基于MATLAB实现的用于应用布格重力异常数据反演地下异常密度体+使用说明文档.zip

U S E R M A N U A L "G R O W T H 2.0" A 3-D gravity inversion tool based on exploration of model possibilities by Antonio G. Camacho Instituto de Astronomia y Geodesia (CSIC-UCM) Facultad de CC. Matematicas Ciudad Universitaria, 28040 Madrid (Spain) e-mail: antonio_camacho@mat.ucm.es 1. INTRODUCTION This computational tool carries out a 3-D inversion of gravity data. Characteristics of the method are the following: (1) solution for 3-D model space, (2) acceptance of non-gridded non-planar low-precision imprecise data, (3) calculation can start for an empty body or optionally from for an initial “seed” structure, (4) automatic determination of a linear regional gravity trend from the data, (5) simultaneous inversion for both positive and negative density contrasts, (6) inversion for irregularly-shaped structures composed of several individual bodies, (7) inversion accounting for a optional downward density increase, (8) semi-automated data inversion routine. The package is composed of three parts: (a) “GRID3D” to generate a 3D partition of the subsurface volume into parallelepiped elements, (b) “GROWTH” to perform the inversion routine and to obtain a 3D anomalous density model, and (c) “VIEW” for visual representation of the input data, the inversion model and modelling residuals. The current version of the tool has been developed from an earlier code [1] and now incorporates several novelties [2]: (1) a Graphical User Interface (GUI), (2) an optional automated routine for determination of parameter ?, which controls the balance between model fitness and smoothness, (3) optional determination of values for minimum density contrast, (4) a robust handling of outlier data, and (5) improved automated data reduction for terrain effects based on anti-correlation with topographic data. The main input is a file "GRA.DAT" containing the coordinates of the gravity stations and the observed anomaly (see #2.2). The method (see [1]) seeks to determine the geometry of an indefinite number of anomalous bodies with prescribed (fixed or variable, positive and/or negative) density contrasts. A 3-D grid of regular cells is taken to represent the subsurface volume. Then, the inversion method fills some of these cells, with the possible density contrast, to reproduce the anomalous structures. This software is composed of three Fortran 77 codes: GRID3D.FOR, GROWTH.FOR and VIEW.FOR. The first is a preliminary program to define the geometry of the 3-D grid and the values of several parameters. The second is the main inversion program. Finally, VIEW.FOR provide graphics representation of the obtained models. The suggested application process is to start with low resolution models (large cells, ramdon exploration) which permits a fast test of the suitable values for the inversion parameters (lambda value, density contrasts, smoothing, etc.). After that, a high resolution model, with systematic exploration approach, can be obtained as the final result and displayed by means of the graphics program. 2. PROGRAM "GRID3D.FOR": Parameters of the Growth gravity inversion. 2.1. AIM: to create an ASCII file (PRI.DAT), containing a 3-D grid of the subsurface volume and values for several parameters, that will be used in the program GROWTH.FOR of 3-D gravity inversion 2.2. INPUTS. 2.2.1. Input files: -> file "GRA.DAT": The basic input ASCII file, named "GRA.DAT" (as default), contains a line corresponding to each gravity benchmark with the following values: x-coordinate (m), y-coordinate (m), altitude (m) (throughout the software package, elevation and depth values are positive above sea level and negative below sea level, respectively), gravity anomaly (uGal) (1 uGal=10-8 m/s2). Two additional columns are included: a gravity error estimate (uGal)for each anomaly value, and the value for terrain correction (uGal) corresponding to unit density (1 kg/m3). Values for error estimation will be employed and propagated only optionally for initial relative weighting of the data. Values for terrain correction will be employed only optionally for re-estimation of a value for terrain density . Both complementary values could be filled with arbitrary numbers and neglected in the process. The end of data will be the last line or can be indicated by a line of “zeros”. example: 340088. 3124256. 2175.71 265997. 20. 6100. 340142. 3123662. 2156.86 267454. 20. 5870. 340177. 3123096. 2143.85 269611. 20. 5912. 340254. 3122723. 2121.40 271007. 20. 5990. 340420. 3122348. 2102.92 271329. 20. 6605. ................................................ 346003. 3101773. 15.00 203420. 100. 727. 0 0 0 0 0 0 -> optionally, ASCII file "MOD.DAT": previous model, according to the model format (see format of GRI.DAT in the Output),as produced previously by the GROWTH gravity inversion. 2.2.2. Values for several parameters in a dialog form through the Graphical User Interface (GUI): First step (left hand pane): names of the input and output files (default values are provided). Paths can be used. It is necessary to press “Run/OK” at the end of each step. Second step (right hand pane): geometrical parameters (default values are provided). - Maximum depth (m) or the model bottom. Negative values below sea level as usual. - Mean length (m) for the side of the parallelepiped cells. Shallow cells will have smaller length and deep cells will have larger length. - Seed with a previous model. Checking this box will base the partitioning routine on results from a previous model (default name “MOD.DAT”). In doing so, only cells previously filled with an anomalous density contrast and those in their close proximity are propagated. This procedure is computationally less demanding than partitioning of the entire subsurface volume. Third step (bottom): repetition. If the resulting number m of cells is too high (>80,000 in this version) the check box “Re-run” allows for a new calculation. Upon clicking “Run”, the resultant 3D cell partition model is saved by default in the file “GRI.DAT”. 2.3. OUTPUT -> File "PRI.DAT": 3-D grid of the subsurface volume and values for several parameters to be used in the program GROWTH.FOR of gravity inversion. The general format of this ASCII file (and of the model file MOD.DAT) is: nc,fe,xm,ym,zm, side, step, cod, grad x(1),y(1),tx(1),ty(1),zt(1),zb(1),d(1) x(2),y(2),tx(2),ty(2),zt(2),zb(2),d(2) .......................................... x(nc),y(nc),tx(nc),ty(nc),zt(nc),zb(nc),d(nc) where: nc: total number of cells (parallelepiped) of the model fe: scale factor applied for the model coordinates (to store cell parameters into an integer format). xm,ym: mean planar coordinates (in metres) for the survey area. zm: mean altitude (im metres) for the survey area. side: adopted mean side (in metres) for the cells in the 3D partition step: distance (in metres) for step in the further correlation analysis. cod: 0 - if there is not