Carsten Brockmann

Analysis of Thematic Mapper data for studying the suspended matter distribution in the coastal area of the German Bight (North Sea)

Abstract Thematic Mapper data were analyzed with respect to its capability for mapping the complex structure and dynamics of suspeded matter distribution in the coastal area of the German Bight (North Sea). Three independent pieces of information were found by factor analysis of all seven TM channels: suspended matter concentration, atmospheric scattering, and sea surface temperature. For the required atmospheric correction the signal to noise ratios of Channels 5 and 7 have to be improved by averaging over 25×25 pixels, which allows us also to monitor aerosol optical depth and aerosol type over cloudfree water surfaces. Near surface suspended matter concentrations may be detected with an accuracy of factor

Geolocation Assessment of MERIS GlobCover Orthorectified Products

The GlobCover project has developed a service dedicated to the generation of multiyear global land cover maps at 300-m spatial resolution using as its main source of data the full-resolution full-swath (300 m) data (FRS) acquired by the MERIS sensor on-board the ENVISAT satellite. As multiple single daily orbits have to be combined in one single data set, an accurate relative and absolute geolocation of GlobCover orthorectified products is required and needs to be assessed. We describe in this paper the main steps of the orthorectification pre-processing chain as well as the validation methodology and geometric performance assessments. Final results are very satisfactory with an absolute geolocation error of 77-m rms and a relative geolocation error of 51-m rms.

On Line Validation Exercise (OLIVE): A Web Based Service for the Validation of Medium Resolution Land Products. Application to FAPAR Products

The OLIVE (On Line Interactive Validation Exercise) platform is dedicated to the validation of global biophysical products such as LAI (Leaf Area Index) and FAPAR (Fraction of Absorbed Photosynthetically Active Radiation). It was developed under the framework of the CEOS (Committee on Earth Observation Satellites) Land Product Validation (LPV) sub-group. OLIVE has three main objectives: (i) to provide a consistent and centralized information on the definition of the biophysical variables, as well as a description of the main available products and their performances (ii) to provide transparency and traceability by an online validation procedure compliant with the CEOS LPV and QA4EO (Quality Assurance for Earth Observation) recommendations (iii) and finally, to provide a tool to benchmark new products, update product validation results and host new ground measurement sites for accuracy assessment. The functionalities and algorithms of OLIVE are described to provide full transparency of its procedures to the community. The validation process and typical results are illustrated for three FAPAR products: GEOV1 (VEGETATION sensor), MGVIo (MERIS sensor) and MODIS collection 5 FPAR. OLIVE is available on the European Space Agency CAL/VAL portal), including full documentation, validation exercise results, and product extracts.

Automated Training Sample Extraction for Global Land Cover Mapping

Land cover is one of the essential climate variables of the ESA Climate Change Initiative (CCI). In this context, the Land Cover CCI (LC CCI) project aims at building global land cover maps suitable for climate modeling based on Earth observation by satellite sensors. The challenge is to generate a set of successive maps that are both accurate and consistent over time. To do so, operational methods for the automated classification of optical images are investigated. The proposed approach consists of a locally trained classification using an automated selection of training samples from existing, but outdated land cover information. Combinations of local extraction (based on spatial criteria) and self-cleaning of training samples (based on spectral criteria) are quantitatively assessed. Two large study areas, one in Eurasia and the other in South America, are considered. The proposed morphological cleaning of the training samples leads to higher accuracies than the statistical outlier removal in the spectral domain. An optimal neighborhood has been identified for the local sample extraction. The results are coherent for the two test areas, showing an improvement of the overall accuracy compared with the original reference datasets and a significant reduction of macroscopic errors. More importantly, the proposed method partly controls the reliability of existing land cover maps as sources of training samples for supervised classification.

