Multiwavelength imaging photometer for the topside observation of gravity waves

Abstract

An imaging instrument is being developed for the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. This instrument images the small, few km scale structure of the earth airglow. The measurement permits the remote sensing of the temperature and intensity fluctuations produced by atmospheric gravity waves propagating through the mesopause region. Instrument modules look in the nadir direction to observe the fine structure of the airglow. Other modules look at the limb in the satellite orbit plane to monitor the limb altitude profiles. The measurement is performed by observing the rotational temperature of the 02(0,0) band at 762 nm in nadir and limb. The waves also modulate the airgiow intensity and the instrument will record the modulations of the 02(0,0), 02(0,1) and OH emissions in the nadir. The nadir channels of the instrument use a wide angle telecentric imager in which the distortion of the image is closely controlled so that the motion of the satellite can be compensated during the extended integration time by Time Delayed Integration (TDI) mode of scanning of the CCD. The TDI method requires the CCD pixel columns to be aligned parallel with the orbital velocity vector and the shifting of the rows to be synchronized with the satellite motion. Through TDI scanning the imager can stare at a target at atmospheric altitude for an extended exposure dui'ation. Each telecentric instrument module contains a single filter, and adjacent wavelength bands are imaged simultaneously by passing the light through the filter at different angles. The limb imagers use CCD-s in the frame transfer mode.