Progress in Remote Sensing of Grass Senescence: A Review on the Challenges and Opportunities

Grass senescence estimation in rangeland is particularly important for monitoring the conditions of forage quality and quantity. During senescence, grasses lose their nutrients from the leaves to the root and thereby affecting forage productivity. Studies on the remote sensing of grasslands have been conducted during the senescent phenological stage. However, despite the efforts made in previous remote sensing studies on grass senescence, its role in estimating grass senescence is rudimentary. More so, the strengths and limitations presented by the newly developed remote sensing instruments in grass senescence estimation are not well documented. This work, therefore, provides a detailed overview on the progress of remote sensing applications in characterizing grass senescence. The review further highlights the challenges and opportunities presented by these techniques. Overall, the review indicates that studies on remotely sensed grass senescence are focused on understanding biophysical and biochemical properties, and these studies identify the leaf area index, biomass, and chlorophyll content, among others, as the key indicators of grass senescence. Nonetheless, recent scientific research highlights a mismatch between studies on the grass senescence and the development in remote sensing technologies. The use of sophisticated and robust time-series analysis techniques together with improved sensing characteristics from the new generation sensors seem to present new opportunities for the optimal quantification of grass senescence at resolutions complementary to the spatial extents of the rangelands. We, therefore, recommend further research in this field through the adoption of new satellite technologies and advanced spatial data analytics to enhance the monitoring of rangeland resources.