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Building a more resilient food system for sustainable development and reducing uncertainty in global food markets both require concurrent and near-real-time and reliable crop information for decision making. Satellite-driven crop monitoring has become a main method to derive crop information at local, regional, and global scales by revealing the spatial and temporal dimensions of crop growth status and production. However, there is a lack of quantitative, objective, and robust methods to ensure the reliability of crop information, which reduces the applicability of crop monitoring and leads to uncertain and undesirable consequences. In this paper, we review recent progress in crop monitoring and identify the challenges and opportunities in future efforts. We find that satellite-derived metrics do not fully capture determinants of crop production and do not quantitatively interpret crop growth status; the latter can be advanced by integrating effective satellite-derived metrics and new onboard sensors. We have identified that ground data accessibility and the negative effects of knowledge-based analyses are two essential issues in crop monitoring that reduce the applicability of crop monitoring for decisions on food security. Crowdsourcing is one solution to overcome the restrictions of ground-truth data accessibility. We argue that user participation in the complete process of crop monitoring could improve the reliability of crop information. Encouraging users to obtain crop information from multiple sources could prevent unconscious biases. Finally, there is a need to avoid conflicts of interest in publishing publicly available crop information. The paper identifies the challenges and opportunities of crop monitoring with remote sensing. In-situ data accessibility and the negative effects of knowledge-based analysis are essential to reduce the applicability of crop monitoring. [ABSTRACT FROM AUTHOR]

Throughout the VEGETATION programme, the Flemish Institute for Technological Research (VITO) uninterruptedly hosted the prime user segment of both VEGETATION 1 and VEGETATION 2 multispectral instruments on board the Satellite Pour l’Observation de la Terre 4 (SPOT 4) and SPOT 5 satellites. Operational since the launch of SPOT 4 in March 1998, and foreseen to continue at least until the end of the SPOT 5 mission (anticipated in spring 2014), this user segment comprises a processing facility (PF), actively receiving, processing, correcting, archiving, and distributing the VEGETATION data and derived added-value products. First and foremost, the VEGETATION programme has been serving the needs of operational users – both institutional and commercial – requesting data in near-real time. However, scientific and educational users too benefited significantly, in particular from VEGETATION’s unique time series of the Earth’s land cover, and more specifically the vegetation cover. Over the years, the centralized archive houses processed data covering the equivalent of 11,000 times the Earth’s surface, and delivered more than 50 terapixels to around 10.000 users. As such, VEGETATION’s mission is a prime example of what Europe wants to achieve through the Global Monitoring for Environment and Security (GMES) initiative: truly operational services providing reliable and up-to-date information. This article describes the processing facility, the way the data and products are archived, the different dissemination channels as well as the data policy adopted and the users served. One of the recent evolutions, the development of an entirely new product distribution facility (PDF), implemented as part of the Project for On-Board Autonomy – Vegetation (PROBA-V) user segment is discussed. [ABSTRACT FROM PUBLISHER]

The Système Pour l’Observation de la Terre 5 – VEGETATION 2 (SPOT 5 – VGT2) instrument started to drift in orbit from early 2011, but currently the overpass time is still within mission requirements (less than 20 min deviation from 10:30 local equator crossing time). To determine the operational lifetime of the VGT2 instrument, it was necessary to investigate the impact of orbital drift beyond these mission requirements such that the VGT time series remains consistent over time. To this purpose, the impact of orbital drift on reflectance values and on the normalized difference vegetation index (NDVI) from the VGT1 instrument (onboard SPOT 4) in the period May 2009 to April 2012 was investigated using paired observations from VGT1 and VGT2. The comparison is thus a relative one, which has the advantage that land-cover change or trends in land-cover change are not interfering with the analysis. VGT2 acted as the reference against which the VGT1 data were compared. First, the magnitude of the solar zenith angle (SZA) change in the overlapping time period was investigated. This SZA change is largest near the equator and decreases considerably with increasing latitude. The overpass difference of VGT1 and VGT2 of 37 min resulted in maximum SZA changes of 9°, which is still well within the SZA variability of standard VGT products (i.e. 20°). Second, for a number of selected sites of 1° × 1° size with one dominant land cover, we investigated in detail the time evolution of some measures of agreement and disagreement. In the third analysis, systematic subsamples of the global images were used. From these images, the relative difference between VGT1 and VGT2 – with VGT2 as reference – was assessed as a function of the SZA of VGT2 and for different ranges of SZA difference. An increase of 10–20% in the relative difference between VGT1 and VGT2 was observed for the four spectral bands. The impact on the NDVI was negligible. Based on the obtained results, an alternative compositing approach is formulated in order to maintain the quality of the VGT standard products with a similar orbital drift as investigated in this study. [ABSTRACT FROM PUBLISHER]

