text: The analytical near infrared (NIR) region spans the range from 780 nm to 2,500 nm. The absorption bands seen in this spectral range arise from overtones and combination bands of O-H, N-H, C-H and S-H stretching and bending vibrations. Absorption is one to two orders of magnitude smaller in the NIR compared to the MIR; this phenomenon eliminates the need for extensive sample preparation.  Thick and thin samples can be analyzed without any sample preparation, it is possible to acquire NIR chemical images through some packaging materials, and the technique can be used to examine hydrated samples, within limits. Intact samples can be imaged in transmittance or diffuse reflectance.
  The lineshapes for overtone and combination bands tend to be much broader and more overlapped than for the fundamental bands seen in the MIR. Often, multivariate methods are used to separate spectral signatures of sample components.  NIR chemical imaging is particularly useful for performing rapid, reproducible and non-destructive analyses of known materials.  NIR imaging instruments are typically based on a hyperspectral camera, a tunable filter or an FT-IR interferometer.  External light source is always needed, such as sun (outdoor scans, remote sensing) or a halogen lamp (laboratory, industrial measurements).