  This paper for the first time addresses the concepts of regional gradient
observability for the Riemann-Liouville time fractional order diffusion system
in an interested subregion of the whole domain without the knowledge of the
initial vector and its gradient. The Riemann-Liouville time fractional order
diffusion system which replaces the first order time derivative of normal
diffusion system by a Riemann-Liouville time fractional order derivative of
order $\alpha\in (0,1]$ is used to well characterize those anomalous
sub-diffusion processes. The characterizations of the strategic sensors when
the system under consideration is regional gradient observability are explored.
We then describe an approach leading to the reconstruction of the initial
gradient in the considered subregion with zero residual gradient vector. At
last, to illustrate the effectiveness of our results, we present several
application examples where the sensors are zone, pointwise or filament ones.
