LANDSAT 7 - GROUND SEGMENT ACTIVITIES AT THE GERMAN REMOTE SENSING DATA CENTER Günter Strunz (*), Hans-Dietrich Bettac (**), Jörg Gredel (*), Klaus-Dieter Reiniger (*) & Gunter Schreier (*) Deutsches Fernerkundungsdatenzentrum (DFD) DLR (*) Oberpfaffenhofen, D-82234 Wessling, Germany (**) Neustrelitz, Kalkhorstweg 53, D-17235 Neustrelitz, Germany phone: +49 8153 28 1314 fax: + 49 8153 28 1445 email: Guenter.Strunz@dlr.de KEYWORDS: Landsat-7, ETM+ ABSTRACT The Landsat Program has continuously provided data to a broad user community since 1972. With the successful launch of Landsat 7 on April 15, 1999 the availability of Landsat data will be continued and essentially extended by its Enhanced Thematic Mapper Plus (ETM+) instrument. The German Remote Sensing Data Center (DFD) will operate a Landsat 7 International Ground Station in Europe as part of the Earthnet Programme of the European Space Agency ESA and at other locations world-wide. The paper gives an overview on the present status of the Landsat 7 ground segment at the DFD. The main mission and sensor characteristics are briefly explained. The role of the DFD as Landsat 7 ground station including data acquisition, product generation and distribution is outlined and the DFD s data utilization concept is described. The Scientific Data Pool as central part of the DFD strategy to support research and pilot applications is explained. 1 INTRODUCTION Dating back to the launch of Landsat 1 in July 1972, the Landsat series provides the longest, most consistently acquired and continuously available data set in Earth observation remote sensing. At least one Landsat system has been acquiring and transmitting data from space every day for about 27 years. These data have been used world-wide on a regional and global scale for land use and land cover mapping, monitoring and assessment of changes in natural resources, documenting natural and manmade disasters, contributing to research in global change, and providing valuable material for education purposes. An overview on the Landsat Program is given in LAUER ET AL. (1997) and MIKA (1997). With the successful launch of Landsat 7 on April 15, 1999 the availability of Landsat data will be continued and essentially extended by its Enhanced Thematic Mapper Plus (ETM+) instrument. Continuation is an important issue due to several reasons. The repetitive coverage of land and coastal surfaces is needed for the monitoring of seasonal changes. With its spectral bands in the visible, nearinfrared, short-wave and thermal infrared at a spatial resolution of 30 m, the Landsat system provides capabilities, which are currently not matched by any other remote sensing system. The valuable extensions and technical improvements of the ETM+ sensor compared to the TM sensors on Landsat 4 and 5 significantly broaden the application spectrum of Landsat 7. Moreover, due to the change in the program management and data policy for Landsat 7, this system is of growing interest for the world-wide remote sensing community. The acquisition, processing, archiving and distribution of data will be done by the primary U.S. ground station and a world wide network of International Ground Stations (IGS). The German Remote Sensing Data Center (DFD) will operate a Landsat 7 International Ground Station as part of the Earthnet Programme of the European Space Agency ESA.
The paper gives an overview on the present status and the planned configuration of the Landsat 7 ground segment at the DFD. The main mission and sensor characteristics are briefly explained. The role of the DFD as Landsat 7 ground station including data acquisition, product generation and distribution is outlined and the DFD s data utilization concept is described. The Scientific Data Pool as central part of the DFD strategy to support research and pilot applications is explained. implemented to stabilize the satellite and keep the instrument pointed to the Earth within 0.05 degrees (Figure 1). 2 MISSION AND SENSOR CHARACTERISTICS 2.1 Program Management The Landsat 7 program is established by an U.S. Presidential Decision Directive issued in May 1994. It is managed cooperatively by the National Aeronautics and Space Administration (NASA) and U.S. Geological Survey (USGS). According to this NASA is responsible for the design, development, launch and on-orbit checkout of the satellite; design, development, and installation of the ground system; providing the flight operations team; and operating the satellite until October 2000; and Fig. 1: Landsat 7 satellite (http://landsat.gsfc.nasa.gov) The ETM+ instrument is an eight-band multispectral scanning radiometer with several improvements compared to the TM sensor (Figure 2). The spectral bands are given in Table 1, where changes compared to TM are shown in bold. An additional panchromatic band provides data of 15 m ground resolution and the thermal infrared channel has an improved resolution of 60 m. USGS is responsible for capture, processing, and distribution of the data; mission management; maintaining a long-term archive of Landsat data; and in October 2000 will take over satellite operations. The National Oceanic and Atmospheric Administration (NOAA), which was initially responsible for management oversight of Landsat 7 operations and for direct management of the spacecraft and instrument, is no longer directly involved in the program. 2.2 Orbit and Sensor Landsat 7 is operated in a near-polar orbit with a sun-synchronous 98-degree inclination at an altitude of 705 km. The descending equatorial crossing time is 10 a.m. with an orbital period of 98.9 minutes. The orbit is adjusted so that its 16-day repeat cycle coincides with the Landsat Worldwide Reference System. A three-axis attitude control system is Fig. 2: ETM+ sensor (http://landsat.gsfc.nasa.gov) The band-to-band registration of all bands will be done with an accuracy of 0.3 pixel (90 % level). The swath width remains unchanged at 185 km acrosstrack.
