CN113189660B - Method and system for observing array type land time-varying gravity and gradient field - Google Patents
Method and system for observing array type land time-varying gravity and gradient field Download PDFInfo
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Abstract
The invention relates to an observation method and a system for an array type land time-varying gravity and gradient field, wherein the method is provided with a specific observation pier array and a reference point, and combines an absolute gravity measurement step, a positioning step, a relative gravity measurement step and a data processing step to obtain the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measurement point.
Description
Technical Field
The invention relates to the technical field of flow gravity observation, in particular to an observation method and an observation system for an array type land time-varying gravity and gradient field.
Background
The gravity field is taken as a basic geophysical field, and the static abnormal characteristics and dynamic time variation of the gravity field can provide important physical field information for researching the deep crust structure and properties. Modern scientific research considers that earth dynamics processes such as earthquake, groundwater, volcanic activity, various structural motions, vertical deformation of crust and the like all cause a certain degree of earth gravity field change. The sensitivity of the gravitational field to mass motion or change signals makes the gravitational field suitable for quantitatively researching the space-time characteristics of various earth system processes, and is an important data index.
In order to determine the gravity value and continuously monitor its change, the main method in use is to conduct flow gravity observation. Flow gravimetric co-detection of seismic systems has been done for over 40 years, and large-scale absolute gravimetric detection has been done for nearly 15 years, and flow gravimetric observational networks consisting of 4000 relative gravity points and 100 absolute gravity points have been established nationally. The current-stage land time-varying gravity observation mainly adopts a ground fixed-point repeated observation mode to realize the monitoring of a time-varying gravity field.
However, in a long-term practical process, many defects existing in the existing earthquake flow gravity observation network and the observation method thereof are gradually highlighted:
1. the absolute gravity point is few. The absolute gravity measurement has strong reliability and high precision, but because the measurement equipment is expensive and the required observation condition is harsh, the control measurement can only be carried out on a few basic points in the gravity measurement network at present (the proportion of the absolute gravity points is less than 1:40);
2. gravity vertical gradient measurement is only used as an auxiliary measurement for calculating absolute gravity measurement values to ground values, and the gravity vertical gradient does not play a role in field source inversion;
3. the flow gravity measurement net mainly uses relative gravity observation, and the measurement point spacing is uneven. The method generally adopts a one-time round trip observation method for saving the observation of the whole network, namely, A-B-C-D … … D-C-B-A, but not a three-way observation method, namely, A-B-C … …, but the whole network is also completed for a plurality of months. If the three-pass observation method is adopted, the construction time is more than 1 time. However, the 'one round trip observation method' has the defects that the closing time of the measuring line is longer, the closing time of one measuring line is 1-3 days, and the data is greatly influenced by uncertainty drift;
4. The measurement and data adjustment adopts the form of absolute control and relative measurement, and the transmission error can be reduced as much as possible only by introducing absolute gravity value in the large-range relative gravity measurement. The method is limited by the number of absolute gravity devices and the coverage of measuring points, the influence of instrument drift, lattice value coefficient influence, measurement error, environmental interference and the like cannot be completely subtracted, the data precision and reliability are influenced, and the application of data results is further limited;
5. the absolute observation is not synchronous with the relative observation time, so that the subsequent data adjustment is greatly influenced; the absolute measurement is different from the relative measurement in the measurement unit, so that the absolute control and the relative measurement in the gravity adjustment are not synchronously influenced, the accuracy of the measured data is reduced, and the effectiveness of the measured data is seriously influenced;
6. the relative gravity measuring points are limited by natural conditions and closing time limit of the measuring lines, the measuring points are distributed around the road with convenient traffic, and the environmental factors are complex. The single measuring point has limited observation time and single measuring item, and is only used for gravity joint measurement.
Disclosure of Invention
In order to solve the problems in the prior art, on the basis of the existing 'absolute control + relative measurement' gravity measurement network, the invention designs an observation method for an array type land time-varying gravity and gradient field, sets a specific observation pier array and a reference point, combines an absolute gravity measurement step, a positioning step and a relative gravity measurement step, acquires the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measurement point and the measurement point elevation result, namely, the invention can obtain a high-precision gravity field signal through a more efficient field comprehensive measurement mode and more accurately identifies a field source gravity signal with a specific space-time scale. The invention also relates to an observation system of the array type land time-varying gravity and gradient field.
The invention adopts the following technical scheme:
the method is characterized in that an observation pier array is arranged outside a land measurement site and a datum point is arranged in the land measurement site, the observation pier array comprises a plurality of observation piers which are arranged according to a field source sensitivity array, the lower ends of the observation piers are all fixed in the ground, the upper ends of the observation piers are exposed on the ground, and measuring points are arranged at the bottoms and the surfaces of the observation piers exposed on the ground, and the method further comprises the following steps:
an absolute gravity measurement step, namely setting an absolute gravity meter at the datum point, and further measuring the gravity point value of the datum point to provide an absolute gravity datum of the land measurement site, wherein the datum point is the first measuring point of all the relative gravity simultaneous measurements;
a positioning step, namely performing GNSS positioning on each observation pier to obtain longitude, latitude, elevation and relative elevation of each measuring point position;
a relative gravity measurement step, namely sequentially carrying out relative gravity joint measurement on a relative gravity instrument from a datum point along each measurement point of each observation pier, wherein a gravity joint measurement path at least makes a round trip at each measurement point and returns to the datum point to obtain gravity readings of the relative gravity instrument at the datum point and each measurement point, and finishing the measurement of the horizontal gradient and the vertical gradient of gravity;
And a data processing step, wherein a data processing terminal acquires the gravity reading of the relative gravimeter, and performs calculation processing by combining the data acquired in the positioning step and the gravity point value of the datum point provided by the absolute gravimeter to acquire the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point.
