The scale and resolution of the imagery gathered by UAS is ideal for crop monitoring and precision agriculture, whether the crop is broad acre variety such as poppies or barley, an intensive crop such as lettuce, an orchard crop such as apples, or a vineyard. The size of the area to be monitored dictates which UAV platform is most appropriate and the characteristics of the crop that need to be assessed dictates the type of sensor. The TerraLuma team have been evaluating various aircraft carrying a range of sensors to assess the potential applications of UAS for crop monitoring. In this case study we will summarise those studies through examples of datasets that have been produced using the equipment listed here.
Image acquisition with a consumer grade compact camera
The first agricultural images were taken with a Canon G10 and a modified G10 that could acquire images in the near infrared (NIR). These images can give insight into the relative vigour of vegetation but the wavelength range is broad and the NIR reflectance is difficult to quantify making it difficult to get anything more than a qualitative understanding of crop health.
Image acquisition with the 6-band multispectral camera, the thermal infrared camera and a digital SLR camera
The MiniMCA camera provided our next multispectral view of crops. In this case a barley crop was imaged that had had varying levels of nitrogen applied and the areas of high nitrogen application showed significant differences in the red edge and NIR bands.The narrow (10 nm) bands acquired by the MiniMCA provides the ability to derive spectral indices such as the the Normalised Vegetation Difference Index (NDVI) and Photochemical Reflectance Index (PRI). The FLIR thermal camera acquires coarser resolution data that can provide insight into plant stress and irrigation efficiency. The UAV captures an image every second and we have developed automated mosaicking tools to provide high resolution mosaics of crops from both multispectral and standard colour photography. As can be seen below and in other case studies these multiple views of an area can be used to derive high resolution digital surface models (DSMs).
Image acquisition with the hyperspectral pushbroom scanner
The most recent experiments have been with a small hyperspectral sensor and the results are promising. As can been seen in the examples below the high number of narrow bands provide the ability to derive biophysical and biochemical characteristics from the continuous spectrum in the visible and NIR wavelengths.