Monitoring the development of maize vegetation period with radar and multispectral satellite images

Changes in climate and population are critical elements for food security. Agriculture is expected to be greatly affected by the decrease in water resources due to the climate change. On the other hand, the population of the world continues to increase rapidly. In a world in which the population continuously increases, managing the environmental resources better and maintaining sufficient levels of crop production are necessary. In this respect, monitoring agricultural activities is of great importance. Agricultural targets show a dynamic feature throughout the growing season. Hence, the conditions of soil and crop in agricultural areas change from day to day throughout the growing season. Traditional ground-based monitoring activities to obtain soil and crop conditions information are highly time-consuming and costly. The remote sensing technique allows monitoring of agricultural areas throughout the growing season by reducing time and costs. In this study, it is aimed to monitor the development of maize vegetation period by using Synthetic Aperture Radar (SAR) and multispectral satellite images. In accordance with this purpose, Sentinel-1 SAR satellite images and Sentinel-2 multispectral satellite images were used, which are freely available and have high spatial and temporal resolution. In the study carried out at Akdeniz University / Faculty of Agriculture, Aksu Research and Application Farm, the silage corn plant was observed. During the period from planting to harvesting of maize, backscatter values and interferometric coherence values obtained from Sentinel-1 satellite images, and Normalized Difference Vegetation Index (NDVI) values and the values of other biophysical variables (LAI, fCover, and CW) obtained from Sentinel-2 satellite images were examined. In addition, plant heights were also calculated using Sentinel-1 satellite images. It was observed that NDVI, LAI, fCover and CW values were generally low until the plant height reached a certain level, after that they increased as the plant grew, then reached saturation and remained at approximately the same levels, showed a slight decrease before harvest, and a sharp decreased after harvest. It was observed that the backscatter values generally decreased after planting, increased as the plant grew, then reached saturation and remained at approximately the same levels, and decreased with drying green residues after harvest. It was observed that interferometric coherence values were generally high before planting, the interferometric coherence values obtained from satellite image pairs during planting decreased sharply, the interferometric coherence values obtained from the satellite image pairs before the plants started to germinate increased again, the interferometric coherence values decreased and remained low as the plants grew up until the harvest, and the interferometric coherence values increased after harvest. NDVI, LAI, fCover and CW values were remained insensitive to tillage practices such as planting, chisel, interrow hoeing and irrigation. Backscatter and interferometric coherence values were found to be sensitive to planting operations. It was observed that the backscatter values were also sensitive to irrigation operations. In addition, it has been determined that NDVI, LAI, fCover and CW values were affected by cloud cover and/or fog in the immediate surroundings of the study area. On the other hand, it was observed that the backscatter and interferometric coherence values were also significantly affected by precipitation events. Within the scope of this study, the average plant height was calculated with an error of approximately 50 cm using Sentinel-1 satellite images. However, due to the high difference between the minimum and maximum plant height values calculated from Sentinel-1 satellite images and high standard deviation; it has been determined that the average plant height value calculated from Sentinel-1 satellite images was close to the actual plant height value accidentally.