Horizontal scale and movement of tidal front zone, front in the western regions of Korea in summer are studied in conjunction with numerical model and NOAH-11 satellite data analysis(AVHRR multi -channel sea surface temperature). In numerical model result, tidal mixing is dominant in the southeast region of Hwanghae, near field of Taean, Kyunggi bay, near field of Jangsan cape, Seoan bay, mid-east Chinese coast. But the results of the NOAH infra-red image analysis show that low surface temperature by tidal mixing is clear in the southeast region of Hwanghae, near field of Taean, near field of Jangsan cape but not in the Kyunggi bay, Seoan bay and mid- east Chinese coast in August and September, temperature gradient of frontal zone in the southwest region of Hwanghae is 0.05°∼0.1℃/㎞ and tidal mixing is dominant in the near field of Maenggal kundo and Hajodo and low surface temperature extends southwesrward. Early in August, west-east front(0.2°∼0.6℃/㎞) on the south region of Jindo moves northward and persists at east half on the joining line of Jindo and Sohuksando late September. The axis of front on the west region of Jindo is northeast~sorthwest early in August and moves westward until late September The tidal mixing in the near field of Jangsan cape is dominant in the region between Jangsan cape and Baengyougdo early in August and between Baengyougdo and Daechungkundo in late September. The axis of front on the west region of Jangsan cape is south-north and its temperature gradient is 0.2°∼0.4℃/㎞.

20cm 태양망원경이 소백산 천문대에서 대덕 천문우주과학연구소로 이전 설치된 후, 1987년 6월 19일 부터 1990년 11월 30일까지 흑점관측을 수행하여 343개의 흑점관측자료를 얻었다. 본 관측기간중 일일 평균 흑점상대수는 83.4로, 매일 평균 5개의 흑점군과 30개의 흑점이 관측되었다. 관측된 월평균 흑점상대수를 분석한 결과에 의하면 1986년 9월에 시작한 제22 태양활동 주기의 극대기는 1989년 9월경으로 밝혀졌다. 국제 흑점 상대수와 비교 가능한 292개의 관측 자료를 사용하여 대덕 태양망원경의 규격화 상수 K를 결정하였으며, 그 간은 소백산 천문대의 규격화 산수 0.87보다 큰 1.08로 밝혀진다.

The multiquadric terrain equation reproduces topography which is much closer to the real one than the digital terrain model. Also, terrain correction calculated by using the multiquadric terrain model shows a better result than that of digital terrain model. The accuracy of terrain correction depends on the accuracy of terrain data. Therefore, determination of the mean elevation of a terrain compartment by taking simple average of the maximum and minimum terrain height is not recommended. To obtain more accurate mean elevation of a compartment, a smaller scale topographic map such as 1:5,000 map is desirable for reading terrain data. But 1:25,000 map can be used for practical use. The pattern size of 250m×250m compartment is appeared to be suitable for near correction(D-F range), and 5㎞×5㎞ size for far correction. The computer program developed in this research can be used in all cases of surface and subsurface gravity surveys.

The purpose of this study is to investigate basic parameters which are essential for tidal correction of gravity data. This study involves computation of the theoretical values and laboratory measurements of tidal force of gravity. The theoretical variation of tidal force was computed according to the relative position of moon and sun on the celestial sphere by using a computer program Gravity measurements were carried out in Seoul University for 120 operation-hours, and also in coastal area in Incheon for 48 operation-hours. The gravimetric factor (δ) and phase delay were determined by comparing theoretical values with measured gravity data. Summarized results of this study are as follows ; (1) The gravimetric factor in Seoul is in the range of 1.22∼1.36(avg.=1.28) and the phase delay is in the range of 0.1∼0.3 hours (avg.=0.16 hours). (2) The mean garvimetric factor in Incheon is 1.31 and mean phase delay is 0.025 hours (3) The difference of mean gravimetric factor between in Seoul and in Incheon is 0.03 and that of phase delay is 8 minutes.

The authors analyzed the daily catch data which were obtained from two different regions at the Southern Sea in Korea, Neungpo, Geoje island and Yangwhagum, Namhae island, during three or four years in 1978, 1981-1985, in order to know the fishing characteristics of the set net fisheries. The favorable fishing season was summer in the southern sea. The total catches during one year were greatly affected by those several day when the dominant species of fish were caught in large quantities. The dominant species of fish at Neungpo were little horse mackerel, sand lance, sardine, hair tail, spanish mackerel and common mackerel, and those at Yangwhagun were anchovy, little horse mackerel, sardine, spanish mackerel and gizzard shad, in order of catch. Especially, the little horse mackerel and the sardine appeared to make up very big schools at both Neungpo and Yangwhagum. The occurrence seasons of the dominant species were different by the region, but generally those were earlier at western part than at eastern part of the Southern Sea in Korea.

The earthquake source parameters of Daegu and Incheon Earthquakes occurred on July, 1985 are redetermined and compared with those reported by Central Meteorological Office of Korea(CMO). Instead of the travel time table used in CMO, the seismic velocity structure calculated from the explosion seismic records of the southern part of Korea is adopted in determining source parameters, P-wave and S-P wave arrival times obtained from seismograms recorded in the networks of KIER and JMA including CMO are used. The discrepancies of determined epicenter and focal depth between CMO and the present work appear to be 6∼8 ㎞ and about 10 ㎞, respectively. In conclusion, the potential error included in epicenter of the Korean instrumental earthquake data is supposed to be about 10 km for the earthquakes(M$gt;3) occurred within the CMO network. However, the error will probably be more than 10 ㎞ for smaller earthquakes or earthquakes of the outside of the network.

The computation of the undulation of the Moho discontinuity from gravity data has frequently been carried out by the application of the Fourier series and the Sinc function (sin x/x), However, no serious effort has been attempted to examine the suitability of data and the adaptability of implicit assumptions required in such methods. This paper deals with model studies for comparison of the Fourier series and Sinc function methods, and examinations of several criteria for obtaining meaningful results. Also, an inversion method based on mass plane concept has been devised to complement the weakness of the above two methods. This method has been appeared as an effective scheme for increasing depth computation points so that a more detailed undulation is obtained.

The offshore magnetic data were analyzed to determine the depth of magnetic basement of Kyungi-bay. The mean depth to the basement was computed by a power spectral analysis method. To determine the relief of magnetic basement, the total magnetic intensity data were first reduced to the pole and transformed to a pseudo-gravimetric anomaly data using the Poisson's relation. The relief of basement was estimated from the downward continued pseudo-gravimetric anomaly data to the mean depth. In the process of data preparation, Tuckey and Harming filter was used to suppress the near surface effect of short wavelength. A band-pass filter was also applied before downward continuation. From the result of this study, it is appeared that the magnetic basement rock is ccmposed of mainly granite gneiss and depth to the basement rock is varied from 300m to 500m. The relief of magnetic basement is appeared to reflect the general topography in this area.