Remotely sensed real-time quantification of biophysical and biochemical traits of Citrus (Citrus sinensis L.) fruit orchards - A review

Remote sensing provides accurate and cost-effective solution to quantify the biophysical and biochemical traits of citrus fruit orchards. Timely information on these traits can be used to design real-time computerized applications for site-specific orchard management, yield estimation, and scheduling precise and proper application of inputs thus growing net returns and optimizing resource utilization. Retrieval of these traits has been playing an important role during the last 30 years with steady improvement in remote sensing platforms and sensors and the techniques and methods forthwith. However, with dense canopy, variable illumination conditions and saturation effects caused by seasonal dynamics of leaf and canopy pigments combined with high year-round leaf density pose challenges for the accurate and precise inference of biophysical and biochemical traits in citrus fruit orchards. Concerning these challenges in the pursuit of earth observation, the present paper aims to provide a comprehensive and in-depth review of the remotely sensed technologies and applications for real-time and state-of-the-science retrieval of biophysical and biochemical traits of citrus fruit orchards. Establishing a database of citrus traits at leaf, canopy and orchard level is very important for future smart agriculture to help farmers for site-specific orchard management, plan farm management practices, selection of best cultivars, scheduling precise and proper application of inputs in citrus production paradigm; thus growing net returns and optimize resource utilization. Technical methods for different levels of remote sensing acquisition have also been elaborated highlighting the current situation of citrus traits acquired by remote sensing.