Quantifying Vegetation Biophysical Variables from Imaging Spectroscopy Data: A Review on Retrieval Methods

An unprecedented spectroscopic data stream will soon become available with forthcoming Earth-observing satellite missions equipped with imaging spectroradiometers. This data stream will open up a vast array of opportunities to quantify a diversity of biochemical and structural vegetation properties. The processing requirements for such large data streams require reliable retrieval techniques enabling the spatiotemporally explicit quantification of biophysical variables. With the aim of preparing for this new era of Earth observation, this review summarizes the state-of-the-art retrieval methods that have been applied in experimental imaging spectroscopy studies inferring all kinds of vegetation biophysical variables. Identified retrieval methods are categorized into: (1) parametric regression, including vegetation indices, shape indices and spectral transformations; (2) nonparametric regression, including linear and nonlinear machine learning regression algorithms; (3) physically based, including inversion of radiative transfer models (RTMs) using numerical optimization and look-up table approaches; and (4) hybrid regression methods, which combine RTM simulations with machine learning regression methods. For each of these categories, an overview of widely applied methods with application to mapping vegetation properties is given. In view of processing imaging spectroscopy data, a critical aspect involves the challenge of dealing with spectral multicollinearity. The ability to provide robust estimates, retrieval uncertainties and acceptable retrieval processing speed are other important aspects in view of operational processing. Recommendations towards new-generation spectroscopy-based processing chains for operational production of biophysical variables are given

Transboundary WEF nexus analysis: a case study of the Songwe River Basin

In Mabhaudhi, Tafadzwanashe; Senzanje, A.; Modi, A.; Jewitt, G.; Massawe, F. (Eds.). Water - energy - food nexus narratives and resource securities: a global south perspective. Amsterdam, Netherlands: ElsevierOver the past decade, the water, energy, and food (WEF) nexus approach has evolved to become a focus of the Southern African Development Community (SADC) development strategies. However, a lack of empirical evidence, appropriate methods, and qualitative and quantitative tools to implement the WEF nexus approach has been highlighted. This chapter describes the application of the WEF nexus approach in the Songwe River Basin (SRB) located on the border between Malawi and Tanzania as a demonstration of how this lack of evidence and tools is starting to be addressed. The basin is currently facing rapid population growth, which is leading to a considerable increase in resource demand and environmental issues and has been identified as a priority basin for SADC. The SRB Development Programme (SRBDP) includes several projects that collectively aim to improve the environmental and socioeconomic status of the basin. The integrated approach proposed to assess the SRBDP's expected outcomes through a WEF nexus lens is based on the development and application of qualitative and quantitative tools that support decision-makers to assess feasible sustainable development pathways in the basin, and more broadly in the SADC region. This chapter focuses on the qualitative analysis of the WEF nexus system and explains the process of identifying the major sectors and subsectors involved in the SRBDP, the main interlinkages between them, and potential synergies and trade-offs assessing how decisions made in a sector may influence others. The qualitative analysis of the SRB shows that although the projects included in the SRBDP are expected to have positive impacts on the environment and the socioeconomic system of the basin, downsides that may have an impact on human and ecosystem health are also possible. Early identification of such issues can help to limit detrimental impacts in the future. In the analysis, potential Sustainable Development Goals (SDGs), objectives, and indicators that may be addressed in the SRB are identified, highlighting the importance of applying the holistic approach to enhance and boost the achievement of SDGs in the basin

Water-energy-food nexus tools in theory and practice: a systematic review

Sector-based resource management approaches partly contribute to the insecurities in water, energy and food sectors and resources. These approaches fail to acknowledge and capture the interlinkages between these connected resources, a key strength in the water-energy-food (WEF) nexus approach. However, the multi-centric, multidimensional, and spatiotemporally dynamic WEF nexus is complex and uncertain, thus requiring dedicated tools that can unpack it. Various sources have blamed the slow uptake and practical implementation of the WEF nexus on the unavailability of appropriate tools and models. To confirm those claims with evidence, literature on WEF nexus tools was searched from Scopus and Web of Science and systematically reviewed using the PRISMA protocol. It was found that the WEF nexus tools are being developed increasingly, with a current cumulative number of at least 46 tools and models. However, their majority (61%) is unreachable to the intended users. Some available tools are in code format, which can undermine their applicability by users without programming skills. A good majority (70%) lack key capabilities such as geospatial features and transferability in spatial scale and geographic scope. Only 30% of the tools are applicable at local scales. In contrast, some tools are restricted in geographic scope and scale of application, for example, ANEMI 3 and WEF models for large and household scales, respectively. Most (61%) of the tools lack wide application in actual case studies; this was partly attributed to the tools not being readily available. Thus, efforts should be made to disseminate and ensure end-users’ uptake and application of developed tools. Alternatively, the user-friendly tools should be developed on-demand as requested and inspired by potential clients. Developers should consider utility, transferability and scalability across uses and users when improving existing tools and developing new tools so that they are adaptable, only requiring new, specific location-adapted inputs and data. Where and when it is necessary to capture spatial dynamics of the WEF nexus, tools should be geographic information system (GIS)-enabled for automatic WEF nexus location selection, geospatial mapping, and visualization. Such GIS-enabled WEF nexus tools can provide a bird’s eye view of hotspots and champions of WEF nexus practices

EO-WEF: a earth observations for water, energy, and food nexus geotool for spatial data visualization and generation

In Mabhaudhi, Tafadzwanashe; Senzanje, A.; Modi, A.; Jewitt, G.; Massawe, F. (Eds.). Water - energy - food nexus narratives and resource securities: a global south perspective. Amsterdam, Netherlands: ElsevierWEF (water–energy–food) nexus analyses have become a rapidly growing field since the Conference on Water, Energy and Food Security Nexus–Solutions for the Green Economy in Bonn in 2011. They have the potential to help stakeholders and policymakers to better understand the interlinkages between the different components of a nexus system and lead to solutions that are socially and environmentally beneficial. However, assembling wide-scope nexus has been challenged by issues such as proprietary considerations and data evolution over time, among others. Earth observations (EOs) have a huge offering of data sets that can provide data for most of the components of a nexus at a relatively low cost and various temporal and spatial resolutions. Furthermore, the advent of cloud computing has made possible the processing of massive information. This chapter introduces the Earth Observation for WEF nexus (EO-WEF), a multisectorial information system to visualize customizable data and generate time series data at any location. Google Earth Engine, a cloud computing platform that includes data archives of regularly updated EO and scientific data sets for a period of more than 40 years, powers this application. The capability of EO-WEF in generating spatial data was tested in the Songwe River Basin case study. Overall, the EO-WEF application provides data for key variables of a nexus that can be supplemented by other kinds of data that cannot be captured by EOs