-day variation, J. Geophys. Int., 141, 149-156, 2000.
Chen, J., C. Shum, C. Wilson, D. Chambers, and B. Tapley, Seasonal sea level change from TOPEX/POSEIDON observation and thermal observation, J. of Geodesy, 73, 638-647, 2000.
Kwon, J., C. Jekeli, and S. Han, Absolute kinematic GPS positioning using satellite clock estimation every 1 second. In: Geodesy Beyond 2000, K.-P. Schwarz (ed.), International Association of Geodesy Symposia, Vol.121, pp.343-348, Springer-Verlag,Berlin, 1999.
Jekeli, C., An analysis of vertical deflections derived from high-degree spherical harmonic models. Journal of Geodesy, 73, 10-22, 1999.
Jekeli, C., The determination of gravitational potential differences from satellite-to-satellite tracking, Celestial Mechanics and Dynamical Astronomy, 75(2), 85-100, 1999.
Jekeli, C. and J. Kwon, Results of airborne vector (3-D) gravimetry. Geophysical Research Letters, 26(23), 3533-3536, 1999.
Jekeli, C., Calibration/validation methods for GRACE. In: Geodesy Beyond 2000, K.-P. Schwarz (ed.), International Association of Geodesy Symposia, Vol.121, pp.83-88, Springer-Verlag,Berlin, 1999.
Jekeli, C., The world of gravity according to Rapp. In: International Association of Geodesy Symposia, vol.119, editors: R. Forsberg, M. Feissel, R. Dietrich, pp.79-91, Springer-Verlag, Berlin. 1998.
Pavlis, E., B. Chao, C. Hwang, C. Liu, C. Shum, C. Tseng, and M. Yang, Geodetic applications of the ROCSAT-3/COSMIC mission, Towards an Integrated Global Geodetic Observing System (IGGOS), International Association of Geodesy Symposia, Vol. 120, editors: R. Rummel, H. Drewes, W. Bosch, H. Hornik, pp. 214-217, Springer-Verlag Berlin, October, 1998.
Jekeli, C., An analysis of vertical deflections derived from high-degree spherical harmonic models, J. of Geodesy, 73, 10-22, 1998.
Chambers, D., J. Ries, C. Shum, and B. Tapley, On the use of tide gauges to determine altimeter drift, J. Geophys. Res., 103 (C6), 12885-12890, 1998.
Wingham, D., A. Ridout, R. Scharroo, R. Arthern, and C. Shum, Antarctic elevation change 1992-1996, Science, October, 1998.
Urban, T., T. Pekker, B. Tapley, G. Kruizinga, and C. Shum, A muti-year comparison of wet troposphere corrections from TOPEX and ERS-1 radiometers, in preparation for submission to J. Geophys. Res., 1998.
Rapp, D., F. Lemoine, N. Pavlis, S. Kenyon, E. Pavlis, and B. Chao, New high-resolution model developed for Earth's gravitational field, EOS, Trans. American Geophysical Union, 79, 9(p. 113-117), March, 1998.
Rapp, D., Comparison of altimeter derived and ship gravity anomalies in the vicinity of the Gulf of California, Marine Geodesy, 21(1-15), 1998.
Jekeli, C., The world of gravity according to Rapp, Geodesy on the move, Gravity Geoid, Geodynamics, and Antarctica; IAG Scientific Assembly, 3-9 September 1997, Rio de Janeiro; Volume 119, pp.79-91, Springer Verlag, 1998.
Shum, C., P. Woodworth, O. Andersen, G. Egbert, O. Francis, C. King, S. Klosko, C. Le Provost, X. Li, J. Molines, M. Parke, R. Ray, M. Schlax, D. Stammer, C. Tierney, P. Vincent, and C. Wunsch, Accuracy assessment of recent ocean tide models, J. Geophys. Res., 102(C11), 25,173-25,194, November, 1997.
Rapp, D., and Y. Yi, Role of ocean variability and dynamic ocean topography in the recovery of the mean sea surface and gravity anomalies from satellite altimeter data, J. of Geodesy, 71(10), 617-629, September, 1997.
Rapp, D., Use of potential coefficient models for geoid undulation determinations using a spherical harmonic representation of the height anomaly/geoid undulation difference, J. of Geodesy, 71(5), 1997.
Jekeli, C., and R. Garcia, GPS phase accelerations for moving-base vector gravimetry. J. of Geodesy, 71(10), 630-639, 1997.
Jekeli, C., The effect of Earth’s gravity on precise, short-term, 3-D free-inertial navigation. Navigation, 44(3), 347-357, 1997.
Cheng, M., C. Shum and B. Tapley, Determination of long-term changes in the Earths gravity field from satellite laser ranging observations, J. Geophys. Res., 102(B10), 22,377-22,390, 1997.
Tapley, B., C. Shum, J. Ries, S. Poole, P.A.M. Abusali, S. Bettadpur, R. Eanes, M. Kim, H. Rim, and B. Schutz, The TEG-3 geopotential model, Proc. GravGeoMar96 Symposium, International Association of Geodesy Symposia, 117 (K. Schwarz, Ed.), Springer-Verlag GmbH & Co. KG, May, 1997.
Urban, T., C. Shum, G. Kruizinga, B. Tapley, D. Bilitza, and D. Yuan, Comparison of ionospheric models for single-frequency radar altimeters, Adv. Space Res., 20 (9), 1,769-1772, 1997.
Chen, J., C. Wilson, and C. Shum, Impact of sea level variations on geodetic observations, Annales Geophysicae, EGS, Supplement I, 15(C79), 1997.
SELECTED LIST OF PAPERS:
Shum, C., D. Brzezinska, B. Hazelton, G. Jeffress, D. Martin, Y. Yi, and C. Zhao, The use of GPS for measuring water vapor and sea level, Fifth Symposium on Integrated Observing Systems, Albuquerque, NM, Jan, 2001.
ABSTRACT
The use of ground based GPS network (e.g., Suominet, [Ware et al., 2000]) or spaceborne GPS-to-Low-Earth-Orbiter (LEO) GPS limb-sounding techniques for retrieving atmospheric profiles have been demonstrated [e.g., Rocken et al., 1997]. The use of GPS as a water level measurement [e.g., Parke et al., 1997] has also been demonstrated. In this paper, we will discuss the use of the proposed Ohio State University continuous GPS stations (located in Columbus, Lake Erie, and Gulf of Mexico offshore oil platform) for integrated measurements of atmospheric water vapor, sea level, and with other applications such as precise calibrations of spaceborne radar altimeters. Specifically, measurement sampling in space and time will be discussed using the ground based stations and the current and future spaceborne measurements for the potential of near-real time retrieval of atmospheric profiles to improve regional weather forecasting.
Yu, N., C. Shum, Y. Yu and C. Zhao, Accuracy Assessment of Ocean Tide Models in the China Seas, The 3-rd Across-the-Strait Geomatics Conference, HongKong, Dec. 11-14, 2000.
