Restoration of chopped and nodded images in infrared astronomy

In thermal infrared astronomy a differential technique is used for extracting the weak astronomical image from the large background due to the environment. The resulting images, the so-called chopped and nodded images, present large negative values and provide reliable representations uniquely in the case of isolated sources. In this paper we discuss the mathematical properties of the problem of restoring the original image from its chopped and nodded version and we investigate an iterative regularization method, the so-called projected Landweber method, for approximating non-negative solutions of the problem. This method provides satisfactory results in some cases but, in general, the restored images are still affected by several artifacts. We suggest an observation strategy which, combined with our proposed restoration method, can significantly reduce the effect of these artifacts.