The correlation of the 1981--1990 (~23 to ~50 AU) data of three instruments, the ultraviolet photometer (UV), the charged particle instrument (CPI), and the trapped radiation detector (TRD), on board Pioneer 10 is investigated. The reduction of the data necessary for applying a fast Fourier transform (FFT) algorithm is described. A cross correlation function between the hydrogen Lyman &agr; backscattered radiation, used as a solar cycle proxy, and the cosmic ray fluxes is obtained from the FFT algorithm. The time lag in the anticorrelation function between the galactic cosmic rays and the Lyman &agr; line is used to determine the distance to the solar wind termination shock (75 AU), under the assumption that the cosmic ray modulation boundary for low-energy particles and the termination shock are coincident. The ratio of the upwind termination shock distance to the downwind shock distance is determined to be 2/3 using the Voyager 1 position in 1996.¿ 1997 American Geophysical Union