Study And Application Of Highprecision Normalized Full Gradient Of Gravity Anomaly Method

Normalized full gradient of gravity anomaly method is uses in the ground the actual high accuracy gravity anomaly value definite fate source distributed one method. Namely in the known ground's high accuracy gravity value, through the analytic continuation, the derivation, calculates in the xoz cross section in the different depth gravity horizontal derivative and the vertical derivative value, then extracts the gravity normalization total gradient value, and draws up the gravity normalization total gradient sectional drawing, definite field source position and distribution.The present paper take studies the gravity normalization total gradient the method, the technology as the main body goal, obtained the gravity normalization total gradient to the different method the effect to carry on system's contrastive analysis, proposed the high accuracy gravity normalization total gradient's method, took a seat the field downward continuation cosine spectrum repetitive process.1.Gravitational potential first derivative and analytic continuation research Through contrasts the Fourier transformation and DCT the transformation in the horizontal first derivative, the vertical first derivative, the upward continuation and the downward continuation contrastive analysis, obtains the following conclusion:①In the horizontal first derivative computation, the DCT transformation's biggest error in the survey line vertex, is only 0.003×10-9/s2, does not have the error in other measuring points; the fourier transformation's biggest error middle the survey line, reduces gradually toward the both sides, the biggest error for 0.032×10-9/s2, may see, the DCT transformation in the horizontal derivative conversion, the precision is bigger than the Fourier transformation by far. In vertical first derivative, both precision quite, DCT transformation biggest error for 0.104×10-9/s2, Fourier transformation biggest error for 0.109×10-9/s2. In the whole said that the DCT transformation the precision is bigger than the Fourier transformation far in derivative seeking, the precision is specially higher in the horizontal first derivative.②In the upward continuation computation, the DCT transformation and the Fourier transformation's precision quite, the DCT transformation's biggest error is 0.104 10-6m/s2, the Fourier transformation biggest error is: 0.105 10-6m/s2; In downward continuation computation, because on both extends the factor is the improperly posed factor, the stability is bad, works as when extends working hours is apart from is slightly big, can present the higher mode of oscillation phenomenon, this kind of shake when a distance is big submerged the wanted signal completely. When joins the smooth factor, the Fourier transformation caused the oscillation amplitude to decrease, the DCT transformation's effect had the good improvement, but under extended the depth to continue to increase, still will present the higher mode of oscillation, namely under extended the depth to be still limited, but the relative Fourier transformation, not only the complete retention primary signal, moreover expanded under extended the depth..③The upward continuation is in position field processing one commonly used method, not only may use for the noise elimination, moreover may carry on the field the separation. Works as extends one suitably highly (not suitable oversized, generally 1~2 spot distances, after high accuracy available half spot distance), the neighboring random disturbance superimposes mutually, counter-balances mutually; Works as extends appropriately to one (this article uses between neighboring high analytic continuation value correlation coefficient selection on best to extend highly highly), on extends the value to be possible to take the region field approximately the unusual value, subtracts on this with the ground in gravity anomaly value to extend the value, obtains the local field unusual value, thus achieves the separation field the function.④In the potential field data processing explanation, the potential field data downward continuation operation is many potential field data processing and in the inversion method technology core operation, but the position field downward continuation is different with the position field upward continuation, it is a typical improperly posed problem, main performance for computation instability. Xu Shizhe proposed the integral repetitive process can solve the position field downward continuation unstable problem well. This article based on this, inferred based on the DCT transformation downward continuation repetitive process, has confirmed this method usability and the computational method accuracy through the model experiment. Contrasts the Fourier transformation and the DCT transformation downward continuation, the large scale expansion under extended the depth.2. With the second degree of vertical cylinders slivers overlay gravity anomalies for second degree in uniform, non-uniform Anticline model calculation of gravity anomaliesThe inhomogeneous anticline model gravity anomaly computation this article to propose one kind calculated two degree body weight strength unusual high accuracy computational method, namely the linear element law, any two degrees bodies might cut the geologic body along x axis