The Selection of Initial Information in Iterative Shift-and-AddTechnique for Astronomical Image Reconstruction

On the principle of "iterative shift-and-add technique"^1,2 for astronomical image reconstruction,a proper datum point for shifting and adding the speckle images of an observed object can be determined by an iterative process in some methods.One of these methods is the correlation algorithm of information of the object image structure with the speckle images,then the maximum value point of the cross correlation can be used for a proper datum point. In the iterative shift-and-add technique,How to select the initial information in the first step is the key to open the process of the iterative shift-and-add.The character of the initial information of the object and a method to pick up the information are discussed. After giving the basic definition of the iterative shift-and-add technique which proposed by us recently,the mathematics model of an object image described by δ function is posed.In view of the model,three conditions which should be satisfied with by initial information of the object image structure are pointed.1).The initial information should be composed by discrete point sources described by δ function.2).The geometric distribution of the points of initial information should be equal to the geometric structutre of a certain part of the object image.3).The intensity of every point source of initial information can be all same value. The most important character of initial information is that it must contain information of the structure of the object image,because the fact that the maximum value point of the cross correlation between informaion and the speckle images of the object will determine the position of the maximun strong diffraction limited image of the object hid in the speckles of every speckle image. Following the character of the initial information some methods for taking the initial information are got.The different methods will be used for different objects.For example,if an object image has only one outstanding bright point source,because this piont source will produce the maximum strong point image in every speckle image,the position of the maximum strong point image can be selected as the datum point to shift and add speckle images,so that iterative shift-and-add will become a simple shift-and-add method^3,4 in which only one step iterative is needed.For other objects,the simple shift-and-add method and the speckle inteferometry⁷ will be used,because the "ghost point"^3,4 or autocorrelation in the resultes of these mathods have information of the image structure of the object.At the last,some experiments of image reconstruction with these methods are given.