ABSTRACT
The first comprehensive ocean tide model is developed in 1980 by E. Schwiderski, the availability of the TOPEX/POSEIDON spaceborne radar altimeter observations has allowed development of more than 10 improved barotropic tide models in 1995, and the same number of further improved models by 2000. The TOPEX/POSEIDON global barotropic ocean tide models developed during 1994-1996 have been assessed as with accuracy of 2-3 cm rms in the deep ocean, a spatial resolution on the order of 50 km, and with significantly degraded accuracy near coastal regions [Shum et al., 1997; Desai et al.,1997]. The next generations of ocean tide models are now available taking advantage of more than 6 years of TOPEX/POSEIDON (T/P) altimeter data and more sophisticated hydrodynamical modeling and associated assimilation techniques. Potential improvement in the tide model includes reduction of aliasing, improved accuracy in the long-period tides and in the coastal regions. We have conducted a study to assess the current ocean tide model prediction capability primarily in the global coastal region, especially in the coastal region of Yellow sea. Independent data including pelagic tidal constants from bottom gauges, and radar altimeter and crossover measurements. One application of this study is for sea level studies. This study is supported by APSG (Asian-Pacific Space Geodesy) project. More than six new global ocean tide models have been evaluated and preliminary results indicate significant errors in the coastal seas still remain. The improved knowledge of tides allows interdisciplinary studies including the lunar deceleration caused by tidal frictions as well as geophysical studies of Earth’s internal structure.
Shum, C., C. Zhao, Y.Yi, C. Reigber, A. Braun, T. Scheone, D. Wolf, P. Woodworth, Determination and characterization of global mean sea level change, ERS-ENVISAT Symposium, Gothenbury, Sweden, October 2000.
ABSTRACT
Sea level change represents consequences of complicated interactions of the solid Earth-atmosphere-hydrosphere-ocean-cryosphere system and in part forced by human-originated greenhouse effect. Estimates of the last century (40-100 years) sea level change are about 1-2.5 mm/yr (IPCC 1995, Warrick et al. 1996). Although there is no firm evidence of an acceleration in the rate of sea level rise over this time period [Woodworth, 1990], the projected future sea level rise is 13 +/- 4 cm during the next 40 years (1987-2027), and 61 cm over the next 100 years (1987-2087) [Woodworth, 1995]. The secular or long-term sea level change studies have primarily used tide gauges located near coastal regions and continental margins or near islands. The estimate has deficiencies from vertical land movements (e.g., due to postglacial rebound and local land motion) and the associated vertical datum knowledge, and the fact that the data only covers less than 5% of the global ocean. Satellite radar altimetry measurement, both historic and current (Geos-3, Seasat, Geosat, ERS-1, TOPEX/POSEIDON, ERS-2, GFO-1, and future (Envisat, Jason-1, NPOESS), would provide global coverage has much shorter data span (less than 10 years of continuous data), and have measurement uncertainties caused by respective instrument biases and drifts. In this study, we will provide an analysis of the present-day global mean sea level change using multiple mission altimeter measurements and tide gauge data. Geosat, ERS-1, ERS-2 and Envisat (future mission) data cover critical portion of the polar oceans and this paper will focus on their contributions to the global sea level studies. Second part of the study is intended to provide a characterization of the sea level change by using modern observations, including global sea surface temperature (spaceborne and in situ), ice extents, postglacial rebound models, glacier and ice sheet mass balance data.
Schoene, T., A. Braun, C. Reiber, M. Rentsch, and C. Shum, Concept for using GPS-Buoys for RA drift monitoring, ERS-ENVISAT Symposium, Gothenbury, Sweden, October 2000.
ABSTRACT
Radar altimetry is a valuable tool for measuring instantaneous sea levels or mean sea surface heights. Until today a long series of measurements from different altimeter missions exist. A main problem in using these data for determination of sea level changes are the biases between the missions and a only weakly determined drift of the different sensors. For the past and current missions different strategies are used for calibration and drift monitoring, e.g. using crossovers or tide gauges as a height reference. The disadvantage of all calibration methods is, that no direct measurement beneath the sub-satellite tracks are available and, therefore, models has to be used to account for e.g. the sea surface slope or time varying signals. A more reliable method exists, when using oil platforms equipped with GPS and tide gauges beneath the sub-tracks. Unfortunately, only a few of them are probable located. With the availability of PGS a different strategy can be applied. As shown for ERS and Topex/Poseidon, a GPS-equipped buoy, anchored beneath a sub-track, can be used as a height reference. Since GPS-derived coordinates are ITRF-referenced, an absolute calibration is possible. Until today only lightweight buoys were deployed. Therefore, no long-term sensor for the calibration and drift monitoring exists. A ruggedized GPS-buoy will be deployed in the North Sea in the context of a large German sea level monitoring project. An ENVISAT crossover, which intersects with a Topex/Poseidon and GFO sub-track, will be chosen. The lifetime of the buoy is expected to be several years, therefore, a long-term calibration, drift monitoring and inter-calibration of different missions will be possible. A second buoy will be deployed in the Gulf of Mexico. In addition, the buoy will be equipped with supplementary sensors, like wind speed, gyros and air pressure sensors, allowing a broader use for calibration, e.g. of wind speed or significant wave heights.
Shum, C., B. Chao, E. Pavlis, and C. Zhao, Space geodesy and climate change studies using COSMIC mission, COSMIC Workshop, COSPAR Symposia, Taipei, Taiwan, Sept. 27-29, 2000.
B. Chao, C. Hwang, C. Liu, E. Pavlis, C. Shum, C. Tseng, and M. Yang, Global gravitational applications of ROCSAT-3/COSMIC, COSMIC Workshop, COSPAR Symposia, Taipei, Taiwan, Sept. 27-29, 2000.
ABSTRACT
The ROCSAT3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) mission consists of a constellation of 6 low-earth orbiting satellites. In conducting the atmospheric limb sounding using the GPS radio occultation technique (which is the main objective of the mission), the satellite orbits are precisely determined at any given moment by GPS "high-low" satellite-to-satellite tracking. These precise orbit determination (POD) data contain useful information about the Earth's gravitational field and its time variations, for both geophysical and climate-related research.. In one scenario, it is envisioned that opportunities exist during the first year of orbit adjusting phase, when pairs of satellites are flying in tandem, providing unique opportunity to cancel out non-gravitational effects (air drag and radiation pressure) in the orbits and allowing "clean" detection of gravitational signals. Our preliminary simulations show that the use of these orbit data can yield an order of magnitude improvement over the state-of-the-art global gravity model EGM96 out to degree and order 20 (spatial resolution of 1000 km). Equally important, the temporal variation signals of low-degree harmonics can be obtained at the 800 km operational altitude (where the non-gravitational forces is weaker and can be better modeled and removed) during the lifetime of the mission. The time-varying gravity is becoming an important data source for studying climate-related global changes, especially in anticipating the launch of the 5-year GRACE mission in 2001. Although not as precise as what GRACE promises to achieve, COSMIC represents independent and potentially complementary observations for the new time-varying gravity research.
Shum, C., C. Jekeli, C. Kuo, and Y. Yi, Monitoring lake level changes using satellite altimetry and GPS-buoys, National Sea Grant College Program a Program Assessment Team (PAT) visit, Ohio State University, September 25, 2000.
Shum, C., and N. Yu, Accuracy assessment of contemporary Earth Ocean tide models, 14th International Symposium on Earth Tides, Mizusawa, Japan, August 28-Septemeber 1, 2000.