direction (model body), then regarded as separately each thin slice two degree body normal barrel thin slice, calculated the gravity anomaly value, then obtained all thin slice's gravity anomaly value superimposition two degree geologic body gravity anomaly values. This article used this method to realize two degrees bodies evenly, the inhomogeneous anticline model gravity anomaly the computation, took the error analysis through the choice even density's infinite length horizontal cylinder the contrast object, the error analysis result indicates this method the feasibility and the computed result reliability.3. Adopts the Panel method implementation three-dimensional uniform, non-uniform spherical model calculation of gravity anomaliesThe inhomogeneous spherical crown model gravity anomaly computation the computation spherical crown model gravity anomaly, the spherical crown along the horizontal direction cuts certain uniform thickness thin slice, regards as a vertical cylinder approximately each thin slice, uses each circular cylinder the gravity anomaly the superimposition to calculate the spherical crown model the gravity anomaly. Vertical cylinder's gravity anomaly expression is very complex, the inconvenient direct use, this article uses the integral approximate method to replace the integral, calculated the vertical cylinder gravity anomaly the approximate expression. Carries on the error analysis through the choice even density spheroid as the erroneous contrast's object, indicated that this method the computation meets the high accuracy requirement without the error, has confirmed this method accuracy and the result reliability.4. Evaluating the gravity of the normalized full gradient anomaly method At present seeks the gravity normalization total gradient computational method to include: Fourier's series law, Fourier method of transformation, DCT law. Because in the observed gravity value has the random error and the superficial part disturbance, can obtain the varying degree enlargement in the downward continuation and the derivative conversion, simultaneously the survey line vertex causes the GH field to appear false interrupted exceptionally, therefore has joined the smooth factor separately in the derivative conversion and the downward continuation factor, and calls it the computation gravity normalization total gradient"the combination filtering".①Introduces in the Fourier's series"the combination filtering", obtains the gravity normalization total gradient with"the synthesis filtering"the relativity, confirmed this method obtained the GH field to reduce to the overtone number dependence, had the good stability.②In view of the fact that the above three method's downward continuation factor has the instability and the integral repetitive process in the downward continuation good results, myself proposed one new seeking gravity normalization total gradient's computational method, takes a seat the field downward continuation cosine spectrum repetitive process. Has studied this method GH field characteristic, the overtone number and the burying depth relations through the model experiment.③The different method computation two degree body anticline model's gravity normalization total gradient field's characteristic is similar, in the even density's anticline model, GH the field displays a single maximum value characteristic, this extreme point position approximately with model body's center of mass superposition; In the inhomogeneous density's anticline model, the GH field displays"two Gao Jia one lowly"the typical oil storage characteristic. Even, the inhomogeneous three degree body spherical crown model's GH field and two degree body anticline model is similar.④Four computation gravity normalization total gradient's method through the model experiment contrastive analysis, must go too far the field downward continuation cosine spectrum repetitive process mainly to have 3 merits: (1) The best overtone counts N the value to be possible to be in some section of scope number, the GH field maximum value counts N to the overtone the dependence to be weak, namely this method obtains the GH field to have the stability; (2) Extends when the survey line vertex the depth is big not assumes exceptionally appears, explained this method when downward continuation the boundary does not have the vibration or the vibration is small; (3) Regardless of being superimposes the region field to superimpose the geologic body, the GH field can reflect that the superficial part geologic body the information, a GH maximum value position and the geologic body center of mass tally.The gravity normalization total gradient method is one kind of solution gravity anomaly the inversion method. In recent years was getting more and more thorough about the normalized total gradient method's research, the computational method were many and varied. This mainly benefits in the normalized total gradient method computation does not need the supplemental condition, the application is quite simple, and can semi-definite measure land the determination geologic body position, therefore widely uses in studying the oil gas structure or carrying on the oil gas examination. Therefore the research high accuracy's gravity normalization total gradient's computational method has the significant practical significance and the big social economy benefit.