  This work is concerned with the inverse source problem of locating multiple
multipolar sources from boundary measurements for the Helmholtz equation. We
develop simple and effective sampling schemes for location acquisition of the
sources with a single wavenumber. Our algorithms are based on some novel
indicator functions whose indicating behaviors could be used to locate multiple
multipolar sources. The inversion schemes are totally "direct" in the sense
that only simple integral calculations are involved in evaluating the indicator
functions. Rigorous mathematical justifications are provided and extensive
numerical examples are presented to demonstrate the effectiveness, robustness
and efficiency of the proposed methods.