ALBEDOMAP: MERIS land surface albedo retrieval using data fusion with MODIS BRDF and its validation using contemporaneous EO and in situ data products

A representative albedo is required by ESA for the improved retrieval of atmospheric products, such as water vapour, from the ENVISAT-MERIS instrument. This albedo is required at 13 of the 15 spectral channels of MERIS. An algorithm is described which has been applied to the generation of a global albedo for these 13 spectral bands of MERIS over 16-day time periods at a resolution of 0.05deg for the time period from June 2002 to December 2006. Inputs to this algorithm include improved cloud and snow detection, aerosol correction using the MERIS data itself and derived Spectral surface Directional Reflectances, SDRs (Schroder et ah, Preusker et al, see, http://envisat.esa. int/workshops/meris_aatsr2005/). Owing to the lack of sufficient directional samples for most of the Earths land surface, even for a monthly compositing time period, direct inversion of BRDF parameters for MERIS are not possible worldwide. Instead the 16-day Collection 4 MODIS BRDFs at 0.05deg resolution (derived using either full inversions or magnitude inversions from the MOD43 values) were employed in a magnitude inversion scheme for the 4 common MERIS (490plusmn5 [b3], 560plusmn5 [b5], 665plusmn5 [b7], 865plusmn10 [bl3]) bands with MODIS (459-479 {b3}, 545-565 {b4}, 620-670 {bl}, 841-8766 {b2}). The impact of applying Terra-only compared to Terra+Aqua-combined are here compared and presented. In keeping with previously reported results, there are larger numbers of full MODIS inversions (and consequently better MERIS albedos) for the combined BRDF but the total number of MODIS BRDF retrievals remains stubbornly similar. Spectral interpolation to the remaining 9 MERIS bands and to 3 broadband regions (0.4-0.7 mum, 0.7-3 mum, 0.4-3 mum) is then performed using polynomial look-up tables derived by Dr Shunlin Liang (University of Maryland). As spectral albedo data is required on monthly time-steps for most applications, a simple- minded weighting function based on the fractional time-period of each 16-day time period within a month was adopted for creating monthly products from 16-day products at 10km and 0.1deg. Global products on a 16-day time-step are being generated for the whole time period using both Terra-only and, where available, Terra+Aqua-combined Collection 4 MODlS-BRDFs. These EO products have been compared against contemporaneous MODIS spectral albedos (over 16-days) which have been gap-filled (Moody et al., 2005) as well as Collection 5 products, where available. Satellite intercomparisons have also been performed for monthly products of the monthly MERIS spectral albedo products for common bands against M1SR level-3 and POLDER level-3 products as well as for a subset of M1SR level-2 instantaneous products and the results will be shown here. Finally, inter-comparisons are shown of these EO products against ground-based albedometer measurements for a site in Finland will be presented as representative of one of several worldwide sites available through the CA VE taking into account, where necessary, issues associated with land cover heterogeneity.

Calvalus: Full-mission EO cal/val, processing and exploitation services

ESAs Earth Observation (EO) missions provide a unique dataset of observational data of our environment. Calibration, algorithm development and validation of the derived products are indispensable tasks for an efficient exploitation of EO data and form the basis for reliable scientific conclusions. In spite of its importance, the cal/val and algorithm development work is often hindered by insufficient means to access data, time consuming work used to identify suitable in-situ data matching the EO data, incompatible software and limited possibilities for a rapid prototyping and testing of ideas. In view of the amount of data produced by the future ESAs series of Sentinel satellites, a very efficient technological backbone is required to maintain the ability of ensuring data quality and algorithm performance. Brockmann Consult has developed such a backbone based on leading edge technologies within an ESA R&D study. Calvalus is a new processing system that utilises the map-reduce programming model with a distributed file system.

Ocean Colour Climate Change Initiative — Approach and initial results

The Ocean-Colour Climate-Change Initiative (OC-CCI) aims to create a long-term, consistent, error-characterised time series of ocean-colour products, for use in climate change studies. Climate Change Initiative is a programme of the European Space Agency devoted to using satellites to generate climate quality time series data of Essential Climate Variables (ECVs) identified by the Global Climate Observing System (GCOS). Within the ocean colour CCI project, a user consultation was undertaken, targeting both the climate modelling community and the Earth Observation community. Taking the user requirements into account, a set of criteria was developed, for selecting the best ocean-colour algorithms for climate research. Candidate atmospheric correction algorithms and in water algorithms have been submitted to a round robin comparison. The overall best performers are being used to generate test products, to be evaluated further.

