여러 센서들의 배열을 이용한 최근의 해양 자력구배 측정시스템의 개발을 통하여 넓은 오염지역의 조사를 빠르게 수행할 수 있게 되었다. 그러나 물밑의 UXO 는 조류에 의해 이동할 수 있으며 따라서 이런 환경에서의 복원과정은 정적이라기 보다는 동적이 되었다. 이는 곧 성공적인 복원을 위해서는 탐지가 거의 실시간으로 이루어져야 함을 말한다. 그러므로 해양 자력탐사자료로부터 물밑 물체의 신호를 빠르게 탐지할 수 있는 신속한 해석법이 필요하다. 이 논문에서는 물밑 UXO 의 위치 및 특성을 알아내는 신속한 방법을 소개하였다. 먼저 대상체의 정밀 탐지를 위해 자력구배자료의 해석기법(해석적 신호와 Euler 방법)을 이용하며, 반복적 선형 최소자승법을 이용해 대상체의 자기 특성을 얻어낸다. 이 방법은 알고 있는 대상체에 대해 무작위 잡음을 더한 이론적 해양 자력이상에 적용되었으며, 일본의 해양 자력구배탐사 자료를 이용하여 실질적인 유용성을 예시하였다.
여러 센서들의 배열을 이용한 최근의 해양 자력구배 측정시스템의 개발을 통하여 넓은 오염지역의 조사를 빠르게 수행할 수 있게 되었다. 그러나 물밑의 UXO 는 조류에 의해 이동할 수 있으며 따라서 이런 환경에서의 복원과정은 정적이라기 보다는 동적이 되었다. 이는 곧 성공적인 복원을 위해서는 탐지가 거의 실시간으로 이루어져야 함을 말한다. 그러므로 해양 자력탐사자료로부터 물밑 물체의 신호를 빠르게 탐지할 수 있는 신속한 해석법이 필요하다. 이 논문에서는 물밑 UXO 의 위치 및 특성을 알아내는 신속한 방법을 소개하였다. 먼저 대상체의 정밀 탐지를 위해 자력구배자료의 해석기법(해석적 신호와 Euler 방법)을 이용하며, 반복적 선형 최소자승법을 이용해 대상체의 자기 특성을 얻어낸다. 이 방법은 알고 있는 대상체에 대해 무작위 잡음을 더한 이론적 해양 자력이상에 적용되었으며, 일본의 해양 자력구배탐사 자료를 이용하여 실질적인 유용성을 예시하였다.
Recent development of marine magnetic gradient systems, using arrays of sensors, has made it possible to survey large contaminated areas very quickly. However, underwater Unexploded Ordnances (UXO) can be moved by water currents. Because of this mobility, the cleanup process in such situations becom...
Recent development of marine magnetic gradient systems, using arrays of sensors, has made it possible to survey large contaminated areas very quickly. However, underwater Unexploded Ordnances (UXO) can be moved by water currents. Because of this mobility, the cleanup process in such situations becomes dynamic rather than static. This implies that detection should occur in near real-time for successful remediation. Therefore, there is a need for a fast interpretation method to rapidly detect signatures of underwater objects in marine magnetic data. In this paper, we present a fast method for location and characterization of underwater UXOs. The approach utilises gradient interpretation techniques (analytic signal and Euler methods) to locate the objects precisely. Then, using an iterative linear least-squares technique, we obtain the magnetization characteristics of the sources. The approach was applied to a theoretical marine magnetic anomaly, with random errors, over a known source. We demonstrate the practical utility of the method using marine magnetic gradient data from Japan.
