Christopher J. Paciorek, "Bayesian Smoothing of Irregularly-spaced Data Using Fourier Basis Functions" (August 2006)".  Harvard University Biostatistics Working Paper Series. Working Paper 47.
http://www.bepress.com/harvardbiostat/paper47

Paciorek, C.J. 2006. Bayesian Smoothing of Irregularly-spaced Data Using Fourier Basis Functions. Harvard University Biostatistics Working Paper Series. Working Paper 47.  http://www.bepress.com/harvardbiostat/paper47