BAND SPECTRAL RANGE VIS (Blue) 0.45 0.52 µm 30 m VIS (Green) 0.52 0.60 µm 30 m VIS (Red) 0.63 0.69 µm 30 m NIR 0.76 0.90 µm 30 m SWIR 1.55 1.75 µm 30 m SWIR 2.08 2.35 µm 30 m LWIR (thermal) 10.4 12.5 µm 60 m PAN 0.52-0.90 µm 15 m SPATIAL RESOLUTION Tab. 1: Landsat 7 ETM+ spectral bands and spatial resolution The radiometric accuracy will be 5 % in all bands, which is a significant improvement compared to the previous TM sensor. The radiometric calibration is based on an internal calibrator assembly, which presents a lamp and a blackbody source to the detector arrays, and two new solar calibrators. Also, ground truth methods will be used for the determination of calibration coefficients. An more detailed description of orbit and sensor characterictics is e.g. given in DOLAN ET AL. (1998), ELLICKSON (1998). 2.3 Ground Segment The primary U.S. ground station is located at the Earth Resources Observation Systems (EROS) Data Center (EDC) in Sioux Falls. Stations near Fairbanks, Alaska, and Svalbard, Norway, are also used to receive data. A network of International Ground Stations (IGS) is being established. The location of the existing IGS and the respective acquisition circles are shown in Figure 3. Communications with the ground is provided by a two-way communication system. The command uplink and the housekeeping telemetry downlink is provided via S-band, while all the science data are downlinked via X-band. The data transmission to the ground segment is done at a rate of 150 Mbps, which consists of two 75 Mbps data streams as I and Q channels (AQPSK) of one X-band carrier. Three directivity antennas, which focus the data stream on the requesting ground station, are used to downlink data in encrypted format. The satellite is capable of Fig. 3: Landsat 7 Ground Stations (location and acquisition circles)
transmitting 150 Mbps to as many as three IGS s simultaneously, or simultaneous transmission to one U.S. ground station at 300 Mbps and one IGS at 150 Mbps. Furthermore, Landsat 7 is equipped with a solid sate recorder with a capacity of storing 380 Gigabits of data, which corresponds to about 100 scenes. The 300 Mbps downlink permits either recorder playback at twice the record rate or simultaneous recorder playback and real-time imaging over the continental U.S. The IGS have no access to the solid state recorder. Landsat 7 will image and transmit to the ground an average of 532 scenes per day, which consist of real-time data and recorded data to EDC and realtime data to the IGS. The ground system at the EDC will be capable of capturing and processing 250 scenes (level 0R) per day and delivering at least 100 scenes (level 0 and 1) to users every day. A maximum of 25 of these scenes can be geometrically and radiometrically corrected to level 1G (250 m accuracy, 1σ, without ground control). The users can specify several processing options, e.g. projection, grid size and spectral bands. All data captured will be available for user ordering within 24 hours of the reception at EDC. The Landsat 7 data policy also changes considerably. The data pricing in the U.S. intends to recover the cost of fulfilling user requests (COFUR). That price is based on the requirement to offset all costs of spacecraft and mission operations as well as ground processing with income fees from the international ground stations and from the sale of products (DRAEGER ET AL., 1997). Initially, level 0R data will be priced at $ 475 and level 1 products at $ 600 per scene. These prices will be reviewed annually. The IGS s, which have to pay a structured fee for the reception of Landsat 7 data, are free to define their prices according to their needs. 2.4 Current status (August 1999) The on-orbit initialization and verification has been completed successfully. On June 28 the nominal orbit was achieved, and the Landsat 7 program entered into a pre-operational phase. Since then, Landsat 7 has acquired data according to the nominal orbit cycle. If activities proceed as planned, Landsat 7 data products will be available for distribution from EDC on or about August 15, 1999. 3 DLR LANDSAT 7 GROUND SEGMENT As part of the Earthnet Programme of the European Space Agency ESA, the German Remote Sensing Data Center (DFD) operates a Landsat 7 International Ground Station in Neustrelitz. Furthermore, DFD offers its world-wide stations for data reception on a project basis. A corresponding Memorandum of Understanding is currently being negotiated between DLR and the Landsat Program Management. 3.1 ESA Earthnet Ground Station at DFD The DFD National Ground Station at Neustrelitz is upgraded for the acquisition, processing, archiving, and distribution of Landsat 7 data. This is based on a contract between the German Aerospace Center (DLR) and ESA. The operational scenario for the acquisition and processing of Landsat 7 data by the DFD station in Neustrelitz will be harmonized by ESA among the Earthnet stations in Europe. On July 28, 1999 the first Landsat 7 image has been acquired in Neustrelitz. In the current preoperational phase the data acquisition, processing and archiving capabilities will be optimised within the next weeks to provide a fully operational service. Landsat 7 full resolution products will be available at the end of October 1999. 