  Transmission eigenchannels and quasi-normal modes are powerful bases for
describing wave transport and controlling transmission and energy storage in
disordered media. Here we elucidate the connection between these approaches by
expressing the transmission matrix (TM) at a particular frequency as a sum of
TMs for individual modes drawn from a broad spectral range. The wide range of
transmission eigenvalues and correlation frequencies of eigenchannels of
transmission is explained by the increasingly off-resonant excitation of modes
contributing to eigenchannels with decreasing transmission and by the phasing
between these contributions.
