## 1 Introduction
To overcome the limitations of dynamic inspection using TPS-DS, researchers have proposed spatial phase shift digital shearography (SPS-DS). [PERSON] and [PERSON] [13] used three cameras to acquire multiple images at the same time for real-time inspection and used conventional phase calculation methods. However, the approach was costly and complex to build, and did not meet the requirements of industry. [PERSON] et al. [14] have carried out modifications to a Michelson interferometer-based system to achieve a larger field of view and used spatial carrier frequency phase shifting to obtain the final phase map. The SPS-DS system thus reported can be used for real-time inspection as an NDE tool on WTB. However, the computational cost of the spatial carrier frequency is high and the confocal point between two lenses is hard to maintain in practice. [PERSON] et al. [15] have proposed an SPS-DS technique using micro-polarisers at each small pixel as a carrier on a CCD or CMOS camera. The polarisation has four directions on its array at each pixel of the camera, where with the combination of the circular direction of the oscillation, the phase of interfered beam passing through the micro-polariser is doubled. [PERSON] and [PERSON] [16] further developed the approach using a Michelson interferometer-based setup, but this is yet to be made practical for NDE as the experimental configuration and the sample do not match industrial material. The interferometric technique has been applied on shearography in [17] with relatively low signal-to-noise ratio using a Mach-Zehnder interferometer configuration. A more promising set-up of the SPS-DS has been developed by the combination of spatiotemporal phase-shifting technique and 3D Fourier transform [18; 19] with pixelated SPS-DS by fully using simple configuration of the Michelson interferometry-based setup on shearography [20]. The approach achieved a relatively ideal phase map of a hollow artificial cylinder with uniformly exerted air pressure as the loading method. However, in context of NDT and industrial application, these set of trials lacked real-world verifications on industrial material. WTB is a typical type of facility using composite material for which defect information is nowadays required in real-time and on-board the system. The samples used in most studies of shearography are almost always simple and easy to detect the defects in, whereas in practical NDT inspection processes on-board WTBs, the defects are neither presupposed nor artificial. Moreover, the loading methods applied mainly exert stress evenly on the surface using facilities such as vacuum hood or force loading. These loading methods are suitable for static environments where it is easy to produce a high-quality phase map for the imaging process. However, these approaches are difficult to realise and control in dynamic on-board inspection, and significant efforts need to be made to design adequate loading and control systems for application. By comparison with the loading methods hereinbefore, dynamic loading methods such as heat flow or heating lamp are more feasible to realise as they are easy to control, even remotely, thus complying with on-site NDT conditions in practice. In this study, a shearography system based on a simple setup of Michelson interferometry using pixelated spatial phase shift was used for the dynamic inspection of delamination defects on a real WTB. Heat flow was used as the loading method. The objective of this work was to validate that the proposed system could be applied on-board a real WTB without using any complicated control for the PZT stepper or complex optical table that could hardly be applied on a platform for in situ WTB inspection. The essence of the proposed method is to optimise the micro-polarised spatial phase shift shearography system by using a carrier modulation algorithm and adding a windowed Fourier filter. Moreover, the proposed method was applied on an actual blade sample to examine its capability for detecting the defects in a practical experimental setting.