Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil. Observatório Nacional/MCTI, Rio de Janeiro, Brazil.
Gravity observations adjustment is studied having in view to take full advantage of the modern technology of gravity measurement. We present here results of a test performed with the mathematical model proposed by our group, on the adjustment of gravity observations carried out on network design. Additionally, considering the recent improvement on instrumental technology in gravimetry, that model was modified to take into account possible nonlinear local datum scale factors, in a 1900 mGal range network, and to check its significance for microgal precision measurements. The data set of the Brazilian Fundamental Gravity Network was used as case study. With about 1900 mGal gravity range and 11 control stations the Brazilian Fundamental Gravity Network (BFGN) was used as case study. It was established mainly with the use of LaCoste & Romberg, model G, gravimeters and new additional observations with Scintrex CG-5 gravimeters. The observables involved in the model are instrumental reading, calibration functions of the gravimeters used and the absolute gravity values at the control stations. Gravity values at the gravity stations and local datum scale factors for each gravimeter were determined by least square method. The results indicate good adaptation of the tested model to network adjustments. The gravity value in the IFE-172 control station, located in Santa Maria, had the largest estimated correction of ?10.4 μGal (1 μGal = 10 nm/s2), and the largest residual for an observed reading was estimated in 0.043 reading unit. The largest correction to the calibration functions was estimated in 6.9 × 10-6mGal/reading unit.
I. Escobar, F. Berquó and A. Papa, "Adjustment of Gravity Observations towards a Microgal Precision," International Journal of Geosciences, Vol. 4 No. 1, 2013, pp. 98-107. doi: 10.4236/ijg.2013.41010.
[1] F. J. S. S. Dias and I. P. Escobar, “A Model for Adjustment of Differential Gravity Measurements with Simul taneous Gravimeters Calibration,” Journal of Geodesy, Vol. 75, No. 2, 2001, pp. 151-156. doi:10.1007/s001900100168 [2] I. P. Escobar, “Rede Gravimétrica Fundamental Brasileira, uma Tradi??o de 10 anos no Observatório Nacional,” Revista Geofísica IPGH, Vol. 26, 1987. [3] W. Torge, L. Timmen, R. H. Roder and M. Schnull, “The IFE Absolute Gravity Program South America 1988 1991,” Deutsche Geodatische Kommission, Munchen, 1994. [4] I. P. Escobar, N. C. Sá, J. J. Dantas and F. J. S. S. Dias, “The Observatório Nacional Agulhas Negras Gravity Ca libration Line,” Brazilian Journal of Geophysics, Vol. 14, No. 1, 1996, pp. 59-68. [5] M. A. Sousa and A. A. Santos, “Absolute Gravimetry on the Agulhas Negras Calibration Line,” Revista Brasileira de Geofísica, Vol. 28, No. 2, 2010, pp. 165-174. doi:10.1590/S0102-261X2010000200002 [6] E. Parseliunas, P. Petroskevicius, R. Birvydiene and R. Obuchovski, “Investigation of the Automatic Gravimeters Scintrex CG-5 and Analysis of Gravimetric Measure ments,” The 8th International Conference, Vilnius, 19-20 May 2011. [7] T. Oja, T. Nikolenko, K. Türk, A. Ellmann and H. Jür genson, “Calibration Results of Different Type Spring Gravimeters from the Repeated Measurements of Estonian Calibration Line,” NKG General Assembly, 2010. [8] T. Oja, T. Nikolenko, K. Türk, A. Ellmann and H. Jürgenson, “Analysis of Gravimetric Observations Made by Scintrex CG-5,” The 7th International Conference, Vilnius, 22-23 May 2008. [9] I. M. Longman, “Formulas for Computing the Tide Ac celeration Due to the Moon and the Sun,” Journal of Geo physical Research, Vol. 64, No. 12, 1959, pp. 2351-2356. doi:10.1029/JZ064i012p02351 [10] LaCoste & Romberg, “Instruction Manual Model G&D Gravity Meters,” Austin, 2004. [11] C. H. Angus and B. G. Brulé, “Vibration-Induced Drift in LaCoste & Romberg Geodetic Gravimeters,” Journal of Geophysics Research, Vol. 72, No. 8, 1967, pp. 2187 2197. doi:10.1029/JZ072i008p02187 [12] V. D. Yushkin, “Operating Experience with CG5 Gravi meters,” Measurement Techniques, Vol. 54, No. 5, 2011, pp. 486-489. doi:10.1007/s11018-011-9753-5 [13] SCINTREX, “CG-5 Scintrex Autograv System Operation Manual,” Revision 7, Canada, 2010. [14] M. Lederer, “Accuracy of the Relative Gravity Measurement,” Acta Geodynamica et Geomaterialia, Vol. 6, No. 3, 2009, pp. 383-390. [15] F. J. S. S. Dias, “Um Modelo Matemático para Ajusta mento Gravimétrico com Aprimoramento das Fun??es de Calibra??o dos Gravímetros LaCoste & Romberg,” MSc. Thesis, Observatório Nacional, Rio de Janeiro, 1997. [16] I. P. Escobar “Injun??es Relativas em Ajustamento Gra vimétrico,” Publica??o do Observatório Nacional, MSc Thesis, UFPR, Curitiba, No. 2, 1998.