Detection of oceanic thermal fronts off Korea with the Defense Meteorological Satellites.
The scanning radiometers on the satellites of the Defense Meteorological Satellite Program (DMSP) have provided useful thermal infrared (8-13 mm) imagery of the oceanic regions near the Korean Peninsula. The near real-time thermal infrared data (at 3.7 km spatial resolution) provided temperatures some 2-10 degrees C cooler than the actual surface measurements. The thermal gradients were faithuflly reproduced, however, and relative temperature differences to less than 0.1 °C were successfully estimated from the imagery. A combination of methods, including albedo differnece, temperature threshholding, time-stability, and pattern recognition, was used to avoid possible confusion with atmposhperic temperature and humidity gradients. The oceanic thermal from between the Tsushima Current and the Korean coastal waters was routinely detected and displayed on the electro-optically contoured thermal imagery. The contour intervals are 1.6 °C, and noise-induced effects give a thermal resolution of 0.8 °C. Temperature differences across the front of 3.29 °C (s = 0.42 °C) were measured by seven ship crossings, and temperature differemces of 3.3 °C (s = 0.4 °C) were estimated from five satellite overpasses. Thermal patterns of a one-sided divergence and a cyclonic eddy were detected in the coastal waters at the flow separation where the western edge of the Tsushima Current curves away from the coast into the Sea of Japan. A critique of the oceanographic capabilities and limitations of the system is provided as a guide to potential users.