The National Imagery Interpretability Rating Scale (NIIRS) is a subjective scale used for rating the quality of imagery acquired from various types of imaging systems. The NIIRS defines different levels of image quality/interpretability based on the types of tasks an analyst can perform with images of a given NIIRS rating. The idea is that imagery analysts should be able to perform more demanding interpretation tasks as the quality of the imagery increases.
The NIIRS consists of 10 levels, from 0 (worst quality) to 9 (best quality).
Because different types of imagery support different types of interpretation tasks, individual NIIRS has been developed for four major imaging types: Visible, Radar, Infrared, and Multispectral.
References
NIIRS Wikipedia(Text) CC BY-SA