# Remote Sensing for Precision Agriculture: Sentinel-2 Improved Features and Applications
## 4 Sentinel-2: Comparative Advantages and Future Work  
The Sentinel-2 spatial resolution and number and positioning of spectral reflectance bands excel at cropland and crop type classification, as well as monitoring of crops phenology, namely by enabling the measurement of growth (biomass) and health (stress symptoms) separately. Furthermore, as reviewed, red-edge bands are also effective for monitoring nitrogen status, and therefore optimizing fertilization practices. The literature-proven VIs using the red-edge bands have proven robust indicators of plant N status that can be useful for agricultural monitoring. Due to Sentinel-2 red-edge bands characteristics, the biophysical parameters estimation obtained with these multispectral indexes have higher accuracy than other satellites [96]. Hence, the revisit time of 5 days, the red-edge band, and the higher resolution sets an improved management perspective.  
The combination of available sensors also remains an excellent opportunity for improvement. For instance, Sentinel-2 has limitations towards estimating evapotranspiration and water stress due to its lack of any thermal bands, and as such data fusion with other complimentary sensors may generate opportunities to coordinate data with available thermal bands such as NASA's MODIS or Landsat-8 [97]. However, the spatial resolution of their thermal bands (1 km and 100 m, respectively) might be a downside for some agricultural applications that require more detail. Other possible approaches are the combination of optical imagery of Sentinel-2 and thermal bands from the sensors on board Sentinel-3 to obtain crop evapotranspiration, which is promising for bridging the gap and monitoring evapotranspiration with a higher resolution [98]. Besides that, the combination of Sentinel-2 optical bands and Sentinel-1 C-band Synthetic Aperture Radar has successfully been used for mapping soil moisture and irrigation demands [99].  
Another challenge is pest monitoring, where pest early warning systems are useful to predict outbreaks and are generally based on weather information, and intensive and time-consuming field work. Being able to use Sentinel-2, or other remote sensing instruments, to assess pest distribution would be of great importance, considering the current globalization of invasive pests and their sudden effects. Nonetheless, a bottleneck is found here, on the one hand the pixel resolution makes it very difficult to monitor pests and generally only when damage is significant it can be sensed. On the other hand, it is a challenge to differentiate the reflectance patterns of plants due to biotic stresses and see what the exact cause of the stress is. The combination of ground, drone, and satellite sensors might be a way to go, with some regional and technical limitations that need to be overcome.  
Soils are generally not considered at the expense of other parameters. However, the importance of SOC, which is gaining interest within the sustainable agriculture paradigm, can be monitored with Sentinel-2. This can help to overcome this fact and move forward into precision agriculture and soil sustainability. Regarding soils, monitoring cropland pollution due to heavy metals is important to ensure food safety. It is relevant to see that three papers reviewed in this issue had rice and China as the case study [90; 91; 92] where serious pollution problems in this sense happen [100].  
Sen2-Agri has set the structure for a coordinated field monitoring platform which will likely lead to a multi-country precision agriculture initiative. In developing countries, on the other hand, this platform, and similar ones using Sentinel-2 data, can contribute to food safety and help farmers in managing their crops. Due to the small fields, intercropping practices and terrain-derived issues crop monitoring strategies need to be tuned in order to successfully manage these areas.