ABSTRACT
The advent of modern space geodetic measurements as well as sophisticated hydrodynamical modeling have initiated improved development of global ocean tide models (within latitude bounds of 60 degrees) during the last decade. 15 years after the development of the first comprehensive Earth ocean tide model in 1980 by E. Schwiderski, the availability of the TOPEX/POSEIDON spaceborne radar altimeter observations has allowed development of more than 10 improved barotropic tide models in 1995, and the same number of further improved models by 2000. The improvement of tide modeling also benefited from the analysis of precise tracking data collected for a number of Earth-orbiting geodetic satellites. The improved knowledge of tides allows interdisciplinary studies including the lunar deceleration caused by tidal frictions as well as geophysical studies of Earth’s internal structure. This paper provides an updated accuracy assessment of the predictive capability of the available global ocean tide models, with emphasis on the coastal regions and in polar oceans. Although the deep ocean barotropic tides are estimated to be accurate to 2-3 cm rms, the coastal and shallow and beneath ice shelf tides are largely unknown. In addition, internal tides forced by complicated ocean bottom topography are very much a research topic. This paper will also examine several new space geodetic measurement which could potentially contribute to the further improvement of understanding ocean tidal science on the planet Earth.
Shum, C., B. Chao, E. Pavlis, and C. Zhao, Space geodesy and climate change studies using COSMIC mission, COSPAR Colloquium, Green Bay, Taiwan, Sept. 27-29, 2000.
ABSTRACT
The constellation for the upcoming (2004 launch) COSMIC mission satellites, which consists of 6 low-Earth-orbit (LEO) mini-satellites in formation for a possible lifetime of up to 5 years, provides an unique opportunity for advancing research in areas of space geodesy and geodynamics. The COSMIC mission has primary scientific objectives including advancing research in meteorology and space weather [Kuo et al., 1999]. It is anticipated that the COSMIC satellites each carrying a geodetic quality dual-frequency GPS receiver will contribute towards improving the accuracy and the link of the regional reference system and 3-D datum (especially within Taiwan) to the IERS terrestrial reference system, improving the orbit accuracy of the GPS satellites through the high-low GPS orbit determination for COSMIC satellites, improving the determination of long wavelength temporal gravity signals which are climate-sensitive, and the potential to improve the global surface pressure field, especially in the Southern Ocean and over Antarctica. The pressure field improvement will have significant applications in the studies of Earth's geophysical fluid balance, temporal gravity, Earth rotation, ice sheet mass balance, sea level change, and global climate changes. This paper will address each of the science components to quantify their respective contributions to space geodesy and climate change studies using COSMIC measurements.
Shum, C., Proposed support of RISE team for lunar science research, National Astronomical Observatory, Mizusawa, Iwate, Japan, September 4, 2000.
Shum, C., Proposed GRACE calibration in Antarctica, National Astronomical Observatory, Mizusawa, Iwate, Japan, September 2, 2000.
Jekeli, C. and R. Garcia, Local geoid determination within situ geopotential data obtained from satellite-to-satellite tracking, IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, Banff, Canada, July 31-August 4, 2000.
Kwon, J., and C. Jekeli, The inefficacy of stochastic gravity models in airborne IMU/GPS vector gravimetry. IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, Banff, Canada, July 31-August 4, 2000.
Han, S., C. Jekeli, and J. Kwon, Precision absolute GPS positioning and its use to obtain kinematic acceleration. IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, Banff, Canada, July 31-August 4, 2000.
Zhao, C., C. Shum, N. Yu, and A. Trupin, Oceanic mass variations using radar altimeters and gravity measurements, IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, Banff, Canada, July 31-August 4, 2000.
Cheng, K, C. Shum, M. Parke, K. Snow, S. Han, J. Benjamin, D. Martin, and G. Mader, GPS-Buoy water level instrument: Applications for radar altimeter calibration, IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, Baniff, Canada, July 31-August 4, 2000.
Baessler, M., R. Dietrich, R. Metzig, Z. Lu, and C. Shum, Study of Filchner-Ronne ice shelf ice stream dynamics using SAR interferometry, IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, July 31-August 4, 2000.
Trupin, A., and C. Shum, Determinations of polar ice mass balance from gravity, IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, July 31-August 4, paper submitted, 2000.
Shum, C., and C. Zhao, GFO-1 radar altimeter data product verifications, GFO Operational Evaluation meeting, U.S. Naval Observatory, Washington, D.C., July 20, 2000.
Shum, C., H. Tseng, and B. Schaffrin, Application of spherical wavelets to solution of the terrestrial gravity field model, NIMA NURI Symposium, USGS, Reston, Virginia, July 18, 2000.
Jekeli, C., New measurement concepts for determining Earth’s gravity vector field, annual progress report, NIMA NURI Symposium, USGS, Reston, Virginia, July 18, 2000.
Zhao, C., D. Bilitza, C. Shum, S. Schaer, G. Beutler, and S. Ge, Evaluation of ionosphere models using dual-frequency radar altimeter measurements, COSPAR meeting, Warsaw, Poland, July 16-23, 2000.
Shum, C., A. Trupin, N. Yu, and C. Zhao, Oceanic and ice sheet mass variations from gravity missions, Invited, Spring AGU Meeting, Washington D.C. May 30-June 3, 2000.
Lillibridge, J., C. Shum, R. Cheney, C. Zhao, Calibration/Validation results for Geosat follow-on, Spring AGU Meeting, Washington D.C. May 30-June 3, 2000.
Martinez-Benjamin, J., M. Martinez-Garcia, J. Garate, J. Martin-Davila, J. Ferrandiz, M. Vigo-Aguiar, M. Ortiz-Castellon, J. Talaya, B. Perez, G. Kruizinga, B. Haines, O. Colombo, B. Chao, C. Shum, M. Parke,, S. Han, and K. Cheng, The T/P CATALA altimeter calibration campaign, Spring AGU Meeting, Washington D.C. May 30-June 3, 2000.
Chao, B. , E. Pavlis , C. Huang , C. Liu , C. Shum C. Tseng , and M. Yang, Space Geodesy on COSMIC, White Paper to: Dr. Lou Lee, National Space Program Office (NSPO), Taiwan, May 22, 2000.
Zhao, C., and C. Shum, Effect of AOCS thrusters on Cryosat precision orbit determination, 4th Cryosat Science Advisory Group Meeting, ESA/ESTEC, Noordwijk, The Netherland, May 11-12, 2000.
Shum, C., Assessment of DORIS and high-low GPS tracking systems on Cryosat, 4th Cryosat Science Advisory Group Meeting, ESA/ESTEC, Noordwijk, The Netherland, May 11-12, 2000.
Shum, C., J. Finkelstein , C. Zhao, J. Lillibridge, Y. Yi, and P.A.M. Abusali, Initial analysis of GFO-1 radar altimeter data, 25th General Assembly of the EGS in Nice, France, April 24-29, 2000.
Shum, C., A. Trupin, and C. Zhao, Ice sheet mass balance from temporal gravity field observations, 25th General Assembly of the EGS in Nice, France, April 24-29, 2000.
Tseng, H., C. Shum, C. Zhao, and J. Lin, Absolute sea level measurements from tide gauges and adjacent geodetic station vertical motion solutions, 25th General Assembly of the EGS in Nice, France, April 24-29, 2000.
