Through theoretical analysis, we have previously proposed a method to measure an isoplanatic angle over a finite distance using three receiver apertures and a synthetic point source. Here, we present the validation experiment for this method. Through careful experimental design, the atmospheric coherence length for spherical waves propagating in the opposite direction was measured and converted to an isoplanatic angle as the true value for comparison. In general, the direct measurement of an isoplanatic angle agrees well with the true value in clear-air periods. Experimental results confirm our method for measuring an isoplanatic angle over a finite distance. The experiment resulted in the first time-diagram of an isoplanatic angle in finite distance ever measured through spherical-wave scintillation.