Sensors At Different Heights and for Various Crops

Sensors that estimate normalized difference vegetative index (NDVI) can increase nitrogen use efficiency and help meet the expected increased food demand; however, current devices are cost prohibitive to small farming operations. The objectives of this study were to determine the relationship of GreenSeeker (GS) sensor and HandHeld Crop Sensor (HHCS), manufactured by Trimble, when used to collect NDVI data at different heights, by different operators, in several crops; and to determine the reliability of the less-costly HHCS to accurately collect NDVI data. Tests were conducted in Stillwater, Oklahoma, in the fall of 2012. Both sensors were operated by two operators at 60 and 100 cm above the bare soil or crop canopy. Regression, correlation, and analysis of variance, were performed in SAS. Correlation coefficient (R 2 ) between HHCS and GS readings averaged 0.95, indicating a strong correlation between sensor readings. There was no significant effect of operator, heigth, or their interactions; however, although readings between sensors were highly correlated, they were significantly different. Mean NDVI colleted via GS averaged 0.43 as compared to 0.39 via HHCS, with a root mean square error (RMSE) of 0.049 across all 1200 collected values, witha trend of slight underestimation of NDVI values by the HHCS. Results indicates that NDVI readings are independent of operator or height collected, and despite the high correlation between