The Remote Atmospheric and Ionospheric Detection System (RAIDS) is new NASA experiment studying the Earth's
thermosphere and ionosphere from a vantage point on the International Space Station (ISS). RAIDS along with a
companion hyperspectral imaging experiment were launched in September 2009 to operate as the first US payload on the
Japanese Experiment Module-Exposed Facility. The scientific objectives of the RAIDS experiment are to study the
temperature of the lower thermosphere (100-200 km), to measure composition and chemistry of the lower thermosphere
and ionosphere, and to measure the initial source of O+ 83.4 nm emission. The RAIDS sensor complement includes
three photometers, three spectrometers, and two spectrographs which span the wavelength range 50-874 nm and scan or
image the atmospheric limb 90-300 km. After installation aboard the ISS, RAIDS underwent a 30-day checkout period
before entering science operations. RAIDS is serving as a pathfinder for atmospheric remote sensing from the ISS, and
the experiment team gained valuable operational insights using this space platform throughout the first year of the
mission. This paper describes key aspects of experiment performance relevant to interpreting RAIDS science data and
designing future atmospheric remote sensing experiments for the ISS.
This paper presents an analysis of the sensitivity changes experienced by three of the eight sensors that comprise
the Remote Atmospheric and Ionospheric Detection System (RAIDS) after more than a year operating on board
the International Space Station (ISS). These sensors are the Extreme Ultraviolet Spectrograph (EUVS) that
covers 550-1100 Å, the Middle Ultraviolet (MUV) spectrometer that covers 1900-3100Å, and the Near Infrared
Spectrometer (NIRS) that covers 7220-8740 Å. The scientific goal for RAIDS is comprehensive remote sensing of
the temperature, composition, and structure of the lower thermosphere and ionosphere from 85-200 km. RAIDS
was installed on the ISS Japanese Expansion Module External Facility (JEM-EF) in September of 2009. After
initial checkout the sensors began routine operations that are only interrupted for sensor safety by occasional
ISS maneuvers as well as a few days per month when the orbit imparts a risk from exposure to the Sun. This
history of measurements has been used to evaluate the rate of degradation of the RAIDS sensors exposed to an
environment with significant sources of particulate and molecular contamination. The RAIDS EUVS, including
both contamination and detector gain sag, has shown an overall signal loss rate of 0.2% per day since the start
of the mission, with an upper boundary of 0.13% per day attributed solely to contamination effects. This upper
boundary is driven by uncertainty in the change in the emission field due to changing solar conditions, and there
is strong evidence that the true loss due to contamination is significantly smaller. The MUV and NIRS have
shown stability to within 1% over the first year of operations.
Measurements of aerosol UV optical depths are described as part of an ongoing study of surface ultraviolet irradiances over the southwestern United States. Global UV irradiances are continuously monitored using a moderate-bandwidth radiometer (Biospherical, GUV-511), which has been in operation since June 1997. Irradiances at 305 and 320 nm are used to derive column ozone; erythemal doses are determined with the additional consideration of 340 and 380-nm irradiances. The clear sky relationship between ozone and UV dose is well characterized by a power law with an exponent that decreases with increasing solar zenith angle, from 1.12 to 0.99 between solar zenith angles of 20 and 60 degrees. Most recently, aerosol optical depths at 340 nm have been estimated using standard direct sun techniques applied to model corrected global measurements. These are compared with direct sun measurements (Solar Light, Microtops II) over a five-month period. Mean values agree well, but daily observations show differences in aerosol optical depths of up to 0.1, with direct sun measurements indicating larger variability. Aerosol optical depths inferred from global irradiances vary between a minimum of about 0.03 in winter and a maximum of 0.10 in summer.
A new spectrally precise approach to Schumann-Runge synthesis has been devised, employing nine (9) different spectral arrays containing polynomial coefficients. The coefficients were fit to calculated cross sections obtained from a detailed Schumann-Runge model that incorporates the most recent high resolution spectroscopic data for a temperature range between 130 and 500K. This large data base is being used to reexamine the existing parameterizations of UV transmission and photolysis. In addition, it is now possible to extend atmospheric radiance codes further into the ultraviolet. Initial implementation has been accomplished for the MODTRAN code as part of the eventual development of AURIC, the Atmospheric Ultraviolet Radiance Integrated Code.