3.2 ESA Earthnet Processing Facility The standard processing of data will be done at Neustrelitz as an ESA Earthnet Processing Facility. ESA provides all Earthnet stations with identical Data Processing Systems (DPS). These systems implement the ingestion of satellite data in real time or from high density tapes (HDT), the synchronisation and formatting of ingested data and the archiving of data in frame synchronized form on digital linear tapes (DLT). Browse images and metadata are produced and passed to the catalogue system. Standard products (raw and system corrected level) are generated on request of ESA and Eurimage, the commercial distributor appointed by ESA. Moreover, the order handling, the communications between the ground station and the centralized ESA catalogue, and the data exchange between the ground stations and ESA as well as EDC are monitored and controlled by the DPS (BERUTI, 1997, IGS-REPORT, 1998).
The Landsat 7 products (draft version) offered by Eurimage will cover full resolution, public relation, and low resolution products. For full resolution products the size can be selected from full (185 km), quarter (90 km), mini (50 km) and micro (25 km) scenes. Public relation products will be provided online or via CD-ROM, which include 3 bands or the panchromatic band only. The image size is 1,000 * 1,000 pixels; the data are compressed for fast dissemination. Low resolution products are browse images with 180 m resolution (3 bands and pan) and fast delivery images for monitoring and detection, which will be available within 3 hours after acquisition at 180 m resolution. cooperate with EDC as well as Eurimage to develop new value added Landsat 7 products. 4 DATA UTILIZATION CONCEPT In agreement with ESA and Eurimage the DFD is elaborating a concept for Landsat 7 data utilization to stimulate and establish the application of ETM+ data in the scientific and commercial community. 4.1 Objectives The main objectives of this concept are to 3.3 Value Added Products The value adding processing will be implemented at Oberpfaffenhofen, based on an initiative of DFD supported by ESA and Eurimage. The value added products consist of high quality geocoded terrain corrected image products, and various thematic products. The geocoding system will be based on the Image Assessment System (IAS) software, which is operated at the EDC. The aim is to generate orthorectified, terrain corrected products. The algorithm uses Earth ellipsoid and terrain surface information in conjunction with spacecraft ephemeries and attitude data together with knowledge of the ETM+ instrument and Landsat 7 satellite geometry. The processing algorithms include payload correction data (PCD) processing, mirror scan correction data (MSCD) processing, sensor and platform geometric modelling, precision correction using ground control, and terrain correction. A highly automated determination of ground control points is envisaged. Therefore, a database of ground control points (GCP) will be generated from the panchromatic data, which completely covers Germany and parts of Europe. The algorithms are based on DFD's experience with a GCP data base for Landsat TM with approx. 2,500 points. The definition of thematic products and the development of the relevant algorithms will be done in course of scientific cooperations with universities and research institutes. Furthermore, DFD will set up a Scientific Data Pool, develop sophisticated methods for information extraction, establish new application fields, cooperate with and transfer technology to commercial partners, and stimulate research and applications by organizing workshops and seminars. 4.2 The Scientific Data Pool The Scientific Data Pool (SDP) will cover scientific (research) applications and pilot applications. Both can use data from complete coverage of Germany and selected regions in Europe. All scenes, which are part of the SDP, must be at least one year old. The selection of the scenes is done by DFD according to Image quality criteria and project demands. Both applications can include data from DFD s archived Landsat TM and MSS data, which are older than 10 years. Processing, archiving, and distribution of all SDP data will be performed at DFD, which includes high quality geocoded products as well as value-added products. The definition of value-added products from the SDP is done by DFD and will be extended according to the development of new algorithms and new applications. The availability of products can be queried via the Web interface of the DFD, where these products will be flagged and clearly marked as SDP data.
