CN110646858A - Submarine gravity measurement middle-far one-region terrain correction calculation method - Google Patents
Submarine gravity measurement middle-far one-region terrain correction calculation method Download PDFInfo
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Abstract
The invention relates to a middle area-far area terrain correction calculation method in submarine gravity measurement, belonging to the gravity measurement field, the method comprises establishing a submarine terrain node network, selecting four nearest nodes of a submarine gravity measuring point in the submarine terrain node network, calculating the terrain correction value of each node by using a correction calculation formula, and interpolating to the gravity measuring point position by a bilinear interpolation method in direction X, Y to be used as the terrain correction value of the gravity measuring point, aiming at the characteristics of submarine gravity measurement, fully considering the influence of seawater gravity on gravity measurement, providing a submarine gravity terrain correction calculation method for correcting the influence of seawater gravity, deducing a middle area-far area terrain correction calculation formula which can be suitable for the gravity measurement from a coastline to the submarine all-sea area, the method improves the accuracy of correcting the topography of the submarine gravity measurement, and further improves the abnormal accuracy of the submarine gravity measurement.
Description
Technical Field
The invention relates to a method for correcting and calculating the topography of a middle area and a far area in submarine gravity measurement, in particular to the method for correcting and calculating the topography within the range of 100 m-20000 m in submarine high-precision gravity measurement, and belongs to the field of gravity measurement.
Background
At present, in the various modifications of the submarine gravity measurement, the terrain correction value is almost the same order of magnitude as the gravity abnormal value generated by an abnormal body, and the accuracy of the terrain correction plays a key role in the accuracy of gravity exploration and interpretation. The terrain correction calculation formula of the middle area-the far area specified by the national gravity survey standard is as follows:
the values of the parameters in the formula are as follows:
ρ1-average density of crust of 2.67X 103g/cm3；
l is integration grid distance;
Cij-integrating constants, selecting trapezoidal coefficients;
rij-the distance between the integration node (i, j) and the calculation point;
hij-the difference in elevation between the integration node (i, j) and the calculation point
When the submarine gravity measurement work is carried out, the influence of seawater is not considered when the terrain correction is carried out by adopting the formula (1), and the water body correction is not carried out when the terrain is corrected. Along with the expansion of the gravity measurement work to the sea area, when the submarine gravity measurement is carried out, especially when the submarine high-precision gravity measurement is carried out, the correction method of the topography of the middle area to the far area directly influences the accuracy of the gravity anomaly calculation and influences the precision of the gravity anomaly.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a correction calculation method for the topography of a middle area-a far area in the submarine gravity measurement.
The technical scheme of the invention is as follows:
a terrain correction calculation method for a middle area and a far area in submarine gravity measurement comprises the following steps:
(1) dividing the terrain around the gravity measuring point as the center into a plurality of small blocks by using the collected submarine topography map, and establishing a submarine topography node network;
(2) determining the position of a gravity measuring point in a submarine topography node network according to the submarine gravity measuring point coordinates;
(3) selecting four nearest nodes of the seabed gravity measuring point in a seabed terrain node network, wherein the four nodes are named as A, B, C, D;
(4) calculating the terrain correction value delta g of each node according to the submarine terrain node network by using a formula (2)A、△gB、△gC、△gD。
Correcting a calculation formula:
the values of the parameters in formula (2) are as follows:
ρ0the density of the seawater is 1.03 x 103g/cm3；
h0-height values of gravity measurement points;
Sijunderwater topographic coefficient when (h)ij+h0) When the value is negative, the value is 1, (h)ij+h0) Taking 0 when the value is not negative;
Tijthe water topographic coefficient when (h)ij+h0) When the value is negative, 0 is taken, (h)ij+h0) Taking 1 when the value is not negative;
ρ1-average density of crust of 2.67X 103g/cm3；
l is integration grid distance;
Cij-integrating constants, selecting trapezoidal coefficients;
rij-the distance between the integration node (i, j) and the calculation point;
hij-the elevation difference between the integration node (i, j) and the calculation point;
g-universal constant of gravity (6.67X 10)-11m3/(kg·s2))；
The left delta g of the formula 2 is a terrain correction value, and the elevation value h of the gravity measurement point is used when the terrain correction value of the node is calculated0Instead of elevation values for four nodes, i.e. h in the formula when calculating the terrain correction value for each node0All the gravity measuring points have the same elevation value;
(5) interpolating to the position of the gravity measuring point by an X, Y direction bilinear interpolation method according to the topographic correction value of the peripheral node of the gravity measuring point to be used as the topographic correction value of the gravity measuring point;
(6) and (5) comprehensively correcting the influence of the rocks and the seawater on the gravity measurement through the gravity measuring point terrain correction value calculated in the step (5), wherein the obtained gravity measuring point terrain correction value is used for accurately calculating the grid abnormal value.
