Irrigation accounts for about 80% consumptive use of water in the Northwest of United States. Even small increases in water use efficiency can improve crop production, yield, and have more water available for alternative uses. Center pivot irrigation systems are widely recognized in the irrigation industry for being one of the most efficient sprinkler systems. In recent years, there has been a shift from high pressure impact sprinklers on the top of center pivots to Mid Elevation Spray Application (MESA) sprinkler configurations and towards Low Elevation Spray Application (LESA) sprinklers. Although LESA offers range of benefits over MESA, such technologies have grower adoption concerns as the effects of these systems on the crop growth and yield are unknown. In this study, these parameters were evaluated for LESA and MESA using a small Unmanned Aerial System (UAS) integrated with multispectral and thermal imaging sensors, in corn (Zea mays var. indentata) and mint (Mentha spicata and Mentha × piperita). The field experiment was designed to have two adjacent spans of a center pivot sprinkler irrigation system with LESA and MESA in both the fields located in the state of Washington, USA.  Aerial data was collected throughout the crop growing season and analyzed using image processing algorithms, custom developed in Matlab® to observe the temporal variation of the above-mentioned crop parameters for both sprinkler system configurations. Various vegetation indices and canopy temperature was extracted from the imaging data and compared for the LESA and MESA irrigated areas. Two sample T-test was performed to find if there was any significant difference at 5% level in the observed parameters between LESA and MESA.  

Results showed that for mint, LESA irrigated areas had more average crop vigor and similar canopy temperature during the entire crop growth season though the difference was not significant. The LESA irrigated areas had significantly more crop vigor and less canopy temperature till the mid growth season which is the phase that determines the yield, according to many prior studies. However, for corn, MESA had more crop vigor and a cooler canopy than LESA throughout the season. Though the difference in crop vigor was not significant, the MESA irrigated canopy areas was significantly cooler than LESA irrigated areas. The results were anticipated, as the sprinkler heads used in LESA were being pulled off in corn field, causing the weighted hose to damage the corn which could be observed from the aerial images. A different kind of sprinkler head was used after this incident. However, some strips of corn had already been damaged. The damaged strips could not cause any significant difference in the canopy vigor with the MESA irrigated areas. As LESA had similar effect on canopy as MESA, LESA could be installed in mint and corn fields, backed up by several benefits of this system over MESA made in other studies, improving the water efficiency. Also, the methods developed could be used for other applications related to precision and sustainable agriculture.