<div class="htmlview paragraph">Operational Modal Analysis, also known as Output Only Modal Analysis or Ambient Modal Analysis, has for over a decade been used for extracting modal parameters from civil engineering structures and is now also being used for mechanical structures, such as on-road and in-flight testing.</div> <div class="htmlview paragraph">The advantage of this method is that no artificial excitation needs to be applied to the structure and if artificial loading is required, the force does not need to be measured. All parameter estimation is based on the response signals, thereby minimising the amount of work required for test preparation.</div> <div class="htmlview paragraph">As the loading force is unknown in Operational Modal Analysis, specially designed modal parameter estimation techniques need to be used. In classical modal analysis many validation tools are based upon the known force, but if this is not known, other validation tools must be implemented. In addition, different estimation techniques are used, so that results can be compared.</div> <div class="htmlview paragraph"> <figure id="F1" class="figure"> <div class="graphic-wrapper"><img class="article-figure figure" src="2003-01-1599_fig0001.jpg" alt="No Caption Available"/></div> </figure> </div> <div class="htmlview paragraph">Two classes of identifiers will be described in this paper. A frequency domain based method (Frequency Domain Decomposition) and a time domain based (Stochastic Subspace Identification). Results from both methods will be discussed and compared.</div> <div class="htmlview paragraph">The paper discusses in general the use of Operational Modal Analysis on cars. Results are shown on a fully assembled car.</div> <div class="htmlview paragraph">For further background of the technique please refer to <span class="xref">ref. [1]</span> and <span class="xref">ref [2]</span>.</div>