Michael Rast

The EnMAP Spaceborne Imaging Spectroscopy Mission for Earth Observation

Imaging spectroscopy, also known as hyperspectral remote sensing, is based on the characterization of Earth surface materials and processes through spectrally-resolved measurements of the light interacting with matter. The potential of imaging spectroscopy for Earth remote sensing has been demonstrated since the 1980s. However, most of the developments and applications in imaging spectroscopy have largely relied on airborne spectrometers, as the amount and quality of space-based imaging spectroscopy data remain relatively low to date. The upcoming Environmental Mapping and Analysis Program (EnMAP) German imaging spectroscopy mission is intended to fill this gap. An overview of the main characteristics and current status of the mission is provided in this contribution. The core payload of EnMAP consists of a dual-spectrometer instrument measuring in the optical spectral range between 420 and 2450 nm with a spectral sampling distance varying between 5 and 12 nm and a reference signal-to-noise ratio of 400:1 in the visible and near-infrared and 180:1 in the shortwave-infrared parts of the spectrum. EnMAP images will cover a 30 km-wide area in the across-track direction with a ground sampling distance of 30 m. An across-track tilted observation capability will enable a target revisit time of up to four days at the Equator and better at high latitudes. EnMAP will contribute to the development and exploitation of spaceborne imaging spectroscopy applications by making high-quality data freely available to scientific users worldwide.

Estimation of soil and vegetation temperatures with multiangular thermal infrared observations: IMGRASS, HEIFE, and SGP 1997 experiments

The potential of directional observations in the thermal infrared region for land surface studies is a largely uncharted area of research. The availability of the dual-view Along Track Scanning Radiometer (ATSR) observations led to explore new opportunities in this direction. In the context of studies on heat transfer at heterogeneous land surfaces, multiangular thermal infrared (TIR) observations offer the opportunity of overcoming fundamental difficulties in modeling sparse canopies. Three case studies were performed on the estimation of the component temperatures of foliage and soil. The first one included the use of multi-temporal field measurements at view angles of 0°, 23° and 52°. The second and third one were done with directional ATSR observations at view angles of 0° and 53° only. The first one was a contribution to the Inner-Mongolia Grassland Atmosphere Surface Study (IMGRASS) experiment in China, the second to the Hei He International Field Experiment (HEIFE) in China and the third one to the Southern Great Plains 1997 (SGP 1997) experiment in Oklahoma, United States. The IMGRASS experiment provided useful insights on the applicability of a simple linear mixture model to the analysis of observed radiance. The HEIFE case study was focused on the large oasis of Zhang-Ye and led to useful estimates of soil and vegetation temperatures. The SGP 1997 contributed a better understanding of the impact of spatial heterogeneity on the accuracy of retrieved foliage and soil temperatures. Limitations in the approach due to varying radiative and boundary layer forcing and to the difference in spatial resolution between the forward and the nadir view are evaluated through a combination of modeling studies and analysis of field data.

The use of ERS-1/2 Tandem interferometric coherence in the estimation of agricultural crop heights

In this study, the relationship between ERS-1/2 SAR Tandem interferometric coherence and the height of sugar beet, potato, and winter wheat is investigated using measurements of crop growth and coherence. The development of both coherence and crop height is observed to be approximately linear during the early growing season, and linear crop-specific relationships between Tandem coherence and the heights of the studied crops are derived. The coherence of all the studied crops decreases as the crop heights increase, a probable explanation for this is that as the crop grows, it screens the ground more effectively, and a greater part of the incident radar energy is backscattered from vegetation that decorrelates more rapidly than the more stable soil. The relatively dense canopies of the root crops sugar beet and potato screen the ground considerably more effectively than the cereal crop winter wheat. This study gives a strong indication that ERS-1/2 Tandem interferometric coherence is related to the height of agricultural crops, and that this relationship can be used to retrieve crop heights.

ESA Medium Resolution Imaging Spectrometer MERIS

The Medium Resolution Imaging Spectrometer (MERIS), developed by the European Space Agency (ESA) for the Envisat polar orbit Earth mission, belongs to a new generation of ocean colour sensors which will yield a major improvement in the knowledge of such a crucial processes as the ocean contribution to the carbon cycle. The global mission of MERIS will have a major contribution to scientific projects which seek to understand the role of oceans and ocean productivity in the climate system and our ability to forecast change through models. Secondary objectives of the MERIS mission will be directed to the measurement of atmospheric parameters associated with clouds, water vapour and aerosols in addition to land surface parameters, important in particular for the understanding of vegetation processes. MERIS measures the radiance reflected from the Earths surface in the visible and near infra-red part of the spectrum. Data are transmitted in fifteen spectral bands of programmable width and location. The instrument features two spatial resolution and several observation and calibration modes selectable by ground command. This paper gives an overview ofthe instrument mission, its concept and data products. Keywords: MERIS, ENVISAT, Imaging Spectrometer, Ocean colour

Supporting Earth-Observation Calibration and Validation: A new generation of tools for crowdsourcing and citizen science

Citizens are providing vast amounts of georeferenced data in the form of in situ data collections as well as interpretations and digitization of Earth-observation (EO) data sets. These new data streams have considerable potential for supporting the calibration and validation of current and future products derived from EO. We provide a general introduction to this growing area of interest and review existing crowdsourcing and citizen science (CS) initiatives of relevance to EO. We then draw upon our own experiences to provide case studies that highlight different types of data collection and citizen engagement and discuss the various barriers to adoption. Finally, we highlight opportunities for how citizens can become part of an integrated EO monitoring system in the framework of the European Union (EU) space program, including Copernicus and other monitoring initiatives.

