AIS reception from a CubeSat in LEO

The primary payloads on board the AAUSAT3 satellite are two different AIS receivers, one is a traditional hardware-based receiver, the other one is a software-defined radio receiver. The hardware-based receiver has been developed around an ADF-7020 transceiver, with an appropriate LNA in front. The SDR-based receiver is developed around the similar ADF-7021, which in addition to the bit-stream output also features an output of the 200 kHz I/Q IF signal. This analogue signal is in turn sampled at around 750 kHz and then processed by a DSP. The 1U AAUSAT3 CubeSat was launched on 25 February 2013 into a low-Earth orbit with a semi-major axis of 7156 km, i.e. 800 km altitude, near circular, dusk-dawn Sun-synchronous orbit. From this orbit the AIS antenna system, which consists of a dipole antenna, has a foot print diameter of approximately 6000 km. During the first pass over the primary ground station at Aalborg University, basic telemetry and the first few AIS messages were downloaded. During the first 14 days of the mission, the two receivers managed to detect more than 100,000 different AIS messages from ships all around the world, and more than 35,000 of these messages have been successfully downlinked to the AAU ground station for further processing. In this paper we will explain how the two different AIS receivers are working, provide an analysis of the capabilities of the receivers in orbit, and will present some of the preliminary performance metrics which have been found for the two receivers.