Scripps Oceanography scientist Veerabhadran Ramanathan reported that instrument-bearing autonomous unmanned aerial vehicles (AUAVs) completed 18 successful data-gathering missions in pollution-filled skies over the Maldives, an island chain nation south of India. During the Maldives AUAV Campaign (MAC), groupings of three aircraft flew in synchronous vertical formation, which allowed onboard instruments to observe conditions below, inside and above clouds simultaneously. Researchers hope the data produced during the flights will reveal in unprecedented detail how pollution particles contribute to the formation of clouds and the resulting dimming from the polluted clouds.
Stacked flights with manned aircraft have been attempted, but rarely. The difficulty and cost of assembling and coordinating three similar aircraft have prevented the sort of repeated measurements required to sample clouds adequately.
"Based on MAC's success it is possible that in five years, hundreds of lightweight AUAVs will be documenting how human beings are polluting the planet and hopefully provide an early warning system for potential environmental disasters in the future," said Ramanathan.
The skies over the Indian Ocean visibly bear the imprint of human activities in Southeast Asia, frequently in the coverage of what are termed atmospheric brown clouds, particulate-laden haze and cumulus clouds that frequently blanket the region. The role that dust and aerosols from industrial, urban and agricultural emissions play in creating such a brown haze is an important variable to researchers who study anthropogenic climate change, specifically how human activities could be changing the planet's albedo, or reflectivity. Cloud cover cools Earth's surface by reflecting solar radiation back into space. In recent years, researchers have come to realize that pollution in the atmosphere and the dimming and cooling it causes could actually be leading scientists to underestimate the true magnitude of global-warming trends observed in recent decades.
Ramanathan has led a consortium of academic and industrial partners in the development of aircraft and integrating them with miniaturized instruments that can obtain aerosol-cloud-solar radiation data in remote regions once considered unobtainable: multi-dimensional portraits of clouds created in polluted environments over periods of several tens of hours. The "Manta" AUAVs, constructed by Tucson, Ariz. firm Advanced Ceramics Research (ACR), represent a feat of miniaturization (an ACR flight team supported Ramanathan's research by flying more than 100 hours in gathering the atmospheric data).
Each AUAV bears an instrument package that weighs less than five kilograms (11 pounds). The packages developed by the Scripps team include sensors for measuring solar radiation, cloud-drop size and concentrations, particle size and concentrations, turbulence, humidities and temperatures.
Flights took place between March 6 and March 31, taking off from an airport on the island of Hanimaadhoo in the Maldives. Each AUAV tracked a separate component of brown cloud formation. The lowest, flying beneath the cloud, quantified the input of pollution particles and measured quantities of light that penetrated the clouds. The aircraft flying through the cloud measured the cloud's response to the introduction of particles. The aircraft flying above the cloud measured the amount of sunlight reflected by the clouds into space and the export of particles out of the clouds.
"MAC has demonstrated that lightweight AUAVs and their miniaturized instruments are an effective and inexpensive means of simultaneously sampling clouds in polluted environments from within and from all sides," said Jay Fein, program director in the National Science Foundation's Division of Atmospheric Sciences. "They will serve as critically important additions to our atmospheric measurement capability in addressing one of the major outstanding issues in climate change science: How does pollution affect cloud microphysical and radiative processes in the context of weather and climate?"
"We are excited about being involved in the study of atmospheric brown cloud affects using cutting edge flight control software we developed in our unmanned aerial vehicles," said Anthony Mulligan, CEO of Advanced Ceramics Research. "Our employees are proud to have provided Scripps scientists a way to further their research and look forward to continue to provide them a low-cost, effective way to gather additional information."
The research was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration (NOAA), the National Aeronautics and Space Administration (NASA), the G. Unger Vetlesen Foundation and the Alderson Foundation. The researchers also wish to acknowledge the support of the United Nations Environmental Program and the support and cooperation of the Republic of Maldives.
More details of the campaign and Project Atmospheric Brown Clouds, of which MAC is a component, are available at www-c4.ucsd.edu/ProjectABC.