The aim of this master's thesis was to review and compare available non-destructive and semi-non-destructive techniques for assessing decay and to compare them with visual assessment of decay presence and the degree of decay estimated by hyperspectral imaging. Firstly we visually assessed several samples of spruce beams and beech sleepers. Then, we compared the results obtained from testing the samples using the screw withdrawal method, Pilodyn method, ultrasonic velocity measurement, and resistograph. For an accurate evaluation of the results obtained, we compared the results of the non-destructive techniques with the density measurements of smaller sections of the sample slices. We also compared the decay with images obtained by scanning with a hyperspectral camera. We found that visual assessment alone does not provide an accurate evaluation of the wood's condition. Semi-non-destructive techniques give a sufficiently rough estimate of the wood's condition to make correct decisions, but it must be considered that all techniques, except for the resistograph, assess the condition of the wood more on the surface, and we cannot know what is inside. The choice of techniques depends on the time available, budget, applicability, and equipment accessibility. In conclusion, we determined that a single semi-non-destructive technique is usually not sufficient, and therefore, a combination of several different techniques should be used.
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