Two-parameter regularization of ill-posed spherical pseudo-differential equations in the space of continuous functions

In this paper, a two-step regularization method is used to solve an ill posed spherical pseudo differential equation in the presence of noisy data. For the first step of regularization we approximate the data by means of a spherical polynomial that minimizes a functional with a penalty term consisting of the squared norm in a Sobolev space. The second step is a regularizecl collocation method. An error bound is obtained in the uniform norm, which is potentially smaller than that for either the noise reduction alone or the regularized collocation alone. We discuss an a posteriori parameter choice, and present some numerical experiments, which support the claimed superiority of the two-step method. (C) 2015 Elsevier Inc. All rights reserved.