mission. Public use of data should also be expected and encouraged. However, most public users may not be able to afford commercial rates for access to data.

Finally, in the committee's opinion the various user communities may be served best by very different distribution architectures. Public use interests may be served by open, distributed architectures such as that used by NOAA or proposed by the Earth Science Information Partners (ESIP-3) federation. Commercial interests may be served best by highly centralized and restrictive architectures.

The committee recommends that NASA investigate flexible mixed-mode architectures with some form of “selective availability” such that data acquired for commercial purposes are not freely and widely disseminated. Other data, particularly those obtained for purposes of public use, could be directly down-linked under an open architecture model. Some data may be deemed of scientific value but with some potential commercial value; these could be made available only for research and commercial use during a specified time period. The ground segment could be supported by funding to process data into usable (Level 0) products and to disseminate the data through appropriate Distributed Active Archive Centers on a cost-recovery basis.

An alternative approach is to transmit unprocessed data to a distributed set of ground stations. All data would be transmitted in unprocessed form and be accessible by any interested user. Processing software would be provided to any user and could be carried out at any standard UNIX-class workstation. Because such an approach to data distribution would eliminate a centralized processing system and its associated costs, in the committee's opinion it should still be considered for small SAR. If this approach is followed, it would determine the practical upper limit on down-link data rate.

However, there may be innovative approaches that could protect both research and commercial communities. For example, some commercial applications have a short shelf life; thus, older data sets may have little commercial value but will still be valuable to the research community. Given the longer time scales for many terrestrial applications, however, the commercial shelf life may be many years for some data sets.

The committee recommends that NASA establish a policy to provide the greatest access for researchers while minimizing costs and, at the same time, protecting any legitimate commercial rights. This will not be easy because radar remote sensing will likely be at the confluence of research and commercial interests for the foreseeable future.

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