# Ten Years of TerraSAR-X Operations
## Extension of the TerraSAR-X Ground Segment
### Near-Real Time Capabilities  
In the beginning, Near-Real Time (NRT) support had not been a strong TerraSAR-X stake holder requirement. Nevertheless, all of the basic products have been offered in a NRT flavor since the  
Figure 1: Sketch of main subsystems and components of the common TerraSAR-X/TanDEM-X ground segment. TanDEM-X mission specific parts are in grey.  
beginning of the mission. Sampling and resolution in the NRT products are identical to those of the standard product. The product latency after downlink is typically about 10 min. Processing has to rely upon auxiliary information, which is available at the same time as the raw data. The usage of a predicted orbit results in a reduced geolocation accuracy, the non-availability of instrument house-keeping parameters in a reduced radiometric accuracy. Data takes foreseen for NRT processing are marked as such both in space and on ground, and thus allow for a completely data-driven privileged handling from reception into processing and dissemination.  
Within the seven years, the NRT capabilities have been further improved. Receiving stations with online data connection to NSG are grouped into the NRT station pool (currently consisting of NSG and SvalSat). Mission planning uses the next possible contact from the station pool for the downlink of a NRT data take and schedules it as soon as possible within this contact, i.e., at the beginning for already completed acquisitions and--if the remaining contact time allows--within for acquisitions that were taken during the contact.  
NRT support for maritime applications has been introduced in 2012 starting with a ship detection service. Wind and wave products that are based on Stripmap multi-look ground range detected products followed in 2016 [13]. In case of ship detection, Automatic Identification System (AIS) data are processed in real time and the obtained information is merged into the SAR based detection results. Ship detection information is provided in a number of different formats, e.g., as ESRI shape file layer, GML, or Google KMZ files assembled with a geocoded quicklook image. Dissemination options include secure FTP variants and electronic mail. Whereas, the ship detection service is already available for external users, wind and wave products are currently provided for selected science projects only. The wind product provides derived wind field information for the estimated wind speed and direction calculated relative to a standard reference height of 10 m (U10) on a raster of two by two kilometers. The wave product contains sea state information about the significant wave height on a raster of three by three kilometers. The core processor to derive those value added products is the SAR AIS Integrated NRT Toolbox [14]. The SAINT processor calls the processes for the various maritime products in parallel. Thus, obtained information is made available instantaneously for the other information extraction processes.  
For selected NRT applications, e.g., vessel navigation support in polar-regions, quicklook images of the high-resolution TerraSAR-X products, or further derived information of limited data amount are sufficient. Consequently, TerraSAR-X processing systems were installed both at GARS and ISSF in 2015 enabling the identical NRT product generation, as done at the central processing system. Following a nominal NRT production run, a dedicated station NRT quicklook process generates geocoded quicklook products of a size smaller than 5 Mbyte, which are e.g., suitable for e-mail transfer to NRT users on-board vessels or at research stations with Internet access. Handling of station NRT orders is fully integrated into the payload ground segment. Orders may be placed by authorized users, the derived production requests are routed accordingly into the appropriate station [12].