People go to considerable lengths to get a good cup of coffee. Few, however, could top a US research team assembled to guarantee that the beans that come off the plantations are at their absolute best.

A group lead by a geographer from Clark University of Worcester, Massachusetts, plans to use a pilotless aircraft that will fly over Hawaiian coffee plantations. Its main cargo is a high-resolution digital camera that will take images of the plants below and let growers know, down to the day, when their crops should be harvested.

Partners in the research include scientists from the US National Aeronautics and Space Administration (NASA) and will involve the use of a "Pathfinder-Plus" aircraft provided by AeroVironment of Monrovia, California.

NASA has quite a substantial programme, both military and civilian, that studies the use of unpiloted aircraft. In keeping with that organisation's love of jargon, these planes are known as UAVs (uninhabited aerial vehicles). It might be over the top but it does describe what they do.

The principal investigator is Prof Stan Herwitz, professor of biogeography and earth sciences within the Department of Geography at Clark University. The key to the work depends on being able to identify the colour of the coffee beans from the air.

Their colour provides a definitive readout of when the coffee beans are at their best and when they should be picked. "The experiment is tying together a future vision in aeronautics," Prof Herwitz explained.

The object is to improve the efficiency of spotting fields that are ready for harvest. The current practice is for workers to watch fields ripening and then make a decision to harvest. Fields are often assessed only on the basis of a few plants, so when the mechanical harvesters go in and literally shake the beans off the plants, they recover beans at a variety of stages.

The harvest is made more complicated by the fact that fields can ripen at different times and the team works 24 hours a day to bring in the crop during the four-week harvesting period. "An almost everyday view of the fields would be useful," Prof Herwitz said.

The Pathfinder-Plus will help them do just that. It is a remarkable fly-by-wire device that runs on solar power and that, in theory, can fly at 80,000 feet. It has a wingspan of 120 feet yet is launched by hand with staff holding either wingtip. It has eight propellers and, once these provide lift, the aircraft glides smoothly into the sky, travelling at just 30 m.p.h.

"There will be a fleet of these and they could be up for months," Prof Herwitz said.

The wing is almost entirely covered with solar panels, but current versions cannot stay airborne at night because of battery capacity. By 2003, however, there will be versions carrying batteries charged by the solar panels that will be able to stay up indefinitely.

The aircraft will loiter in the air above the coffee plantations at about 20,000 feet, he explained. The cameras will carry powerful lenses that will show the coffee plants in sufficient detail.

The pictures captured by the cameras will be transmitted to an operator on the ground who will see in real time what the plane sees and get a bird's-eye view of the fields.

The plan is to make the operation of the system as simple and straightforward as possible, Prof Herwitz said. The operator will be able to identify which fields are ready for harvesting with much greater accuracy than with current practice.

Part of the project involves identifying which part of the colour spectrum to use when identifying ripe beans. Initially the system will only deliver visible light images but there are plans to try assessing the beans in the near future by infra-red light wavelengths, Prof Herwitz added. They will also look at using certain filters to get better data to identify ripe crops.

The UAV will be deployed over the largest coffee plantation in the US, owned by the Kauai Coffee Company. The coffee industry will have access to the findings produced by Prof Herwitz.

The project arose after NASA issued a call for proposals asking for researchers to submit projects that relied on UAVs. It chose two projects, which together will receive $8 million (#9.1 million) support over their four-year life.

The second successful project is equally intriguing. It involves the use of another UAV, the ALTUS, built by General Atomics of San Diego California, which will fly around and through thunderstorms.

Overseen by researchers from the University of Alabama at Huntsville, the team is trying to understand how lightning forms and dissipates during a thunderstorm. The ALTUS can reach heights of 55,000 feet and will carry equipment to observe and record information taken from deep within the storm.

It will fly out of the Kennedy Space Centre in Florida and will be sent up as soon as a thunderhead is spotted on the horizon. It also uses specialised aircraft to carry earth-viewing scientific payloads to deliver new data.