  An analysis of the backscattering data for the Schr\"odinger operator in odd
dimensions $n\ge 3$ motivates the introduction of the backscattering transform
$B: C_0^\infty ({\mathbb R}^n;{\mathbb C})\to C^\infty ({\mathbb R}^n; {\mathbb
C})$. This is an entire analytic mapping and we write $ Bv = \sum_1^\infty B_Nv
$ where $B_Nv$ is the $N$:th order term in the power series expansion at $v=0$.
In this paper we study estimates for $B_Nv$ in $H_{(s)}$ spaces, and prove that
$Bv$ is entire analytic in $v \in H_{(s)}\cap \Cal E'$ when $s\ge (n-3)/2$.
