인공위성 레이더고도 측정값으로부터 유도된 중력이상으로턱터 남극 드레이크해협의 해저지형을 계산하기 위해 Gravity-Geologic Method(GGM)를 적용하였다. 총 6548개의 음항측심자료 중 2/3는 control depth로, 나머지는 결과 검증을 위한 check point 자료로 이용하였다. 효과적인 계산을 위해 해수와 해저지형의 밀도차이는 check point를 이용, 9.0 gm/㎤로 가정하였다. Control depth로부터 광역중력이상을 계산하였고, 이를 Sandwell & Smith(1997)의 중력이상으로부터 제거하여 해저지형의 기복에 의한 중력 효과를 계산하였으며, 이로부터 해저지형을 복원하였다. Selective Merging 기법을 개발하여 복원된 해저지형과 고주파 측심자료를 효과적으로 합성하였다. 복원된 해저지형은 한국해양연구원의 측심자료, GEODAS 및 전지구 모델 ETOPO5 결과와 각각 0.91, 0.92, 0.85의 상관계수를 갖으며, Selective Merging을 이용한 최종 결과는 GEODAS 및 Smith Sandwell(1997)의 결과와 각각 0.948 및 0.954의 상관관계 및 449.8, 441.3 m의 RMS 오차를 갖는다. GGM을 이용하여 계산된 해저지형은 측심이 충분히 이루어지지 않은 지역의 경우 전지구모델(ETOPO5)이나 자료의 양이 불충분한 음항측심에 의한 결과보다 우수한 것으로 나타났다.
인공위성 레이더고도 측정값으로부터 유도된 중력이상으로턱터 남극 드레이크해협의 해저지형을 계산하기 위해 Gravity-Geologic Method(GGM)를 적용하였다. 총 6548개의 음항측심자료 중 2/3는 control depth로, 나머지는 결과 검증을 위한 check point 자료로 이용하였다. 효과적인 계산을 위해 해수와 해저지형의 밀도차이는 check point를 이용, 9.0 gm/㎤로 가정하였다. Control depth로부터 광역중력이상을 계산하였고, 이를 Sandwell & Smith(1997)의 중력이상으로부터 제거하여 해저지형의 기복에 의한 중력 효과를 계산하였으며, 이로부터 해저지형을 복원하였다. Selective Merging 기법을 개발하여 복원된 해저지형과 고주파 측심자료를 효과적으로 합성하였다. 복원된 해저지형은 한국해양연구원의 측심자료, GEODAS 및 전지구 모델 ETOPO5 결과와 각각 0.91, 0.92, 0.85의 상관계수를 갖으며, Selective Merging을 이용한 최종 결과는 GEODAS 및 Smith Sandwell(1997)의 결과와 각각 0.948 및 0.954의 상관관계 및 449.8, 441.3 m의 RMS 오차를 갖는다. GGM을 이용하여 계산된 해저지형은 측심이 충분히 이루어지지 않은 지역의 경우 전지구모델(ETOPO5)이나 자료의 양이 불충분한 음항측심에 의한 결과보다 우수한 것으로 나타났다.
The Gravity-Geologic Method (GGM) was implemented for bathymetric determinations in the Drake Passage, Antarctica, using global marine Free-air Gravity Anomalies (FAGA) data sets by Sandwell and Smith (1997) and local echo sounding measurements. Of the 6548 bathymetric sounding measurements, two thi...
The Gravity-Geologic Method (GGM) was implemented for bathymetric determinations in the Drake Passage, Antarctica, using global marine Free-air Gravity Anomalies (FAGA) data sets by Sandwell and Smith (1997) and local echo sounding measurements. Of the 6548 bathymetric sounding measurements, two thirds of these points were used as control depths, while the remaining values were used as checkpoints. A density contrast of 9.0 gm/㎤ was selected based on the checkpoints predictions with changes in the density contrast assumed between the seawater and ocean bottom topographic mass. Control depths from the echo soundings were used to determine regional gravity components that were removed from FAGA to estimate the gravity effects of the bathymetry. These gravity effects were converted to bathymetry by inversion. In particular, a selective merging technique was developed to effectively combine the echo sounding depths with the GGM bathymetiy to enhance high frequency components along the shipborne sounding tracklines. For the rugged bathymetry of the research area, the GGM bathymetry shows correlation coefficients (CC) of 0.91, 0.92, and 0.85 with local shipborne sounding by KORDI, GEODAS, and a global ETOPO5 model, respectively. The enhanced GGM by selective merging shows imploved CCs of 0.948 and 0.954 with GEODAS and Smith & Sandwell (1997)'s predictions with RMS differences of 449.8 and 441.3 meters. The global marine FAGA data sets and other bathymetric models ensure that the GGM can be used in conjunction with shipborne bathymetry from echo sounding to extend the coverage into the unmapped regions, which should generate better results than simply gridding the sparse data or relying upon lower resolution global data sets such as ETOPO5.
