Restoration methods for astronomical images at mid-infrared wavelengths

Ground-based astronomical observations at mid-infrared wavelengths (around 10-20 microns) face the problem of extracting the weak astronomical signal from the large background due to atmosphere and telescope emission. The solution is provided by a differential technique, known as chopping and nodding , which can be modeled as the application of a second-difference operator to the image detectable in the absence of background. However, since the chopped and nodded images are distorted by large negative counterparts of the sources, a method for restoring the original non-negative image is required. In our previous work we proposed a viable iterative method which provides, in some cases, restored images affected by annoying artifacts, related to the huge non-uniqueness of the restoration problem. Therefore in this paper we present an alternative method which can be used when the source morphology or the data acquisition strategy allows to reduce the degree of non-uniqueness of the solution. By means of numerical simulations, we show that the new method does not produce the artifacts of the previous one and the implications of this result are briefly discussed.