A fact known from direct observation.
A premise from which conclusions are drawn.
A floating reference point, or SLDMB, used to evaluate surface currents in a body of water. Often employed by coastal search and rescue.
A fixed reference point or set of reference points which precisely define a system of measurement or a coordinate system.
To provide missing data points by using a mathematical model to extrapolate values that are outside the range of a measuring device.
Systematic observation of places and people by visual, aural, electronic, photographic or other means.
Continuous monitoring of disease occurrence for example.
Close observation of an individual or group; person or persons under suspicion.
In criminal law, an investigation process by which police gather evidence about crimes, or suspected crime, through continued observation of persons or places.