Ship Detectability of Satellite-Based Radio Frequency Data in a Congested Area

This study examined the association between radio frequency (RF) data and ships in a congested area, with a focus on the Busan Port region in South Korea. RF datasets consisting of one L-band, four S-band, and two X-band frequencies were used in conjunction with Automatic Identification System (AIS) and Small Fishing Vessel Tracking System (V-Pass) data collected during the corresponding RF data periods. A distance-based association approach was applied, and the RF–ship association ratio (RSAR) was estimated as the ratio between the number of AIS-reported vessels associated with RF data and the total number of AIS-reported vessels present within the time period. The results indicate low overall RSAR in the congested region, with 6.5% for L-band, 1.7–24.6% for S-band, and 7.7–17.2% for X-band. Under stable high-pressure conditions (101.4–102.2 kPa) and light breeze conditions (0.9–3.6 m/s), atmospheric impacts on the RSAR can be considered minimal. Moreover, to indicate the relationship between the acquired RF signal and vessel congestion, a congestion index (CI) was derived from AIS and V-Pass data using a spatial grid-based method. The CI density maps within the congested region indicate that the acquired RF signals exist dominantly in low-congested areas.