Construction crews are almost done erecting a large research tower nearly two miles south of the Vineyard.

For weeks, a well-lighted barge and tugboat have been involved in a large-scale project due south of Edgartown Great Pond. They've been assembling what will be an all-season steel tower loaded with instruments that will collect weather and ocean data. The tower will rise 68 feet above sea level when it is finished at the end of this week.

The project, known as the Air-Sea Interaction Tower, or ASIT, is headed by the Woods Hole Oceanographic Institution (WHOI) and funded mostly by the Department of Defense. Among other uses, it will take sea and air measurements for the military and be tied into the Woods Hole Oceanographic Institution's Martha's Vineyard Coastal Observatory already at South Beach.

A source told the Vineyard Gazette that the tower is also tied to homeland security issues. The source could not discuss the matter further, because the information is classified.

Albert J. (Sandy) Williams 3rd is a principal investigator for WHOI and is familiar with the project's instruments. Mr. Williams said on Friday that the tower will greatly help WHOI measure and monitor the atmosphere and ocean during fair and rough weather.

"We'll watch northeasters," he said. "This is an extension of the observatory at South Beach. It's about two miles from the meteorological tower at Katama and about a mile and a half offshore."

Mr. Williams said the tower is sponsored by the Navy department's Office of Naval Research. "All together, they are spending $8 million. There are other components other than the tower. The Navy has concerns about how their radar works, whether they are reliable seeing over the horizon."

Mr. Williams said the Navy wants to see how temperature, humidity and fog impact radar accuracy. Apparently the interaction between the ocean and the atmosphere is an essential part to understanding how to make radar more precise.

"They have to know when you are on an aircraft carrier whether they are seeing an enemy aircraft at 250 miles or not," he said.

On August 3, a 54-year-old pilot died when the small plane he was operating crashed in fair weather just south of Long Point in West Tisbury. The pilot - Timothy L. Crawford of Idaho Falls, Ida. - was piloting a single-engine, Long-EZ aircraft after taking off from Barnstable Municipal Airport. Mr. Crawford, a scientist working on a tower-related Navy project, was carrying important air measuring equipment.

Mr. Williams said that after an investigation it was determined that Mr. Crawford had suffered a massive stroke while in the air. Mr. Williams said Mr. Crawford, an employee of the National Oceanic and Atmospheric Administration, was deeply involved with WHOI on this project. "He was one of our principal investigators," Mr. Williams said.

Homeland security issues had been part of Mr. Crawford's work for the Navy, a source told the Gazette.

The tower is being erected by RDA Construction of South Boston, which is using a 170-foot-by-70-foot barge equipped with a crane capable of rising 180 feet. The name of the Boston-based vessel is Mr. Barge. A 100-year-old tugboat called Venus is also involved.

Anyone walking along South Beach at night can see the bright lights in use.

When completed, the tower will be roughly the same height as the Buzzards Bay Tower, but not as bulky. Its instruments will be able to measure light, movement of sediment and ocean mixing. The tower is in 50 feet of water.

Mr. Williams said the tower will ultimately be tied in electronically with the Martha's Vineyard Coastal Observatory, construction of which began two years ago and is mostly complete.

The observatory includes an array of different underwater and surface devices ideally suited for scientific research. Mr. Williams said the institution already has an observatory facing east in New Jersey. The fact that this observatory faces south gives them a vantage point they don't otherwise have.

WHOI also likes the fact that the equipment is so close to Woods Hole. "I have two instruments to measure the sedimentary movement of the bottom," Mr. Williams said. "I have two more instruments to go in in the next two weeks."

Funding for the tower was provided by the Office of Naval Research as part of the Coupled Boundary Layers and Air-Sea Transfer (CBLAST) program which will begin experiments in the summer of 2003. They will use the tower, buoys, moorings, aircraft and research vessels.

According to a release from WHOI, the CBLAST main objective is to "improve our understanding of ocean-atmosphere interactions in low to moderate winds to improve marine weather forecasts and ocean circulation models."

The device is built to survive for at least 10 years in extreme offshore conditions. But "it is currently permitted to operate for the next five years and its continued operations will be evaluated at that time," according to the release.

Martha's Vineyard Coastal Observatory has a lot of weather information available online. There is also a live video camera pointed over South Beach. For more information, visit