This research addresses the possibilities of the combined use of airborne hyperspectral imaging spectroscopy, airborne laser scanning, and seaborne sonar to study the sediment dynamics in the back-, fore-, and nearshore continuum. In May 2009, airborne light detection and ranging (LiDAR) and hyperspectral data were acquired at low tide of the beach in Ostend, Belgium. In June 2009, seaborne side-scan sonar and single- and multibeam depth and backscatter data were acquired in the nearshore part of the Ostend coastal area at high tide. Both LiDAR and single- and multibeam data were used to create a topographic reference of the back- to nearshore continuum, with an average vertical accuracy of 10 cm. This reference framework was used, in combination with historical data, to study the morphological evolution over the last few years. Hyperspectral data, optionally combined with LiDAR-derived intensity, slope, and elevation data, were used for sedimentological mapping of the back- and foreshore area. Both multibeam backscatter and side-scan sonar data were used to produce a sedimentary surface facies map of the nearshore area. Because no automatic classification of subtle seabed gradients is yet available, the data were manually screened to produce 12 sedimentary classes. Subsequently, the airborne- and seaborne-derived maps were combined to construct an integrated sedimentological and morphological map of the entire area. This was used to interpret and formulate statements about the sediment dynamics of the area. [ABSTRACT FROM AUTHOR]

For maintaining the tidal waterways in the Scheldt basin, including the rivers Rupel and Durme and a large part of the Nete catchment, and for ecological monitoring of the mud flats, salt marshes and riverbank vegetation, the Flemish government needs detailed maps of these rivers and their bank structures. These maps indicate not only vegetation types, plant associations and sediment types but also hard structures, such as quays, locks, sluices and roads. Different remote sensing techniques were used to collect the data necessary to produce the required detailed maps. During the months of July and August 2007 an airborne flight campaign took place to collect hyperspectral and LiDAR data of the Scheldt basin and the Nete catchments. These rivers have a total length of about 240 km. The Airborne Imaging Spectrometer for Applications (AISA) Eagle sensor acquired hyperspectral data in 32 spectral bands covering the visible/near-infrared (VIS/NIR) part of the electromagnetic spectrum with a ground resolution of 1 m. A multiple binary classification algorithm based on Fisher's linear discriminant analysis (LDA) was used to map the salt marshes and riverbank vegetation. Ground truth information, that is vegetation and sediment types, together with their geographical locations collected around the time of the flight campaign, was used to train the classifier in the later classification step. Laser scanning was performed using the Riegl LMS-Q560. The LiDAR dataset obtained had a resolution of at least 1 point per m2 and was used to produce a digital elevation model (DEM) that contains all elements of the terrain. From this DEM a digital terrain model (DTM) was derived by applying appropriate filtering techniques. The elevation models were used primarily to derive information on the height, slope and aspect of the banks and dikes, but they also served as expert knowledge in the classification of the mud flats and bank vegetation. Overall, this work illustrates how airborne hyperspectral and LiDAR data can be used to derive highly detailed maps of the sediments, vegetation and hard structures along tidal rivers in large river basins. It also shows how large datasets can be handled in an expert system, in combination with different classification techniques, to produce the required result and accuracy. [ABSTRACT FROM AUTHOR]

This paper addresses the possibilities of the combined use of airborne hyperspectral data and airborne laserscanning data to study sand dynamics on the Belgian backshore and foreshore. In August 2000, August 2001, and October 2002, airborne hyperspectral imagery was acquired with a CASI-2 sensor from the entire Belgian beach at low tide. Hyperspectral images contain a reflectance spectrum for each pixel. The characteristics of this spectrum are influenced by the state, the composition, and the structure of the topsoil of the beach. After radiometric, geometric, and atmospheric correction of the images, a normalization of the spectral signatures was necessary to allow comparison of wet and dry pixels. Consequently, the first derivative of the normalized spectra was taken, followed by a spectral angle mapper algorithm that was used to perform a supervised classification. The beach was classified into eight sand classes. Almost simultaneous with the first two CASI campaigns (in September 2000 and September 2001), a laserscan survey was performed to generate digital terrain models with a mean vertical accuracy of 5 cm. By differencing both digital terrain models, a map with sedimentation and erosion zones could be extracted. The combined interpretation of the erosion/sedimentation map with the classified hyperspectral data yields an appropriate method for studying the processes of sand transport along the Belgian coastline. The method was tried out with success on the Belgian east coast. [ABSTRACT FROM AUTHOR]