  The creation and justification of the methods for minimax estimation of
parameters of the external boundary value problems for the Helmholtz equation
in unbounded domains are considered. When observations are distributed in
subdomains, the determination of minimax estimates is reduced to the solution
of integro-differential equations in bounded domains. When observations are
distributed on a system of surfaces the problem is reduced to solving integral
equations on an unclosed bounded surface which is a union of the boundary of
the domain and this system of surfaces. Minimax estimation of the solutions to
the boundary value problems from point observations is also studied.
