We present a general methodology for evaluating the capabilities of a general lidar system encompassing both backscatter (elastic and Raman lidar) and topographic targets. By introducing a well-defined atmospheric reference medium and by individually examining and decomposing the contributions of lidar system parameters including lidar transmitter power, field of view, receiver noise, atmospheric conditions, and sky background on the signal-to-noise ratio, 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, and so on.