GPS/INS Integration Using Kalman Filtering for Shipborne Navigation Yashar Balazadegan Iran Email: yashar.balazadegan@gmail.com Mohammad.A.Rajabi Email: marajabi@ut.ac.ir The need for a positioning system which works in different environmental conditions has led researches to use GPS aided INS. Despite all of the advantages of GPS, there are instances that due to signal lost GPS is not able to provide any position. Besides, GPS bandwidth is too small for some specific applications such as photogrammetery. Moreover, most of GPS errors are due to the effect of propagation media. In other words, errors are not accumulated over time. This means that GPS positions are reliable in long term. On the other hand, INS is an autonomous system which is able to provide positions in any environment with a high bandwidth. However, INS errors are generally accumulated over time which puts the long term reliability of system under question. This shows that GPS and INS are two complementary systems and cover each others deficiencies. This paper reviews the fundamentals of both GPS and INS systems and discusses the integration process of differential GPS observations with medium accuracy INS measurements using loosely coupled integration method. It is shown that the positioning error reaches up to 18 m after GPS signals are lost for 250 seconds.