Hardware-accelerated CCD readout smear correction for Fast Solar Polarimeter

Abstract

Shutterless frame store charge-coupled devices (CCDs) are commonly used in ground-based solar observations, but the characteristical readout smear error of such devices hinders an application of frame store CCDs to autonomous missions. The combination of polarimetric modulation and image accumulation disables a correction of this error via software-based post-facto processing if in addition microvibrations occur during flight. This paper presents the first FPGA-based architecture for online smear correction of images from frame store CCDs, which allows for the usage of a certain frame store CCD camera on a balloon-borne solar observatory. First, we explore fast convolution-based algorithms with respect to their properties for an implementation. Afterwards, a hardware architecture is derived and implemented. Our results show that 400 frames of megapixel size can be corrected per second, maintaining an acceptable power consumption of less than 12 Watt. Finally, we discuss the circuit and show the degrees of freedom for further designs.