Rosette scanning infrared seeker - function and analysis

A study of a rosette scanning infrared seeker (RSIS) and its characteristics has been made. The rosette pattern is generated by two counter rotating optical elements. The rotation frequencies determine the appearance of the rosette pattern, e.g. the number of petals and the width of the petal. The report describes how the parameters of the RSIS affect the pattern and how the system calculates the position of the target from the detector signal. The RSIS scans a single small detector across the total field of view (TFOV) in a rosette pattern. The area that the detector sees in every moment is the instantaneous FOV (IFOV). If the IFOV is small the system gets better resolution, but if the IFOV is too small the performance of the RSIS can deteriorate. Calculations to get the smallest IFOV which can be used to get full scan coverage in the TFOV are described in the report. Two programs have been developed during the study. The first model has been implemented in Matlab and the other in C++. In the Matlab program it is possible to study individual images to get answers to fundamental questions. In the C++ program the RSIS can be used on a sequence of images and it is therefore possible to simulate target tracking. The C++ model has also been integrated with the framework EwSim, which makes it possible to do real time simulations. Further some counter-countermeasures for the RSIS are discussed. Five methods are described and four of them are implemented in the C++ model.