Preferably, the gravity joint measurement path of the relative gravity measurement step is from a reference point to a measurement point of a pier bottom of a first observation pier, and after the first observation pier makes a round trip with the measurement point of the pier bottom-pier surface-pier bottom, the measurement point of the pier bottom of a second observation pier is moved to the measurement point of the pier bottom of the second observation pier, and after the second observation pier makes a round trip with the measurement point of the pier bottom-pier surface-pier bottom, the measurement point of the pier bottom of a next observation pier is moved to the measurement point of the pier bottom of the first observation pier, and so on, until the measurement point of the pier bottom of the last observation pier makes a round trip with the measurement point of the pier bottom-pier surface-pier bottom of the last observation pier, the measurement point of the pier bottom of the last observation pier is returned to the reference point in turn.
Preferably, the gravity combined measurement path of the relative gravity measurement step is from a reference point to a measurement point of a pier surface of a first observation pier, and after the first observation pier makes a round trip with the measurement point of the pier surface-pier bottom-pier surface, the measurement point of the pier surface of a second observation pier is moved to, and after the second observation pier makes a round trip with the measurement point of the pier surface-pier bottom-pier surface, the measurement point of the pier surface of a next observation pier is moved to, and so on, until the last observation pier makes a round trip with the measurement point of the pier surface-pier bottom-pier surface, the measurement point of the pier surface of a last observation pier is moved to, and then the measurement point of the pier surface of each observation pier is sequentially moved back from the measurement point of the pier surface of the last observation pier, until the measurement point of the pier surface of the first observation pier is returned to the reference point.
Preferably, the step of measuring the relative gravity performs main measurement by using the gravity combined measurement path, and performs auxiliary measurement after the main measurement, wherein the auxiliary measurement is to sequentially and diagonally combine the relative gravity meter from the datum point along each measurement point of each observation pier to obtain gravity readings of the relative gravity meter at the datum point and each measurement point, and the main measurement and the auxiliary measurement are combined to jointly complete the measurement of the horizontal gradient and the vertical gradient of the gravity.
Preferably, each observation pier arranged in an array is arranged on the ground at equal height, and the distance and the pier height of each observation pier in the array are adjusted according to the field condition, the field source characteristics and the field source sensitivity of different measurement methods; each observation pier is rectangular, T-shaped, L-shaped or stepped, and at least has a right angle arrangement.
Preferably, the number of observation piers in the observation pier array is 4-9, and the interval between each observation pier is 20-50 m.
Preferably, the absolute gravimeter adopted in the absolute gravimetric measurement step comprises an FG5 absolute gravimeter and/or an a10 absolute gravimeter, wherein the FG5 absolute gravimeter measures and selects not less than 12 cell data, and the a10 absolute gravimeter measures and selects not less than 24 cell data; the falling times of each combination lattice data are not less than 100 times, and the qualified falling times are not less than 75 times.
Preferably, the observation piers are 4 and rectangular, and the main measurement is performed at 9 positions of the reference point and the measurement point in the gravity combined measurement path in total in the relative gravity measurement step, and the auxiliary measurement is performed at 13 positions of the reference point and the measurement point in the diagonal combined measurement path in total.
The observation system for the array type land time-varying gravity and gradient field is characterized by comprising an absolute gravimeter, a relative gravimeter, a positioning device, a data processing terminal, an observation pier array positioned outside a land measurement field and a reference point positioned in the land measurement field, wherein the observation pier array comprises a plurality of observation piers which are arranged according to the field source sensitivity array, the lower ends of the observation piers are all fixed in the ground, the upper ends of the observation piers are exposed on the ground, the bottoms and the surfaces of the observation piers exposed on the ground are all provided with measurement points, the absolute gravimeter, the relative gravimeter and the positioning device are all connected with the data processing terminal,
The absolute gravimeter is arranged on the datum point and is used for measuring the gravity point value of the datum point to provide an absolute gravity datum of a land measurement site, and the datum point is the first measuring point of all the relative gravity joint measurements;
the positioning device is used for performing GNSS positioning on each observation pier to obtain longitude, latitude, elevation and relative elevation of each measuring point position;
the relative gravity meter is used for sequentially carrying out relative gravity joint measurement along each measuring point of each observation pier from the datum point, a gravity joint measurement path at least reciprocates once at each measuring point and returns to the datum point to obtain gravity readings of the relative gravity meter at the datum point and each measuring point, and the measurement of the horizontal gradient and the vertical gradient of the gravity is completed;
the data processing terminal is used for acquiring the gravity reading of the relative gravimeter and carrying out calculation processing by combining the data obtained by the positioning device and the gravity point value of the datum point provided by the absolute gravimeter to obtain the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point.
Preferably, the relative gravity meter performs main measurement along the gravity joint measurement path of the pier bottom and pier surface measuring points of each observation pier, and performs auxiliary measurement after the main measurement is performed, wherein the auxiliary measurement is to perform the relative gravity meter diagonal joint measurement sequentially along each measuring point of each observation pier from the datum point, so as to obtain gravity readings of the relative gravity meter at the datum point and each measuring point, and the main measurement and the auxiliary measurement are combined to jointly complete the measurement of the gravity horizontal gradient and the vertical gradient.
The invention has the technical effects that:
the invention designs an observation method of an array type land time-varying gravity field and a gradient field, or an observation method of an array type land time-varying gravity field and a gravity gradient field, wherein an observation pier array is arranged outside a land measurement field, a reference point is arranged in the land measurement field, an absolute gravity measurement step, a positioning step and a relative gravity measurement step are sequentially carried out, after the gravity point value of the reference point is measured, relative gravity joint measurement is carried out sequentially along the measurement points of all the observation piers from the reference point, so that the measurement of the gravity horizontal gradient and the vertical gradient is completed, and then the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of all the measurement points are obtained through data processing. For a single site, the gravity vertical gradient has higher signal-to-noise ratio on the change caused by a shallow signal source compared with the conventional gravity measurement, the gravity horizontal gradient can be used for analyzing the sensitivity of the underground field source, and the sensitivity area range of an observation network is adjusted by utilizing the sum and difference operation of the observation points in the data processing process by designing the combined observation among the measurement points of a plurality of observation piers, so that the gravity signal of the field source with a specific space-time scale can be better identified. If the important dangerous area is located, the gradient array gravity observation network constructed by the array type land time-varying gravity and gradient field observation method can completely replace the traditional flow gravity observation network. The absolute gravity observation is carried out on each site of the gradient array measuring network, and the absolute gravity observation and the relative gravity observation are carried out at the same time, so that high-precision gravity field signals can be given out. The gravity and gradient field measurement is completed in one field, only an observer is needed to carry the instrument in the field by gravity joint measurement between points, the measurement of each point is quasi-static, the lattice dropping of the instrument is avoided as much as possible, and the joint measurement mode can effectively monitor instrument drift, so that the observation method ensures high accuracy of results. The gradient array observation net composed of several gradient array observation fields does not need to increase any cost in the field implementation process, such as joint measurement among 2 fields. Because each site has absolute gravity measurement, networking is only on the aspects of data processing and research, the field is not involved, and the field workload is not increased.
