If the sensor to be evaluated were a new radar system, requirements might include a set of statements such as 'the radar beam shall sweep through 360 degrees of airspace. One complete rotation of the beam shall be accomplished in no more than 5 seconds. Positional error of radar plots shall be no greater than 20%.' For an online social media ‘radar’ system, we derive a high-level set of generic system requirements shown in Table 1 (for the purposes of prototype development, this is not an exhaustive set of all possible system requirements) from published very high-level electronic radar system specifications (Lockheed Martin, 2010; Thales Raytheon Systems, 2011; Wolff, 2009). First we need to define ‘online social media radar’. Maybury (2010) defines a ‘social radar’ as a tool that “needs to sense perceptions, attitudes, beliefs and behaviors” and that it would use signatures “and correlation to sense, if not forecast, a broad spectrum of phenomena” including changing trends in population behaviors. For the purposes of this study, we initially define our prototype ‘online social media radar’ as a software tool, which uses correlation of data gathered from online social media to sense and forecast sizes of crowd formations.