Candidates interested in using data from the SDP have to provide a project description in advance, clearly indicating the aims of the project and the data sets necessary to carry out the project. Details on the form of the proposals will be available from DFD within the next months. Two complete coverages of Germany per year will be selected for the SDP, which includes a maximum of about 80 scenes per year. Additonally, scenes of Europe out of the Neustrelitz coverage will be freely selectable. A number of 20 scenes per year is envisaged for the SDP. Access to the SDP is restricted. The proposals are evaluated according to the following criteria. In the field of scientific applications proposals are invited which develop new methods for information extraction (including data fusion); define new ETM+ data products; support the calibration and validation of ETM+ data products; support education in ETM+ data usage by generating lecture and demonstration material; stimulate ETM+ research and applications by workshops, seminars and courses. In the field of pilot applications proposals are invited which develop and establish new fields of application; demonstrate applications in new customer segments. The proposals will be reviewed and evaluated by DFD and Eurimage according to the relevance of the proposed project to the objectives of the SDP, the merit of the project from the scientific or application viewpoint, and the degree of innovation. Following the approval of the proposed project, data sets necessary to carry out the projects will be provided to the selected Principal Investigators at a reduced price, which will be calculated according to COFUR conditions. Principal Investigators have to submit a project report and are asked to present their results at special workshops organized by DFD and Eurimage. The joint publication of info sheets and other material is envisaged, as well as putting results on the Internet in various forms. 5 SUMMARY The Landsat Program has provided data to a broad user community for more than 27 years. With the launch of Landsat 7 and its Enhanced Thematic Mapper Plus (ETM+) instrument, this program will be continued and essentially extended. DLR s German Remote Sensing Data Center (DFD) will operate a Landsat 7 International Ground Station in Europe as part of the Earthnet Programme and at other locations world-wide. DFD will be responsible for data acquisition, product generation, and distribution. The DFD utilization concept for Landsat 7 in the Earthnet framework, which is agreed on with ESA and Eurimage, aims at the stimulation and long-term establishment of ETM+ data usage in the scientific and commercial community. The Scientific Data Pool as central part of the DFD strategy will support research and pilot applications. REFERENCES BERUTI, V. (1997): Technical Specification for Upgrading of Current Landsat 5/6 and SPOT Software System to the Landsat 7 and SPOT 4. SOW, Issue 3. DOLAN, K., SABELHAUS, P. & D. WILLIAMS (1998): Landsat 7 - Extending 25 Years of Global Coverage. Proceedings of the 27 th International Symposium on Remote Sensing of Environment, June 8-12, Tromsø, Norway, pp. 622-625. DRAEGER, W., HOLM, T., LAUER, D. & R.J. THOMPSON (1997): The Availability of Landsat Data: Past, Present, Future. Photogrammetric Engineering and Remote Sensing, 63(7), pp. 869-875. ELLICKSON, J. (1998): A Preview of Landsat 7 Mission Operations Building on the Landsat Heritage. Proceedings of the 27 th International Symposium on Remote Sensing of Environment, June 8-12, Tromsø, Norway, pp. 626-628.
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