Recent development of marine magnetic gradient systems, using arrays of sensors, has made it possible to survey large contaminated areas very quickly. However, underwater Unexploded Ordnances (UXO) can be moved by water currents. Because of this mobility, the cleanup process in such situations becomes dynamic rather than static. This implies that detection should occur in near real-time for successful remediation. Therefore, there is a need for a fast interpretation method to rapidly detect signatures of underwater objects in marine magnetic data. In this paper, we present a fast method for location and characterization of underwater UXOs. The approach utilises gradient interpretation techniques (analytic signal and Euler methods) to locate the objects precisely. Then, using an iterative linear least-squares technique, we obtain the magnetization characteristics of the sources. The approach was applied to a theoretical marine magnetic anomaly, with random errors, over a known source. We demonstrate the practical utility of the method using marine magnetic gradient data from Japan.
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문제 정의
Examples of these techniques are the analytic signal and Euler methods. In this paper, we describe a fast procedure for target location and characterization of underwater steel objects. In our procedure, target location is initially estimated using an analytic signal approach (Salem et al.
제안 방법
Once the source location is estimated using the Euler method, source magnetization parameters can be obtained using a simple method. The method is based on using tentative sets of inclination and declination and estimating the magnetic moment from the observed vertical gradiometer data. The set of inclination and declination that is associated with minimum errors in a least squares sense is selected.
In this paper, we have presented a fast procedure for location and characterization of underwater UXO. The procedure utilises gradient interpretation techniques (analytic signal and Euler methods) to locate the objects precisely.
대상 데이터
m2 in an ambient magnetic field with an inclination of 30° and a declination of 0°. The data are calculated at an interval of 0.5 m on a grid of 20 m x 20 m extent, with the dipole placed at the centre of the grid (x = 10 m and y = 10 m from the origin) and at a depth of 3 m. The data have been contaminated by an additive random noise with zero mean and a standard deviation of 1 nT/m.
, 2003). In this survey, a boat with a GPS positioning system was used and 16 fluxgate vertical magnetic gradiometers (Figure 3) were towed behind the boat. Each vertical gradiometer consists of two vertical component sensors separated by 1 m.
In this experimental test, different types of UXO objects were buried at depths between 0 and 1 m below the sea bottom in an area of approximately 440 m2. Measuring the exact value for the depth of each object was difficult.
Measuring the exact value for the depth of each object was difficult. Measurements were made at a distance of 1 m above the sea bottom along three tracks with a length of 20 m. The magnetic field of the Earth at the test site has an inclination of 47.
이론/모형
, 1990) is then used to define more precisely the actual location of the source. Using this estimated source location, magnetization source parameters are estimated using an iterative linear least squares approach. The practical utility of the procedure is demonstrated using theoretical and field examples of marine magnetic gradient data.
However, location errors may occur because the method uses single values at the peaks. Therefore, we consider this source location to be an initial estimate and seek a more precise location using the Euler method, which uses several data values and utilises a least squares approach.
Contour interval 5 nT/m2. Circle shows the estimated horizontal location using the analytic signal method. Square indicates the data window for the Euler method.
25 m. The requisite derivatives for the analytic signal and Euler method were computed in the frequency domain using the FFT method. Figure 6 is the AAS} map of the observed data, after applying upward continuation.
In applying the procedure, the analytic signal method first detected the initial locations of the sources and then the Euler method was applied, using a data window of 2.5 m x 2.5 m, centred above the initial estimated locations. From the same data window, magnetization parameters were estimated using a set of tentative sets of inclination and declinations with an interval of 2°.
In this paper, we have presented a fast procedure for location and characterization of underwater UXO. The procedure utilises gradient interpretation techniques (analytic signal and Euler methods) to locate the objects precisely. Using an iterative linear least-squares approach, magnetization characteristics of the source are also obtained.
성능/효과
To estimate the magnetization source parameters, the estimated source location values were used together with tentative sets of inclination and declination at an interval of 5°. Our procedure again gave good results for the magnetization source parameters (predicting inclination = 30°, declination = 0°, and magnetic moment is 9.6 A.m2). The inclination and declination are estimated exactly and the error in the estimated magnetic moment is less than 5%.
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