The radar experiment connects the geometry of spacetime with an observers
measurement of spatial length. We investigate the radar experiment on Finsler
spacetimes which leads to a general definition of radar orthogonality and radar
length. The directions radar orthogonal to an observer form the spatial equal
time surface an observer experiences and the radar length is the physical
length the observer associates to spatial objects. We demonstrate these
concepts on a forth order polynomial Finsler spacetime geometry which may
emerge from area metric or pre-metric linear electrodynamics or in quantum
gravity phenomenology. In an explicit generalisation of Minkowski spacetime
geometry we derive the deviation from the euclidean spatial length measure in
an observers rest frame explicitly.Comment: 18 pages, 7 figures, axes label in figures corrected, journal
references adde
