Overview -- Studying Winter Clouds

Clouds play a large part in climate. Scientists are gradually learning just how large their role is. Only with accurate knowledge of the amount of cloudiness around the globe can scientists begin to understand the underlying mechanisms of climate change needed to predict future climate conditions. Many clouds, especially thin cirrus high in the atmosphere and cumulus and stratus clouds near the earth's surface, are difficult to monitor when the ground is covered by snow and ice. Jointly with the National Aeronautics and Space Administration (NASA), the University of Wisconsin-Madison's Space Science and Engineering Center is conducting the WINter Cloud Experiment (WINCE) January 23 to February 13, 1997 from Truax Field in Madison. During WINCE, an instrumented NASA ER-2 high altitude research aircraft will be flown to learn more about detecting clouds from space in winter conditions. WINCE will provide important data with which scientists can improve cloud detection for future satellite instruments such as the MODerate resolution Imaging Spectroradiometer (MODIS). This NASA research instrument, scheduled for launch in mid-1998 as part of Mission to Planet Earth, will assess earth climate trends of which clouds are such an important component.

WINCE is jointly hosted by the University of Wisconsin's Space Science Engineering Center and the 115 Fighter Wing, Wisconsin Air National Guard, at Truax Field which will provide necessary faciliites for supporting the NASA ER-2 research aircraft operations. Madison-based Persoft is providing communications equipment to facilitate remote data transfer to and from SSEC computers, about 5 miles away from Truax Field. Persoft specializes in PC-to-host software and wireless network connectivity solutions.

UW scientists Steve Ackerman, William Smith and Paul Menzel will head the scientific analysis of the data set, along with NASA scientists Dorothy Hall, Jim Spinhirne and Jim Wang of the Goddard Space Flight Center near Washington, DC. Their research findings will be applied to cloud detection algorithms for the MODIS and other future satellite instruments. "The high altitude nature of the ER-2 (20 km or 65000 feet) is a key element of WINCE. It allows our instruments to make cloud measurements much as they would from a satellite platform. That makes it possible for us to improve our cloud detection capability before the satellite is ever launched," says Ackerman.

During WINCE, multispectral radiometric measurements of clouds and the earth will be made by the MODIS Airborne Simulator (MAS), the High-resolution Interferometer Sounder (HIS) and the Microwave Imaging Radiometer (MIR) remote sensing instruments on the ER-2. The measurements combine observations of the microwave, infrared, and visible energy from clouds, atmosphere and earth into a single measurement that can be used to analyze the physical mechanisms important for weather prediction and climate change. Signatures of clouds over snow-covered ground are revealed using reflectance and temperature data derived from these measurements. "In a visible image, both clouds and snow-covered terrain are highly reflective, so they're hard to tell apart," Paul Menzel explained. "In the infrared, cold clouds and cold terrain emit roughly the same thermal energy. Only with multispectral imaging can we hope to separate clouds from snow and ice-covered terrain." Cloud height measurements from the Cloud Lidar System (CLS) onboard the ER-2 can verify the position and thickness of clouds in the radiometric data. That data, when combined with the radiometric measurements, allows UW scientists to examine the underlying signature of the cloud itself.

The MAS and HIS data sets will receive particular attention at UW. Researchers have used MAS data as a tool to test the accuracy of algorithms ranging from sea surface temperature to cloud particle physics thanks to MAS's broad (visible to infrared) spectral coverage and high (50 meter) spatial resolution. UW researchers have also contributed to MAS development. For WINCE, MAS will provide visible and thermal images of clouds and the earth much in the same way that MODIS will on board a satellite beginning in 1998. Findings from MAS data will be used to directly improve the cloud detection capability of MODIS. Data from the HIS instrument, developed and built at SSEC, will provide precise detail of the earth-atmosphere system energy pattern through its interferometer technology. The HIS high spectral resolution data excels in unscrambling combined cloud, atmosphere and ground signal into its separate components. According to Bill Smith, "the combined HIS and MAS observations during the WINCE campaign will provide a preview of those to be achieved from NASA's Earth Observing System Satellites to be in orbit near the turn of the next century and beyond."

--Chris Moeller & Terri Gregory

Contact: Terri Gregory, 263-3373, terri.gregory@ssec.wisc.edu

Send corrections or suggestions for the WINCE Homepage to: wayne.feltz@ssec.wisc.edu

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