Funded by NASA's Office of Commercial Programs, the ATLAS (Airborne Terrestrial Applications Sensor) is a 15-channel multispectral imager for remote sensing applications under development at the Stennis Space Center (MS). This paper describes the overall ATLAS system design, functional sub-systems, and projected sensor performance characteristics (SNR, NETD, etc). In order to satisfy a variety of applications, both wide spectral coverage (0.45 - 12.2 micrometers ), as well as variable spatial resolution (2 - 25 m), are provided. The optics train includes a linescan mirror, Dall-Kirkham telescope, and three spectrometers. The ATLAS sensor package has a 7.5-inch entrance aperture, 2.0 mrad ifov, total field of view of 73 degree(s), and scan rates of 6 - 50 rev/sec. The spectrometer channels are divided as follows: VIS/NIR, 6 channels: 0.45 - 0.90 micrometers ; SWIR/MWIR, 3 channels: 1.55 - 4.20 micrometers ; and TIR, 6 channels: 8.2 - 12.2 micrometers . The ATLAS system combines the functionality of the TIMS (Thermal Infrared Multispectral Scanner) and the CAMS (Calibrated Airborne Multispectral Scanner), currently deployed, calibrated, and maintained by the Advanced Sensor Development Laboratory at Stennis Space Center. The major optical sub- systems, radiometric calibration sources, signal conditioning electronics, and other functions, will be described. ATLAS system specifications will also be presented.