WASHINGTON - Undersea explorer Robert Ballard leans back and smiles at the screens arrayed above his desk. One displays a view of a remote operating vessel, another scans along a seafloor never before viewed by humans. It's the Black Sea, not far from Ukraine, a region long closed to outsiders and now yielding a treasure trove of Byzantine vessels that met their ends 1,000 or more years ago. For Ballard the archaeologist, those vessels and their contents are a delight. For Ballard the explorer, the modern technology he's testing for the National Oceanic and Atmospheric Administration is pretty exciting, too....