Effect of Height, Tilt and Twist Angles of an Active Reflectance Sensor on Ndvi Measurements

Abstract

The application of nitrogen (N) fertilizer is complex and expensive, so its correct management has financial and environmental benefits. The use of optical proximity sensors is a promising technique. However, the movement of the agricultural machinery or of the person carrying the sensor will result in height differences and/or different tilt and twist angles with respect to the canopy. We considered whether these variations would affect the reflectance measurement. In this study, we took normalized difference vegetation index (NDVI) readings of a wheat canopy, to which 90 kg ha-1 of urea had been applied in stage 5, and observed the NDVI in stages 6, 8 and 10.5. We also tested soybeans, to which 90 kg ha-1 of urea had been applied in stage R1, and took NDVI readings in stages R2 and R5. Our goal was to study the effects of the position of an active reflectance sensor (GreenSeeker) on the NDVI index at different heights and at different angles to the canopy. We observed that the height of the sensor affected the NDVI depending on the stage of the plant and that angles up to 15° of the sensor did not directly affect the readings.

Cultivo de berenjena (Solanum melongena L.) en hidroponía bajo invernadero y malla sombra con estrés salino

“…En este estudio, el cultivo bajo malla sombra mostró el mayor valor del NVDI con 0,66, en comparación con el invernadero (Tabla 1). En otro estudio, el cultivo de trigo, el NDVI mostró un comportamiento inverso con respecto a la radiación; es decir, a mayor incidencia de radiación solar menor NDVI, disminuyó de valores entre 0,82-0,84 a 0,68 (Stocker et al, 2019).…”

Development of a Low-Cost Open-Source Platform Connected to the Internet for Acquisition of Environmental Parameters and Soil Moisture

“…The measurements of solar irradiance on the horizontal plane (Stocker et al, 2019) were performed with an ML-01 pyranometer (EKO Instruments Co., Ltd, Tokyo, Japan), calibrated in August 2019. This device has a sensor of silicon photodiode with a spectral response of 400-1100 nm, measurement range from 0 to 2000 W m −2 , response lower than 1 ms, and output from 0 to 100 mV.…”

Nitrogen fertilization for wheat following soybean and interfering factors on spectral reflectance readings

“…However, sensor readings can be affected directly or indirectly by several factors. Combining light source and measurement distance can result in different spectral reflectance readings [33]. Depending on the measurement distance, the sensor can result in different viewing angles and a chance of footprint size, automatically changing the monitored area [13,36].…”