A numerical-relativity calculation yields in general a solution of the Einstein equations including also a radiative part, which is in practice computed in a region of finite extent. Since gravitational radiation is properly defined only at null infinity and in an appropriate coordinate system, the accurate estimation of the emitted gravitational waves represents an old and non-trivial problem in numerical relativity. A number of methods have been developed over the years to “extract” the radiative part of the solution from a numerical simulation and these include: quadrupole formulas, gauge-invariant metric perturbations, Weyl scalars, and characteristic extraction. We review and discuss each method, in terms of both its theoretical background as well as its implementation. Finally, we provide a brief comparison of the various methods in terms of their inherent advantages and disadvantages.

数值相对论计算通常会产生爱因斯坦方程的解，其中还包括辐射部分，其实际上是在有限范围的区域中计算的。由于引力辐射仅在零无穷远和适当的坐标系中被正确定义，因此对发射的引力波的准确估计代表了数值相对论中一个古老且重要的问题。多年来，人们开发了多种方法来从数值模拟中“提取”解的辐射部分，其中包括：四极公式、规范不变度量扰动、Weyl 标量和特征提取。我们从理论背景和实施方面回顾和讨论每种方法。最后，我们对各种方法的固有优点和缺点进行了简要比较。