  Let $B^H = \{ B^H(t), t\in\mathbb{R}^N \}$ be an $(N,d)$-fractional Brownian
sheet with Hurst index $H=(H_1,\dotsc,H_N)\in (0,1)^N$. The main objective of
the present paper is to study the Hausdorff dimension of the image sets
$B^H(F+t)$, $F\subset\mathbb{R}^N$ and $t\in\mathbb{R}^N$, in the dimension
case $d<\tfrac{1}{H_1}+\cdots+\tfrac{1}{H_N}$. Following the seminal work of
Kaufman (1989), we establish uniform dimensional properties on $B^H$, answering
questions raised by Khoshnevisan et al (2006) and Wu and Xiao (2009).
  For the purpose of this work, we introduce a refinement of the sectorial
local-nondeterminism property which can be of independent interest to the study
of other fine properties of fractional Brownian sheets.