The invention adopts a small-range array layout to carry out measurement, and is completed in one place, thereby greatly reducing the measurement range, avoiding the labor of the boat and the car of the traditional flowing gravity measuring net more than 400km per day, reducing the field workload, facilitating the measurement and execution and reducing the measurement cost. The measuring point is generally positioned in the earthquake station, the environmental interference is small, and the high-speed social development is not destroyed. The construction standard of the newly-built gravity gradient observation array is far higher than that of the relative gravity measuring point, and the gravity gradient observation array can be permanently used. The time for completing the site measurement is less, the personnel work is more efficient, the 2-3 person observation teams can firstly erect an absolute gravimeter and GPS equipment for continuous measurement, and the observer performs the joint measurement of the XYZ three-way gravity gradient observation array while the absolute gravimeter and the GPS equipment work, and the time for 1 site measurement is only about 2 days. Because the zone is small, located only within the station, the relative gravity measurement closure time is shortened. The gravity measurement carried out on the XYZ three-direction gravity gradient observation array can be closed to an absolute gravity point at any time, so that the influence of instrument drift on a adjustment result is effectively reduced, the misalignment of measurement data caused by the lattice dropping of the instrument is avoided, and the data is more reliable.
In addition, the method can effectively acquire gravity gradient signal data in the vertical and horizontal directions and construct a regional gravity gradient field. The gravity gradient signal is sensitive to the field source position information, and the distance between observation piers in the array and the pier height from the bottom surface to the top surface of the observation piers are designed and adjusted according to the characteristics and sensitivity of the field source to be detected, so that the inversion of the field sources with different depths can be completed, and the field source gravity signal with a specific space-time scale can be more accurately identified.
Drawings
FIG. 1 is a flow chart of the method of observing the array type land time-varying gravity and gradient fields of the present invention.
FIG. 2 is a schematic diagram of one embodiment of an array of observation piers.
Fig. 3a and 3b are graphs of field source sensitivity analysis for gravity observation.
FIGS. 4a-4c are graphs of field source sensitivity analysis of different horizontal spacing gravity level difference signals;
FIGS. 5a-5c are graphs of gravity level difference signal sensitivity analysis for different vertical heights;
FIG. 6 is a schematic diagram of one embodiment of a relative gravimetric joint measurement of horizontal and vertical gradients of gravity.
Fig. 7 shows a schematic representation of a second embodiment of a relative gravimetric joint measurement of horizontal and vertical gradients of gravity.
FIG. 8 is a schematic diagram of one embodiment of a diagonal joint measurement of gravity horizontal and vertical gradient measurements.
Fig. 9 is a schematic diagram of an application scenario of the array type terrestrial time-varying gravity and gradient field observation system of the present invention.
Fig. 10 is a schematic of horizontal gradient results.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
The invention relates to an observation method of array type land time-varying gravity and gradient field, as shown in the flow chart of figure 1, an observation pier array is arranged outside a land measurement field and a datum point is arranged in the land measurement field, the observation pier array comprises a plurality of observation piers which are arranged according to the field source sensibility array, the lower ends of the observation piers are all fixed in the ground, the upper ends of the observation piers are exposed on the ground, and the pier surfaces and the pier bottoms of the observation piers exposed on the ground are all provided with measuring points, and the method further comprises the following steps: an absolute gravity measurement step, namely setting an absolute gravity meter at the datum point, and further measuring the gravity point value of the datum point to provide an absolute gravity datum of the land measurement site, wherein the datum point is the first measuring point of all the relative gravity joint measurement; a positioning step, namely performing GNSS positioning and leveling measurement on each observation pier to obtain longitude, latitude, elevation and relative elevation of each measuring point position; a relative gravity measurement step, namely sequentially carrying out relative gravity joint measurement on a relative gravity instrument from a datum point along each measurement point of each observation pier, wherein a gravity joint measurement path at least makes a round trip at each measurement point and returns to the datum point to obtain gravity readings of the relative gravity instrument at the datum point and each measurement point, and finishing the measurement of the horizontal gradient and the vertical gradient of gravity; and a data processing step, wherein a data processing terminal acquires the gravity reading of the relative gravimeter, and performs calculation processing by combining the data acquired in the positioning step and the gravity point value of the datum point provided by the absolute gravimeter to acquire the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point and the measuring point elevation result.
FIG. 2 is a schematic diagram of one embodiment of an array of observation piers for terrestrial time-varying gravity and gradient fields. The invention relates to a land measurement site outdoor 1, which comprises a plurality of observation piers 2, wherein the lower ends of the observation piers 2 are fixed in the ground, the ground can extend to bedrock to ensure the stability of measuring points, the upper ends of the observation piers 2 are exposed on the ground, and the bottoms and the faces of the observation piers 2 exposed on the ground are provided with measuring points. Preferably, the array is composed of n (n is more than or equal to 3) observation piers with equal heights (from the bottom surface of the pier to the top surface of the pier) and bottom surfaces and top surfaces, at least 1 right-angle arrangement is formed, the horizontal gravity gradients in the XY two directions can be obtained through the right-angle arrangement array, and each observation pier with equal heights and bottom surfaces and top surfaces can obtain the vertical gravity gradient in the Z direction. The in-array observation piers are designed according to DB/T19-2006, DB/T39-2010, DB/T5-2003. The distance and pier height of each observation pier in the array are adjusted according to field conditions, field source characteristics and field source sensitivity of different measuring methods, each observation pier is rectangular, T-shaped, L-shaped or stepped, 4-9 observation piers in the observation pier array are arranged in a rectangular mode, the distance between each observation pier is 20-50 m, 4 observation piers 2 in the embodiment shown in fig. 2 are arranged in a rectangular mode, the distance between each observation pier is 24m, and the pier height is 0.8m.
