Context : The imaging and timing properties of \gamma -ray emission from electromagnetic cascades initiated by very-high-energy ( VHE ) \gamma -rays in the intergalactic medium depend on the strength B and correlation length \lambda _ { B } of intergalactic magnetic fields ( IGMF ) .

Aims : We study the possibility of measuring both B and \lambda _ { B } via observations of the cascade emission with \gamma -ray telescopes .

Methods : For each measurement method , we find two characteristics of the cascade signal , which are sensitive to the IGMF B and \lambda _ { B } values in different combinations .
For the case of IGMF measurement using the observation of extended emission around extragalactic VHE \gamma -ray sources , the two characteristics are the slope of the surface brightness profile and the overall size of the cascade source .
For the case of IGMF measurement from the time delayed emission , these two characteristics are the initial slope of the cascade emission light curve and the overall duration of the cascade signal .

Results : We show that measurement of the slope of the cascade induced extended emission and/or light curve can both potentially provide measure of the IGMF correlation length , provided it lies within the range 10 kpc \lesssim \lambda _ { B } \lesssim 1 Mpc .
For correlation lengths outside this range , gamma-ray observations can provide upper or lower bound on \lambda _ { B } .
The latter of the two methods holds great promise in the near future for providing a measurement/constraint using measurements from present/next-generation \gamma -ray-telescopes .

Conclusions : Measurement of the IGMF correlation length will provide an important constraint on its origin .
In particular , it will enable to distinguish between an IGMF of galactic wind origin from an IGMF of cosmological origin .