The Gravity-Geologic Method (GGM) was implemented for bathymetric determinations in the Drake Passage, Antarctica, using global marine Free-air Gravity Anomalies (FAGA) data sets by Sandwell and Smith (1997) and local echo sounding measurements. Of the 6548 bathymetric sounding measurements, two thirds of these points were used as control depths, while the remaining values were used as checkpoints. A density contrast of 9.0 gm/㎤ was selected based on the checkpoints predictions with changes in the density contrast assumed between the seawater and ocean bottom topographic mass. Control depths from the echo soundings were used to determine regional gravity components that were removed from FAGA to estimate the gravity effects of the bathymetry. These gravity effects were converted to bathymetry by inversion. In particular, a selective merging technique was developed to effectively combine the echo sounding depths with the GGM bathymetiy to enhance high frequency components along the shipborne sounding tracklines. For the rugged bathymetry of the research area, the GGM bathymetry shows correlation coefficients (CC) of 0.91, 0.92, and 0.85 with local shipborne sounding by KORDI, GEODAS, and a global ETOPO5 model, respectively. The enhanced GGM by selective merging shows imploved CCs of 0.948 and 0.954 with GEODAS and Smith & Sandwell (1997)'s predictions with RMS differences of 449.8 and 441.3 meters. The global marine FAGA data sets and other bathymetric models ensure that the GGM can be used in conjunction with shipborne bathymetry from echo sounding to extend the coverage into the unmapped regions, which should generate better results than simply gridding the sparse data or relying upon lower resolution global data sets such as ETOPO5.
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문제 정의
The authors thank Prof. Ralph von Frese at The Ohio State University and Dr. Daniel Roman at NGS/NOAA for their reviews and comments on this paper. Elements of this study were produced with support from 1999-2001 National R&D Pro gram of Korea Ministry of Science & Technology (Energy/Resources 99-03) and from Polar Research Division of Korean Ocean Research and Devel opment Institute.
제안 방법
Table 1. Comparison of correlation coefficients (CC) between the original GGM bathymetry (before selective merging of GGM) and KORDI, Checkpoint, GEODAS, ETOPO5 bathymetrics. RMS differences between the GGM, KORDI, and Checkpoint bathymetries are also shown in parenthesis (unit in meter).
In particular a selective merging technique was developed to effectively combine the echo sound ing depths with the GGM bathymetry to enhance high frequency components along the shipbome sounding tracklines. For the rugged bathymetry of the research area, the GGM bathymetry shows correlation coefficients (CC) of 0.91, 0.92, and 0.85 with local shipbome sounding by KORDI, GEODAS, and a global ETOPO5 model, respec tively. The enhanced GGM by selective merging shows improved CCs of 0.
In this study, the utility of the Gravity-Geologic Method (GGM) was investigated to estimate improved bathymetry (i.e., seafloor topography) in the Drake Passage, Antarctica. In the study area, there are irregular, and sparse shipbome mea surements of sea floor depth, but uniform and dense satellite altimeter measurements are also available.
, 1993. The GGM bathymetric determinations were compared with bathymetric check values (i.e., bathymetry estimated only from the check points) to determine the statistical improvement that may be available from utilizing the enhanced gravity predictions.
8A. The black lines with tri angle symbols denote bathymetry from sonar soundings, and the gray lines with square symbols denote bathymetry estimated by the GGM in this study. For Profile #7 in Fig.
대상 데이터
In order to test the veracity of GGM in a deep, rugged ocean bottom environment, the area 56.1-57.7° W and 60.25~61.25° S in the Drake Passage, Antarctica, was selected (Fig. 1). The selected area is well covered with the 2-minute altimetry-implied FAGA by Sand well and Smith (1997) that were used as observed anomalies gOBS (marked with black dots) and bathymetric data (black lines) from KORDIs shipbome who soundings (Fig.
이론/모형
The Gravity-Geologic Method (GGM) was imple mented for bathymetric determinations in the Drake Passage, Antarctica, using global marine Free-air Gravity Anomalies (FAGA) data sets by Sandwell and Smith (1997) and KORDI's local echo sound ing measurements. Of the 6548 bathymetric sound ing measurements, two thirds were used as control depths, while the remaining values were used as checkpoints.
성능/효과
Trade-off diagram for selecting a density contrast in the study area. Although not a geologically reasonable value, a density contrast of 9.0 gm/㎝3 was selected because the RMS differences between the GGM predictions and the checkpoints converge to 29.2 m as the density contrast is increased.
In the study area, FAGA and bathymetries were found not consistent in the complex topographic area due to geologic and tectonic features such as the South Shetland Trench and the South Scotia. This may be explained by the fact that both bathy metric undulations and horizontal density varia tions contribute to the altimetry-implied gravity anomalies, and, hence, the resulting altimetry- derived bathymetries are distorted.
89, respectively (Table 1). The RMS dif ference between GGM and KORDI bathymetries (bathymetry estimated by KORDls shipbome sound ings only) is 562.2 meter, which is 6.6% greater than the RMS between GGM and checkpoint bathymetries, indicating the GGM prediction in this study is reliable.
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