Shum, C., C. Zhao, H-Z. Tseng and P. Woodworth, 20th century sea level change in the Pacific basin, Keynote speaker, presented at the Pacific Islands Conference on Climate Change, Climate Variability and Sea Level Rise, National Auditorium, Rarotonga, Cook Islands, April 2-7, 2000.
Jekeli, C., Overview of research in gravity field measurement and modeling at OSU. DARPA (Yehuda Avniel) and NIMA (Bill Stein and Paul Salamonowicz) visit to GSS, Ohio State University, February 28, 2000.
Shum, C., Geophysical inverse problem: Gravity field solution, DARPA/NIMA visit to GSS, Ohio State University, February 28, 2000.
Shum, C., Radar altimeter absolute calibration plan and campaign results, Envisat Absolute Calibration Meeting, Barcelona, Spain, February 16, 2000.
Dietrich, R., W. Korth, C. Shum, and G. Hamilton, Proposed E. Antarctic GLAS calibration site, GLAS Science Team Meeting, GSFC, Greenbelt, Maryland, December 27-29, 1999.
Jekeli, C., J. Kwon, and C. Shum, Methods and results of airborne vector gravimetry using INS/GPS, Fall AGU Meeting, San Francisco, December 13-17, 1999.
Yu., N., C. Shum, C. Morris and M. Parke, Accuracy assessment of ocean tide models in the coastal region, Fall AGU Meeting, San Francisco, December 13-17, 1999.
Urban, T., J. Ries, C. Shum, and B. Tapley, Two decades of global sea-level measurements from satellite altimetry, Fall AGU Meeting, San Francisco, December 13-17, 1999.
Trupin, A., and C. Shum, Inverting the gravity field for polar ice mass balance, Fall AGU Meeting, San Francisco, December 13-17, 1999.
Parke, M., and C. Shum, GPS-Buoy results, GOMOMS NOPP Project Meeting, New Orleans, LA, 1999.
Shum, C. and M. Parke, Altimeter and scatteorometer analysis results, GOMOMS NOPP Project Meeting, New Orleans, LA, 1999.
Jekeli, C., In situ geopotential data from GRACE, GRACE Science Working Team Meeting, University of Texas Center for Space Research, Austin, Texas, December 9-10, 1999.
Shum, C., Status report on GRACE calibration: proposed Antarctica calibration/validation activities, GRACE Fifth Science working Team Meeting, UT/CSR, Austin, Texas, December 9-10, 1999.
Shum. C., Y. Yi, C. Zhao, M. Parke, K. Cheng, H. Tseng, D. Martin, and G. Mader, Preliminary results: TOPEX side B altimeter calibration campaigns, Jason SWT Meeting, St. Raphael, France, October 25-27, 1999.
Shum, C., T. Baker, C. Huang, and W. Scherer, Status report on Asia-Pacific Space Geodynamics Program sea level working group, Asia Pacific Space Geodynamics Program Plenary Session, GPS99 in Tsukuba, Japan, October 18-22, 1999.
Shum, C., C. Zhao, T. Urban, and P. Woodworth, Determination and characterization of global mean sea level change, First EGS Vening Meinesz Conference on "Global and Regional Sea-Level Changes and the Hydrological Cycle", Loiri-Porto San Paolo, Sardinia, Italy, October 4-7, 1999.
Shum, C., C. Huang, D. Martin, M. Parke, W. Scherer, P. Woodworth, Combining GPS, tide gauge and radar altimetry in the determination of mean sea level variations, GPS99 meeting, Tsukuba, Japan, October, 1999.
Chao, B., C. Hwang, C. Liu, E. Pavlis, C. Shum, C. Tseng, and M. Yang, Global geodetic applications of ROCSAT-3/COSMIC, GPS99 meeting, Tsukuba, Japan, October, 1999.
Jekeli, C. and J. Kwon, Airborne vector gravimetry using INS/GPS – results, IUGG Symposia, Birmingham, UK, July 18-30, 1999.
Kwon, J., C. Jekeli, and S. Han, Absolute kinematic GPS positioning using satellite clock estimation every 1 second, IUGG Symposia, Birmingham, UK, July 18-30, 1999.
Jekeli, C., Calibration/validation methods for GRACE, IUGG Symposia, Birmingham, UK, July 18-30, 1999.
Shum, C, H. Tseng, C. Zhao, T. Urban, B. Tapley, M. Anzenhofer, and P. Woodworth, Determination and characterization of long-term mean sea level change, IUGG Symposia, JSG11, Birmingham, UK, July 18-30, 1999.
Shum, C., and A. Trupin, Polar gravity mapping from future satellite missions, invited, IUGG Symposia, JSA09, Birmingham, U.K., July 1999.
Parke, M., C. Shum, K. Snow, K. Cheng, G. Mader, D. Martin, F. Kelly. N. Guinasso, G. Jeffress, R. Gutierrez, B. Schutz and J. Blaha, Sea level from GPS buoys. IUGG Symposia, Birmingham, UK, July 18-30, 1999.
Yi, Y., C. Shum, H. Tseng, M. Anzenhofer, M. Rentsch, and C. Hwang. On the advances of marine gravity anomaly models determined from GEOSAT, ERS-1 and TOPEX/POSEIDON satellite radar altimetry, IUGG Symposia, G3, Birmingham, UK, July 18-30, 1999.
Urban, T., J. Ries, B. Tapley, and C. Shum, The integration of twenty-five years of sea-level measurements from satellite altimetry, IUGG Symposia, JSG11, Birmingham, UK, , July 18-30, 1999.
Shum, C., Envisat RA2 Algorithm Review Meeting, ESA/ESRIN, Frascati, Italy, June, 1999.
Jekeli, C., New measurement concepts for determining Earth’s gravity vector field. NURI Symposium, George Mason University, VA., June 2-3, 1999.
Jekeli, C., Airborne vector gravimetry using INS and GPS-review, results, and future plans at OSU, Ohio State University, June 1, 1999.
Shum, C., M. Parke, Y. Yi, C. Zhao, K. Cheng, H. Tseng, M. Anzenhofer, C. Reigber, J. Benjamin-Martinez, J. Blaha, R. Dietrich, G. Liebsch, K. Novotny, G. Kruizinga, C. Morris, R. Francis, D. Martin, G. Mader, and T. Urban, Absolute altimeter calibration and validation of multiple radar altimeters, invited presentation, Proc. Intergovernmental Oceanographic Commission Group of Experts Sixth Session on the Global Sea Level Observing System, Toulouse, France, May 10-14, 1999.
Shum, C., H. Tseng, C. Huang, D. Zheng, B. Iz, Y. Q. Chen, W. Scheren, P. Woodworth, and M. Anzenhofer, Asia-pacific space geodynamics (APSG) project sea level studies status report, GLOSS Group of Experts Meeting, invited presentation, APSG Sea Level, Toulouse, France, May, 1999.
Shum, C., Y. Yi, C. Zhao, M. Parke, K. Cheng, J. Lin, K. Snow, H. Tseng, D. Martin and G Mader, TOPEX Side B altimeter calibration results, TSB Calibration Meeting, NASA/GSFC, April, 1999.
Shum, C., Measuring ice mass balance: issues and possible calibration/validation campaigns, GRACE SWT Fourth Science Working Team Meeting, London, April 1999.
Shum, C., and C. Jekeli, Regional gravity: potential calibration/validation opportunity, GRACE SWT Fourth Science Working Team Meeting, London, April 1999.