The distance and height of observation piers in the array can be adjusted according to field conditions, field source characteristics and field source sensitivity of different measurement methods, and the principle is as follows:
first, land gravity anomalies caused by different depth field sources are discussed. Table 1 simulates a disk model of two different field source parameters. The field source burial depth of the model 1 is 10m, so that gravity abnormality caused by common underground water over exploitation can be simulated; the field source of the model 2 has a buried depth of 10km, which is equivalent to the depth of most natural earthquakes. R, H, Z in the table represents the disk radius, thickness and top depth, respectively; g (x, y) represents the gravity anomaly of the model on the observation point with the horizontal and vertical coordinate positions of (x, y) right above the center of the disc, and the unit is micro gamma; the unit of the coordinate position (x, y) is m. As shown in Table 1, the four coordinate positions are arranged in a rectangular array, and gravity anomalies of about 34 micro-gamma can be observed for both model 1 and model 2 just above the center of the disk. However, gravity anomalies caused by model 1 on land significantly decay with increasing coordinate position and field source distance. While the gravity anomaly caused by model 2 on land is substantially uniform at 4 coordinate points. Therefore, in the small-scale array gravity observation system, the gravity anomaly caused by the shallow field source is obviously attenuated along with the increase of the coordinate position and the field source distance, and the gravity anomaly caused by the deep field source is more consistent in signal characteristics.
Table 1 theoretical gravity anomaly calculation based on disc model
Second, introducing cumulative sensitivityThe sensitivity of data acquired by different observation modes of earth-surface land and satellite gravity, horizontal gravity difference (which can be converted into a gravity horizontal gradient) and vertical gravity difference (which can be converted into a gravity vertical gradient) to field sources is discussed. The earth's surface observable gravity anomaly may be considered as the integral of the remaining mass of the subsurface medium, provided that we discretize the subsurface medium into units of equal volume, each unit contributing to the earth's surface observation point gravity anomaly at unit density as A i The ratio of the sum of the contribution of each unit to the contribution of all units can be defined as the accumulated sensitivity f, so that a field source sensitivity calculation result can be obtained. For earth surface gravity observation, the sensitivity range of the underground medium is distributed in a reverse fan shape, and the field source sensitivity is fast attenuated in the horizontal direction and is larger than that in the vertical direction. FIG. 3a is a plot of field source sensitivity analysis for gravity observation, as shown, it is easy to see that the closer to the observation point the cell contribution is greater, which means that the landing surface measurement is more sensitive to shallow field source density variations. If 11 point arrays are constructed in an equidistant arrangement on the surface, the sensitivity distribution characteristics shown in FIG. 3b can be obtained on average after superposition observation. The superimposed observation array can effectively reduce the sensitivity level of shallow field source substances and improve the signal-to-noise ratio of gravity signals reflecting deep field sources. Therefore, the array is formed by a plurality of measuring points on the earth surface, the sensitive area range of the observation network is adjusted by utilizing the sum and difference operation of the observation points, and the inversion of field sources with different depths can be completed.
Fig. 4a-4c are field source sensitivity analysis diagrams of gravity level difference signals with different horizontal pitches, wherein the model is represented by km units, but scale units in the diagrams are suitable for scaling in equal proportion according to different purposes, such as the coordinate units are uniformly changed into m, and the sensitivity calculation result is unchanged. Figures 4a-c show gravity level difference sensitivity characteristics at 1km,2km and 3km distances, respectively. As shown in the figure, the field source sensitive area range gradually increases from a shallow source to a deep source along with the increase of the observation interval.
FIGS. 5a-5c are gravity level difference signal sensitivity analysis graphs of different vertical heights, and model construction is the same as that of FIGS. 4a-4 c. As shown in the figure, the vertical observation sensitive area is mainly concentrated below the observation point, but the horizontal direction is easily interfered by the shallow field source body. According to the sensitivity characteristics shown in fig. 5a-c, the gravity level differences of different heights are measured, so that the method is more suitable for researching the shallow field source parameter problem.
From the above, it can be seen that the model shown in fig. 3b is based on the field source sensitivity result given by the superposition method, and is more suitable for suppressing shallow interference and separating out deep field source signals; the gravity level difference or gradient method shown in fig. 4a-4c and fig. 5a-5c can adjust the horizontal and vertical intervals between observation points, and is more suitable for analyzing the gravity signal of the shallow source and suppressing the gravity effect of the deep field source. Therefore, in actual operation, the observation pier array can be designed and built according to different measurement objects. Considering the environmental conditions of the measuring station, it is generally preferable to build an array of 4-9 observation piers, with a dot spacing of 20-50m, at least 1 square arrangement.
In order to observe the land time-varying gravity and gradient field and obtain the gravity point value, vertical gravity gradient and horizontal gravity gradient of the measuring point, the invention designs a set of high-efficiency, time-saving and high-precision gravity joint measuring method, which mainly comprises the following steps: absolute gravimetric measurement, GNSS measurement positioning, relative gravimetric measurement and data processing.
First, an absolute gravimetric measurement step. If an existing absolute gravity observation point in a land site (such as a seismic station) can be directly utilized, if not, a new point is built according to the seismic industry standard DB/T39-2010. According to the standard DB/T39-2010 of the earthquake industry, an observation chamber and a buried datum point are required to be built, wherein the datum point is an absolute gravity observation point and can be arranged on an absolute gravity observation pier (for distinguishing from an observation pier arranged in an outdoor observation pier array for relative gravity measurement, the observation pier is called a datum pier later), and the specification of a pier surface is not smaller than 1000mm multiplied by 1000mm; the pier surface is preferably 200mm higher than the ground, and the pier surface flatness is preferably 6mm. The timeliness of measurement is considered, and the flat and stable ground of the existing observation piers or the underlying offices of the station can be used as a temporary absolute gravity point.
