Iterative fast equivalent-layer technique INTRODUCTION The equivalent layer technique (Dampney, 1969) has been used for: 1) interpolating and gridding data, 2) computing the upward (or downward) continuation of data, 3) computing the reduction to the pole of magnetic data, 4) merging multiple datasets and, 5) jointly processing multiple components of airborne gravity gradient data. The classical equivalent layer technique consists in constructing a linear system of equations and solving a linear inverse problem to estimate a set of coefficients describing a discrete layer of equivalent sources. Usually, the equivalent layer technique deals with intractable large-scaled matrix computations for processing large data sets. This obstacle propels the development of computational strategies to make the equivalent layer technique computationally efficient. APPLICATION TO REAL DATA BACKGROUND AND NEW INSIGHTS The Dirichlet integral, that is also called upward continuation integral (Henderson, 1970) is defined as: CONCLUSIONS • A new fast iterative equivalent-layer technique for processing gravity data grounded on excess mass constraint. • Iteratively, our approach estimates the mass distribution that fits the gravity data within the measurement errors. • The initial approximation to a mass distribution is proportional to the gravity observation • Iteratively, we estimate a mass distribution correction that is proportional to the residual gravity data. • This mass distribution correction is the excess mass constraint. • The algorithm has low processing time and computer memory usage AIM Faced with the demand for fast and computationally efficient equivalent layer method able to handle with large datasets, we have developed a new iterative equivalent layer technique that do not solve linear systems. We validate our method using synthetic and real data. For full details of the proposed method please read Siqueira et al. (2017). ACKNOWLEDGEMENTS This research is supported by the Brazilian agencies CNPq (307135/2014-4) and FAPERJ (E-26/203. 091/2016) and CAPES. The authors thank Bell Geospace Inc. for permission to use the real data. REFERENCES Dampney, C. N. G. [1969] The equivalent source technique. Geophysics, 34, 39–53. Henderson, R. G. [1970] On the validity of the use of the upward continuation integral for total magnetic intensity data. Geophysics, 35, 916–919. Grant, F. and G. West [1965] Interpretation theory in applied geophysics: McGraw-Hill. Oliveira Jr, V.C. and Barbosa, V.C.F. [2013] 3-D radial gravity gradient inversion. Geophysical Journal International, 195, 883–902. Siqueira, F.C.L., Oliveira Jr, V.C. and Barbosa, V.C.F. [2017] Fast iterative equivalent-layer technique for gravity data processing: A method grounded on excess mass constraint. Geophysics, 82, G57–G69. Uieda, L., Oliveira Jr, V. C. and Barbosa, V. C. F. [2013] Modeling the Earth with Fatiando a Terra. Proceedings of the 12th Python in Science Conference, 91–98. CONTACT INFORMATION valcris@on.br – OBSERVATÓRIO NACIONAL, RIO DE JANEIRO, BRAZIL FILLIPE C. L. SIQUEIRA1, VANDERLEI C. OLIVEIRA JR1 and VALERIA C. F. BARBOSA1 1 Observatório Nacional, Rio Janeiro, Brazil                               d d z z y x z z g o i i i o i 1 ) , , g( 2 1 2 / 1 2 2 2 N Potential-field observations can be exactly reproduced by a continuous and infinite 2D physical-property distribution Potential-field observations produced by a 3D physical-property distribution Equivalent-layer principle y x E Depth z 2D physical-property distribution • This 2D physical-property distribution is approximated by a finite set of equivalent sources arrayed in a layer with finite horizontal dimensions and located below the observation surface. We assume that the set of equivalent sources are distributed in a regular grid with a constant depth zo forming an equivalent layer y x N E z Depth Layer of equivalent sources Equivalent sources (e.g., point masses) zo where gi ≡