In this paper we present a series of monthly gravity field solutions from Gravity Recovery and Climate Experiment(GRACE) range measurements using modified short arc approach,in which the ambiguity of range measurements is eliminated via differentiating two adjacent range measurements.The data used for developing our monthly gravity field model are same as Tongji-GRACEOl model except that the range measurements are used to replace the range rate measurements,and our model is truncated to degree and order 60,spanning Jan.2004 to Dec.2010 also same as Tongji-GRACE01 model.Based on the comparison results of the C_(2,0),C_(2,1),S_(2,1),and C_(15,15),S_(15,15),time series and the global mass change signals as well as the mass change time series in Amazon area of our model with those of Tongji-GRACE01 model,we can conclude that our monthly gravity field model is comparable with Tongji-GRACE01 monthly model.
The seven co-located sites of the Crustal Movement Observation Network of China(CMONOC) in Shanghai, Wuhan, Kunming, Beijing, Xi'an, Changchun, and Urumqi are equipped with Global Navigation Satellite System(GNSS), very long baseline interferometry(VLBI), and satellite laser ranging(SLR) equipment. Co-location surveying of these sites was performed in 2012 and the accuracies of the solved tie vectors are approximately 5 mm.This paper proposes a mathematical model that handles the least squares adjustment of the 3D control network and calculates the tie vectors in one step, using all the available constraints in the adjustment. Using the new mathematical model, local tie vectors can be more precisely determined and their covariance more reasonably estimated.
The Antarctic ice sheet is the largest block of ice on Earth,a tiny change of its ice sheet will have a significant impact on sea level change,so it plays an important role in global climate change. The Gravity Recovery and Climate Experiment( GRACE) mission,launched in 2002,provides an alternative method to monitor the Antarctic ice mass variation. The latest Release Level 05( RL05) version of GRACE time-variable gravity( TVG) data,derived from GRACE observations with improved quality and time-span over 10 years,were released by three GRACE data centers( CSR,JPL and GFZ) in April 2012,which gives us a chance to re-estimate the ice mass change over Antarctic more accurately. In this paper,we examine ice mass changes in regional scale,including Antarctic Peninsula( AP,West Antarctica),Amundsen Sea Embayment( ASE,West Antarctica),Lambert-Amery System( LAS,East Antarctica) and 27 drainage basins based on three data sets.The AP mass change rates are- 12. 03 ± 0. 74 Gt / a( CSR,2004- 2012),- 13. 92 ± 2. 33 Gt / a( JPL,2004- 2012),- 12. 28 ± 0. 76 Gt / a( GFZ,2005- 2012),with an acceleration of- 1. 50 ± 0. 25 Gt / a2,-1. 54 ± 0. 26 Gt / a2,- 0. 46 ± 0. 28 Gt/a2 respectively,the ASE mass change rates are- 89. 22 ± 1. 93 Gt / a,- 86. 28 ± 2. 20 Gt / a,- 83. 67 ± 1. 76 Gt / a with an acceleration of- 10. 03 ± 0. 65 Gt / a2,- 8. 74 ± 0. 74 Gt / a2and- 5. 69 ± 0. 68 Gt / a2,and the LAS mass change rates are- 4. 31 ± 1. 95 Gt/a,- 7. 29 ± 2. 84 Gt/a,1. 20 ± 1. 35 Gt / a with an acceleration of- 0. 18 ± 0. 62 Gt / a2,3. 55 ± 0. 95 Gt/a2 and 0. 97 ± 0. 49 Gt /a2. The mass change rates derived from the three RL05 data are very close to each other both in AP and ASE with the uncertainties much smaller than the change rates,and mass losses are significantly accelerated since2007 in AP and 2006 in ASE,respectively. However,the mass change rates are significantly different in LAS,negative rate from CSR and JPL data,but positive rate from GFZ data,the uncertainties are even larger than the correspondent change rates