The absolute gravity observation point not only provides an absolute gravity reference of the field, but also is the first measurement point of all relative gravity joint measurement, and the relative gravity measurement transmits the gravity value to each observation position through the joint measurement with the absolute gravity point; in addition, in the relative gravity measurement, it is preferable to measure 1 absolute gravity point every 4 hours and monitor the instrument null shift in real time. The absolute gravimetric observation uses an instrument preferably of FG5 and/or a10 type, the measurement steps of which are identical:
a) Installing an instrument;
b) The cable is connected to the control box;
c) Preheating a laser;
d) Various pre-measurement checks (voltage values of ion pump, rubidium clock, optical path, interference fringes, laser band);
e) Starting a computer, starting g software and setting parameters;
f) Starting data acquisition;
preferably, the following conditions are required to be met during the data acquisition process:
1) Each measuring point FG5 absolute gravimeter is not less than 12 combined grid data, and A10 absolute gravimeter is not less than 24 combined grid data;
2) The falling times of each group are not less than 100 times, the qualified falling times are not less than 75 times, and the group is effective;
3) The observation starting time of each group is set at the whole point or 30 minutes, 1 group is observed by FG5 absolute gravimeter per hour, and 2 groups are observed by A10 absolute gravimeter per hour;
4) The instrument stops working for more than 10 hours, the previous observation is invalid, and the observation needs to be restarted.
And after the data acquisition is completed, obtaining an absolute gravity point value of the absolute gravity observation point.
A second step, a positioning step, a GNSS measuring positioning. If a GPS reference station in an existing global navigation system GNSS in a land-based site (such as a seismic station) can be directly utilized. If not, a new point is built according to the common standard stone of the national standard GBT 18314-2009. The timeliness of measurement is considered, an observation pier with good viewing conditions in an observation array can be used, and a homing disc is arranged on the pier surface and connected with global positioning system equipment.
The GPS adopts a satellite positioning-based continuous operation reference station observation mode, continuous observation or differential positioning and other modes to finish the positioning of measuring points conforming to the precision. And (5) leveling measurement between the matching points, and accurately measuring the vertical change of the measuring points. The phase center stability should be better than 1mm in the horizontal direction and 2mm in the vertical direction.
When the site is measured for the first time, GPS positioning and leveling measurement are needed to be carried out on each observation pier, longitude, latitude, elevation and relative elevation of each measurement position are given, point positions are calculated to the same horizontal plane, and the gravity horizontal gradient can be calculated by combining the relative gravity measurement values and the horizontal intervals among the measurement points; and observing the height difference of the bottom surface and the top surface of the pier as a determined value, and combining the relative gravity measurement value to calculate the gravity vertical gradient. In the subsequent repeated observation, the first-time positioning data is utilized to perform horizontal gradient reduction and vertical gradient reduction, but the GPS positioning and the leveling measurement of each point position are still required to be performed on one observation pier, so as to monitor the relative elevation change among the measurement points.
And a third step, a relative gravity measurement step. In order to improve the measurement efficiency and save the measurement time, the invention designs a relative gravity measurement circuit. As an embodiment, taking an example of the arrangement of 4 observation piers in a rectangular array, describing the line design of the relative gravity measurement, as shown in fig. 6, the gravity gradient in the vertical direction can be obtained by the joint measurement of the top surface measurement point and the bottom surface measurement point of each observation pier, the gravity gradient and the gravity point value in the horizontal XY direction can be obtained by the joint measurement between the bottom surface measurement points of each observation pier, and the gravity value of each measurement point can be obtained by introducing the absolute gravity value into the gradient observation array by the measurement of the absolute gravity point. The gravity joint measurement path (i.e., measurement line) of the relative gravity measurement step designed in the present invention is as shown in the figure, the measurement is performed in the observation order of No. 1, 2 … …, from the reference point 1 to the measurement point of the pier bottom of the first observation pier, and after one round trip (2-3-4) with the measurement point of the pier bottom-pier face-pier bottom on the first observation pier, the measurement point 5 of the pier bottom of the second observation pier is made, and after one round trip (5-6-7) with the measurement point of the pier bottom-pier face-pier bottom on the second observation pier, the measurement point 8 of the pier bottom of the next observation pier is made, and so on, until the last observation pier makes a round trip with the measuring point of the pier bottom-pier surface-pier bottom (11-12-13), then goes to the pier bottom 14 of the first observation pier, returns to the measuring point 15 of the pier bottom of the last observation pier, and then returns to the measuring points (16-17-18) of the pier bottom of each observation pier sequentially from the measuring point 15 of the pier bottom of the last observation pier until returning to the measuring point 18 of the pier bottom of the first observation pier and then returning to the datum point 19.
In the measuring process, the absolute gravity point value of the first part is transferred to the gravity value of the gradient observation array of the part through two times of observation of 1 and 2 (18 and 19 when the device is closed), and meanwhile, the calibration of the absolute gravity value is realized, and the influence of zero drift of a monitoring instrument is avoided. 2. The three observations of 3 and 4 complete 1 complete closed joint measurement of vertical gradient measurement, and the two observations of 4 and 5 (17 and 18 in closing) complete the retransmission of the absolute gravity point value of the first part, and simultaneously realize the horizontal gradient measurement on the height of the bottom surface of the observation pier. 5. The combined measurement functions of 6 and 7 are the same as those of 2, 3 and 4, the functions of 7 and 8 are the same as those of 4 and 5, and so on. By adopting the joint measurement method, the XY direction horizontal gradient measurement of 4 points is completed at the cost of only 5 more measurement points; and starting from and ending the absolute measurement point, the whole measurement is completed at the cost of only 2 more measurements, and meanwhile, the calibration of the absolute gravity value is realized. The vertical gradient, the XY horizontal gradient and the relative gravity combined measurement of the observation array are completed by 19 times of measurement, an operator only needs to walk around the field for 2 circles in the whole measurement process, and if the vertical gravity measurement, the horizontal gradient and the relative gravity combined measurement are respectively carried out, 23 times of measurement are needed, and the operator needs to walk around the field for at least 3 circles.
