Many nations are pursuing space-based radar programs. However, for a variety of reasons, it is at best uncertain if these programs can return the quantity and kind of data required to meet the science objectives discussed in this report. Furthermore, many of these systems exist only as concept studies. Given below is a brief assessment of the usefulness of several of these systems for the crustal deformation-, climate-, and ecology-related monitoring and commercial applications important for the nation to undertake:
ALOS. This L-band satellite, listed in Table 8.3, was launched by Japan in early 2006 and is currently operating. The data quality appears high, and, after some trouble with controlling the orbit, the satellite is now delivering test data to the calibration/validation team. ALOS, in a 41-day repeat cycle, will image much of east Asia several times per year. However, it will not image the U.S. swaths more than once or twice per year over its 5-year lifetime due to data rate constraints.
A U.S. interagency working group is trying to offer NASA data-relay capabilities to JAXA to increase coverage over the United States, but it has not yet succeeded. Thus, while these data can yield some engineering studies for L-band SAR, the temporal density is an order of magnitude too sparse to eliminate atmospheric interference or to give insights into transient phenomena. In any case, ALOS will be at the end of its functional lifetime before a new satellite can be launched by the United States, and so it is at best a stop-gap engineering mission.
HJ-1 satellites. China has an ambitious plan to orbit up to 10 radar satellites (4 of which form the HJ-1 series) over the next 10–15 years. Reports by word of mouth that the first satellite was launched last April have not been substantiated in existing Web-reachable documents. It is reputed to have been an L-band system, and the orbit, repeat cycle, and capabilities of the sensor are not widely known. Published reports state that the next two satellites to be launched will be a pair of S-band radars in 2007; these are possibly nearly as effective as L-band radars in reducing decorrelation. However, the panel considers it unlikely that enough data will be made available to the U.S. science community to address its science objectives, and in any case does not see how there will be sufficient participation by U.S. scientists to define the proper orbits and coverage to begin to meet U.S. needs. If U.S.-Chinese relations change drastically, and NASA agrees to support the Chinese space program significantly, then of course these satellites could be useful.
Arkon-2. Arkon-2 is a military system with three radar frequencies. No U.S. scientists are known to have been asked to join a Russian team to plan for scientific use of the sensor. It is possible that the Russian team could decide to place the radar in an orbit useful for scientific radar remote sensing investigations, rather than in a militarily useful orbit, and then sell the data commercially. If that is the case then the United States could consider a make/buy decision on data. Past experience has been that Russian radar data products do not satisfy the science community’s needs with respect to data volume, satellite tasking, orbit geometries, and, most importantly, data quality.
MAPSAR. MAPSAR is a Brazilian radar designed for equatorial coverage of the Amazon region. Even if the capacity of the sensor could be increased and U.S. scientists could acquire satellite data for their use, the conflicts regarding orbit configuration and data allocations are formidable if the same satellite is to be used for the polar regions as well as the Amazon. This is Brazil’s first imaging radar satellite system, and it is difficult to assess whether it will be capable of delivering the amount, type, and quality of data needed to monitor and characterize hazards and to address environmental, climatic, and commercial needs.