  We sketch a method to compute mod $\ell$ Galois representations contained in
the H2 \'etale of surfaces. We apply this method to the case of a
representation with values in GL(3,9) attached to an eigenform over a
congruence subgroup of SL(3). We obtain in particular a polynomial with Galois
group isomorphic to the simple group PSU(3,9) and ramified at 2 and 3 only.