In performing measurements, gravity gradient fields are typically measured with reference to the bottom surface of the observation pier. In order to improve the accuracy of observation, the measurement may be performed again from the absolute point of gravity to the top surface of the pier as a whole, and as shown in fig. 7, the measurement may be performed in the observation order of No. 1 and No. 2 … … 19. The gravity combined measuring path of the relative gravity measuring step is from the datum point 1 to the measuring point 2 of the pier face of the first observation pier, and after the first observation pier makes one round trip with the measuring point of the pier face-pier bottom-pier face (2-3-4), the path goes to the measuring point 5 of the pier face of the second observation pier, and after the second observation pier makes one round trip with the measuring point of the pier face-pier bottom-pier face (5-6-7), the path goes to the measuring point 8 of the pier face of the next observation pier, and so on, until the path goes to the measuring point 14 of the pier face of the first observation pier again after the last observation pier makes one round trip with the measuring point of the pier face-pier bottom-pier face (11-12-13), then the measuring point 15 of the pier face of the last observation pier is returned, and then the measuring points 16-17-18 of the pier faces of the observation piers are sequentially returned from the measuring point of the pier face of the last observation pier to the datum point 19.
Further, the main measurement is performed relative to the gravity measurement step of the gravity joint measurement path shown in fig. 6 and/or fig. 7, and the auxiliary measurement is performed after the main measurement is performed, wherein the auxiliary measurement is to perform the diagonal joint measurement sequentially along each measurement point of each observation pier from the datum point to the gravity meter, obtain the gravity readings of the gravity meter at the datum point and each measurement point, and perform the gravity horizontal gradient measurement and the vertical gradient measurement together with the auxiliary measurement. That is, it is also possible to perform joint measurement of diagonal pier positions in the gradient observation array, as shown in fig. 8, and perform measurement in the observation order of No. 1, 2 … … 14.
In the measurement process, preferably, the measurement step of each measurement point is as follows:
A. leveling the plate relative to the gravity meter;
B. manually turning on the pendulum or manually turning on the "on" key;
C. a manual reading instrument which manually rotates the measuring disc to perform effective reading for at least 3 times; feeding back an automatic reading instrument, at least carrying out 10 effective readings, and suggesting to set the time for each reading to be 60s;
D. a manual lock pendulum or a manual open "off" key.
And a data processing step, wherein a data processing terminal acquires the gravity reading of the relative gravimeter, and performs calculation processing by combining the data acquired in the positioning step and the gravity point value of the datum point provided by the absolute gravimeter to acquire the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point.
The above combined measurement method and measurement method are preferable modes which are experimentally measured. Taking the most commonly used CG-5 relative gravimeter as an example, the current common measurement mode of vertical gradient is to use 2 instruments, and measure 5 groups of closures (namely 11 measurements) in total according to 'down-up-down' (or 'up-down-up') as one closure, wherein each measurement reads 5, and the working time of the instruments is at least 110min; the invention adopts an improved measurement mode, reduces the closing times of 'down-up-down' (or 'up-down-up') to 2 groups (namely 5 measurements), increases the reading number of each measurement to 10, and the working time of the instrument is at least 100min; the measurement time is shortened, and although the closing times are reduced, the data are more stable due to the fact that the observation time of each measurement is increased by 1 time. Through experimental comparison, a common measurement mode is adopted for the stable absolute gravity observation pier in a white house village cave, the environmental precision is +/-1.02 uGal, and under the condition of taking 132 minutes, the standard deviation of the obtained gravity vertical gradient is +/-1.00-2.46; the improved measuring mode is completed in the field outside measuring pier, the environmental precision is +/-1.91 uGal, and the standard deviation of the gravity vertical gradient is +/-1.04-1.18 under the condition of taking 110 minutes. The improved measuring mode obtains a comparable gravity vertical gradient standard deviation under the condition of less time consumption in a measuring environment with poorer environmental precision (namely higher noise).
The invention also relates to an observation system of the array type land time-varying gravity and gradient field, which corresponds to the observation method of the array type land time-varying gravity and gradient field, and can be understood as a system for realizing the observation method of the array type land time-varying gravity and gradient field, the system comprises an absolute gravimeter, a relative gravimeter, a positioning device, a data processing terminal, an observation pier array positioned outside a land measurement field and a datum point positioned in a land measurement field chamber, the observation pier array comprises a plurality of observation piers which are arranged according to a field source sensitivity array, the lower ends of the observation piers are all fixed in the ground, the upper ends of the observation piers are exposed on the ground, the bottoms and the pier surfaces of the observation piers exposed on the ground are all provided with measurement points, and the absolute gravimeter, the relative gravimeter and the positioning device are all connected with the data processing terminal; the absolute gravimeter is arranged on the datum point and is used for measuring the gravity point value of the datum point to provide an absolute gravity datum of a land measurement site, and the datum point is the first measuring point of all the relative gravity joint measurements; the positioning device is used for performing GNSS positioning and leveling combined measurement on each observation pier to obtain longitude, latitude, elevation and relative elevation of each measuring point position; the relative gravity meter is used for sequentially carrying out relative gravity joint measurement along each measuring point of each observation pier from the datum point, a gravity joint measurement path at least reciprocates once at each measuring point and returns to the datum point to obtain gravity readings of the relative gravity meter at the datum point and each measuring point, and the measurement of the horizontal gradient and the vertical gradient of the gravity is completed; the data processing terminal is used for acquiring the gravity reading of the relative gravimeter and carrying out calculation processing by combining the data obtained by the positioning device and the gravity point value of the datum point provided by the absolute gravimeter to obtain the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point.
Preferably, the main measurement is performed along the gravity joint measurement path of the pier bottom and pier surface measurement points of each observation pier relative to the gravity meter, as shown in fig. 6 and 7, and the auxiliary measurement is performed after the main measurement is performed, wherein the auxiliary measurement is performed by sequentially performing the diagonal joint measurement on each measurement point of each observation pier from the reference point relative to the gravity meter, as shown in fig. 8, to obtain the gravity readings of the gravity meter at the reference point and each measurement point, and the main measurement and the auxiliary measurement are combined to jointly complete the gravity horizontal gradient and vertical gradient measurement.
