SEARSPORT, Maine — Just how far around the upper Penobscot Bay region would a controversial 137-foot-tall liquid propane gas storage tank be visible if it’s built?

A balloon test scheduled for Thursday morning aims to answer that question, which has been on the minds of many as the Searsport Planning Board weighs the application from Denver-based DCP Midstream for the proposed $40 million project. The terminal and storage tank would be constructed at the Mack Point industrial zone.

At a meeting earlier in June, planning board members requested that DCP Midstream officials do the test, according to longtime chairman Bruce Probert.

“DCP has the resources and the technology to do these things,” he said. “It should give us a little better perspective.”

DCP Midstream is a private joint venture owned equally by Spectra Energy and ConocoPhillips, and the project already has received approval by entities that include the Maine Department of Environmental Protection, the Army Corps of Engineers, and the U.S. Coast Guard.

It now awaits approval only from the town of Searsport.

According to Roz Elliott, spokesperson for the Colorado company, the balloon test will consist of five large helium balloons. A red balloon that’s about seven feet in diameter will be placed at the highest point of the 14-story tall storage tank. It will be surrounded by four yellow balloons that are about five feet in diameter, which will be placed to represent the height of the sides of the tank.

Once the balloons are airborne, a photographer will move around to different vantage points within Searsport to take high-quality pictures.

“Do you see it from there? Do you not see it from there?” Elliott asked. “It’s really interesting — making sure you have results that have integrity. I think it’s pretty significant.”

She said that several factors may affect the timing of the balloon test, which is scheduled to take place at about 8 a.m. Thursday. If the weather is foggy or windy, the test won’t happen.

“The point is to be able to see the balloons,” Elliott said.

Altogether, the test will take four to six hours and the balloons will be visible for quite some time, she said.

Many opposed to the project also will be taking the opportunity to snap pictures of the balloons from various points within the viewshed, according to Astrig Tanguay of Thanks But No Tank.

She said that while the test may be better than nothing, she and others would greatly prefer to have the company provide a three-dimensional scale model. ConocoPhillips is well able to afford to make a scale model, she said.

“The idea that they’re tethering the balloons up a string that you’ll barely be able to see and telling us it represents a tank that’s 14 stories tall and 220 feet wide is absurd,” she said. “All we’ll see is these dots of balloons that represent a solid, 14-story-high structure.”

Project opponents have been asked to take photos of the balloons at Mack Point from locations around the area including Islesboro, Northport, Bayside, Camden and Frankfort.

According to Tanguay, opponents will try to combine the photos using a computer program that will assimilate them into a three-dimensional image.

“I don’t understand why we’re the ones who have to do it,” she said.

Amy Browne, the news and public affairs director of WERU-FM community radio, said that people who take photographs of the balloons are invited to add them to an album on the station’s Facebook page.

Elliott said that if the weather doesn’t cooperate, the balloon test will be postponed until Friday morning.