  Context: Helioseismic analysis of large-scale flows and structural
inhomogeneities in the Sun requires the computation of sensitivity kernels that
account for the spherical geometry of the Sun, as well as systematic effects
such as line-of-sight projection. Aim: I aim to develop a code to evaluate
helioseismic sensitivity kernels for flows using line-of-sight projected
measurements. Methods: I decomposed the velocity field in a basis of vector
spherical harmonics and computed the kernel components corresponding to the
coefficients of velocity in this basis. The kernels thus computed are radial
functions that set up a 1.5D inverse problem to infer the flow from surface
measurements. I demonstrate that using the angular momentum addition formalism
lets us express the angular dependence of the kernels as bipolar spherical
harmonics, which may be evaluated accurately and efficiently. Results: Kernels
for line-of-sight projected measurements may differ significantly from those
that don't account for projection. Including projection in our analysis does
not increase the computational time significantly. We demonstrate that it is
possible to evaluate kernels for pairs of points that are related through a
rotation by linearly transforming the terms that enter the expression of the
kernel, and that this result holds even for line-of-sight projected kernels.
Conclusion: I developed a Julia code that may be used to evaluate sensitivity
kernels for seismic wave travel times computed using line-of-sight projected
measurements, which is made freely available under the MIT license.
