I and q channels

From Glossary of Meteorology

I and Q channels

(Abbreviation for in-phase and quadrature channels.) In Doppler radar and lidar receivers, the quadrature video channels produced by coherent detection of the IF signal.

The energy in the two channels is in phase quadrature, and they may be considered together to be a single complex signal with frequency components from -F to +F, where F is the passband limit of the low-pass filter used in the demodulator.