Correlation between NDVI and soil sensor data collected by UAV

The development of UAVs and the reduction in the weight of payload-bearing devices is making remote sensing of crops possible. This technology is cheaper, more time-efficient and produces higher resolution images in a non-destructive way. Another important feature of drone imagery is its ability to monitor crops on a regular basis. The raw data collected by drones can be integrated into models for analysis and further corrective measures can be created to improve crop yields. Drones are capable of assessing soil conditions, assisting in irrigation, fertilizer application and monitoring crop health. The Normalized Difference Vegetation Index (NDVI) was used to quantify the greenness of vegetation to assess changes in vegetation density and health. When near-infrared light reaches the leaves of a healthy plant it is reflected back into the atmosphere, as the amount of chlorophyll produced by the plant decreases, less near-infrared radiation is reflected back. The result can then be used to assess the overall health of the plant. The values are calculated for each pixel of your map, giving you an index in the range -1 to 1.

 

4 sampling points (A-D) were selected in the sample area Nyírbator, Hungary. Soil moisture and soil temperature probes were deployed at three depths in the points and data were downloaded during bi-weekly sampling and measurements. The vegetation monitoring of the irrigated and non-irrigated area was carried out by taking NDVI images every 2 weeks using UAV remote sensing. During the NDVI processing of the irrigated area, only the first half of the area was captured for the initial images, at the beginning of the vegetation. NDVI images were processed in Pix4D and ArcGIS Pro software. In ArcGIS Pro, the minimum, maximum, mean and standard deviation values for the study area were observed and subsequently evaluated separately point by point using a zonal statistics algorithm.

 

In the study area, a larger temperature variation is observed for the deployed soil probes at a depth of 10 cm, which underlines the sensitivity of the surface temperature to environmental conditions. With increasing depth, a gradual decrease in temperature is observed, indicating the influence of soil properties on heat retention and dissipation. Consistently fluctuating moisture levels near the surface (at a depth of 10 cm) were observed in response to precipitation or irrigation events. The fluctuation of the curves gradually decreases with increasing depth. At all depth levels, a more consistent linear gradient is observed, reflecting the prolonged drought conditions in the soil. This observation is consistent with the low mean NDVI values observed simultaneously in the same zone. The data show that the irrigated area tends to have higher average NDVI values than the non-irrigated area, which has significantly lower values.

 

 

 

 

This research was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. The research presented in the article was carried out within the framework of the Széchenyi Plan Plus program with the support of the RRF 2.3.1 21 2022 00008 project.