Sea surface velocity vector retrieval using dual-beam interferometry: first demonstration

The dual-beam interferometer consists of two interferometric synthetic aperture radars (InSARs), one squinted at 20/spl deg/ forward of broadside, and the other 20/spl deg/ aft, to allow measurement of vector surface velocity with only a single aircraft pass. Estimates of surface velocity vectors in the coastal region during high tidal flow are presented. The data were gathered over the barrier islands west of Fort Myers, Florida, as part of a March 2004 deployment. Whereas no detailed bathymetry data were available, high-quality aerial photography appears to be a useful tool in inferring bottom topography and possible current obstructions. The retrieved velocity field clearly follows the expected outflow pattern. While comparisons with tidal current magnitudes predicted by the U.S. National Ocean Service do reveal discrepancies of up to 0.5 m/s, these differences are most likely due to the contribution of ocean surface waves to the overall InSAR velocity measurement. Velocity retrievals for the same area based on the data from different tracks show good consistency. The results constitute the first demonstration of vector retrieval of the surface velocity field with a single-pass InSAR system and confirm the robustness of the dual-beam interferometry principle.     

A protocol-centric approach to on-the-fly race detection

We present the design and evaluation of a new data-race-detection technique. Our technique executes at runtime rather than post-mortem, and handles unmodified shared-memory applications that run on top of CVM, a software distributed shared memory system. We do not assume explicit associations between synchronization and shared data, and require neither compiler support nor program source. Instead, we use a binary code re-writer to instrument instructions that may access shared memory. The most novel aspect of our system is that we are able to use information from the underlying memory system implementation in order to reduce the number of comparisons made at runtime. We present an experimental evaluation of our techniques by using our system to look for data races in five common shared-memory programs. We quantify the effect of several optimizations to the basic technique: data flow analysis, instrumentation batching, runtime code modification, and instrumentation inlining. Our system correctly found races in three of the five programs, including two from a standard benchmark suite. The slowdown of this debugging technique averages less than 2.5 for our applications.