Scientists Test Radio-Controlled Helicopter as Tool to Validate Terra Satellite Data

Lori Stiles
May 30, 2000

SCIENCE CONTACT: Alfredo R. Huete, 520-621-3228,

TUCSON, Ariz. -- American and Japanese scientists are about to test a radio-controlled helicopter sensor package over desert, grasslands and forest as a new tool to check remote sensing data on global vegetation from the Terra satellite.

Last month NASA announced that Terra, an international mission and part of NASA_s Earth Sciences Enterprise, was on orbit and "open for business." Terra is the first satellite to daily monitor Earth_s integrated system of atmosphere, lands, oceans, solar radiation and life on a global scale.

This week in Tucson, University of Arizona and Japanese scientists will launch a six-week field campaign using a Japanese radio-controlled helicopter over several Earth Observing System (EOS) land validation core sites. These are internationally recognized sites that scientists use to check, or validate, remote sensing information taken over the long term from the world_s major ecosystems.

Professor Alfredo R. Huete, an EOS scientist who heads the Terrestrial Biophysics and Remote Sensing Program in the UA department of soil, water and environmental sciences, is coordinating the U.S. campaign.

Huete and his group are developing precise measures of vegetation and studying the interactions of soil, climate, vegetation and dead or dying plant material involved in the global carbon budget. They specialize in developing the mathematical "vegetation indices" needed to correctly interpret data taken by Terra_s Moderate-Resolution Imaging Spectroradiometer (MODIS)..

Yoshiaki Honda of the Center for Environmental Remote Sensing (CEReS) at Chiba University near Tokyo has developed the radio controlled helicopter (RC helicopter) sensor package that will be used over validation sites in Arizona, New Mexico, Kansas, Montana, British Colombia and Oregon during the next six weeks.

Honda_s group prototyped and successfully tested their RC helicopter last year in the Mongolian grasslands. This site is one of the EOS validation core sites used jointly by MODIS scientists and Japan_s Global Imager (GLI) scientists. Honda is principal investigator for GLI, a global vegetation monitoring experiment equivalent to MODIS. Japan_s space agency, NASDA, will launch GLI aboard ADEOS2 in early 2001.

Honda and members of Huete_s group are driving a rental truck carrying the RC helicopter from Los Angeles to Tucson today (May 30). Another 13 Japanese scientists and industry representatives from Yamaha Corp., which manufactured the prototype helicopter, will fly into Tucson tomorrow afternoon.

Huete, Honda and their teams will meet at the UA Environmental Research Laboratory at the Tucson International Airport at 9 a.m. on Thursday, June 1, to finalize their Tucson test flight plans and to unpack, assemble and check the helicopter.

Huete said there are three possible core validation sites in the Tucson area for the June 2 -4 field observations. One is near Reddington Pass north of Tucson. The two others, near Tombstone, are the Walnut Gulch Experimental Watershed in the San Pedro riparian zone and the Audubon ranch southeast of Sonoita.

Honda, Huete and their team members then leave for the next site, Jornada, N.Mex., on June 5.

>From there, the observation schedule, including travel time to the site -

Jornada (New Mexico) _ June 6 _ 10
Carlsbad (New Mexico) _ June 11 _ 12 (a demonstration site)
Konza Prairie (Kansas) _ June 14 _ 17
Missoula (Montana) _ June 18 _ 23
Victoria (British Columbia, Canada) _ June 24 _ 29
Otter (Oregon) _ June 30 _ July 3

Scientists from each of these sites are coordinating their field measurements and satellite acquisitions with the planned helicopter overflights, Huete said. "The on-site measurements provide a _ground truth_ of actual vegetation, soil and land cover conditions, providing independent performance estimates of how well satellites can measure the land surface and its seasonal- and long-term changes," he added.

"Since the Terra satellite returns data from around the globe every day, it is important that the upcoming RC helicopter campaign cover a wide range of biomes and land cover conditions, from arid and semi-arid deserts to the grasslands of the Great Plains and the forests of Canada and the Pacific Northwest," Huete said. The stop in western Montana is to explore the use of the RC helicopter system in monitoring and assessing forest fire conditions and damage, he added.

The RC helicopter "ground truth" measurement system is very useful to characterize the optical properties of the core validation sites, Huete said: "What makes this system unique is that the helicopter can get data from all possible angles. That_s very important to the satellite system, because the satellite views any given spot on Earth almost every day, but at different angles over all the different surfaces _ desert shrub, or forest tree or grassland."

The RC helicopter can be manually operated and guided by GPS (Global Positioning System). Researchers will program an onboard computer so that the helicopter hovers over GPS- defined locations. The unit can fly up to altitudes of 100 meters and as far away as 200 meters horizontally from the operator. It must refuel every 90 minutes.

The helicopter carries an onboard spectroradiometer for measuring energy reflected from the ground surface. At its maximum 100-meter altitude, there is no atmospheric "contamination" in the data, so scientists can determine the optical relationships between the reflectance data and the physical properties of different land covers such as green vegetation biomass, leaf area index, percent green vegetation cover, and soil and litter properties..

The RC helicopter was actually developed for spraying agricultural chemicals. It can hover to an accuracy within 20 cm from its programmed point and carry a payload that weighs 30 kg at sea level, providing ample opportunity to mount a variety of sensors.

Huete and his colleagues are working to get an accurate picture of how photosynthetically active vegetation covering Earth_s land surfaces is changing over space and time. With Terra, Huete said, scientists have "unprecedented opportunities for satellite mapping of deforestation, land degradation, drought, and agriculture, range and forest productivity." He said scientists are excited because they have "the opportunity to document and monitor biospheric health, and measure the sustainability of human life on planet Earth."

**** EDITORS NOTE _ Photos of the RC helicopter and fieldwork by UA and Chiba University researchers , along with cutlines, are in a folder titled "huete," which is available by ftp at the host site Use anonymous login with an e-mail address as the password.

Or point your web browser to the following URLs:

Fig. 1 RC helicopter in Mongolia
Fig. 2 Close up view of helicopter
Fig. 3 Close up of mounted sensors
Fig. 4 Helicopter in action
Fig 5 Vegetation field measurements at Audubon Ranch, Ariz. Researcher Hiroki Yoshioka (standing) and Chiba University student Asako Konda
Fig. 6 Ceptometer transect measurements at Konza Prairie, July 1999. Ceptometer is used to measure vegetation photosynthetic activity. Laerte Ferreira, a doctoral student, is pictured.
Fig. 7 Yoke-gased radiometric measurments at Konza Prairie, July 1999. Student Fricky Keita with hand-held radiometer mimicking what the satellite measures in glue, green, red, and near-infrared bands
Fig 8. Student Pamela Nagler uses ceptometer in making vegetation measurements in the Colorado River riparian zone. ****

***Relevant web links:

The Mongolia experiment is described at with the RC helicopter measurement component described at

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