(a) a measurement F0(x, y, δt) of the signals detected is provided; (b) on the one hand a first value F1(X, y, δt) is provided, termed the “integration” value and on the other hand a second value F2(x, y, δt) termed the “count” value is provided; (c) a value Fe(x0, y0, δt) of a number of signals is estimated from a combination of first F1(X0, y0, δt) and second F2(x0, y0, δt) values, on the basis of a criterion of detection in the neighborhood.