Luo Zhicai

Trend of mass change in the Antarctic ice sheet recovered from the GRACE temporal gravity field

It is important to quantify mass variations in the Antarctic ice sheet to study the global sea-level rise and climate change. A hybrid filtering scheme employing a combination of the decorrelated filter P3M6 and 300 km Fan filter was used, and the surface mass variations over the Antarctic are recovered from GRACE CSR RL04 monthly gravity field models from August 2002 to June 2010. After deduction of leakage errors using the GLDAS hydrological model and postglacial rebound effects using the glacial isostatic adjustment model IJ05, the variations in the ice sheet mass are obtained. The results reveal that the rate of melting of the Antarctic ice sheet is 80.0 Gt/a and increasing and contributes 0.22 mm/a to the global sea-level rise; the mass loss rate is 78.3 Gt/a in the West Antarctic and 1.6 Gt/a in the East Antarctic. The average mass loss rate increases from 39.3 Gt/a for the period 2002–2005 to 104.2 Gt/a for the period 2006–2010, and its corresponding contribution to the global sea-level rise increases from 0.11 to 0.29 mm/a, which indicates accelerated ice mass loss over the Antarctic since 2006. Moreover, the mass accumulation rates for Enderby Land and Wilkes Land along the coast of East Antarctica decrease for the period 2006–2008 but increase evidently after 2009.

Accuracy analysis for SST gravity field model in China

Taking China as the region for test the potential of the new satellite gravity technique, satelliteto-satellite tracking for improving the accuracy of regional gravity field model is studied. With WDM94 as reference, the gravity anomaly residuals of three models, the latest two GRACE global gravity field model (EIGEN_GRACE02S, GGM02S) and EGM96, are computed and compared. The causes for the differences among the residuals of the three models are discussed. The comparison between the residuals shows that in the selected region, EIGEN_GRACE02S or GGM02S is better than EGM96 in lower degree part (less than 110 degree). Additionally, through the analysis of the model gravity anomaly residuals, it is found that some systematic errors with periodical properties exist in the higher degree part of EIGEN and GGM models, the results can also be taken as references in the validation of the SST gravity data.

Spectral Representation and Analysis of the KBR Precision Based on the Earth Gravity Spectrum

Satellite-to-Satellite Tracking in low-low model (SST-ll) is a new technique to resolve the series of problems met in the determination of the earths gravity field. As the key technique of SST-ll, KBR can get SST-ll measurements directly. So the KBR performance analysis is the first step in SST-ll design. In this paper, assuming that the satellite pairs of SST-ll are in near circle polar orbits, the spectrum relationship between the earth gravity field and KBR is established using analytic method. And then some examples are analyzed, the suggestions and conclusions are drawn from these examples. The research results could be taken as a reference for future satellite gravity project of China.

A NEW MODELLING METHOD FOR EVALUATING EXTERNAL DISTURBING POTENTIAL BASED ON THEORY OF UNIFIED REPRESENTATION OF GRAVITATIONAL FIELD

For a special use a new modelling method of evaluating external disturbing potential is presented in this paper. Being different from classical methods in physical geodesy this method is grounded upon the theory of unified representation of gravitational field. The models created in this way are particularly satisfactory for a high-speed computation of gravitational field in low altitude because they take account of topographic effects and have their kernel functions with simple structure and weak singularity.

Monitoring the dynamic characteristics of tall buildings by GPS technique

Dynamic characteristics of large structures, such as tall buildings, longspan suspension, cable-stayed bridges and tall chimneys, are key to assess their drift and stress conditions. The dynamic characteristics of large structures are difficult to measure directly under the condition of earthquakes or strong winds using traditional techniques such as laser collimator, total station and accelerometers. Therefore there is a great need for developing new method or technique for this purpose. Recent advances in Global Positioning System (GPS) technology provide a great opportunity to monitor long-period changes of structures reliably. GPS receivers capable to gauge the motion at the centimeter or sub-centimeter level with sampling frequency 10Hz or even 20 Hz are now available from several manufacturers. To the authors’ knowledge, the capability of identifying dynamic characteristics from GPS observations has not been widely verified. For the feasibility study on using kinematic GPS technology to identify the dynamic characteristics of tall buildings, some experiments were conducted in a simulative environment. This paper discusses in detail the experiment device, and the ways through them GPS data are recorded, processed and analyzed. With post-processing version of NovAtel’s Softsurv software and auto-regressive (AR) spectral analysis method, relative displacements and corresponding vibrating frequencies have been derived from GPS observations. The results indicate that the dynamic characteristics can be identified accurately by kinematic GPS technology.