With the increasing role that unmanned aerial systems (UAS) are playing in data collection for environmental studies, two key challenges relate to harmonizing and providing standardized guidance for data collection, and also establishing protocols that are applicable across a broad range of environments and conditions. In this context, a network of scientists are cooperating within the framework of the Harmonious Project to develop and promote harmonized mapping strategies and disseminate operational guidance to ensure best practice for data collection and interpretation. The culmination of these efforts is summarized in the present manuscript. Through this synthesis study, we identify the many interdependencies of each step in the collection and processing chain, and outline approaches to formalize and ensure a successful workflow and product development. Given the number of environmental conditions, constraints, and variables that could possibly be explored from UAS platforms, it is impractical to provide protocols that can be applied universally under all scenarios. However, it is possible to collate and systematically order the fragmented knowledge on UAS collection and analysis to identify the best practices that can best ensure the streamlined and rigorous development of scientific products.
Traditionally, most irrigation practices in Southern Europe have been based on gravity-fed surface irrigation systems. Currently, these systems remain a relevant typology in the European Union (EU) member states of the Mediterranean areas, where it is often the only sustainable method for farmers due to the small size of agricultural holdings, their reduced capacity and readiness to invest and the low ratio between yield profits and irrigation costs. In the last several years, in response to European and national directives, surface irrigation has garnered increasing attention at the political and bureaucratic levels due to frequent criticisms of its postulated low efficiency and high water wastage. However, these systems commonly provide a number of ecosystem services and nature-based solutions that increase the positive externalities in different rural socio-ecological contexts and often have the potential to extend these services and provide solutions that are compatible with economical sustainability. This study aims to discuss the prospects for new practices and for the rehabilitation and modernization of the gravity-fed surface irrigation systems in EU Mediterranean areas to enhance water efficiency, thus gaining both economic advantages and environmental benefits. The difficulties, stimuli for improvements and peculiarities of the irrigation water management of four rural environments located in Italy, Spain and Portugal were analyzed and compared to the current state of the gravity-fed surface irrigation systems with hypothetical future improvements achievable by innovative technologies and practices. In these different case studies, the current gravity-fed surface irrigation systems have an obsolete regulatory structure; water-use efficiency is not a driving criterion for the management of the conveyance and distribution canal network, and farmers are not yet adequately encouraged to adopt more efficient gravity-fed irrigation practices. A continuous knowledge exchange is thus necessary for the interaction of all irrigation water managers and farmers to improve their eco-efficiency and to preserve and promote their cultural heritage across the entire water supply and delivery chains. We argue that the best way forward will require precisely targeted rehabilitation measures of gravity-fed surface irrigation systems based on the integrated use of decision support services, gate automation, remote and feedback controls and real-time flow optimization.
Smart-irrigation systems are a hot topic in irrigation management. Satellite imaging, sensors and controls, communication technologies and irrigation decision models are readily available. The price of the required technology is being reduced year after year, and its implementation in agriculture gives real-time information that allows for more accurate management of water resources. Even so, the adaptation of existing technologies to particular situations that the irrigation management is facing in different agro-environmental contexts is needed. This Special Issue addresses the application of different smart-irrigation technologies in four different research areas: (1) remote sensing-based estimates of crop evapotranspiration, (2) Information and Communication Technologies (ICTs) for smart-irrigation, (3) precision irrigation models and controls, and (4) the price of natural resources. The nine papers presented in this special issue cover a wide range of practical applications, and this editorial summarizes each of them.
Duckweed species, particularly Lemna minor, are widely found in freshwaters all over the world. This macrophyte provides multiple ecosystems’ functions and services, but its excessive proliferation can have negative environmental impacts (including ecological and socio-economic impacts). This work explores the use of remote sensing tools for mapping the dynamics of Lemna minor in open watercourses, which could contribute to identifying suitable monitoring programs and integrated management practices. The study focuses on a selected section of the Lis River (Portugal), a small river that is often affected by water pollution. The study approach uses spatiotemporal multispectral data from the Sentinel-2 satellite and from 2021 and investigates the potential of remote sensing-based vegetation and water indices (Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Difference Aquatic Vegetation Index (NDAVI), Green Red Vegetation Index (GRVI), Normalized Difference Water Index (NDWI)) for detecting duckweeds’ infestation and its severity. The NDAVI was identified as the vegetation index (VI) that better depicted the presence of duckweeds in the surface of the water course; however, results obtained for the other VIs are also encouraging, with NDVI showing a response that is very similar to NDAVI. Results are promising regarding the ability of remote sensing products to provide insight into the behavior of Lemna minor and to identify problematic sections along small watercourses.
Rice cultivation is one of the largest users of the world’s freshwater resources. The contribution of remote sensing observations for identifying the conditions under which rice is cultivated, particularly throughout the growing season, can be instrumental for water, and crop management. Data from different remote sensing platforms are being used in agriculture, namely to detecting anomalies in crops. This is attempted by calculating vegetation indices (VI) that are based on different vegetation reflectance bands, especially those that rely on the Red, Green, and near-infrared bands, such as the Normalised Difference Vegetation Index (NDVI) or the Green Normalised Difference Vegetation Index (GNDVI). However, particular features of different crops and growing conditions justify that some indices are more adequate than others on a case-to-case basis, according to the different vegetation’s spectral signatures. In recent years, a vegetation index related to the Red Edge reflectance band, the Normalised Difference Red Edge (NDRE) has shown potential to be used as a tool to support agricultural management practices; this edge band, by taking a transition position, is very sensitive to changes in vegetation properties. This work, focusing on the rice crop and the application of different irrigation practices, explores the capability of several VIs calculated from different reflectance bands to detect variability, at the plot scale, in rice cultivation in the Lower Mondego region (Portugal). The remote sensing data were obtained from satellite Sentinel-2A imagery and using a multispectral camera mounted on an Unmanned Aerial System (UAS). By comparing several vegetation indices, we found that NDRE is particularly useful for identifying non-homogeneities in irrigation and crop growth in rice fields. Since few satellite sensors are sensible in the Red Edge band and none has the spatial resolution offered by UAS, this study explores the potential of UAS to be used as a useful support information tool in rice farming and precision agriculture, regarding irrigation, and agronomic management.
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