Imaging the Earth's surface through the atmosphere presents many challenges. But the launch Oct. 31 of a satellite carrying an advanced multispectral thermal imager could overcome them. The instrument's 15-band sensor system is designed to correct for atmospheric conditions and to achieve improved radiometric accuracy. The instrument has spectral bands ranging from blue to long-wave infrared and can correct for atmospheric water vapor, aerosols and thin clouds at the same spatial resolution as the infrared imaging bands, said Paul G. Weber, leader of the space and remote sensing sciences group at the US Department of Energy's Los Alamos National Laboratory. That will provide greater capability compared with other eyes in the sky that rely on fewer spectral bands. Spot 4 uses three bands to obtain an image, while Landsat uses seven. Hughes Research Laboratories in Santa Barbara, Calif., built the focal plane array using three sensor chip assemblies with 12.5- and 50-µm pixels. The detectors are made of Si, InSb and HgCdTe. The instrument gathers light via a three-mirror anastigmat optical assembly built by Hughes Danbury Optical Systems in Danbury, Conn. Easy interpretation Each pixel in the detector array captures light from a fixed amount of ground below, known as the ground-sampling distance. Depending on the wavelength, the multispectral imager will have a ground-sampling distance of between 5 and 20 meters, with the smaller ground-sampling distance in the visible range. That compares with 10 to 20 meters for Spot. Once launched, the satellite will follow a sun-synchronous orbit around the poles, putting it at any given point at about the same local time every day. This will enable data to be interpreted more easily because the angle of light from the sun changes only slightly from day to day. Ground crews will check the on-board ability to correct for atmospheric conditions by correlating images to conditions they observe at target sites. The instrument will be turned to a variety of imaging jobs, including industrial facilities, lakes and national parks. It will provide data on surface temperature, water quality and the health of vegetation. "We might be looking at the level of stress in vegetation due to adjacent industrial activity," Weber said. Through these practical jobs, the Department of Energy hopes to gather information about imaging that can be used in future systems to detect weapons facilities.