Pre-prints

M.Bertero, P.Boccacci, M.Robberto,
in  Proc. SPIE, Vol. 3354, Infrared Astronomical Instrumentation,ed. A.M.Fowler,  877-886, 1998

An inversion method for the restoration of chopped and nodded images

We present an iterative inversion method for the restoration  of chopped  and nodded images, typical of thermal  infrared astronomy with ground based telescopes.  The method computes the smallest solution subjected to the  constraint of positivity.
The restored images exhibit artifacts, related to the chopping amplitude, which can be predicted by looking at the mathematical structure of the problem. However these effects can be strongly reduced by combining a few (2-4) images taken with different chopping/nodding throws of small amplitude.  Preliminary results on synthetic data are very promising. Restored images show high cosmetic quality and a typical restoration error smaller than 10%.
We also present restorations of real images taken at the UKIRT telescope with the MAX camera. The availability of an image restoration method for mid-IR images would have a major impact on the telescope design and observing strategy at these wavelengths.

The compressed postscript version of this paper is available through anonymous ftp at ftp.disi.unige.it in:
 /person/BerteroM/chop_spie.ps.gz

M.Bertero, P.Boccacci, F.Di Benedetto, M.Robberto
in  Inverse Problems, 15, 1999

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.

The compressed postscript version of this paper is available through anonymous ftp at ftp.disi.unige.it in:
 /person/BerteroM/chopping.ps.gz
 

M.Bertero, P.Boccacci, M.Robberto

Image restoration in thermal infrared astronomy

A major problem in the imaging of a celestial  source at mid infrared wavelengths ( > 2.4 microns) is the presence of a large background due to the thermal emission of the atmosphere and the telescope. Various differential techniques are used for extracting  the weak signal emitted by the source. In this paper, after a brief presentation of these techniques, we describe a method proposed by the authors for the restoration of the original image and we discuss the artifacts generated by the inversion algorithm. The relationship between these artifacts and the structure of the imaging matrix suggests two methods, one computational and one observational, for their reduction. The two methods are applied to the restoration of images taken at the UKIRT telescope and the improvement of image quality obtained by means of them is demonstrated.

The compressed postscript version of this paper is available through anonymous ftp at ftp.disi.unige.it in:
 /person/BerteroM/chop_bul.ps.gz

M.Bertero, M. Miyakawa, P. Boccacci, F. Conte, K. Orikasa, M. Furutani

Image restoration in chirp-pulse microwave CT (CP-MCT)

Chirp-Pulse Microwave Computed Tomography (CP-MCT) is a technique for imaging the distribution of temperature variations inside biological tissues. Even if resolution and contrast are adequate to this purpose, a further improvement of image quality is desirable. In this paper we discuss the blur of CP-MCT images and we propose a method for estimating the corresponding Point Spread Function (PSF). To this purpose we use both a measured and a computed projection of a cylindrical phantom. We find a good agreement between the two cases. Finally the estimated PSF is used for deconvolving data corresponding to various kinds of cylindrical phantoms. We use an iterative nonlinear deconvolution method which assures nonnegative solutions and we demonstrate the improvement of image quality which can be obtained in such a way.
 

The compressed postscript version of this paper is available through anonymous ftp at ftp.disi.unige.it in:
 /person/BerteroM/chirp.ps.gz