Obscured Ship Signals Over Ninety Kilometers at Arecibo

Abstract

This paper will discuss the coherent interference which has been determined to be ships on the ocean, and review the ship signal phenomenon that has been detected numerous times with the incoherent scatter radar at the Arecibo Observatory in Puerto Rico. V-shaped coherent structures have been observed when the magnitude of raw power bounced back to the receiver is plotted against time and altitude. These structures have been determined to be ships due to the slow velocity of the objects, the high amount of power reflected back to the receiver and the relatively short range. While the radar apparatus at Arecibo is the world’s most sensitive and is able to monitor electron density changes in the different regions of the ionosphere it is unable to detect large cruise ships beyond a distance of 90 kilometers. The main reason for this is that the radar at Arecibo was never intended to monitor ships as the dish and antenna are aimed directly towards the sky. However, we will investigate the reason why ship signals observed at Arecibo are not able to be detected beyond a range of 90 kilometers and demonstrate that the causation for the inability of the radar to detect ships beyond this range is due to the line of sight of the radar at this specific location and the curvature of the Earth.