Active Sensor Performance – Dependence to Measuring Height, Light Intensity and Device Temperature
B. Mistele, U. Schmidhalter, S. Kipp
Technical University Munich
For land use management, agriculture, and crop management spectral remote sensing is widely used. Ground-based sensing is particularly advantageous allowing to directly link on-site spectral information with agronomic algorithms. Sensors are nowadays most frequently used in site-specific oriented applications of fertilizers, but similarly site-specific applications of growth regulators, herbicides and pesticides become more often adopted.
Generally little is known about the effects of external as well as internal factors influencing the performance of active sensing systems. Such knowledge is however indispensable, particularly becoming important when only small differences among plant canopies or cultivars have to be detected. Factors to be known include effects of the sensor-target distance and temperature and radiation effects on the performance of the sensors. Although manufacturers indicate sensors’ performance being independent of ambient light conditions, this attribute was tested for three different active sensors (Ntech GreenSeeker RT100, Holland Scientific CropCircle ACS 470, YARA N-Sensor ALS) as well as the performance of active sensors under changing device temperature conditions.
Additionally the optimum range of measuring height was indentified for each active sensor. In this study it could be shown that the device temperature of the three different active sensors has an effect on the accuracy of the sensors’ output. By comparing this effect with data of a field trial with varying nitrogen supplies, it became apparent that a device temperature shift of 1 °C can result in deviations in N application rates of 2-3 kg N/ha. However, varying light conditions were evaluated as not affecting the performance. Active sensors showed the same performance under dark and light conditions. A dependency of active sensors on their distance to the crop target became apparent. Accurate measuring distances to the crop canopies were determined that enable stabile sensor outputs during measurements of plants with different heights.