Review of Understanding of Earth’s Hydrological Cycle: Observations, Theory and Modelling

Water is our most precious and arguably most undervalued natural resource. It is essential for life on our planet, for food production and economic development. Moreover, water plays a fundamental role in shaping weather and climate. However, with the growing global population, the planet’s water resources are constantly under threat from overuse and pollution. In addition, the effects of a changing climate are thought to be leading to an increased frequency of extreme weather causing floods, landslides and drought. The need to understand and monitor our environment and its resources, including advancing our knowledge of the hydrological cycle, has never been more important and apparent. The best approach to do so on a global scale is from space. This paper provides an overview of the major components of the hydrological cycle, the status of their observations from space and related data products and models for hydrological variable retrievals. It also lists the current and planned satellite missions contributing to advancing our understanding of the hydrological cycle on a global scale. Further details of the hydrological cycle are substantiated in several of the other papers in this Special Issue.

Preface: The Environmental Mapping and Analysis Program (EnMAP) Mission: Preparing for Its Scientific Exploitation

The imaging spectroscopy mission EnMAP aims to assess the state and evolution of terrestrial and aquatic ecosystems, examine the multifaceted impacts of human activities, and support a sustainable use of natural resources. Once in operation (scheduled to launch in 2019), EnMAP will provide high-quality observations in the visible to near-infrared and shortwave-infrared spectral range. The scientific preparation of the mission comprises an extensive science program. This special issue presents a collection of research articles, demonstrating the potential of EnMAP for various applications along with overview articles on the mission and software tools developed within its scientific preparation.

The European Space Agency's Earth Observation Program

In 2014 the space community is celebrating the 50th anniversary of European cooperation in space, 50 years of unique achievements. This paper provides an overview of the Earth Observation activities of the European Space Agency.

Retrieval of vegetation properties from combined hyperspectral/multiangular optical measurements: results from the DAISEX campaigns

Quantitative vegetation monitoring by means of remote sensing methods, beyond simple spectral indices, is an objective for the next generation of satellite systems, such as the ESA Earth Explorer Core Mission candidate SPECTRA (Surface Processes and Ecosystem Changes Through Response Analysis). In order to derive and validate methods for retrieval of biophysical information, and in particular vegetation properties from hyperspectral / multiangular measurements, a series of campaigns genetically called DAISEX (Digital Airborne Imaging Spectrometer Experiment) were carried out in La Mancha, Spain, from 1998-2000. A combination of aircrafts carrying different sensors and flying in different configurations allowed to get a complete dataset of hyperspectral and multiangular data acquired simultaneously, together with the necessary atmospheric information and ground data needed for validation of biophysical retrievals. A two-years study funded by ESA has exploited in depth the DAISEX dataset to evaluate the accuracy achieved in the retrieval of each one of the different vegetation properties, by using different methods applied over the same dataset. The results have shown potentials and limitations, but have allowed to set accuracy limits realistically achievable and to set more precise requirements for future developments.

Understanding vegetation response to climate variability from space: the scientific objectives, the approach and the concept of the SPECTRA mission

The goal of the SPECTRA mission is to improve the description of those processes by means of better constraints on and parameterizations of the associated models. The prime objective of SPECTRA is to determine the amount, assess the conditions and understand the response of terrestrial vegetation to climate variability and its role in the coupled cycles of energy, water and carbon. The amount and state of vegetation will be determined by the combination of observed vegetation properties and data assimilation. Specifically, the mission will characterize the amount and state of vegetation with observations of the following variables: (1) fractional vegetation cover; (2) Fraction Absorbed Photosynthetically Active Radiation (FAPAR); (3) albedo; (4) Leaf Area Index (LAI); (5) leaf chlorophyll content; (6) leaf water content; (7) foliage temperature; (8) soil temperature; (9) fractional cover of living and dead biomass. SPECTRA will provide spatially distributed observations (maps) of the key vegetation properties at the spatial resolution of one image pixel and a temporal frequency of one week or lower. Each map will cover an area of 50 km/spl times/50 km. The SPECTRA mission is being studied by the European Space Agency to address these scientific issues. The mission comprises the following elements: a space segment consisting of an imaging spectrometer covering the region 400 nm-2400 nm with a nominal spectral resolution of 10 nm and of an agile platform to perform subsequent, along track observations at seven view angles between -70/spl deg/ and +70/spl deg/; a ground segment consisting of a core data processing facility and specialized Centers of Excellence to guarantee to a wide and diverse community access to higher level data products and to specialized data assimilation systems; and a field segment consisting of 50 to 100 dedicated sites where teams of investigators evaluate the observations and assimilate them in models describing the functioning of terrestrial ecosystems.