Abstract

Satellite laser ranging systems typically use ultrashort, high-energy pulses generated from Q-switched ruby lasers or mode-locked Nd:YAG lasers. The average power transmitted in these systems is of the order of 1 W. The range error is proportional to the laser pulse width and inversely proportional to the square root of the number of received signal photoelectrons. An alternative ranging system is proposed which uses a laser diode array as the optical source and a pseudo-noise (PN) code as the ranging signal. For a laser diode array with output power of ~1 W and nanosecond PN code chip duration, range accuracy approaches that of the pulsed laser systems. In this analysis, the maximum likelihood (ML) estimator for photon arrival times is derived for the PN code modulated system taking into account shot noise and background radiation. A correlation receiver is determined to be the optimum receiver using the ML criterion. A bound on the mean-square error of the range estimate is determined for differentiable PN code waveforms. The conditions for which this bound can be used are shown to depend on the number of received signal and background photocounts.

© 1986 Optical Society of America