Bart Deronde

Mapping of coral reefs using hyperspectral CASI data; a case study: Fordata, Tanimbar, Indonesia

Airborne remote sensing with a CASI‐550 sensor has been used to map the benthic coverage and the bottom topography of the Pulau Nukaha coral reef located in the Tanimbar Archipelago (Southeast Moluccas, Eastern Indonesia). The image classification method adopted was performed in three steps. Firstly, five geomorphological reef components were identified using a supervised spectral angle mapping algorithm in combination with data collected during the field survey, i.e. benthic cover type, percentage cover and depth. Secondly, benthic cover mapping was performed for each of the five geomorphological components separately using an unsupervised hierarchical clustering algorithm followed by class aggregation using both spectral and spatial information. Finally, 16 benthic cover classes could be labelled using the benthic cover data collected during the field survey. The overall classification accuracy, calculated on the biological diverse fore reef, was 73% with a kappa coefficient of 0.63. A reliable bathymetric model (up to a depth of 15 m) of the Pulau Nukaha reef was also obtained using a semi‐analytical radiative transfer model. When compared with independent in‐situ depth measurements, the result proved relatively accurate (mean residual error: −0.9 m) and was consistent with the seabed topography (Pearson correlation coefficient: 86%).

Use of Airborne Hyperspectral Data and Laserscan Data to Study Beach Morphodynamics along the Belgian Coast

Abstract 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.

Synergy of Airborne Digital Camera and Lidar Data to Map Coastal Dune Vegetation

Abstract Driven by the successful applications of lidar in forestry and the availability of lidar technology, new research is being carried out in other ecosystems. While lidar data have often been used to study tall forest ecosystems, this study explores the utility of lidar in the lower-canopy ecosystems of the Belgian coastal dune belt. This area is largely covered by marram dune, moss dune, grassland, scrubs and some woodland. Small diameter (0.4 m) footprint lidar was applied to derive the canopy height by analyzing the first and last pulse returns simultaneously. The investigation focused on whether the height of low-canopy ecosystems could be mapped with adequate accuracy. An error analysis was performed first on flat terrain (i.e., tennis court and parking lot) and then on vegetation canopy. The mapping of coastal dune vegetation is necessary to establish the strength of the dune belt. Dune vegetation fixes the sand dunes, protecting them from erosion and from possible breakthroughs threatening the historically reclaimed land (polders) situated inland from the dunes. Next, multispectral data was acquired from a digital camera with visual and near infrared channels. The digital camera overflight was not conducted on the same platform as the lidar. After ortho-rectification of the multispectral image, the data of both sources were fused. The limited spectral information delivered by the digital camera was not able to provide a sufficiently detailed and accurate vegetation map. The fusion with lidar data provided the extra information needed to obtain the desired vegetation and dune strength maps. A total of fourteen classes were defined, of which twelve cover vegetation. It was shown that overall classification accuracy improved 16%, from 55% to 71% after data fusion.

15 years of processing and dissemination of SPOT-VEGETATION products

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.

Ten-daily global composites of METOP-AVHRR

Systematic scanning of the earth surface could be achieved for the first time in 1978, with the launch of the earth observation system NOAA-AVHRR. Some twenty years later, the SPOT-VEGETATION instrument introduced significant improvements at the levels of image quality, timeliness and availability. Since the start in April 1998, VITO is responsible for the central processing, archiving and distribution of the VEGETATION data. This paper briefly announces how a similar service is being established at VITO to provide the same kind of image data from the recently launched METOP-AVHRR.

Integration of Optical and Acoustic Remote Sensing Data over the Backshore–Foreshore–Nearshore Continuum: A Case Study in Ostend (Belgium)

ABSTRACT Bertels, L.; Houthuys, R.; Deronde, B.; Janssens, R.; Verfaillie, E., and Van Lancker, V., 2012. Integration of optical and acoustic remote sensing data over the backshore-foreshore-nearshore continuum: a case study in Ostend (Belgium). 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.

Large-scale mapping of the riverbanks, mud flats and salt marshes of the Scheldt basin, using airborne imaging spectroscopy and LiDAR

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 Fishers 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.

Sediment facies classification of a sandy shoreline by means of airborne imaging spectroscopy

Airborne imaging spectroscopy data (AISA Eagle and HyMap) were applied to classify the sediments of a sandy beach in seven sand type classes. On the AISA‐Eagle data, several classification strategies were tried out and compared with each other. The best classification results were obtained applying a linear discriminant classifier (LDC) in combination with feature selection based on sequential floating forward search (SFFS). The statistical LDC was used in a multiple binary approach. In the first step, the original bands were used in the classification, but transformation of the bands to wavelet coefficients enhanced the accuracy obtained. The combination of LDC with SFFS resulted in an overall accuracy of 82% (using three wavelet coefficients). Replacing the LDC with the non‐statistical SAM algorithm reduced the overall accuracy to 74% (using all bands or wavelet coefficients). When applying LDC, the optimal number of bands/wavelet coefficients to be used was defined: using more than two bands or three wavelet coefficients did not result in a higher classification accuracy. Finally, the HyMap data, featuring 126 bands in the VNIR‐SWIR range, were used to demonstrate that the VNIR range outperforms the SWIR range for this application.

Imaging Spectroscopy And Integrated CoastalZone Management: A Promising Marriage

This paper provides an overview of the coastal and marine applications which make use of Imaging Spectroscopy (IS), recently under development in Vito. It should be considered as a concise overview rather than an in depth presentation of one application or development. The first two applications focus on sediment mapping; firstly, a classification of sediment habitat types of the Molenplaat, a tidal sand bank in the Westerschelde, is presented. By means of feature selection and a supervised binary classification approach the sediment is classified according to its grain size, moisture content, organic matter content and chlorophyll-a concentration. The second application uses airborne IS to classify the different sand types present along the Belgian coast, in combination with airborne laserscanning to derive accurate erosion maps. The combination of both data products results in a method which proves to be very suited to monitoring the sand transport processes along the Belgian coast. Afterwards two aquatic applications are presented; in the first, coral reef communities in Indonesia are classified. Extensive field work served to collect a spectral library which is used to classify the coral reef communities in as much detail and as accurately as possible. The second aquatic application addresses the difficult challenge of quantifying the amount of suspended sediment and chlorophyll-a in water and rivers; this is performed by inversion of a bio-optical model using a set of Specific Inherent Optical Properties (SIOP’s) measured in-situ. Many marine applications ask for some specific processing steps which are inherent to the aquatic environment. Therefore the last study in this overview focuses on the atmospheric correction above water bodies. Due to the high absorption and transmission of water bodies the reflected radiation level is low compared to land. To extract this small signal from a much greater base of other radiance a very accurate atmospheric correction algorithm is required. Therefore a specific atmospheric correction algorithm, WATCOR, has been developed to account for the marine atmospheric conditions as well as for the air-water interface. www.witpress.com, ISSN 1743-3541 (on-line)