Fig. 9 is a schematic diagram of an application scenario embodiment of the array type terrestrial time-varying gravity and gradient field observation method or system of the present invention, specifically, a terrestrial time-varying gravity and gradient field observation array built in the earth-viewing station field of beijing country. This embodiment essentially comprises # 01- #09 observation piers arranged in a 3 x 3 array, a relative gravity gauge, a GPS reference station, and #10 reference points and corresponding absolute gravity gauges. Applicant has performed terrestrial time-varying gravity and gradient field observations at 5 months 2017 and 10 months 2017, respectively, using the embodiment of fig. 9, wherein the simultaneous measurements of fig. 6, 7, 8 are used in sequence with respect to the gravity observation method to ensure high accuracy of the results. The observation means comprise absolute gravity measurement, relative gravity measurement, GNSS measurement, leveling measurement and necessary auxiliary measurement work, and the obtained physical quantity is the gravity value, horizontal gravity gradient and vertical gravity gradient of each point. The data processing step is to obtain a gravity reading of a relative gravimeter by a data processing terminal, calculate and process the gravity point value of a datum point provided by an absolute gravimeter and the data obtained by the positioning step, obtain the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point, and the measurement result is as follows:
1) Vertical gradient measurement results
First, we define the relative error E to evaluate the degree of deviation of the vertical gradient value of each observation pier from the overall gradient array. The relative error formula is:
g in i For the vertical gradient value of the ith observation pad,
is the average value of the vertical gradients of the gradient array, E i The relative error of the vertical gradient of the pier is observed for the ith.
The vertical gradient measurements for the observation piers of gradient arrays #01- #09 are shown in table 2. As can be seen from table 2, the vertical gradient values of the #06 observation pier are small compared to the other piers. Therefore, when calculating the average value of the vertical gradient of the gradient array, the two cases of including the #06 observation pier and not including the #06 observation pier are respectively considered, and the average values are respectively
(containing # 06) and
(without # 06). The relative error E was calculated in each case and the results are shown in table 2.
Table 2 white house village field test vertical gradient results (example)
The result of the relative error measurement shows that the vertical gradient value of the #06 observation pier deviates greatly, and especially under the condition of not containing the #06 result, the relative error value of the #06 observation pier exceeds that of other observation piers by 3 times, and the vertical gradient is regarded as abnormal. After checking the vertical gradient observation data and calculation results of each observation pier, and confirming that the observation environment of the observation pier # 06 is found to be 1m on the south side 1m of the observation pier # 06, about 1m 1.5m stones are present, and preliminary estimation is performed according to the gravity formula, which is considered to be the main reason for the lower vertical gradient of the observation pier # 06.
2) Horizontal gradient measurement results
The measurement results of the horizontal gradients of #01- #09 observation piers (i.e., the ratio of the horizontal gravity level difference between the observation piers to the distance) in the beijing national earth viewing station test sites are shown in table 3. And according to GNSS and leveling results, the gravity value of each observation pier is calculated to the same height by taking the #09 observation pier as a reference, and then the horizontal gradient is calculated.
Table 3 white house village field test horizontal gradient results (example)
In fig. 10, the horizontal gravity gradient calculated by calculating the gravity values of all observation piers to the height of #09 observation piers is shown, the arrow direction in the figure represents the difference direction of the horizontal level difference, and the horizontal gradient unit in fig. 10 is uGal/m.
As shown in fig. 10, in the direction #01- #02- #03, the horizontal gradient changes less, and there is no apparent regularity; in the directions #01- #08- #07, the horizontal gradient is positive, the gravity value is always increased, and in the directions, a certain gravity horizontal gradient trend exists. In order to further ascertain the horizontal gradient characteristics in the field and study the field gravity field change characteristics, se:Sub>A gravity profile is designed in the direction of an encryption profile which is laid by taking the direction of se:Sub>A large arrow shown in fig. 10, and inversion is carried out on the result to obtain se:Sub>A conclusion (the underground density graduation is obtained after inversion, se:Sub>A low-density distribution arese:Sub>A is se:Sub>A low-speed layer), namely, in the field of the earth viewing platform in Beijing country, se:Sub>A low-speed layer, namely, se:Sub>A karst cave exists at the position of 80m underground in the C-A profile (north-south direction).
According to the measurement result, the method can obtain a high-precision gravity value and a gravity field signal through a more efficient field comprehensive measurement mode, and accurately invert and identify the field source gravity signal with a specific space-time scale.
It should be noted that the above-described embodiments will enable those skilled in the art to more fully understand the invention, but do not limit it in any way. Therefore, although the present invention has been described in detail with reference to the drawings and examples, it will be understood by those skilled in the art that the present invention may be modified or equivalent, and in all cases, all technical solutions and modifications which do not depart from the spirit and scope of the present invention are intended to be included in the scope of the present invention.
Claims (10)
1. The method is characterized in that an observation pier array is arranged outside a land measurement site and a datum point is arranged in the land measurement site, the observation pier array comprises a plurality of observation piers which are arranged according to a field source sensitivity array, the lower ends of the observation piers are all fixed in the ground, the upper ends of the observation piers are exposed on the ground, and measuring points are arranged at the bottoms and the surfaces of the observation piers exposed on the ground, and the method further comprises the following steps:
An absolute gravity measurement step, namely setting an absolute gravity meter at the datum point, and further measuring the gravity point value of the datum point to provide an absolute gravity datum of the land measurement site, wherein the datum point is the first measuring point of all the relative gravity simultaneous measurements;
a positioning step, namely performing GNSS positioning on each observation pier to obtain longitude, latitude, elevation and relative elevation of each measuring point position;
a relative gravity measurement step, namely sequentially carrying out relative gravity joint measurement on a relative gravity meter from a datum point along each measurement point of each observation pier, wherein a gravity joint measurement path at least reciprocates once at each measurement point and returns to the datum point to obtain gravity readings of the relative gravity meter at the datum point and each measurement point, obtaining XY two-direction gravity horizontal gradients through a right-angle array, obtaining a Z-direction gravity vertical gradient for each equal-height observation pier with a bottom surface and a top surface, and completing measurement of the gravity horizontal gradients and the vertical gradients;
and a data processing step, wherein a data processing terminal acquires the gravity reading of the relative gravimeter, and performs calculation processing by combining the data acquired in the positioning step and the gravity point value of the datum point provided by the absolute gravimeter to acquire the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point.
