The SUS-OAT experiments were carried out in the Ulleung Basin of the East Sea/Japan Sea during summer season. The SUS-OAT system consisted of aircraft deployed shots as sources and a vertical line array (VLA) tethered by a receiver ship were used to survey a large area where a mesoscale warm eddy appears frequently. Two separate experiments were carried out such that explosive charge set to detonate at 800 ft depth were dropped in a rectangular (120x120km) ('97 experiment) and a circular pattern (30 and 60km radius around a receiver, '98 experiment). Sources were a rapidly deployable SUS charge (MK 61 MOD 0 and MK 64 MOD 0), and receiver is a fixed vertical line array, 90m in length (150-240m and 270-360m in receiver depth), composed of 10 elements equally spaced. Fig. 1 shows the location of the receiver ship (VLA receiver), the positions of SUS charges, AXBT and sonobuoy drops. The experimental area has a nearly flat bottom with deeper than 2,000m in depth.
a) '97 experiment(June)
b) '98 experiment(August)
Fig. 1. Location maps of the SUS-OAT experiment. The positions of the SUS, AXBT and sonobuoy drops are marked with “*”, and “◇”, and “□”, respectively.
3. Results
To measure the horizontal temperature fields, the rectangular area is divided into 50 grids every 10 minute for '97 experiment and the circular area is divided into 36 grids every 30 degree for the inner circle and 15 degree for the outer circle for '98 experiment. The reference ray paths are computed by range-independent model in canonical ocean. The canonical ocean has been determined based on the historical data. The singular value decomposition (SVD) method that has been known to be the most powerful one (Lee, 1993) is used to obtain the horizontal perturbation of the temperature fields. Horizontal distributlons of temperature fields at 150m and 200m depth show a weak warm eddy observed by AXBT (Fig. 2).