Anzenhofer, M., A. Braun, M. Rentsch, C. Reigber, and C. Shum, Coastal Altimetry and Application, EGS, The Hague, Netherlands, April 1999.
Nuth, V., C. Wilson, M. Cheng, and C. Shum, The application of radar altimeter to the problem of ice sheet thickness changes, Geophysical Research Abstracts, Vol. 1, No. 1, pp. 217, EGS 24th General Assembly, The Hague, The Netherlands, 1999.
Shum, C., and C. Jekeli, Regional gravity potential calibration/validation opportunities, Measuring ice mass balance: Issues and possible calibration/validation campaigns, GRACE Fourth Science Working Team Meeting, London, United Kingdom, April 16-17, 1999.
Shum, C. and B. Chao, Contributions of COSMIC to Geodesy and Geodynamics, presented Workshop on Low Earth Orbiter Missions: Developing and Integrating Ground and Space Systems for GPS Applications, held at GeoForschungsZentrum Potsdam (GFZ), Potsdam, Germany, March 9-11, 1999.
Shum, C., M. Parke, C. Morris, and E. Rodriguez, SRTM review meeting presentations, at CEEGS, Ohio State University, 1/22/99, and 4/7/99.
Anderson, R., J. Davenport, and C. Jekeli, The determination of gravity data spacing required for inertial navigation, National Technical Meeting of the ION, San Diego, CA., Jan 25-27, 1999.
Parke, M., C. Shum, K. Snow, K. Cheng, F. Kelly, N. Guinasso, G. Jeffress, B. Schutz, M. Ansenhofer, J. Blaha, and J.J. Gonzalez-Alvarez, Measuring sea level in the Gulf of Mexico with a DGPS buoy, presented at INSMAP’98 Meeting, Univ. of Miami, Dec. 1998.
Wilson, C., J. Chen, C. Shum, and B. Chao, Polar motion and length-of-day excitations from continental water storage and the oceans, Fall Meeting of AGU, San Francisco, December 1998.
ABSTRACT
Mass redistribution and movement in continental water storage and the oceans are likely to be the major contributors to the remaining polar motion excitations not accounted for by the atmosphere. We investigate continental water storage change and its excitation of polar motion and length-of-day variation using both assimilated hydrological model and climatological average datasets. We estimate oceanic mass contributions from TOPEX/Poseidon sea level observation and a simplified steric sea level change model. The results are compared with the residual excitations after atmospheric contributions are removed using the NASA GSFC GEOS-1 atmospheric model. This study indicates the following: Continental water storage change plays an important role in exciting polar motion and LOD at seasonal scales; different hydrological models show significant differences with regard to the predicted contribution to earth rotation changes; The assimilated data hydrological model provides better agreement with earth rotation observations; Non-steric sea level changes provides significant excitations to polar motion and LOD over a wide range of time scales.
Nuth, V., C. Wilson, M. Cheng, and C. Shum, Changes of ice sheet thickness from radar altimeter waveforms, Fall Meeting of AGU, San Francisco, December 1998.
ABSTRACT
The high variability of the ice surface prevents the on-board tracker of a satellite radar altimeter from accurately measuring the arrival time of the radar pulse, which in turn degrades the range measurements. Furthermore, if the change in surface topography is faster than the response time of the tracking algorithm, no range is measured. Accordingly, we must revert to using the recorded waveforms to measure apparent changes in ice sheet elevation over time. A cross-correlation method has been applied to the calculation of the apparent ice sheet elevation changes at the satellite cross-over point. This approach recovers only changes in the ice thickness over time, but the advantage is that we do not need a waveform model function in order to estimate the retracking correction. We report on the preliminary results obtained from approximately one year of ERS-1 data over the Antarctic Ice Sheet. The results indicate that during the period of September 1992 and July 1993, the ice elevation in Antarctica appeared to undergo changes on the order of a few tens of cm in amplitude, with some areas reaching as high as a meter.
Rapp, D., Ocean Domain Definitions and Orthonormal Expansions, Civil and Environmental Engineering and Geodetic Science Seminar, Ohio State University, November, 1998.
ABSTRACT
This talk describes the results of a recently completed study on the use of ocean domains for spherical harmonic and orthonormal expansions. The study expanded the work of Hwang to find the expansion limitation (maximum degree) of currently used ocean domains for dynamic ocean topography representation and looked for ocean domain definitions that could be used for higher degree orthonormal expansions than currently used. Results for the POCM4B DOT model were obtained for degree 30 and 36 expansions. In addition geoid undulation accuracy estimates were obtained in different domains for several geopotential models including EGM96.
Shum, C., Using satellite geodesy to understand Earth system dynamics, invited lecture at Technical University Dresden, Dresden, Germany, October, 1998.
Shum, C., M. Parke, M. Anzenhofer, J. Blaha, F. Kelly, and D. Martin, Status of Gulf of Mexico radar altimeter calibration site: Preliminary results on GPS-Buoy sea level cruise experiment, TOPEX/POSEIDON and Jason-1 Science Working Team Meeting, Keystone, CO, October 1998.
Parke, M., C. Shum, K. Snow, K. Cheng, M. Anzenhofer, J. Blaha, F. Kelly, G. Jeffress, N. Guinasso, and G. Mader, Preliminary results from GPS-Buoy cruise experiment for radar altimeter calibration, TOPEX/POSEIDON and Jason-1 Science Working Team Meeting, Keystone, CO, October 1998.
ABSTRACT
GPS-buoy sea level measurements were taken on a Texas A&M cruise in April 1998 in the Gulf of Mexico along two TOPEX/POSEIDON tracks and an ERS-2 track. CDT data were also taken along the tracks. The presentation intends to summarize preliminary results obtained todate on the use of GPS-buoy sea level measurements for practical absolute calibration of radar altimeters in the Gulf of Mexico Mobil Platform.
Shum, C., M. Anzenhofer, and J. Ries, Contribution of altimetry missions to space geodesy, Towards an Integrated Global Geodetic Observing System, International Symposium of IAG Section II, Munich, Germany, October 5-9, 1998.
ABSTRACT
Spaceborne satellite radar altimeters have demonstrated their abilities to provide global synoptic measurements of the sea surface topography with a temporal sampling of weeks and approaching an absolute accuracy of 3-4 cm rms. There are three currently operating spaceborne radar altimeters (TOPEX/POSEIDON,ÜERS-2 and GFO-1), with others planned at the beginning of the next Millennium (Jason-1 and Envisat), as well as historic missions (Geos-3, Seasat, Geosat, and ERS-1). The first Earth spaceborne laser altimeter mission (GLAS/Icesat), scheduled to be launched at the beginning of the next decade with the primary purpose of studying long-term ice sheet mass balance, will also contribute to space geodetic science. TOPEX/POSEIDON (T/P) represents the first satellite mission dedicated to the measurement of the large-scale global ocean circulation. The stringent accuracy requirements placed on the T/P orbit and altimeter measurement system necessitated dedicated efforts which have led to significant advances in contemporary precision orbit determination methodologies, reference frame definition, and in knowledge of the Earth's shape and mass distribution in the ocean. The design and precise computation of the T/P orbit allows the use of the altimetric measurements to provide the most significant advances in the prediction of the ocean tides in the last century. Accuracy of T/P altimetry (its orbits and reference frames) enables establishment of absolute vertical datums for combination with other altimeters, and for the long-term measurement of global mean sea level variations. The geodetic phases of altimetric missions (Geosat and ERS-1) have allowed unprecedented improvement in the spatial resolution and accuracy of models of the mean sea surface, marine geoid, and predicted bathymetry. ERS-1 and ERS-2 radar altimeters have been providing measurements of inner ice sheet topography and its changes. In a few years, the ICESAT laser altimeter will provide more accurate measurements of ice sheet elevation changes, toward the definitive determination of the mass balance of the ice sheets. Finally, accurate and long-term altimetry is a critical component for the combination with the advanced gravity mapping mission(GRACE and CHAMP) measurements to potentially allow separation of oceanic height changes caused by thermal expansion and by mass redistribution as an initial step towards improving understanding of global climate change.