Preferably, in the step (1), the terrain within the range of 20km around the gravity measuring point as the center is divided into a plurality of small blocks, and the submarine terrain node network is established.
Preferably, in step (1), the terrain-segmented small blocks are square small blocks.
Preferably, in step (1), more than 1: the mesh degree of the established node network is more than 5m multiplied by 5 m.
Preferably, in step (5), the bilinear interpolation formula is:
in formula (3): delta gp-a topographical correction value for the gravity measurement point P; delta gA、△gB、△gC、△gD-a terrain correction value for node A, B, C, D; delta x, delta y-node grid distance; (X, Y) -coordinates of a point P of the gravity measuring point; (X)i,Yj) -the coordinates of point a; (X)i,Yj+1) -coordinates of point B; (X)i+1,Yj) -coordinates of point C; (X)i+1,Yj+1) -coordinates of the D-point.
The invention has the beneficial effects that:
the invention provides a submarine gravity terrain correction calculation method for correcting the influence of seawater gravity on gravity measurement by fully considering the influence of the seawater gravity on the gravity measurement aiming at the characteristics of submarine gravity measurement, and deduces a middle-far-one-region terrain correction calculation formula applicable to submarine gravity measurement from a coastline to a deep sea whole sea area so as to improve the precision of submarine gravity measurement terrain correction and further improve the abnormal precision of submarine gravity measurement.
Drawings
FIG. 1 is a schematic diagram of a terrain partitioning domain according to the present invention;
fig. 2 is a schematic view of the terrain effects.
Detailed Description
The present invention will be further described by way of examples, but not limited thereto, with reference to the accompanying drawings.
Example 1:
a terrain correction calculation method for a middle area and a far area in submarine gravity measurement comprises the following steps:
(1) dividing the terrain within the range of 20km around the seabed gravity measuring point as the center into a plurality of small blocks by using the collected seabed topography, and establishing a seabed topography node network; collecting a submarine topography map with a scale of more than 1: 1 ten thousand, wherein the mesh size of the established node network is more than 5m multiplied by 5 m;
(2) determining the position of a gravity measuring point in a submarine topography node network according to the submarine gravity measuring point coordinates;
(3) selecting four nearest nodes (A, B, C, D four nodes in the figure 1) of the seabed gravity measuring point (P point in the figure 1) in the seabed terrain node network;
(4) calculating a terrain correction value Δ g for each node (A, B, C, D in FIG. 1) from the net of subsea terrain nodes using equation (2)A、△gB、△gC、△gD。
Correcting a calculation formula:
the values of the parameters in formula (2) are as follows:
ρ0the density of the seawater is 1.03 x 103g/cm3；
h0-the elevation of the gravity measurement point;
Sijunderwater topographic coefficient when (h)ij+h0) When the value is negative, the value is 1, (h)ij+h0) Taking 0 when the value is not negative;
Tijthe water topographic coefficient when (h)ij+h0) When the value is negative, 0 is taken, (h)ij+h0) Taking 1 when the value is not negative;
ρ1-average density of crust of 2.67X 103g/cm3；
l is integration grid distance;
Cij-integrating constants, selecting trapezoidal coefficients;
rij-the distance between the integration node (i, j) and the calculation point;
hij-the elevation difference between the integration node (i, j) and the calculation point; the calculation point refers to that when the node A is calculated, the node A is the calculation point, when the node B is calculated, the node B is the calculation point, and the rest can be done; the integral nodes refer to all nodes within 20km of a computing point on the terrain node network, such as Q in figure 1ijI.e. one of the integration nodes. Equation 2 is an accumulation equation, i.e., the correction values of all nodes within 20km are accumulated.
G-universal constant of gravity (6.67X 10)-11m3/(kg·s2))；
The left delta g of the formula 2 is a terrain correction value, and the elevation value h of the gravity measurement point is used when the terrain correction value of the node is calculated0Instead of elevation values for four nodes, i.e. h in the formula when calculating the terrain correction value for each node0All the gravity measuring points have the same elevation value.
(5) Interpolating to the position of the gravity measuring point by an X, Y direction bilinear interpolation method according to the topographic correction value of the peripheral node of the gravity measuring point to be used as the topographic correction value of the gravity measuring point;
the bilinear interpolation formula is:
in formula (3): delta gp-a topographical correction value for the gravity measurement point P; delta gA、△gB、△gC、△gD-a terrain correction value for node A, B, C, D; delta x, delta y-node grid distance; (X, Y) -coordinates of a point P of the gravity measuring point; (X)i,Yj) -the coordinates of point a; (X)i,Yj+1) -coordinates of point B; (X)i+1,Yj) -coordinates of point C; (X)i+1,Yj+1) -coordinates of point D;
(6) the influence of the rocks and the seawater on the gravity measurement is comprehensively corrected by the gravity measuring point terrain correction value obtained by the calculation in the step (5), and the obtained gravity measuring point terrain correction value can be used for accurately calculating the grid abnormal value.
