Factors Affecting Active Canopy Sensor Performance and Reflectance Measurements

Abstract

Identifying factors that significantly affect active sensor performance is important if active sensor technologies are to be used effectively in production agriculture. Our objectives were to determine the effects of different lighting conditions on active sensor values, vertical depth penetration of active sensor light into a corn (Zea mays L.) canopy, and differences between canopy reflectance values from single vs. multiple active sensors units. Corn was sensed with the GreenSeeker Green 506 (GS-506) and Crop Circle ACS-210 (CC-210) active canopy sensors. Canopy sensing was conducted during the day and night, with and without artificial light (Study 1). The bottom corn leaves were removed, and sensing was conducted after leaf removal (Study 2). A three-sensor CC-210 unit was used to determine reflectance differences between single and multiple sensors (Study 3). Near-infrared (NIR) and visible (VIS) reflectance values from the CC-210 were not affected by different lighting conditions. The GS-506 generated greater reflectance values during the day, indicating that the sensor measured passive reflectance via sunlight. The GS-506 had greater vertical light penetration into the corn canopy than the CC-210 due to a concentrated field of view. Variation in NIR and VIS reflectance values were found with each of the CC-210 active sensor units but only for NIR with the different sensor combinations (Sensor 2, Sensors 1 and 3, or Sensors 1, 2, and 3). Differences in measured canopy reflectance between single and multiple CC-210 units were due to individual sensor variation of <2%. Results from this study will be useful for improved operation of active sensors in production corn fields.