# Ten Years of TerraSAR-X Operations
## 3 Evolution of SAR Product Portfolio
### Extension of Basic Products
Not only the use of newly created wide-swath sub-beams that differ in pattern tapering from the nominal Stripmap beams allowed for achieving a total swath width of up to 266 km, also variable range bandwidths and processing look factors are used to keep an optimal performance over the whole swath. Its chirp bandwidth is selected for each individual sub-swath, such that the projected ground range resolution of the detected product is kept mostly below 35 m--in the same order as the azimuth resolution--with a nearly constant number of radiometric looks. This allows for a consistent performance in applications like ship or oil spill detection over the full multi-beam swath. Since this mode is mainly designed for maritime applications, a special cross-polar (HV or VH) order option is also provided that increases the contrast between man-made targets and ocean surface at the price of lower sensitivity. Continuous research activities and TMSP upgrades with respect to processing performance, timing, and phase accuracy, as well as geometric precision also improved the SAR product performance and allowed for turning experimental products into operational ones. Additionally, the product characteristics and the level 1 format have been extended to facilitate higher level processing and geo-information retrieval. Some major achievements were:  
* The introduction of operational image noise correction for all radiometrically enhanced (RE) products in December 2008. It is based on a sophisticated statistical evaluation of the thermal noise distribution in SAR images when considering the processing filter noise gains [18]. * Optimized ScanSAR SSC oversampling approaches resulting from InSAR experiments activated in April 2009, which enabled the re-classification of the ScanSAR SSC product from an experimental one into a basic product. * Also, in April 2009, additional quicklook and image files were added to the level 1 product to support quick evaluation and image interpretation based on the statistical properties of the image (see Figure 2 for an example). * In preparation of the TanDEM-X mission with a second satellite to provide TerraSAR-X mission products, an antenna phase pattern correction scheme was introduced in March 2010. Similar to the radiometric beam pattern, the individual phase patterns of the numerous beams of the two instruments differ. The individual patterns are projected onto a digital elevation model of the scene and corrected for in order to generate interferometrically exchangeable SAR products from both. The patterns are also annotated in all of the SSC products. * With the extreme Doppler spectral behavior encountered specifically in the raw data of the newly introduced ST modes and its complex mapping into the focused data, additional annotation files describing the Doppler centroid in the focused image have been added to all complex products in September 2013. These files also facilitate the interferometric processing of burst modes (i.e., ScanSAR). * ST mode images are basically illuminated by the beam footprint that is fixed to one location on the ground. Hence, they show a strong radiometric variation and strong increase of the image noise towards their azimuth borders. To ease this effect, the operational noise correction is also applied by default to the highest resolution spatially enhanced (SE) products of the ST mode since May 2014. * The upgrade of May 2014 also added a new azimuth time tag correction method to the processor, which analyses the absolute Radar frequency and drifts of the internal clock w.r.t. GPS time tags and corrects them in the processed data [19]. Specifically processing enhancements, like the last point, helped to improve the geometric location accuracy and to turn TerraSAR-X into a geodetic measurement instrument [20].