New global land cover mapping exercise in the framework of the ESA Climate Change Initiative

The ESA Climate Change Initiative land cover project focuses on the deriving land cover information driven by requirements for observing Essential Climate Variables. Consultation mechanisms were established with the climate modelling community in order to identify its specific needs in terms of satellite-based global land cover products. Key findings were the needs for successive land cover maps stable over time. As response, an innovative global land cover mapping approach, based on multi-year MERIS and SPOT-Vegetation datasets is proposed. Pre-processing and classification chains able to handle huge amount of data have been developed and a first global land cover map associated to the 2008-2010 epoch is being produced.

An Optical Classification Tool for Global Lake Waters

Shallow and deep lakes receive and recycle organic and inorganic substances from within the confines of these lakes, their watershed and beyond. Hence, a large range in absorption and scattering and extreme differences in optical variability can be found between and within global lakes. This poses a challenge for atmospheric correction and bio-optical algorithms applied to optical remote sensing for water quality monitoring applications. To optimize these applications for the wide variety of lake optical conditions, we adapted a spectral classification scheme based on the concept of optical water types. The optical water types were defined through a cluster analysis of in situ hyperspectral remote sensing reflectance spectra collected by partners and advisors of the European Union 7th Framework Programme (FP7) Global Lakes Sentinel Services (GLaSS) project. The method has been integrated in the Envisat-BEAM software and the Sentinel Application Platform (SNAP) and generates maps of water types from image data. Two variations of water type classification are provided: one based on area-normalized spectral reflectance focusing on spectral shape (6CN, six-class normalized) and one that retains magnitude with no modification to the reflectance signal (6C). This resulted in a protocol, or processing scheme, that can also be applied or adapted for Sentinel-3 Ocean and Land Colour Imager (OLCI) datasets. We apply both treatments to MERIS imagery of a variety of European lakes to demonstrate its applicability. The studied target lakes cover a range of biophysical types, from shallow turbid to deep and clear, as well as eutrophic and dark absorbing waters, rich in colored dissolved organic matter (CDOM). In shallow, high-reflecting Dutch and Estonian lakes with high sediment load, 6C performed better, while in deep, low-reflecting clear Italian and Swedish lakes, 6CN performed better. The 6CN classification of in situ data is promising for very dark, high CDOM, absorbing lakes, but we show that our atmospheric correction of the imagery was insufficient to corroborate this. We anticipate that the application of the protocol to other lakes with unknown in-water characterization, but with comparable biophysical properties will suggest similar atmospheric correction (AC) and in-water retrieval algorithms for global lakes.

Small scale patches of suspended matter and phytoplankton in the Elbe River estuary, German Bight and tidal flats

Abstract Thematic mapper and ship data has been used to study small scale features in coastal waters of the North Sea. Three independent pieces of information from all 7 TM channesl were found with factor analysis: suspended matter concentration, atmospheric scattering and sea surface temperature. Near surface suspended matter concentrations may be detected within a factor of 2. For the required atmospheric correction the signal-to-noise ratio of the channels 5 and 7 has to be improved by averaging over 25 × 25 pixels. Thus TM allows to monitor aerosol optical depth and aerosol type over cloudfree water surfaces. Sea surface temperature is retrievable with an absolute accuracy of 1.0 K as long as radiosonde data are available for the correction of atmospheric effects, while relative temperature variations of 0.5 K are detectable. The patchiness of suspended matter and its relation to underwater topography was analysed with auto- and crosscorrelation: horizontal lengths, where the suspended matter concentration of single pixels are significantly correlated either with each another or with water depth, are m .