## 1 Introduction  
Quality assessment is a critical aspect of the aerospace industry, as the safety and reliability of aircraft depend on the integrity of the materials used in their construction. Overall, the quality assessment of composite materials in the aerospace industry requires a combination of techniques to detect and characterize defects accurately. By using these techniques, manufacturers can ensure that the materials used in aircraft construction meet the required safety and reliability standards, ultimately improving the safety of air travel. Composite materials are widely used in the aerospace industry due to their high strength-to-weight ratio, corrosion resistance, and durability. One of the main challenges in the manufacturing and maintenance of composite structures is the detection and characterization of anomalies that can weaken the material and compromise its performance. Porosity and impact damage are two such flaws currently of great interest in aerospace composite components. Porosity can be defined as the presence of trapped air within the composite matrix or at the interfaces between the matrix and the reinforcing fibers that can occur during the manufacturing process due to incomplete impregnation of the resin or the presence of air bubbles [1]. Porosity has been the subject of several theoretical studies to explore its impact on the mechanical properties of materials and is still actively investigated [2]. Composites may also be at risk of impact damage during production, e.g., tool drop, and more particularly during operation, e.g., bird clash, collisions, or hail strike. High-velocity impacts are usually easily identifiable visually since they may generate substantial structural damage, whilst low-velocity impacts produce barely visible impact damage (BVID) that may be difficult to see. It is, however, very important to detect BVID to avoid its propagation and the subsequent formation of delaminations [3]. Nondestructive testing (NDT) methods such as ultrasonic testing [4] and X-ray radiography [5] have been successfully employed to detect and quantify porosity and BVID in composite materials. Nevertheless, although very effective, these techniques are either considerably time-consuming, require access to both sides of the sample being inspected, and/or are costly. In addition to these NDT techniques, there exist alternative methods that are reportedly very accurate for the detection of defects. Speckle interferometry and digital image correlation are two optical techniques that are commonly used for the NDT of composite materials in the aerospace industry [6]. Both techniques involve the analysis of images to detect defects and assess the quality of the material. Another interesting method is 3D laser Doppler scanning vibrometry which is used to assess the vibration and dynamic behavior of structures [7]. These techniques are very promising although their main limitation is that they require a controlled testing environment to minimize any external disturbances (air turbulence, or temperature fluctuations) that could affect the accuracy of the measurements and their sensitivity to changes in the surface properties. In recent years, infrared thermography (IRT) has emerged as a promising NDT method for detecting and quantifying different kinds of flaws in composite materials including porosity [8] and BVID [9]. IRT is a contactless NDT technique that uses thermal imaging to visualize the temperature distribution on the surface of a material based on the principle that the presence of anomalies in the material will cause local variations in thermal diffusivity, which will result in temperature gradients that can be detected with an infrared camera. Some of the main advantages of IRT with respect to other NDT techniques are its rapidity, cost, and the fact that it does not require access to both sides of the inspected part [10].