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Sentinel-1. This ESA system, based on a C-band radar, cannot address science needs that require a long-wavelength system. Despite Europe’s long history with SAR, the United States should have access to a longer-wavelength system to enable the important next steps described above in this chapter. The nation has benefited from using ESA radars over the last 15 years and will continue to benefit from them in the future; however, a change in technology is needed to achieve real breakthroughs. Although operating future Sentinel radars at the L band or the even longer P band has been discussed, these are concept studies (equivalent to NASA Phase A studies) and not real systems. A commitment by NASA to a real ESA partnership has the potential for substantive cost savings.
Other systems. RADARSAT-2, a Canadian system that will replace RADARSAT-1, is a C-band radar optimized for observations of sea ice. It cannot meet the objectives described in this chapter. TerraSAR-X and TanDEM-X are German radars operating at the even shorter X-band wavelength, and while they are very similar to existing U.S. high-resolution military technology, they likely will suffer from too much decorrelation to provide reliable InSAR over vegetated terrains. TerraSAR-X by itself cannot supply the needed data volume. TanDEM-X, operated in concert with TerraSAR-X, will probably obtain the highest-quality digital elevation model of Earth that will then exist. But it still cannot do repeat-pass interferometry, the cornerstone of all the planned major science objectives.
In summary, the panel notes that the U.S. science community continues to propose L-band InSAR because it appears to be the only known technology for meeting identified Earth observation needs. Repeatpass InSAR methods will make the fine-scale and dense measurements needed to characterize Earth for the several disciplines that have proposed it as the first priority for a new mission.