Non-destructive testing and evaluation methods not only demand various experimental techniques but also adopts efficient post-processing approaches on the obtained experimental data to enhance the defect detection capabilities. Among these, widely used experimental techniques such as pulse compression favourable thermal wave imaging approaches and associated post-processing approaches gained significance due to their capabilities including remote, safe, wide-area inspection along with improved defect detection sensitivity and resolvability. In this work, experiments have been carried out on a glass fibre reinforced polymer material having flat bottom holes as to demonstrate the effectiveness of different pulse compression favourable thermal wave imaging approaches and their defect detection capabilities by considering the signal to noise ratio as a figure of merit. The results clearly indicate that the correlation (matched filter) based post-processing approach offers significantly superior defect detection capabilities compared to the widely used frequency-domain phase analysis-based data processing approach.