Erhard Diedrich

A description of the data-driven SAR data workflow in the TerraSAR-X Payload Ground Segment

TerraSAR-X is a national German satellite providing a high-resolution X-Band SAR instrumentation featuring StripMap, ScanSAR and SpotLight imaging modes in various polarizations. The experimental full polarization mode is carried out using a dual receive antenna capability. An active lifetime of five years is anticipated, the launch is expected in 2006. The TerraSAR-X mission serves both commercial and scientific needs. It is implemented in the frame of a public-private partnership between EADS Astrium GmbH (providing the TerraSAR-X Space Segment) and the German Aerospace Center DLR (providing the TerraSAR-X Ground Segment). The commercial product exploitation rights are with Infoterra GmbH, the scientific ones remain at DLR. The Infoterra business concept foresees the inclusion of a Direct Access Service through which TerraSAR-X data may be directly received by stations either for the sole purpose to produce geo-information products for their own and private applications or to generate and distribute commercial products. Essential tasks of the TerraSAR-X Payload Ground Segment developed (and later operated) by DLR are the SAR payload data reception, their archiving and processing, and the distribution of the generated SAR products to users. This paper summarizes the TerraSAR-X Payload Ground Segment design. It describes the SAR data workflow ranging from the payload data reception at the Neustrelitz Ground Station to the long-term data archiving in the multi-mission Product Library at the German Remote Sensing Data Center. Supplementary data as provided by the TerraSAR-X Mission Operation Segment and used during the data-driven generation of the SAR level 0 products are described together with their dissemination concept. The adaptability of the chosen approach for the operation of a Direct Access Station is addressed

Satellite ground stations with electronic beam steering

In this work, we propose electronic beam steering via antenna arrays as a substitute for large parabolic antennas at satellite ground stations. We concentrate on two array geometries, faceted arrays and hemispherical arrays. A thorough analysis is carried out of the radiation characteristics, the array size, as well as the antenna element distribution and spacing. Moreover, in order to fulfill the requirement of the array design, that is, to achieve a higher gain at low elevation angles where the longer spacecraft to ground station distance leads to a larger range loss, we propose to adjust the number of active antenna elements, i.e., some antenna elements are turned on while others are turned off according to the required level of antenna gain. This also contributes to a concept of an optimized array design for this specific application. In the simulations, the array optimization for both array geometries is further investigated and realized with a realistic ephemeris incorporated. The numerical results support the proposal of replacing large reflector antennas by electronic beam steering via antenna arrays at satellite ground stations.

The tanDEM-X Ground Station Network

This paper describes DLRs Ground Station Network as setup and operated for the TanDEM-X mission payload data reception. It lists the technical layout and operational characteristics of each station. The Station Monitoring and Control System which has been successfully qualified during the TanDEM-X commissioning phase is introduced. Software design aspects are discussed high level. Key features of the Station Monitoring and Control System are provided.

Earth and space observation at the German Antarctic Receiving Station O’Higgins

The German Antarctic Receiving Station (GARS) O’Higgins at the northern tip of the Antarctic Peninsula is a dual purpose facility for earth observation and has existed for more than 20 years. It serves as a satellite ground station for payload data downlink and telecommanding of remote sensing satellites as well as a geodetic observatory for global reference systems and global change. Both applications use the same 9 m diameter radio antenna. Major outcomes of this usage are summarised in this paper. The satellite ground station O’Higgins (OHG) is part of the global ground station network of the German Remote Sensing Data Centre (DFD) operated by the German Aerospace Centre (DLR). It was established in 1991 to provide remote sensing data downlink support within the missions of the European Remote Sensing Satellites ERS-1 and ERS-2. These missions provided valuable insights into the changes of the Antarctic ice shield. Especially after the failure of the on-board data recorder, OHG became an essential downlink station for ERS-2 real-time data transmission. Since 2010, OHG is manned during the entire year, specifically to support the TanDEM-X mission. OHG is a main dump station for payload data, monitoring and telecommanding of the German TerraSAR-X and TanDEM-X satellites. For space geodesy and astrometry the radio antenna O’Higgins significantly improves coverage over the southern hemisphere and plays an essential role within the global Very Long Baseline Interferometry (VLBI) network. In particular the determination of the Earth Orientation Parameters (EOP) and the sky coverage of the International Celestial Reference Frame (ICRF) benefit from the location at a high southern latitude. Further, the resolution of VLBI images of active galactic nuclei (AGN), cosmic radio sources defining the ICRF, improves significantly when O’Higgins is included in the network. The various geodetic instrumentation and the long time series at O’Higgins allow a reliable determination of crustal motions. VLBI station velocities, continuous GNSS measurements and campaign-wise absolute gravity measurements consistently document a vertical rate of about 5 mm/a. This crustal uplift is interpreted as an elastic rebound due to ice loss as a consequence of the ice shelf disintegration in the Prince Gustav Channel in the late 1990s. The outstanding location on the Antarctic continent and its year-around operation make GARS O’Higgins in future increasingly attractive for polar orbiting satellite missions and a vitally important station for the global VLBI network. Future plans call for the development of an observatory for environmentally relevant research. That means that the portfolio of the station will be expanded including the expansion of the infrastructure and the construction and operation of new scientific instruments suitable for long-term measurements and satellite ground truthing.

Tandem-L: Main results of the phase a feasibility study

Tandem-L is a highly innovative SAR satellite mission for the global observation of dynamic processes on the Earths surface with hitherto unknown quality and resolution. Thanks to its novel imaging techniques and its unprecedented acquisition capacity, Tandem-L will deliver urgently needed information for the solution of pressing scientific questions in the areas of the biosphere, geosphere, cryosphere and hydrosphere. The feasibility of Tandem-L has been analyzed and confirmed in the scope of a phase A study, which has been conducted in close cooperation between the German Aerospace Center (DLR) and the German space industry. This paper provides an overview of the Tandem-L mission concept and summarizes the actual development status.