## 3 Line-Scan Hyperspectral Imaging Instruments
### Line-Scan Hyperspectral Systems and Calibrations  
Currently both commercial and custom-designed line-scan hyperspectral imaging systems are used for food and agricultural applications. The commercial integrated systems offer all-in-one solutions for more narrowly defined applications, and are increasingly adopted for routine evaluation of food and agricultural products. Meanwhile, custom-designed systems, which use modular components--such as light sources, imaging spectrographs, image sensors, and sample handling units--can provide more flexibility and versatility than the commercial systems since system components and configurations can be modified and optimized for different applications. Figure 4 shows two custom-designed line-scan hyperspectral imaging systems working in the visible and near-infrared (VNIR) region (Figure 4a) and the short-wavelength infrared (SWIR) region (Figure 4b) [13]. In each system, a 150 W quartz tungsten halogen lamp ([PERSON], MA, USA) is used as the illumination source for reflectance imaging. The light is conveyed from the lamp enclosure via a fiber assembly to form two thin fiber optic line lights (250 mm long each), which are arranged parallel to the transverse direction. Two UV-A (365 nm peak) fluorescent lamp assemblies (Spectronics,  
Figure 3: Wavelength-dispersive imaging spectrographs: (**a**) prism-grating-prism (PGP) transmission imaging spectrograph; and (**b**) Offner reflection imaging spectrograph. Westbury, NY, USA) are also used in the VNIR system for fluorescence imaging. The sensing unit of the VNIR system consists of a 35 mm focal length lens, a reflection imaging spectrograph (Hyperspec VNIR, Headwall Photonics, Fitchburg, MA, USA), and a 1004 (spatial) \(\times\) 1002 (spectral) pixel EMCCD camera (Luca DL 604M, Andor Technology, South Windsor, CT, USA). The nominal wavelength range covered by the VNIR system is from 400 to 1000 nm. For the SWIR system, a 320 (spatial) \(\times\) 256 (spectral) pixel InGaAs camera (XEVA-1.7-320, Xenics, Leuven, Belgium) with a reflection imaging spectrograph (Hyperspec SWIR, Headwall Photonics, Fitchburg, MA, USA) and a 25 mm focal length lens is used to acquire images in a nominal spectral region of 1000-1700 nm. For both systems, line-by-line hyperspectral reflectance or fluorescence images are collected by advancing a computer-controlled one-axis positioning stage in the direction perpendicular to the scanning lines of the imaging spectrographs. Fully-automated data acquisition software was developed for each system using Visual Basic (Microsoft, Redmond, WA, USA). A custom-designed line-scan hyperspectral Raman system [14] is shown in Figure 5. The system can be configured for either a Raman chemical imaging (RCI) mode for surface evaluation (Figure 5a) or a spatially offset Raman spectroscopy (SORS) mode for subsurface evaluation (Figure 5b). In the RCI mode, a 785 nm line laser (Innovative Photonic Solutions, Monmouth Junction, NJ, USA) serves as an excitation source, which is normally projected on the sample surface via a 45\({}^{\circ}\) dichroic beamsplitter. The SORS mode uses a 785 nm point laser (Innovative Photonic Solutions, Monmouth Junction, NJ, USA), which is delivered and focused on the sample surface with an incident angle of 30\({}^{\circ}\) using an optical fiber and a laser focus unit. The RCI and SORS configurations share a common detection module consisting of a transmission imaging spectrograph (ImSpector R10E, Specim, Oulu, Finland) and a 1024 (spatial) \(\times\) 1024 (spectral) pixel CCD camera (iKon-M 934, Andor Technology, South Windsor, CT, USA). A C-mount lens is attached to the spectrograph for aperture and focus adjustment. Two identical 785 nm long-pass filters are used to block the light at and below the laser wavelength (i.e., Rayleigh and anti-Stokes scattering). The system covers a wavenumber range from \(-\)674 to 2865 cm\({}^{-1}\) with a spectral resolution of 14 cm\({}^{-1}\).