4
Data Collection and Dissemination
Several overarching issues should be considered in planning a small SAR mission. Should it be designed for science, public use, or commercial applications? What are the relative priorities? If science prevails, who should have access to the data? If public use prevails, what should be the nature of the data distribution system? If commerce prevails, should NASA be involved? How can a given instrument duty cycle be optimized to meet specific objectives within the framework of overall general priorities?
The committee recommends that any mission design be considered from the perspective of an end-to-end information delivery system. This begins with consideration of the interests to be served by the system and the informational needs of those interests. Provided that these interests and needs are prioritized, engineering trade-offs should be evaluated and optimized for focused suites of applications. The added costs of extra capabilities can be examined with respect to the value of the information. Value is determined by the relative importance or priority (scientific data and public use) or by monetary importance (commercial applications).
It is the committee's view that if NASA proceeds with a small SAR, it should give preference to a mission that optimizes for a specific scientific goal or related application. Additionally, consideration should be given to meeting the needs of public use and commerce within design constraints imposed by the science requirements. Such applications should be selected to address ongoing public needs (such as natural disaster assessment), future high-profile commercial potential (such as forestry or agricultural assessment and global topographic mapping), or specific science demonstrations (such as ice-flow dynamics and volcanic lava flow rates). The duty cycle should be used to build orbit-by-orbit data sets related to these applications so that over the life of the mission, experience would grow to further quantify and validate the objectives set forth.
It is recognized that a highly focused mission is more likely to yield a simple system design with lower overall mission costs. However, the more focused the mission, the more limited is the user constituency over which the associated costs are spread. As a consequence of commercial teaming, a small SAR system—even “enhanced” small SAR with multifrequency capabilities may have a lower cost to NASA than a strictly scientific and highly focused mission. Two factors to be considered are the added value of mission enhancement to NASA science objectives and dual use.
The committee recognizes the importance of flexibility in the data acquisition system. The concept of life-cycle mission design should be applied to minimize conflicts in scheduling changes in operating modes. The various scientific objectives of the LightSAR science plan imply that conflicts will arise and require dissimilar data types over common areas. Such conflicts will be exacerbated by the differing needs of public and commercial users. Mission life-cycle planning can be used to balance conflicting needs weighted by relative priority.
The committee recognizes that there are problems associated with data rights and access to data. It is expected that many data will be dual-use in nature and can serve multiple interests.
The committee recommends that for any small SAR mission NASA ensure that some form of open access be maintained for the research community. Commercial partners will have to be accommodated and their interests protected if they are to provide funding for a small SAR
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.
