1. A method for passive determination of target parameters by directionally selective reception of sound waves which are emitted or transmitted by a target, by means of an arrangement ( 24 ) of waterborne sound sensors in a sonar receiving installation, in particular on a carrier vehicle, from estimated bearing angles which are determined from estimated positions of the target, and bearing angles which are measured by the arrangement ( 24 ) at the measurement location, wherein any bearing angle difference between measured and estimated bearing angles is minimized iteratively and, when the minimum is reached, the estimated position provides the target parameters of an optimized solution for an output of target range, target position, target course, and target velocity, which is updated during each processing cycle in a series of successive processing cycles, wherein a multiplicity of different target tracks (Z(i,j)) are calculated during each processing cycle from possible solutions for the target parameters to be determined (R est , C est , V est ), specifically an assumed target course (C est ), an assumed target range (R est ), and an assumed target velocity (V est ), in that associated bearing angles (B est ) are assumed from the measurement location for each of these possible solutions, in that a quality measure (Q, Q inv ) is calculated along each of the assumed target tracks (Z(i,j)) using the assumed bearing angles (B est ) and taking account of the bearing angles (B meas ) measured at the measurement location, and in that a reliability indicator (ZI R , ZI C , ZI V ) is in each case determined from the distribution of the quality measure (Q, Q, inv ) over each target parameter (R est , C est , V est ) to be determined, and a reliability degree (ZG) is derived from the reliability indicators (ZI R , ZI C , ZI V ) of the respective target parameters (R est , C est , V est ) in order to determine the reliability of the optimized solution, which reliability degree is output by at least one of a numerical value or graphically via a display apparatus.