Jekeli, C., On the Determination of geopotential differences from satellite-to-satellite tracking, submitted to Proceedings of Hotine-Marussi Symposium, Trento, Italy, September 1998.
Jekeli, C., An evaluation of the EGM96 geopotential model based on deflections of the vertical,” presented at the IGC and IGeC 2nd Joint Meeting, Trieste, Italy, September 7-12, 1998.
Jekeli, C., An analysis of geopotential difference determination from satellite-to-satellite tracking,” presented at the IGC and IGeC 2nd Joint Meeting, Trieste, Italy, September 7-12, 1998.
Jekeli, C., Local geopotential measurements using GRACE,” presented at meeting of the U.S. Geoid Committee, National Geodetic Survey, Silver Spring, Maryland, August 18, 1998.
Shum, C., Characterization of sea level rise and land subsidence in East China Sea region combining altimetry, GPS and tide gauges, Preliminary agenda for discussion meeting on "Sea Level Networks in the West Pacific Region including Development of GLOSS in the Region", Taipei, Taiwan, July 20, 1998 (Invited).
Shum, C., Preliminary evaluation of GFO-1 radar altimeter data, Proc. 4th Pacific Ocean Remote Sensing Conference, Qingdao, China, July, 1998.
Shum, C., M. Parke, and P. Abusali, Preliminary assessment of GFO orbit and measurement accuracy, PORSEC 98, Qingdao, China, July, 1998.
Shum, C., M. Parke, M. Guman, C. Huang, D. Zheng, B. Tapley, J. Wang, and P. Woodworth, Observing long-term mean sea level variations in the China Seas, Proc. 4th Pacific Ocean Remote Sensing Conference, Qingdao, China, July, 1998 (Invited).
ABSTRACT
Coastal regions are the center of worldwide population increases, and by the year 2020, over 65% of the world's population will live along continental margins. Changes in climate with the associated sea level rise, and subsidence of populous coastal cities, have major impacts on the global economy, environment, societal and human utilization. Sea level variability occurs over a wide spectrum of both temporal and spatial scales. Sea surface variability occurs locally as microscale ripples, waves, and barometric gradient effects. Surface winds, atmospheric pressure changes, tidal activities, circulation patterns, and meteorological phenomena all contribute to the redistribution of water on the local and regional spatial scales. Recent studies of global sea level change based on long-term coastal tide gauge data (e.g., IPCC studies) have concluded that the global eustatic rate of sea level rise during the last century has been 1-3 mm/yr [e.g., Douglas, 1991] and that the sea level by the year 2070 A.D. may be 20-70 cm higher than today. Regional sea level variations, e.g., in the East China sea, can be much larger, and have been observed to vary on the order of >1 cm/yr over the last few years, although the variations can primarily be attributed to seasonal and interannual variations. The study of regional sea level rise and its mitigation is among the primary scientific objectives of research programs such as the Asian-Pacific Space Geodynamics Project. Over 30 years of 40 Chinese tide gauge sea level data are available in Bohai, Yellow Sea, East China Sea, and South China Sea; and the observed sea level rise near the gauges is 0-2 mm/yr [e.g., Chen, 1996, Ma et al., 1996, Zheng et al., 1995]. Some of these tide gauges have been contributing sea level data to the PSMSL, as part of IOC's GLOSS observational system [Woodworth, 1991]. Using multiple altimetric mission (Geosat, ERS-1, and T/P) sea level measurements and sophisticated techniques to link these altimetric measurement systems [Guman, 1997; Kruizinga, 1997], the observed sea level change over a decade (1986-1996) in the western Pacific basin has been observed to be changing approximately 1-2 mm/yr with an uncertainty of 1 mm/yr [Shum et al., 1996; Guman et al., 1997]. This study reports recent results to link long-term (10-40 years) tide gauge records with accurate geocentric sea level measurement systems (i.e., radar altimeter) and with available GPS-defined datums, for an unambiguous monitoring and interpretation of the regional sea level variations within the China sea basins during the last decade.
Chen, J., C. Wilson, B. Tapley, and C. Shum, Oceanic mass variation from satellite altimetry and geodynamical applications, Proc. 4th Pacific Ocean Remote Sensing Conference, Qingdao, China, July, 1998 (Invited).
ABSTRACT
Mass redistribution and movement within the Earth system, including the atmosphere, ocean, and hydrosphere, and solid earth, are the fundamental driving forces to the observed variable rotation, geocenter motion, and gravitational field variation. We investigate mass variations within the oceans using over 5 years’ TOPEX/POSEIDON satellite altimetry data and a steric sea level change model based on the NOAA World Ocean Atlas 1994 and NMC Optimum Interpolation SST data. The potential oceanic contributions to earth rotation, geocenter motion, and gravitational field variation are computed from TOPEX/POSEIDON sea level anomalies after the steric sea surface height changes are removed. The results show that oceanic mass variation provide significant contributions to most geodetic variables, especially geocenter motion in the X direction, polar motion, and length-of-day variation. The broad band of good agreements between TOPEX/POSEIDON observations and space geodetic measurements is an indication that mass variations within the ocean exist at various time scales and are detectable from modern space geodetic measurements.
Shum, C., J. Ries, B. Tapley, T. Urban, and J. Chen, Observing long-term mean sea level variations using satellite altimetry, Proc. Western Pacific Geophysics Meeting AGU, (Invited), July, 1998.
ABSTRACT
Recent studies of global sea level change based on long-term coastal tide gauge data (e.g., IPCC studies) have concluded that the global eustatic rate of sea level rise during the last century has been 1-3 mm/yr and that the sea level by the year 2070 A.D. may be 20-70 cm higher than today. The ability to measure and to monitor global sea level variations and its potential link to the global warming phenomena is of scientific and social-economical importance. The use of tide gauges to monitor mean sea level variations has the distinct advantage that many tide gauges have over 100 years of records. However, tide gauges have problems of being affected by crustal motions and with inconsistent vertical datums, and they only cover less than 1% of the ocean surface. The use of accurate altimeter measurements from TOPEX/POSEIDON (T/P) has demonstrated its potential to monitor the global sea level with an accuracy approaching 1 mm/yr, provided that instrument and media correction errors can be properly characterized and validated. Altimeter systems, however, have only a short history of data collection . In this study, we report our progress using altimeter data from multiple missions (Seasat, Geosat, ERS-1, and T/P) for the monitoring of the mean sea level variations. Techniques have been developed to provide links of present and historic altimetric measurement systems and to determine the present-day global mean sea level variations. In particular, the determined relative instruments biases between T/P and other systems are –55.0 +/- 19 cm for Geos-3, 34.2 +/- 2.8 cm for Seasat, and 12.1 +/- 1.5 cm for Geosat. The observed global mean sea level change over a decade (1986-1996) has been observed to be approximately 1 +/- 2 mm/yr. Because of the long data span used, the estimated uncertainty has not been affected by some of the uncovered instrument errors, such as the potential drift of the TOPEX Microwave Radiometer. The observed sea level change is primarily due to thermal expansion of the ocean, and will be validated using computed steric sea level change using spaceborne and in situ sea surface temperature data.
