Organization: NASA/GSFC, SSAI
Attached is a one-page summary of the Ocean Biology Processing Group's conceptual feelings on OPeNDAP. Basically, summarizes our most recent conversation. Let us know if this helps with your effort or if there are details we might add. Take care.
Comments on the use of DODS Data Access Protocol for satellite Ocean Color data distribution
In Fall 2004, the GSFC ESDIS Project asked the GSFC Ocean Biology Processing Group (OBPG) to comment on the feasibility of distributing satellite ocean color data via the DODS data access protocol (DAP). The OBPG reviewed the conceptual application of this DAP to the distribution of SeaWiFS and MODIS/Aqua data, generated a list of concerns, and addressed the concerns via the following observations. Note that the OBPG did not install DAP clients and servers to assist with this analysis.
- Summary of DAP architecture -- The DODS DAP uses a client-server model, where client requests are sent across the Internet to a server, which answers with requested data. Clients use standard DAP functions to request data from Servers via the HTTP protocol. Servers are Web servers using CGI routines specific to the format of the served data set. Clients interpret request results into a Client-defined data format. The DAP core is a set of C++ classes for building Servers and Clients.
- Security -- As DAP Servers are, effectively, Web servers and Client requests use the HTTP protocol, methods for maintaining local security and restricting data access are identical to those for existing OBPG Web servers. Access may be restricted at the domain or user levels.
- Ocean Color Data Distribution -- A number of Level-3 satellite data products are already distributed via the DODS DAP (for example, the AVHRR Oceans Pathfinder global equal-angle SST product). Distributing Level-3 SeaWiFS or MODIS ocean color products is, conceptually, equally feasible. Level-3 products, by definition, use a predefined global projection and grid. This facilitates both co-registration with other data products and data sub-setting. At this time, the OBPG does not recommend extending distribution to Level-1 or Level-2 products, which are stored with their native, satellite-swath projection. Also, Level-1 and Level-2 files sizes significantly exceed those of Level-3, and therefore, volume constraints preclude most data centers from indefinitely maintaining these data online.
- Required level-of-effort -- Conceptually, installation and maintenance of a DAP Server requires minimal effort. The majority of the effort would be with metadata file generation. If distribution is limited to Level-3 data, however, where data products and grids are fixed, metadata generation would be fairly straightforward.