Unmanned aircraft system-derived crop height and normalized difference vegetation index metrics for sorghum yield and aphid stress assessment

Authors: STANTON, CARLY - Texas A&M University; STAREK, MICHARL - Texas A&M University; Elliott, Norman - Norm; BREWER, MICHAEL - Texas Agrilife Extension; MAEDA, MURILO - Texas Agrilife Extension; CHU, TIANXING - Texas A&M University

Submitted to: Journal of Applied Remote Sensing (JARS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2017
Publication Date: 6/22/2017
Citation: Stanton, C., Starek, M., Elliott, N.C., Brewer, M., Maeda, M., Chu, T. 2017. Unmanned aircraft system-derived crop height and normalized difference vegetation index metrics for sorghum yield and aphid stress assessment. Journal of Applied Remote Sensing (JARS). 11(2):026035. doi:10.1117/1.JRS.11.026035.

Interpretive Summary: A small, fixed-wing unmanned aerial system (UAS) was used to survey a replicated small plot field experiment designed to estimate sorghum damage caused by an invasive aphid (sugarcane aphid). Plant stress varied among sorghum plots through manipulation of sugarcane aphid densities. Equipped with a consumer-grade near-infrared camera, the UAS was flown on a recurring basis over the 2015 growing season. The raw imagery was processed to generate normalized differenced vegetation index (NDVI) maps of the sorghum plots and 3D point clouds. NDVI and plant height metrics were averaged on a per plot basis and evaluated for their ability to identify aphid induced plant stress. Experimental ground filtering was performed on both metrics and a method filtering low NIR values before NDVI calculation was found to be the most effective. UAS NDVI was compared to NDVI derived from two other platforms and similar trends were found across all platforms. The remotely sensed measures of plant height and NDVI were correlated to plot averages of plant height, yield, and sugarcane aphid density. Negative correlations between aphid density and NDVI were seen near the end of the season in the most damaged crops. The research indicates potential of UAS equipped with a commercially available multispectral camera to detect spatially variable sugarcane aphid injury to sorghum in sorghum fields. The goal is to develop UAS methods for monitoring fields for the purpose of site specific management of sugarcane aphid in commercial sorghum fields.

Technical Abstract: A small, fixed-wing UAS was used to survey a replicated small plot field experiment designed to estimate sorghum damage caused by an invasive aphid. Plant stress varied among 40 plots through manipulation of aphid densities. Equipped with a consumer-grade near-infrared camera, the UAS was flown on a recurring basis over the 2015 growing season. The raw imagery was processed to generate NDVI maps of the fields and 3D point clouds. NDVI and plant height metrics were averaged on a per plot basis and evaluated for their ability to identify aphid induced plant stress. Experimental ground filtering was performed on both metrics and a method filtering low NIR values before NDVI calculation was found to be the most effective. UAS NDVI was compared to NDVI derived from two other platforms and similar trends were found across all platforms. Plot averages of NDVI and canopy height values were compared to per-plot yield at 14% moisture and aphid density. The remotely sensed measures of plant height and NDVI were correlated to plot averages of plant height, yield, and insect density. Negative correlations between aphid density and NDVI were seen near the end of the season in the most damaged crops.