Application of hyperspectral technology in agricultural drought monitoring

Drought is a long-term, potential natural disaster characterized by prolonged and abnormal water shortages. It has a severe impact on the economy, the ecological environment, and especially agricultural production. Therefore, monitoring crop water status and related physiological parameters is crucial for improving crop yields and optimizing water resource utilization.

Common drought index

Drought indices are important indicators for measuring the severity of drought. Commonly used drought indices include the NDVI, NDWI, and TVDI indices. The NDVI index reflects the state of vegetation growth by calculating the reflectance of surface green vegetation, and can accurately reflect the degree of drought. The NDWI index reflects moisture conditions by calculating the ratio of the reflectance of water bodies and vegetation, and can be used to monitor surface soil moisture content. The TVDI index reflects the degree of drought by measuring the difference between surface temperature and vegetation temperature.

Among these, soil moisture and vegetation growth are the most important and direct indicators of drought, and the interpretation of the spectral characteristics of vegetation and soil is an important factor in judging the degree of drought.

Common drought index

Drought can alter land cover, soil moisture, and surface roughness, thereby affecting the energy and water exchange between vegetation, soil, and the atmosphere. Therefore, changes in underlying biophysical factors (such as vegetation index, albedo, and LST) can influence the radiation, heat, and moisture balance of the underlying surface. Generally, the more severe the drought, the lower the NDVI, and the higher the albedo and surface temperature. Even if other factors remain relatively stable, soil moisture will decrease. The Vertical Drought Index (PDI) can be used to monitor drought occurrence.

Xi'an Institute of Optics and Precision Mechanics CAS Aerospace Science and Technology Group Co.,LTD - Crop Drought Monitoring

Using drones to collect visible light and multispectral data, and after orthophoto stitching and index calculation, the distribution of crops in large-scale plots can be displayed intuitively. Figure 1 is a drone image collected on March 19, 2024, before wheat sprouts. Figure 2 is a GCI chlorophyll content distribution map after removing buildings and roads. The lower the GCI index, the lower the vegetation cover, and the higher the GCI index, the higher the vegetation cover. Figure 3 is a surface moisture distribution map of bare soil. The lower the vertical drought index, the higher the soil moisture, and the higher the vertical drought index, the lower the soil moisture.

Research Conclusions and Applications

Currently, remote sensing-based drought monitoring methods have made significant progress. As indicators for each species, nutrient, or soil characteristic continue to evolve and improve, hyperspectral imaging, provided by low-cost, portable devices, continues to offer high-quality, accurate data and has become an important tool for researchers and farmers. The enhanced and routine monitoring capabilities of these devices promise to create a new paradigm for agricultural efficiency.