Abstract: Quantitative identification of coherent structures in the near-wall region of a turbulent boundary layer is a prerequisite for revealing the physical mechanisms of wall turbulence and evaluating drag reduction techniques. The quadrant splitting method is a classical approach for detecting coherent structures, yet its detection performance is significantly influenced by the choice of the threshold. Traditional threshold values are often set empirically within the range of H=1.0\sim 4.5 , which is too broad, heavily relies on experience, and lacks objectivity, thereby limiting the objectivity and physical interpretation of studies on coherent structures in wall turbulence. In this paper, an objective method for determining the threshold H in quadrant splitting is developed based on the spatial autocorrelation function of fluctuating velocity in wall turbulence. This method does not depend on empirical experience and can faithfully reflect the statistical laws of coherent structures in wall turbulence. Using Time-Resolved Particle Image Velocimetry (TR–PIV) experimental data from three types of turbulent boundary layers over smooth, isotropic superhydrophobic, and anisotropic superhydrophobic flat plates, the relationships among spatial autocorrelation analysis, characteristic scale, and the threshold–event average scale are elaborated in detail. A “characteristic scale–threshold matching criterion" is proposed. Experimental results validate that the proposed method offers advantages such as high objectivity, high accuracy, and controllable false/missed detections. The optimal thresholds retrieved under different wall conditions are reasonable, enabling effective identification of burst events in the second and fourth quadrants and deepening the understanding of coherent structure variations in wall-bounded turbulence. This work provides a fundamental tool and a reliable basis for the quantitative comparison and optimal design of drag reduction mechanisms in wall-bounded turbulence.