# Ten Years of TerraSAR-X Operations
## 3 Evolution of SAR Product Portfolio
### Extension of Basic Products  
The ST mode specifically pushes the limits of instrument azimuth beam steering and spectral signal processing, as pointed out in Section 5, but it is also most demanding in terms of reconstructing the \"true\" geometric range history for focusing each target. With synthetic aperture lengths that correspond to more than 60 km orbit path, the inclusion of higher order terms in the focusing algorithm is required, as well as the intrinsic bistatic tropospheric path delay corrections implemented in the TMSP to keep the reconstructed range history within mm of the geometrical one [16]. The ST azimuth resolution is specified as 24 cm which includes some cm margin since the actual height on ground of each focused scatterer has to be considered for focusing parameter calculation. The TMSP uses a coarse built-in DEM for this, but deviations from the local focal plane of merely several tens of meters may cause resolution loss in the range of centimeters. In turn, we could demonstrate that measuring this very small defocusing effect with methods that are similar to auto-focusing can be used to actually determine the absolute elevation of all sufficiently bright individual scatterers in a single ST image [17]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Mode**} & \multirow{2}{*}{**Config.**} & \multirow{2}{*}{**Pol.**} & \multicolumn{2}{c}{**Resolution**} & \multicolumn{2}{c}{**Extent**} \\  & & & **Mode** & **Pol. Channel** & **(Az. x Ground-Rg.)** & **(Az. x Ground-Rg.)** & **Product Variants** \\  & & & & **(m\({}^{2}\))** & **(km\({}^{2}\))** & **(km\({}^{2}\))** \\ \hline \multirow{3}{*}{Stripmap} & \multirow{3}{*}{Single} & HH, VV & \(3.3\times 1.7\ldots 3.5\) & \multirow{3}{*}{\(50\times 30\)} & complex \& \\  & & Dual & HH/VV HH/HV & & & & \\  & & VV/VH & & & & \\  & & Twin 1 & HH/VV & & \(9.5\ldots 13.5\times 9.5\ldots\) & \multirow{3}{*}{\(50\times 15\)} & \multirow{3}{*}{\(50\times 30\)} & detected in RE only \\  & & & & & & \\  & & DRA 2 & Quad & HH/HV/VH/VV & \(6.6\times 1.7\ldots 3.5\) & \multirow{3}{*}{\(50\times 15\)} & complex \& \\  & & DRA & & & & \\  & ATI 2 & Single & HH, VV & \(<\)\(3.3\times 1.7\ldots 3.5\) & \multirow{3}{*}{\(50\times 15\) or 30} & complex only 3  \\ \hline \multirow{3}{*}{Spotlight} & Sliding & \multirow{3}{*}{Single} & HH, VV & \(1.7\times 1.5\ldots 3.5\) & \multirow{3}{*}{\(10\times 10\)} & complex \& \\  & & & & & & \\  & (SL) & & HH/VV & \(3.4\times 1.5\ldots 3.5\) & \multirow{3}{*}{\(10\times 10\)} & complex \& \\  & & Dual & HH/VV & \(3.4\times 1.5\ldots 3.5\) & \multirow{3}{*}{\(50\times 10\)} & complex \& \\  & (HS) & Single & HH, VV & \((1.1\times 0.7\ldots 1.8\); & \multirow{3}{*}{\(5\times 10\) (5\times 6\ldots 10\); } & complex \& \\  & & & & & 300 MHz) & detected in SE/RE \\  & & & & & & \\  & & Dual & HH/VV & \(2.2\times 1.5\ldots 3.5\) & \multirow{3}{*}{\(5\times 10\)} & complex \& \\  & & & & & & \\  & (ST) & Single & HH, VV & \(0.24\times 0.85\ldots 1.7\) & \multirow{3}{*}{\(2.5\ldots 2.8\times 4.6\ldots\)} & complex \& \\  & (ST) & Single & HH, VV & \((300\) MHz only) & \(7.5\) & detected in SE/RE \\ \hline \hline \end{tabular}  
* \({}^{1}\): The Twin mode is a one-beam burst mode with alternating polarizations not suited for interferometry. 2: Dual Receive Antenna (DRA) modes are only available in dedicated campaigns. 3: No azimuth spectral weighting applied on ATI DRA channels. The level 1 product variants are SSC = Single-look Slant-range Complex and the detected variants MGD = Multi-looked Ground-range Detected, GEC = Geocoded Ellipsoid Corrected, EEC = Enhanced Ellipsoid Corrected. The detected products are available as spatially enhanced (SE) or radiometrically enhanced (RE) multi-look flavors. RE variants are noise corrected.  
\end{table} 
Table 1: TerraSAR-X basic and experimental (grey) products. The six-beam wide-ScanSAR mode seems like a straight forward extension of the established four-beam ScanSAR product. It did however introduce completely new approaches in TerraSAR-X mode and product design.