Jekeli, C., New Measurement Concepts for Determining Earth’s Gravity Vector Field, Presented to NIMA at Ohio State University Project Review Meeting, July 1998.
Jekeli, C., Overview of Geodesy Research at OSU. Presented to NIMA at Ohio State University Project Review Meeting, July 1998.
Jekeli, C., and C. Shum, Local gravity field determination using GPS intersatellite velocities and accelerations, Proc. Western Pacific Geophysics Meeting AGU, Taipei, Taiwan, July, 1998.
ABSTRACT
With at least two multiple-satellite, geophysical missions planned for the next five years, where each satellite is equipped with a high quality GPS receiver, the question arises as to the potential for local gravity field model improvement using GPS-determined intersatellite velocities and accelerations. One such mission, GRACE, specifically addresses gravity recovery using dedicated K-band range-rates between two low, polar co-orbiting satellites. Another mission, COSMIC, comprising up to eight satellites, is geared mostly to atmospheric sounding using GPS occultations. Local gravity determination requires strong local support from the system measurements. It is known that horizontal derivatives of the gravitational potential, as might be inferred from intersatellite range-rates, are only weakly correlated locally with the potential. On the other hand, three-dimensional relative velocities of the satellites directly provide the in situ potential difference. Thus satellite GPS is ideally suited, in principle, for local gravity field determination (provided also that non-conservative forces are accounted for, as they are on GRACE). This study investigates the possibilities for improving the local gravity field in consideration of the GPS error budget and other proposed satellite techniques and existing knowledge of the field. The results are based on simulations and show that improvement is possible, especially in polar regions.
Chao, B., C. Hwang, C. Liu, E. Pavlis, C. Shum, C. Tseng, and M. Yang, Global geodetic applications of ROCSAT-3/COSMIC, Proc. Western Pacific Geophysics Meeting AGU, Taipei, Taiwan, July, 1998.
ABSTRACT
The joint Taiwan-U.S. space mission of ROCSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) is to launch in 2001 with a constellation of 6-8 low-earth orbiting satellites to conduct atmospheric limb sounding using the GPS radio occultation technique. Although not the primary scientific objective, it is envisioned that the initial orbit at 400 km altitude with the satellites in tandem will provide a unique opportunity to enable gravity science studies and precision orbit determination experiments. Our simulations show that, depending on the orbit adjusting scenario, the use of these orbit data can yield at least an order of magnitude improvement over the state-of-the-art global gravity model EGM96 out to degree and order 20-40 (spatial resolution of 1000-500 km). Such improvements are useful for the preparation of gravity mission such as GRACE and for current and future altimetry missions. Additionally, useful signals of low-degree temporal variations can be obtained if non-conservative forces prove inconsequential for ROCSAT-3/COSMIC at its final altitude of above 700 km. Other geodetic benefits that can be expected from ROCSAT-3/COSMIC include: (1) Simultaneous solution of the ROCSAT-3/COSMIC and the GPS satellite orbits will improve the GPS orbits, which are essential to all GPS applications. A factor of two improvement can be expected in the GPS satellite orbit accuracy currently at 5-10 cm. (2) Improved estimation of the global surface pressure fields using ROCSAT-3/COSMIC data will be useful for geodynamic and altimetric studies, such as Earth rotation, geocenter, time-varying gravity, and ocean circulation studies. (3) The proposed satellite laser ranging as a secondary tracking system for ROCSAT-3/COSMIC will help establish local datum ties to the conventional terrestrial reference system.
Scherer, W., C. Huang, and C. Shum, Asian-Pacific Space Geodynamics Project sea level research, GLOSS Regional Sea Level Meeting, Taipei, Taiwan, July, 1998.
Iz, H. Baki, and C. Shum, Sea level and GPS projects in Hong Kong and East China Sea, GLOSS Regional Sea Level Meeting, Taipei, Taiwan, July, 1998.
Parke, M., C. Shum, R. Gutierrez, B. Schutz, J. Alvarez, D. Kubitschek, G. Born, F. Kelly, and J. Blaha, Toward regional monitoring of sea level using DGPS buoys, Proc. Western Pacific Geophysics Meeting AGU, Taipei, Taiwan, July, 1998.
ABSTRACT
Precision DGPS buoys have many potential roles in measuring and monitoring of regional sea level. They can densify altimetric measurements for fine scale regional studies. In particular, DGPS measurements have the potential to map sea level variations in the 2-10 day period range which is of great interest to coastal oceanography. They can be used to calibrate altimetric measurements at any ocean location that can be reasonably reached and maintained around the globe. Other potential applications include the practical linking of traditional tide gauges to a well-established geocentric terrestrial reference frame using DGPS. This presentation discusses results of a cruise experiment in the Gulf of Mexico using GPS-buoys to study kinematic positioning issues such as baseline length and optimal instrument design. This paper will also discuss future roles that DGPS buoys might play in the Western Pacific and the issues that need to be resolved before DGPS can play a significant role in oceanographic measurements.
Chen, J., C. Wilson, C. Shum, and B. Tapley, Geodyamical applications of TOPEX/POSEIDON sea level Measurements, Proc. Western Pacific Geophysics Meeting AGU, July, 1998.
Nuth, V., C. Wilson, G. Kruizinga, C. Shum, and B. Tapley, Detecting changes of ice sheet thickness from radar altimeter waveforms, Proc. Western Pacific Geophysics Meeting Program, July, 1998.
ABSTRACT
The high variability of the ice surface prevents the on-board tracker of a satellite radar altimeter from accurately measuring the arrival time of the radar pulse, which in turn degrades the range measurements. Furthermore, if the change in surface topography is faster than the response time of the tracking algorithm, no range is recorded. Accordingly, we must revert to using the recorded waveforms to measure apparent changes in ice sheet elevation over time. Even if this approach is successful, apparent ice sheet elevation may include contributions from changing surface properties, in addition to ice sheet volume change. We use cross-correlation of waveform pairs at the satellite cross-over point as a means to estimate the time delay or lag due to changes in surface elevation. This approach recovers only changes over time, but the advantage is that we do not need a waveform model function in order to estimate the correction to the arrival time. An example using ERS-1 waveform data from a region of Antarctic Ice Sheet is presented.
Parke, M., C. Shum, K. Cheng, H. Tseng, P. Abusali, T. Urban, K. Key, J. Bodi, J. Ries, and J. Lillibridge, Prelimary verification of GFO sea surface height measurements, GFO Mission Data Validation Meeting, Penn State University, July, 1998.
Shum, C., J. Famiglietti, M. Rodell, and J. Wahr, Possible detection of hyrological mass variations using GRACE, APSG 2nd Workshop, Tahiti, May, 1998.
