Robert Meisner

Operational value-adding to AVHRR data over Europe : methods, results, and prospects

Abstract The German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) has been operating a ground segment for High Resolution Picture Transmission (HRPT) data acquisition, archiving, and distribution since the early 1980s. The stations visibility covers all of Europe. DFD started with the generation of thematic level-3 AVHRR value-added products consisting of Multichannel Sea Surface Temperatures (MCSST) and Normalized Difference Vegetation Indices (NDVI) in March 1993 [8]. Additionally, calibrated and registered 5-channel image subsets in two areas have been generated for supporting user-specific applications since 1994 [8]. The status of the current level-3 product generation chain as well as corresponding processing algorithms are presented. Perspectives are introduced to improve the existing products in terms of channel 1 and 2 radiometric optimization by implementing an atmospheric correction scheme, as well as to correct the solar channels for anisotropic reflectance with respect to different surfaces. As AVHRR data proved to be one of the major sources to derive global information on different land-oriented parameters, special emphasis is given in this paper on methods to extract land cover, the fraction of Absorbed Photosynthetic Active Radiation (fAPAR), and Leaf Area Index (LAI) with respect to operational use. Furthermore, different algorithms were discussed to derive Land Surface Temperatures (LST) by estimating surface emissivity based on NDVI time synthesis. First results over Germany are shown, problems addressed, and outlines for operational usage are given.

Computer animation of remote sensing-based time series data sets

Visualization has always played a major role in the exploitation of remote sensing data sets as well as in the confirmation of scientific hypotheses. With the new techniques available for two-dimensional (2D) and three-dimensional (3D) computer animation, the synthesis of different information layers as well as high quality visualizations for the presentation of research tasks and results are becoming increasingly important and popular. The German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) is operationally generating remote-sensing-based time series data sets. This data can be used to generate long term, high quality computer animations for analyzing and presenting the information contained in Earth observation data. Due to clouds or to system specification, data gaps occur in satellite derived time series, which preclude the generation of highest quality computer animations. For this reason different interpolation techniques have been developed primarily for atmospheric research, and they now prove to be a valuable tool for interpolation of a wide range of remote sensing data sets to be used for computer animations.

The Elbe flood

Text Adam Majorosi Contact Nils Sparwasser German Aerospace Center Muenchner Strasse 20 82234 Oberpfaffenhofen/Wessling, Germany +49.8153.281316 nils.sparwasser@dlr.de In August 2002, Europe experienced the worst flooding in more than a century. A particular weather situation led to extreme rainfall and floods that killed over 100 people and forced tens of thousands to leave their homes. For damage assessment and coordination purposes, disaster organizations needed fast access to up-to-date geo-data. Due to the extent of the disaster and the weather conditions, only satellites were able to provide the required images.

Operational generation of AVHRR-based level-3 products at the German Remote Sensing Data Centre: status and perspectives

The German Remote Sensing Data Centre (DFD) of the German Aerospace Research Establishment (DLR) has been operating a ground segment for High Resolution Picture Transmission (HRPT) data acquisition, archiving, and distribution since the early 1980s. The stations visibility covers all of Europe. DFD started with the generation of thematic level-3 AVHRR value-added products consisting of Multichannel Sea Surface Temperatures (MCSST) and Normalized Difference Vegetation Indices (NDVI) in March 1993. Additionally, calibrated and registered 5-channel image subsets in two areas have been generated for supporting user-specific applications since 1994. The status of the current level-3 product generation chain as well as corresponding processing algorithms are presented. Perspectives to improve the existing products in terms of channel 1 and 2 radiometric optimization by implementing of a pre-operational atmospheric correction scheme developed by, as well as possibilities to correct the solar channels for anisotropic reflectance with respect to different surfaces are shown. Further, new level-3 products such as geophysical cloud parameters derived using the APOLLO algorithm are presented. Also, first results from various algorithm tests are presented to define an operational land surface temperature (LST) product by estimating surface emissivity based on NDVI time profiles.

Towards an operational atmospheric correction for AVHRR land surface products

The German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) has been operating a ground segment for high resolution picture transmission (HRPT) data acquisition, archiving, and distribution since the early 1980s. Since 1994 daily normalized difference vegetation index (NDVI) synthesis maps for all of Europe have been derived from Advanced Very High Resolution Radiometer (AVHRR) measurements in near real-time with a horizontal resolution of about 1 km. In 1998 the processing chain has been expanded to European land surface temperatures (LST). Due to the presence and high variability of atmospheric ozone, water vapour and aerosols in time and space, the atmosphere significantly impacts the solar channels and results in erroneous NDVI data and noisy time series. A robust operational near real-time atmospheric correction scheme is presented. Until ENVISAT data is available, total ozone data derived from ERS-2 GOME and water vapour from NOAA-TOVS are considered for correction. An aerosol retrieval scheme based on GOME and ATSR data is currently being developed. For the determination of LST from the AVHRR brightness temperature measurements also an explicit correction of the atmospheric influence, mainly caused by water vapour absorption, is necessary. Therefore a simple split window technique is applied instead of a single channel method in terms of operational processing. The results have been validated over different sites in Germany, Egypt and Jordan.