2. The observation method of claim 1 wherein the gravity-linked path of the relative gravity measurement step is from a reference point to a measurement point of the pier bottom of a first observation pier, and after one round trip with a measurement point of the pier bottom-pier surface-pier bottom on the first observation pier, goes to a measurement point of the pier bottom of a second observation pier, and after one round trip with a measurement point of the pier bottom-pier surface-pier bottom on the second observation pier, goes to a measurement point of the pier bottom of a next observation pier, and so on, until after one round trip with a measurement point of the pier bottom-pier surface-pier bottom on a last observation pier, goes to the pier bottom of the first observation pier, returns to the measurement point of the pier bottom of the last observation pier, and then returns in sequence from the measurement point of the pier bottom of the last observation pier to the measurement point of the pier bottom of the first observation pier, and then returns to the reference point.
3. The method of observing according to claim 1 wherein the gravity-linked path of the relative gravity measurement step is from the reference point to the measurement point of the pier face of the first observation pier, and after one round trip with the measurement point of the pier face-pier bottom-pier face on the first observation pier, goes to the measurement point of the pier face of the second observation pier, and after one round trip with the measurement point of the pier face-pier bottom-pier face on the second observation pier, goes to the measurement point of the pier face of the next observation pier, and so on, until after one round trip with the measurement point of the pier face-pier bottom-pier face on the last observation pier, goes to the pier face of the first observation pier, returns to the measurement point of the pier face of the last observation pier, and then returns in sequence from the measurement point of the pier face of the last observation pier to the measurement point of the pier face of the first observation pier, and then returns to the reference point.
4. A method of observing according to claim 2 or 3 wherein the relative gravity measurement step takes a main measurement along the gravity joint measurement path and takes an auxiliary measurement after the main measurement, wherein the auxiliary measurement is performed by sequentially and diagonally joining the relative gravity meter from the reference point along each measurement point of each observation pier to obtain the gravity readings of the relative gravity meter at the reference point and each measurement point, and the main measurement is combined with the auxiliary measurement to complete the measurement of the horizontal gradient and the vertical gradient of the gravity.
5. The observation method according to claim 4, wherein the observation piers arranged in an array are arranged at the same height on the ground, and the distance and the pier height of the observation piers in the array are adjusted according to the field condition, the field source characteristics and the field source sensitivity of different measurement methods; each observation pier is rectangular, T-shaped, L-shaped or stepped, and at least has a right angle arrangement.
6. The method of claim 5, wherein the number of observation piers in the array of observation piers is 4 to 9, and the pitch of each observation pier is 20 to 50m.
7. The observation method according to claim 1, wherein the absolute gravimeter used in the absolute gravimetric measurement step includes FG5 absolute gravimeter and/or a10 absolute gravimeter, the FG5 absolute gravimeter measures and selects not less than 12 cell data, the a10 absolute gravimeter measures and selects not less than 24 cell data; the falling times of each combination lattice data are not less than 100 times, and the qualified falling times are not less than 75 times.
8. The observation method of claim 6 wherein the observation piers are 4 and rectangular, and the main measurement is performed 19 times in total at 9 positions of the reference point and the measurement point in the gravity combined measurement path, and the auxiliary measurement is performed 13 times in total at 9 positions of the reference point and the measurement point in the gravity combined measurement path.
9. The observation system for the array type land time-varying gravity and gradient field is characterized by comprising an absolute gravimeter, a relative gravimeter, a positioning device, a data processing terminal, an observation pier array positioned outside a land measurement field and a reference point positioned in the land measurement field, wherein the observation pier array comprises a plurality of observation piers which are arranged according to the field source sensitivity array, the lower ends of the observation piers are all fixed in the ground, the upper ends of the observation piers are exposed on the ground, the bottoms and the surfaces of the observation piers exposed on the ground are all provided with measurement points, the absolute gravimeter, the relative gravimeter and the positioning device are all connected with the data processing terminal,
the absolute gravimeter is arranged on the datum point and is used for measuring the gravity point value of the datum point to provide an absolute gravity datum of a land measurement site, and the datum point is the first measuring point of all the relative gravity joint measurements;
The positioning device is used for performing GNSS positioning on each observation pier to obtain longitude, latitude, elevation and relative elevation of each measuring point position;
the relative gravity meter is used for sequentially carrying out relative gravity joint measurement along each measuring point of each observation pier from the datum point, a gravity joint measurement path at least reciprocates once at each measuring point and returns to the datum point to obtain gravity readings of the relative gravity meter at the datum point and each measuring point, gravity horizontal gradients in the XY two directions are obtained through the right-angle array, and equal-height observation piers with the bottom surface and the top surface each obtain gravity vertical gradients in the Z direction to finish the measurement of the gravity horizontal gradients and the vertical gradients;
the data processing terminal is used for acquiring the gravity reading of the relative gravimeter and carrying out calculation processing by combining the data obtained by the positioning device and the gravity point value of the datum point provided by the absolute gravimeter to obtain the gravity point value, the gravity horizontal gradient and the gravity vertical gradient of each measuring point.
10. The observation system of claim 9 wherein the relative gravity meter performs a primary measurement along a gravity joint measurement path of the pier bottom and pier surface measurement points of each observation pier, and further performs an auxiliary measurement after the primary measurement, wherein the auxiliary measurement is performed by sequentially performing the diagonal joint measurement of the relative gravity meter from the reference point along each measurement point of each observation pier, obtaining gravity readings of the relative gravity meter at the reference point and each measurement point, and the primary measurement and the auxiliary measurement are combined to jointly complete the gravity horizontal gradient and the vertical gradient measurement.
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