Simultaneous magnetic decoration of the two sides of a field-cooled (F
C) superconducting sample can provide information about elasticity of
the vortex lattice. We report such a decoration experiment done on a s
ingle crystal of NbSe2 and analyze the behavior of the displacement co
rrelator [u(2)(r,z)] for the FC lattice. The ratio of the elastic cons
tants c(66)/c(44) is found to be strongly renormalized downward, proba
bly by the presence of topological defects.