Data Integration and Visualization for Crisis Applications

Satellite data play an increasingly important role in supporting decision making in disaster management. Rapid data integration and visualization are essential to make data accessible and convey the results in an easier to perceive way. Especially when presenting information to a non-expert audience, visualization of the data and its content improves the understanding of the situation at hand. The paper gives an overview of the current status of data integration and visualisation technologies including an analysis of the advantages and disadvantages of the technologies available. It also highlights several aspects of visualisation strategies using technologies such as predefined landscape models, and tools including 2D and 3D web viewers and globe viewers, and discusses the inextricable link between data integration and visualization.

An interactive CD-ROM on remote sensing-a concept study

The techniques used in remote sensing to provide support for understanding the Earths environment are common sense in the scientific community, but are at times difficult to teach to people not in direct contact with remote sensing at universities and schools. Computer-assisted learning (CAL) offers a new, more efficient way to teach novices the backgrounds and the use of remote sensing data. The combination of simultaneous use of text, images, sound and video offers a more understandable presentation of the techniques used, without the well known constraints of conventional, linear and mono dimensional media. Further more, digital image processing methods and the effects of the steps applied can be shown on screen in real time based on a wide variety of examples and applications. The concept of the CD-ROM to be presented is aimed at higher education facilities like geography classes in high-schools and students at universities as well as potential remote sensing users in the administrative field. Furthermore the potential user community, not yet knowing very much about the benefits that remote sensing can provide them with for their work, can be directly addressed. The CD-ROM is not intended for use by professionals already dealing with remote sensing data, as their knowledge usually already goes beyond what a CD can cover, but it can also help these people in conveying their ideas and their knowledge to others. This approach requires an attractive, easy to understand interface which allows fast and direct access to the information contained on the CD. The inexperienced user will be guided through the CD based on a hypertext-structure. Through a specifically designed interface, the user will get from a very basic level, providing general information on remote-sensing, to more profound chapters which include detailed data. For the more advanced user free navigation through the information content is foreseen to make the CD also an encyclopedia on remote sensing. The prototype to be presented will only show the general concept developed as a skeleton to be filled with information in the next project phase. The part dealing with the physical basics of the electromagnetic field and remote sensing has already been developed to a further stage and will be shown in greater detail. Further measures to be taken will be discussed.

Remote sensing based information for TV-, print- and multi-media applications

The German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) is operationally generating long-term, Europe-wide, remote-sensing based information on vegetation (NDVI from NOAA-AVHRR), sea surface temperature (MCSST from NOAA-AVHRR), ozone concentration (from GOME) and current weather conditions (subsets from NOAA-AVHRR and Meteosat) for scientific applications and for the support of scientific campaigns. The generation of these data sets dates back to 1993 and the processing chain has constantly been optimized and enhanced until today. Access by scientists to DLRs online archive is frequent and the data generated has played an increasingly important ro/spl circ/le in research projects involving land, water and the atmosphere. Public and non-scientific interest in the information provided has been increasing in the past two years. The recent developments, the current situation and future perspectives of these activities are presented.

Operational generation of AVHRR-based land surface temperatures (LST)-a new value adding product from the German Remote Sensing Data Center

The German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) has been receiving, archiving, and distributing high resolution picture transmission (HRPT) data since the early 1980s. The stations visibility covers Europe and its surroundings. DFD started the generation of thematic AVHRR value-added products consisting of multichannel sea surface temperatures (MCSST) and normalized difference vegetation indices (NDVI) in 1993. Calibrated and registered 5-channel image subsets of two areas have been generated for supporting regional applications since 1994. The improvement of the current products as well as the definition of new products has always been of major concern to DFD. The operational generation of land surface temperature (LST) based on estimated emissivity using NDVI time profiles has become operational in May 1998 and provides the user community with daily near-real-time (maximum delay 2 days) LST information for the whole of Europe. New AVHRR based level-3 products such as cloud parameters using the APOLLO algorithm developed by Saunders and Kriebel (1988) have been designed and are operationally generated and archived from January of 1998. A processing scheme for retrospective processing has been developed and will provide historical cloud data of central Europe from the early eighties. An overview is given of the current status of the products mentioned.

Visualization of satellite derived time-series datasets using computer graphics and computer animation

The German Remote Sensing Data Centre (DFD) of the German Aerospace Research Establishment (DLR) is operationally generating remote-sensing based time series datasets. These datasets can be used for example for environmental, climatological and atmospherical research. Bearing in mind the enormous amount of data already generated at DLR from todays missions, even with a comfortable search-engine like ISIS (provided by DLR) it is a major problem to identify those datasets most suitable for a specific research task. Looking into the future, data quantities will increase with new missions like ENVISAT. Therefore, it appears essential to provide the user-community with efficient tools to explore and evaluate these time series-datasets. Visualization forms the most efficient way to explore the contents of vast data quantities and to identify the subsets showing the phenomena of interest in a relatively short time. Synthesis with secondary remote sensing data for visualization offers the possibility of multidimensional data exploration. Finally, visualization is essential for the presentation of a projects purpose and its results. Data gaps in time-series form a problem in visualization as they are prohibitive for stable movement in computer animation. For this reason different interpolation techniques have been developed primarily for atmospheric sensors and now prove to be a valuable tool for interpolation of other remote sensing datasets. A video presentation showing examples of films created at DLR are given.