Hyperspectral geomorphology and crop health monitoring at East Oweinat Farm

Western Egypt's deserts are arid, but the eastern Sahara is even more extreme, receiving only a few centimeters of rainfall annually, earning it the name "ultra-arid." However, during the last Ice Age, the Sahara was a tropical savanna with a climate similar to modern-day Kenya and Tanzania. Annual rainfall was much greater, with numerous rivers and lakes. Hundreds of thousands of years of rainfall have also created vast underground aquifers beneath the shifting sands, known as the Nubian Sandstone Aquifer System (NSAS).

These groundwaters can be used to carry out agriculture in the heart of the desert, and with the implementation of the East Oweinat project, a large central irrigation project has been established in the region.

Project Overview

Construction began in 1997, and this project, along with the Toshka Project, the Darb El Arbein Project, the El Salam Canal Project, and the New Villages Project, is considered one of Egypt's mega-projects. While most of those projects failed to materialize, this project continues to operate normally. Currently, the project covers nearly 5,000 square kilometers. The main crops grown are potatoes, wheat, and medicinal aromatic plants such as chamomile, and there are also some glass greenhouses.

This project, located in the Sahara Desert, is approximately 290 kilometers from the nearest city and 210 kilometers from Lake Toshka. It lies in East Oweinat, west of Toshka. The project's irrigation water comes entirely from deep groundwater within the Nubian sandstone aquifer system. The region is also considered one of the world's flattest areas, with virtually no elevation change, and a diameter of approximately 350 kilometers. Due to its location deep in the desert, the transportation of agricultural products and supplies relies on an airport located to the east of the project site.

The Nubian Sandstone Aquifer System (NSAS) is one of the world's largest fossil groundwater resources. In northern Chad, particularly in the Tibesti and Ennedi mountain regions, seasonal precipitation reaches up to 150 mm/year. This precipitation can lead to both dispersed recharge and concentrated recharge along intermittent flood valleys. Recent research indicates that modern recharge does occur in northern Chad, but to a very limited extent both spatially and temporally. This means that only through rigorous quantitative assessment can the sustainable management of this renewable resource be achieved.

△ Figure 1 Panoramic view of the East Oweinat region taken by the International Space Station in 2018.

△ Figure 2 Landsat satellite image of the EastOweinat Farm project in the UAE (2017)

Figure 3. Details of the EastOweinat Farm project in the UAE, as captured by Landsat satellite (2017).

Figures 1 and 2 show the location and scope of the EastOweinat Farm. The central irrigation plots are scattered deep in the desert and are highly identifiable in satellite imagery.

Figure 3 shows that each irrigation unit has a diameter of approximately 850 meters and an area of ​​about 850 mu (approximately 50 hectares). Figure 3 illustrates the details of this central irrigation farm, with some plots intercropped with potatoes and wheat (or other crops). Some light brown plots may have undergone controlled burning to clear straw in preparation for the next planting season, which is also reflected in the subsequent land cover classification and crop health distribution maps.

△ Figure 4 Soil/groundwater bearing capacity map constructed using WSCM technology

Groundwater resource assessment

Hydrogeological and soil carrying capacity data collected in 2007–2008, including groundwater depth, total dissolved solids, well safety production, sodium adsorption ratio, soil salinity, soil depth, percentage of exchangeable sodium in soil, and cation exchange capacity, were used and integrated into a multi-layered geographic information system (GIS). Weighted spatial capacity modeling (WSCM) techniques were then employed using these layers to determine soil/groundwater capacity zones.

As shown in the figure, in the project area, high and medium soil/groundwater capacity zones account for 89.18% of the total area, while low capacity zones account for only 10.81%. Centrally irrigated farmland is mainly distributed in the high and medium capacity zones of this study area, indicating that irrigated agriculture is suitable for further expansion in this important development area. However, due to the extremely limited water supply of the Nubian Sandstone Aquifer System (NSAS), which should still be considered a non-renewable resource, it remains uncertain whether the East Oweinat region can support a larger-scale centrally irrigated agricultural system. Further assessments of the water demand and stability of this agricultural system can be made by combining meteorological parameters such as evaporation with vegetation indices such as LAI and NDVI to invert biomass.

△ Figure 5. Land parcel type distribution map of EastOweinat Farm based on hyperspectral remote sensing (2024)

△ Figure 6. Distribution map of crop health in the EastOweinat Farm plot based on hyperspectral remote sensing (2024)

Xi'an Institute of Optics and Precision Mechanics CAS Aerospace Science and Technology Group Co.,LTD - Land Parcel Type and Health Monitoring

We used hyperspectral images acquired by XIGUANG-002 satellite on March 24, 2024, to perform land cover classification and crop health assessment on a portion of the East Oweinat Farm.

As shown in Figure 5, three main types of plots were identified during the photography: plots with high vegetation cover currently being cultivated, plots with dark soil cover, and plots with light soil/sand cover. This distribution map basically illustrates the types of main crops grown in the region and the crop rotation situation in different areas. We also noted that some plots in the central and northern regions appear to be covered by sand, exhibiting spectral characteristics similar to deserts; it is currently unclear whether this is temporary fallow or permanent abandonment.

Figure 6 shows the vegetation health distribution in this area. This index, composed of multiple vegetation indices, comprehensively reflects crop health based on chlorophyll, canopy structure, and moisture status. Note that some dark-colored plots lack corresponding health indices, indicating that these plots are wholly or partially covered by dark soil. Meanwhile, most plots in normal production have high health, suggesting that the central irrigation project is currently operating well and has good yield expectations.

△ Figure 7 Comparison of spectral curves of typical plot types in EastOweinat Farm based on hyperspectral remote sensing (2024)

The spectral curves in the image above illustrate the spectral differences between different land cover types, primarily used to distinguish between areas with dark soil cover and vegetation cover. It can be seen that areas with vegetation exhibit a significant red edge effect in the 700-760nm range. Based on the location and slope of the red edge, a red edge vegetation index can be calculated to determine crop coverage and health, enabling more detailed classification.