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Chapter 5:
Imaging Introduction
Since this text discusses imaging spectrometers, it is necessary that some of the basics of imaging be explored. Two types of images may be defined: a two-dimensional, fixed, rectangular frame and a strip map that is two dimensional but with one dimension arbitrarily long. 5.1 The Field of View The field of view may be considered as a collection of picture elements (pixels) or resolution elements (reselms). This field can be imaged onto an array of detector elements in a focal plane array (FPA), or it may be imaged by a single detector or small array that is scanned over the field. I will call the field elements pixels, whether they are measured in linear or angular dimensions. The linear pixel is sometimes called a GSD, for ground spatial distance. The individual detector elements will be called elements. The FPA may be viewed as an array of detector elements, and the idea is to obtain a one-to-one, linear mapping of the pixels onto the elements—or the elements onto the pixels. If there are as many detector elements in the array as there are pixels in the field of view, then the system is called a starer. If not, then some scanning is necessary, and it is called a scanner. The field of view is illustrated in Fig. 5.1. The required electronic bandwidth for such a system is determined by the Shannon sampling theorem, and is B=1 2t d =N v N h 2t f m v m h , where the bandwidth is B, the dwell time on a pixel is t d , N v and N h are the number of pixels and m v and m h are the number of detector elements in the vertical and horizontal directions, and t f is the frame time. In a staring system, the dwell time is equal to the frame time t f .
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