## 5 Overall mission definition and optimization  
Let us now assume that the scientific objectives remain the same as for WSOA onboard Jason-2. Some other applications can be considered over coasts and continental basins (typically some tens of square kilometers), but the weak azimuth resolution of several kilometers prevents from studying small scale surfaces. The study of these other potential applications is not the purpose of this paper. They do not provide us with major constraints on the following optimization of the instrument and the dedicated mission. The additional requirement of observing the entire ocean surface between -80 and 80 degrees latitude is brought up. A secondary objective is to maximise the use of technologies that have already been developed, like the mast and the TWTA (Traveling Wave Tube Amplifier). We focused on areas between 0 and 60 degrees latitude (North and South), as higher latitude areas are well sampled and do not constrain the spatial and temporal coverage. The histogram in Figure 22 (b) confirms the global coverage with less than 1 % unobserved areas (due to the 10 km gaps between  
Figure 22: (a) Number of Hits per cycle of repeatability for a 815 km sun-synchronous orbit over the Indian Ocean (b) Temporal coverage of this orbit between 0 and 60 degrees latitude. nadir and NR). In addition, more than 42 % of the area between -60 and 60 degrees latitude are accessed more than 3 times per cycle. The 9.9156 solar day repeat period of T/P and Jason was chosen to minimize the effects of tidal aliasing (see [29]). One drawback of a 14-day sun-synchronous orbit may lie in the large aliasing periods of the tide harmonics. It may prevent their efficient observation (see Figure 23). However, thanks to T/P and Jason, the major constituents of tides have been mapped with an accuracy better than 2 cm in the deep ocean (see [30]). Shorter wavelengths of the tides may be less well known, but a swath-type observation may provide new insights into the retrieval of small-scale coastal waves (see [31]). For a given interferometric phase uncertainty, the height error is proportional to the wavelength and to the inverse of the interferometric baseline (see Equation (9)). Ka-band could have been considered as a new carrier frequency since it increases the effective baseline by almost a factor of 3. However, because the maximum peak power out of the amplifiers is proportional to the square of the wavelength to first order, selecting the Ka band instead of the Ku band may lead to technological difficulties in terms of power amplification. In addition backscattering coefficients at Ka-band for small view angles have not yet been fully assessed, even though known tower experiments were run using Ka band instruments. New complex and expensive developments of the TWTA and the antenna reflectarrays would be required that are not worth the performance gain. Therefore Ku band remains the right choice as the carrier frequency, also considering that Ku band backscattering coefficients are very well known given all instruments already using this band to perform radar measurements (see [17] and [18]). The baseline length was limited on Jason-2 because of the size of the spacecraft. Returning to a sun-synchronous orbit releases this constraint. The 10 m specified mast length limit imposed by the manufacturer can then be adopted. From an ionospheric perspective, the presence of a dual-frequency nadir altimeter onboard the platform is required as the interferometer uses signals whose carrier frequency is in Ku Band or below. Indeed, it is the only way to very accurately cope with the ionospheric correction. However, section II.2.a showed that the interferometer ground processing procedures could take benefit from the use of GPS data in some specific areas in order to extend the correction throughout the swath. Figure 23: Tidal aliasing comparison between Jason and the proposed sun synchronous 14-day cycle.