The metabolic status of carbon (C) and nitrogen (N) as two essential elements of crop plants has significant influence on the ultimate formation of yield and quality in crop production. Leaf is the major organ of plant photosynthesis and physiological activity, and in leaf tissues the ratio of carbon to nitrogen (C/N), defined as the ratio of LCC (leaf carbon concentration) to LNC (leaf nitrogen concentration), can help people to understand and quantify the carbon and nitrogen metabolism in crop plants, and is a good indicator for synthetically diagnosing the balance of carbon and nitrogen, nutrient status, growth vigor and disease resistance in crop plants. Thus, it is very significant for effective diagnosis and dynamic regulation of crop growth in field to monitor changes of leaf C/N quickly and accurately and in real time.

The traditional methods of determinating crop C or N status have relied substantially on sampling from fields and analysis in laboratories, but have the disadvantages of either destructive measurements with too much energy and time cost or hysteretic evaluations because of chemical assay in labs. In contrast, remote sensing of canopy reflectance acts an essential role in detecting physiological parameters of crop in field, with rapid and large-spatial-area measurement capabilities. Especially, hyperspectral remote sensing with hundreds of narrow bands can probe into the subtle changes of biochemical components (such as leaf chlorophyll content, nitrogen status and water stress) in crop, and markedly characterizes the non-destruction and quickness, and thus the estimates of biochemical parameters in crop plants by means of analyzing spectral characteristics to develop newly effective spectral variables for monitoring these parameters has become the focused interest in the evaluation of crop growth. Nowadays, the mechanism and methods of determinating leaf C/N with remote sensing techniques, especially ground-based hyperspectral measurements, are still placed in the exploring stage.