A general methodology for evaluating the capabilities of a general lidar system encompassing both backscatter (elastic and Raman lidar) and topographic targets is presented. By introducing a well defined atmospheric reference medium and by individually examining and decomposing the contribution of lidar system parameters including lidar transmitter power, fields of view, receiver noise, atmospheric conditions, and sky background on the signal-to-noise-ratio (SNR), we obtain a simple dimensionless parameterization of the lidar system. Using this parameterization, numerical simulations are carried out to determine achievable lidar performance including operation range, minimum detectable gas concentration etc.