Material characterization in the 0.1 – 10 THz range has been a major topic of research sinceits first demonstration 30 years ago. Advances in terahertz generation, detection, and data acquisition havecontributed to improved bandwidth, signal power and signal-to-noise ratio. However, material character-ization is still performed using conventional spectroscopic measurement schemes which require detailedinformation about the test object’s shape, location, orientation relative to the measurement system, and areference measurement. Here, we present a method for reference-free material characterization of dielectricobjects using a terahertz time-domain spectroscopy system withouta prioriknowledge about the objectand its position. The proposed method is based on ellipsometry combined with lensless imaging for theestimation of the refractive index. The method is a multistage procedure designed for small test objects inreflection mode. The diffracted terahertz radiation is separated from the specular reflected radiation in apost-processing step to enable a valid material parameter estimation. In this way, small dielectric objects canbe located, imaged with a sub-mm resolution, and their material parameters extracted.