2.1 Introduction

A subsample target can appear in two different forms. One is a target that is smaller than the sample spatial resolution, in which case the target is embedded in a sample. An example is a vehicle with size of img that can be completely embedded in a single pixel with resolution of img. Another is a target that partially occupies a sample with certain amount of abundance fraction. That is, a target may or may not have its size greater than the sample resolution but it occupies more than one sample with partial abundance fractions. In either case, such a target is considered as a subsample target since it does not fully occupy an entire sample. It should be noted that as shown in Sections 30.2–30.3 in Chapter 30 the abundance fraction of a target contained in a sample can be used to calculate the partial size of the target occupying the sample.

A mixed sample is considered as a sample mixed with a number of target substances with appropriate abundance portions that account for the entire sample. A distinction between a subsample target and a mixed sample is that the latter must have the knowledge of all the target substances present in the sample compared to the former that only needs to know that the target of interest resides in the sample while discarding the information ...

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