what is river sampling for
Fundamentally, river sampling is a web-based convenience sample of opt-in participants that uses a quota sampling approach to build a study sample. The selection method is not probability based, and participants cannot be described as representing any larger defined population.
In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal).