Passive sounding modes for RIME or REASON could enable sub-Jovian HF sounding in the presence of strong decametric radiation. The SNR of passive HF sounding has the potential to exceed that of active HF sounding in a noisy sub-Jovian environment. Active sounding achieves a greater SNR in the presence of quiescent noise and performs better in terms of clutter. Any potential performance improvement by changing the center frequency is marginal relative to other implementation choices.