Application of remote sensing technology in monitoring wheat ripening process

The wheat ripening process is divided into the milk stage, the waxy stage, and the full maturity stage. The final harvest standard for wheat is determined by the degree of maturity of the grains. Generally speaking, the harvest standard for wheat is the grain moisture content, and the general safe storage standard is 12.5%, although this indicator may vary slightly depending on the variety. In practice, wheat is often harvested when it reaches about 90% maturity.

However, in actual production, it is difficult to continuously obtain accurate grain moisture content, requiring manual field sampling, and it is difficult to obtain data over a large area. Furthermore, due to the heterogeneity of soil within a plot, the distribution of moisture content varies, making it impossible to objectively and accurately reflect the moisture content and maturity progress of the entire plot when selecting sampling points. Generally, wheat in soils with better moisture retention matures slightly later, and the influence of regional hot and dry winds leads to rapid changes in moisture content, with different rates of moisture decline in different plots. Therefore, a method is needed that can simultaneously obtain the crop/grain moisture content of the entire plot over a large area.

Wheat ripening remote sensing monitoring

Based on the linear relationship between crop plant moisture content and grain moisture content, satellite remote sensing can be used to monitor the moisture content of the plant canopy and retrieve the grain moisture content, helping users to determine the maturity progress.

Hyperspectral satellite remote sensing can meet the needs of qualitative monitoring and quantitative inversion, and can more accurately determine the maturity of large-area crops from changes in more and more subtle crop physiological parameters (such as anthocyanins, carotenoids, etc.). Based on meteorological conditions, the moisture content of crops is continuously and dynamically monitored before harvest to predict the date when the moisture content in each region reaches the harvest standard.

CAS Xiguang Aerospace - Wheat Maturity Inversion

The figure below shows the distribution of plots and the change in moisture content within the plots over time for a planting management company in Taiping Town, Jingyang County, Xianyang City in 2022. The entire area uses the same wheat variety, but the soil conditions vary across different areas. The Zhongke Xiguang team assessed maturity based on the vegetation moisture index and performed qualitative inversion, presenting the results through multi-period monitoring starting in early May. They also used adaptive thresholding and binary classification methods to determine the overall maturity of the plots, displaying the results as plot vectors.As can be seen, the maturation speed of plots in different regions is not the same. The northeastern region matures later than other regions, by about 7-10 days. 

△Schematic diagram of wheat maturity changes in Taiping Town, Jingyang County, Xianyang City in 2022

△Schematic diagram of wheat maturity in Taiping Town, Jingyang County, Xianyang City, 2022

CAS Xiguang Aerospace - Wheat Maturity Inversion

Meanwhile, the CAS Xiguang team conducted maturity monitoring on wheat planting areas in Chunhua County, slightly north of Taiping Town. Due to the presence of spring corn mixed in some winter wheat plots, the maturity monitoring was somewhat interfered with, but the overall trend could still be observed.Overall, the ripening time is about two weeks later than in Taiping Town.  

△Schematic diagram of wheat maturity changes in Chunhua County, Xianyang City in 2022

△Schematic diagram of wheat maturity in Chunhua County, Xianyang City, in 2022

This large-scale, automated maturity monitoring method can help village and township collectives, large-scale growers, or professional harvesting teams to rationally plan harvesting routes, reduce machine, fuel, and labor costs while improving the overall efficiency of the grain harvesting process, shortening the harvesting window, and reducing the risk of encountering rainfall during harvest.