Over the sea propagation experiments using a SART transponder

The Search And Rescue Transponder (SART) is a new equipment, which must be carried by vessels over 300 gt under the GMDSS regulation (Global Maritime Distress and Safety System). In distress situations, the SART carried into a survival craft would be localized by any marine radar operating at a frequency between 9.2 and 9.5 GHz. Twelve dots appear on the radar screen for each turn. The first dot indicates the location of the survival craft. The quality of this SART detection is considered sufficient when the received signal is above the radar threshold at least for 20 % of the radar turns. We describe and analyse experimental results concerning propagation measurements obtained with such a SART equipment. It is pointed out that the mean slope of the path loss distributions is correlated with the sea state. The measured path losses are generally well fitted by the transponder equation recommended by the ITU, assuming a standard atmosphere. The main discrepancies observed may reasonably be explained by subrefraction conditions.