As shown in fig. 2, compared with the case of flat terrain, when the rock is substituted for seawater (the density of seawater is lower than that of rock) at a point higher than the measurement point O, the gravity value of the point O is reduced by the gravity of the residual terrain mass on the point O due to the component force in the vertical direction; terrain below point O also has a reduced gravity value at point O due to the replacement of rock by seawater. In fig. 2, one point on the left side corresponds to a node above sea level, and two points on the right side correspond to nodes below sea level. Therefore, no matter O1The terrain surrounding the point is high or low, and the terrain influence value of the point will make the gravity value of the point O smaller than that of the case where the terrain surrounding the point O is flat, so that the terrain correction value is always positive. Based on the above consideration, a corrected middle-far area seabed gravity measurement terrain correction formula is established as shown in formula 2, and the method is provided.
Compared with the original terrain correction formula (formula 1), the modified formula (formula 2) fully considers the influence of seawater on the terrain correction, wherein
The correction is that the nodes below the sea level fill the measuring points from the measuring point to the node as the influence of the sea water on the measuring points,
modified by sea levelThe upper node fills the measuring point to the sea level as the influence of the seawater on the measuring point. The terrain correction value calculated by the corrected formula realizes that air is filled above the sea level in the range of 20km of the seabed gravity measuring point, seawater is filled below the sea level to the measuring point, and rock is filled below the measuring point.
Claims (5)
1. A submarine gravity measurement middle-far area terrain correction calculation method is characterized by comprising the following steps:
(1) dividing the terrain around the gravity measuring point as the center into small blocks by using the collected submarine topography map, and establishing a submarine topography node network;
(2) determining the position of a gravity measuring point in a submarine topography node network according to the submarine gravity measuring point coordinates;
(3) selecting four nearest nodes of the seabed gravity measuring point in a seabed terrain node network, wherein the four nodes are named as A, B, C, D;
(4) calculating the terrain correction value delta g of each node according to the submarine terrain node network by using a formula (2)A、△gB、△gC、△gD；
Correcting a calculation formula:
the values of the parameters in formula (2) are as follows:
ρ0the density of the seawater is 1.03 x 103g/cm3；
h0-height values of gravity measurement points;
Sijunderwater topographic coefficient when (h)ij+h0) When the value is negative, the value is 1, (h)ij+h0) Taking 0 when the value is not negative;
Tijthe water topographic coefficient when (h)ij+h0) When the value is negative, 0 is taken, (h)ij+h0) Taking 1 when the value is not negative;
ρ1-average density of crust, 2.67 of103g/cm3；
l is integration grid distance;
Cij-integrating constants, selecting trapezoidal coefficients;
rij-the distance between the integration node (i, j) and the calculation point;
hij-the elevation difference between the integration node (i, j) and the calculation point;
g-universal constant of gravity (6.67X 10)-11m3/(kg·s2))；
The left delta g of the formula 2 is a terrain correction value, and the elevation value h of the gravity measurement point is used when the terrain correction value of the node is calculated0Replacing the elevation values of the four nodes;
(5) interpolating to the position of the gravity measuring point by an X, Y direction bilinear interpolation method according to the topographic correction value of the peripheral node of the gravity measuring point to be used as the topographic correction value of the gravity measuring point;
(6) and (5) comprehensively correcting the influence of the rocks and the seawater on the gravity measurement through the gravity measuring point terrain correction value calculated in the step (5), wherein the obtained gravity measuring point terrain correction value is used for accurately calculating the grid abnormal value.
2. The correction and calculation method for the topography of the middle-distant area in the submarine gravity measurement according to claim 1, wherein in the step (1), the topography within 20km around the gravity measurement point is divided into small blocks to establish the submarine topography node network.
3. The method for correcting and calculating the terrain in the middle-far area in the seafloor gravimetry according to claim 1, wherein in the step (1), the terrain-divided small blocks are square small blocks.
4. The method for correcting and calculating the topography of the middle-to-far area in the submarine gravity measurement according to claim 1, wherein in the step (1), more than 1: the mesh degree of the established node network is more than 5m multiplied by 5 m.
5. The method for correcting and calculating the topography of the middle-to-far area in the submarine gravity measurement according to claim 1, wherein in the step (5), the bilinear interpolation formula of the bilinear interpolation method is as follows:
in formula (3): delta gp-a topographical correction value for the gravity measurement point P; delta gA、△gB、△gC、△gD-a terrain correction value for node A, B, C, D; delta x, delta y-node grid distance; (X, Y) -coordinates of a point P of the gravity measuring point; (X)i,Yj) -the coordinates of point a; (X)i,Yj+1) -coordinates of point B; (X)i+1,Yj) -coordinates of point C; (X)i+1,Yj+1) -coordinates of the D-point.
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