Efficient extraction of Weyl scalars from numerical simulations using a non-orthonormal tetrad

We present a procedure that numerically constructs the Weyl scalars from the characteristic fields of the Weyl tensor evolution system. These characteristic fields are spatial, real, and computed directly from the extrinsic curvature and spatial Ricci tensor, which leads to efficient computation. Further computational efficiency improvements can be made by using a non-orthonormal tetrad defined as in Minkowski space and using an extrapolation procedure. An analysis of the extraction procedure is presented and the possible issue of junk radiation backscattering is addressed.