22 NIR Imaging
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Fig. 22.1 Schematic of NIR spectral image structure: x and y represent spatial dimensions, while
λ represents the wavelength dimension
or interactance. The selection of modality is largely sample dependent, and it is
important to consider the optical properties of the sample and penetration depth
of NIR light within. For example, transmission imaging is generally preferable to
reflectance for materials that absorb high quantities of light in the NIR, such as
aqueous or high water content samples. In order to enable imaging of highly absorbing
samples, it is advisable to work with thin samples and/or work in transmission mode.
If this is not possible, the use of a highly reflective substrate can also improve the
signal-to-noise ratio achievable through transflectance measurements, although the
effectiveness of this approach depends on sample thickness.
The remainder of this chapter is divided into two major sections: NIR imaging
instrumentation and applications, with several illustrative examples provided
throughout.