WSJT ("Weak Signal Communication, by K1JT") offers specific digital protocols
optimized for meteor scatter, ionospheric scatter, and EME (moonbounce)
at VHF/UHF, as well as HF skywave propagation.  The program can decode
fraction-of-a-second signals reflected from ionized meteor trails and
steady signals 10 dB below the audible threshold.

WWW: http://physics.princeton.edu/pulsar/k1jt/wsjtx.html