This paper proposes novel techniques for thermal nondestructive testing based on frequency modulated thermal waves. A mild steel sample having discontinuities at different depths is taken as a test sample. The limited depth resolution of the lock in thermography due to the fixed driving frequency of the excited heat sources is overcome by the proposed new technique. A pulse compression approach is used to detect subsurface discontinuities using linear frequency modulated thermal wave imaging and digitized linear frequency modulated thermal wave imaging. In this way, the peak power for probing the specimen can be decreased markedly by increasing the average transmitted energy, which is proportional to the length of the modulated excitation signal. Comparison between the techniques based on the analog frequency modulated signal and its digital form are presented.