Near Infrared Spectroscopy and Photometry of the Thermosphere from the RAIDS Experiment on the International Space Station

The RAIDS experiment is a suite of eight instruments to be flown aboard the Japanese Experiment Module-Exposed Facility on the International Space Station (ISS) in 2009. Originally designed, built, and integrated onto the NOAA TIROS-J satellite in 1993, the original RAIDS hardware and the mission objectives have been modified for this ISS flight opportunity. A spectrometer and three photometer instruments, operating in a limb scanning geometry, will be used to observe the near infrared spectral radiance of atomic and molecular emission from the Earth’s upper atmospheric airglow. The passbands of the photometers are centered on the atomic lines OI(777.4), OI[630.0], and the 0-0 band of O2 Atmospheric at 765 nm. The spectrometer scans from 725 to 870 nm. These observations will be used in conjunction with the other RAIDS instruments to investigate the properties of the lower thermosphere and to improve understanding of the connections of the region to the space environment, solar energy flux and the lower atmosphere. Specification of the temperature in the lower thermosphere is a major objective of the RAIDS experiment. The NIR set of instruments will be expected to provide a measure of thermospheric temperature from approximately 100 km to 250 km altitude using the spectral distribution of the O2(0-0) Atm band. We will present our photochemical simulation model used to predict the performance of the instruments and to estimate the accuracy to which atmospheric state variables can be specified. The model includes an approach for measurement of the neutral [O2] density profile, a quantity that is difficult to extract from FUV emission spectra as demonstrated on the TIMED GUVI mission. We estimate the probable errors in the specification of [O2] and its variability throughout the lower thermosphere based on anticipated RAIDS data. The model also predicts the surface brightness, expected backgrounds and counting statistics for the photometric measurement of the atomic emissions OI[630], OI(777.4), OII(7320-30), and OI(844.6) in the NIR. Comparisons with previous spectrographic missions will be discussed. The launch of the RAIDS payload is expected in early September, 2009 and we anticipate that on-orbit spectra will be available for this presentation. We will then be able to validate our modeling efforts and provide new insights into the properties of the lower thermosphere.