Shum, C., Absolute calibration of multiple radar altimeters: Scientific justification and plan, Envisat Absolute Calibration Workshop, Barcelona, Spain, March, 1998.
ABSTRACT
The proposed talk will cover NASA's complementary absolute calibration site (Harvest is the main site) in the Gulf of Mexico, primarily for calibration and monitoring of Jason-1 radar altimeter. Experience in the use of GPS-buoy will be one of the topics to be discussed, along with plans to coordinate with the existing and planned calibration sites. A status report will be provided for the Gulf of Mexico site with the potential contribution to the instrument calibration and monitoring for Envisat.
Jekeli, C., Gravimetry Using GPS satellite-to-satellite Tracking,” prepared for GRACE Science Team Meeting, Center for Space Research, University of Texas, Austin, Texas, March, 1998.
Jekeli, C., Continuous aircraft positioning using Global Positioning System aided by Inertial Navigation System. Final report, contract No.8403, OSURF project 732280, Ohio Department of Transportation, 1998.
Jekeli, C., On the differences between vertical deflections from spherical harmonic models and Helmert deflections. Submitted to Section IV Bulletin, General Theory and Methodology, International Association of Geodesy, 1998.
Jekeli, C., Error analysis of padding schemes for DFT’s of convolutions and derivatives. Report in press, Department of Civil and Environmental Engineering and Geodetic Science, Ohio State University, 1998.
Jekeli, C., Algorithms and preliminary experiences with the LN93 and LN100 for airborne vector gravimetry. final report, prepared under Contract F19628-95-K-0020, USAF Phillips Laboratory, 1998.
Shum, C., and C. Jekeli, Contribution of COSMIC mission to geodesy and geodynamics, COSMIC Worshop, Taipei, Taiwan, February, 1998.
Shum, C., Determination of Earth's static and time-varying gravity field, National Astronomical Observatory, Mizusawa, Japan, February, 1998.
Shum, C., Understanding Earth's system dynamics using satellite geodesy, Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan, February, 1998.
Shum, C., Precision orbit determination for ERS-1/-2 for InSAR applications, Civil and Environmental Engineering and Geodetic Science/Byrd Polar Research Center Joint Seminar, Ohio State University, February, 1998.
Shum, C., Understanding Earth system dynamics using satellite geodesy, Civil and Environmental Engineering and Geodetic Science/Byrd Polar Research Center Joint Seminar, Ohio State University, January, 1998.
Rapp, D., The development of a degree 360 expansion of the dynamic ocean topography of the POCM-4M global circulation model, NASA/CR-1998-206877, NAS5-32352, GSFC, Greenbelt, MD, 1998.
Rapp, D., The development of the joint NASA GSFC and the National Imagery and Mapping Agency (NIMA) geopotenteal model EGM96, co-author with F. Lemoine et at., NASA/TP-1998-206861, GSFC, Greenbelt, MD, 1998.
Shum, C., and M. Parke, Scientific requirements for a GPS sea level instrument for radar altimeter calibration, International Scientific Workshop on GPS-Buoy sea level measurement system design, ESA/ESTEC, The Netherlands, December, 1997.
Parke, M., and C. Shum, GPS-Buoy sea level measurement experiences at Harvest and Galveston Bay, Internation Scientific Workshop on GPS-Buoy sea level measurement system design at ESA/ESTEC, The Netherlands, December, 1997.
Shum, C., M. Guman, G. Kruizinga, J. Ries, and B. Tapley, Precision orbit determination and improved linkings for altimetric satellites: implications for establishing long-term geophysical time series, Fall meeting of AGU, San Francisco, December, 1997.
Raofi, B., C. Shum, B. Tapley, and C. Wilson, Ocean's response to atmospheric pressure loading: the inverted barometric approximation for altimetric measurements, Fall meeting of AGU, San Francisco, December, 1997.
Chen, J., C. Wilson, B. Chao, and C. Shum, Global hydrological angular momentum and Earth rotation, Fall meeting of AGU, San Francisco, December, 1997.
Jekeli, C., Gravity Gradiometry - Data acquisition systems and status, Gravity Gradiometry Workshop, Annual SEG Meeting, Dallas, Texas, November, 1997.
Jekeli, C., Gravity Gradiometry - Data acquisition systems and status, Seminar in Geodetic Science and Surveying, Ohio State University, November, 1997.
Shum, C., M. Guman, G. Kruizinga, B. Tapley, and T. Urban, Verification and linking of radar altimeter measurement systems for long-term sea level variation studies, TOPEX/POSEIDON Science Working Team Meeting, Biarritz, France, October, 1997.
Shum, C., Data Verification and improvement towards linking of altimetry system, Proc. TOPEX/POSEIDON Science Team Meeting, Biarritz, France, October, 1997.
Jekeli, C., The world of gravity according to Rapp. Presented at the IAG Scientific Assembly, Symposium 2: Gravity and the Geoid, Rio de Janeiro, Brazil, September, 1997.
Jekeli, C., The edge effect versus cyclic convolution errors in geodetic convolutions by DFT. Presented at the Scientific Assembly of the IAG, Symposium 2: Gravity and the Geoid, Rio de Janeiro, Brazil, September, 1997.
Tapley, B., D. Chambers, C. Shum, and J. Ries, Mean and time-varying long-wavelength topography from TOPEX/POSEIDON altimetry, 1997 Joint Assemblies IAMAS/IAPSO, Melbourne, Australia, July, 1997.
Jekeli, C., 3-D, free-inertial navigation and Earth’s gravity field, Internat’l Symp. on Kinematic Systems in Geodesy, Geomatics, and Navigation (KIS97), Banff, Canada, June, 1997.
Wang, J., F. Dwaik, C. Jekeli, INS, GPS and photogrammetry integration for vector gravimetry, Internat’l Symp. on Kinematic Systems in Geodesy, Geomatics, and Navigation (KIS97), Banff, Canada, June, 1997.
Urban, T., G. Kruizinga, C. Shum, M. Guman, T. Pekker, J. Ries, and B. Tapley, Comparison of wet tropospheric corrections for radar altimeters, Spring meeting of AGU, Baltimore, Maryland, May, 1997.
Chen, J., C. Shum, C. Wilson, and D. Chambers, Sea level variability from TOPEX/POSEIDON and its interpretation, Spring meeting of AGU, Baltimore, Maryland, May, 1997.
Nuth, V., C. Wilson, G. Kruizinga, and C. Shum, The use of satellite altimeter data in the coastal waters, EOS Trans. AGU, 78 (17), S104, Spring Meet. Suppl., May, 1997.
Urban, T., G. Kruizinga, C. Shum, M. Guman, T. Pekker, J. Ries and B. Tapley, Comparison of Wet Troposphere Corrections for Radar Altimeters, EOS Trans. Supplement, Vol. 78, No. 17, S102, April, 1997.
Shum, C., J. Ries, J. Bordi, J. Seago, B. Tapley, and T. Urban, ERS-1/-2 precision orbit determination and accuracy verification, Proc. Second ERS Symposium, Florence, Italy, March, 1997.
Tapley, B., C. Shum, M. Kim, and J. Ries, Geodetic and geodynamic contribution from ERS, Proc. Second ERS Symposium, Florence, Italy, March, 1997.