This software is an improvement on Version 2, which was described in “EOS MLS Level 1B Data Processing, Version 2.2,” NASA Tech Briefs, Vol. 33, No. 5 (May 2009), p. 34. It accepts the EOS MLS Level 0 science/engineering data, and the EOS Aura spacecraft ephemeris/attitude data, and produces calibrated instrument radiances and associated engineering and diagnostic data. This version makes the code more robust, improves calibration, provides more diagnostics outputs, defines the Galactic core more finely, and fixes the equator crossing.
The Level 1 processing software manages several different tasks. It qualifies each data quantity using instrument configuration and checksum data, as well as data transmission quality flags. Statistical tests are applied for data quality and reasonableness. The instrument engineering data (e.g., voltages, currents, temperatures, and encoder angles) is calibrated by the software, and the filter channel space reference measurements are interpolated onto the times of each limb measurement with the interpolates being differenced from the measurements. Filter channel calibration target measurements are interpolated onto the times of each limb measurement, and are used to compute radiometric gain. The total signal power is determined and analyzed by each digital autocorrelator spectrometer (DACS) during each data integration. The software converts each DACS data integration from an autocorrelation measurement in the time domain into a spectral measurement in the frequency domain, and estimates separately the spectrally, smoothly varying and spectrally averaged components of the limb port signal arising from antenna emission and scattering effects. Limb radiances are also calibrated.
The radiance at the limb port of the radiometer module is computed, including non-atmospheric radiance contributions from antenna emission and scattering. It is the task of the retrieval/forward model software (Level 2) to compute the atmospheric component of the limb radiation reaching this interface. It is necessitated by the greatly increased bandwidth of EOS MLS radiometers, and the double-sideband nature of most measurements. Estimates of the random component of uncertainty (noise) on each limb radiance are also determined. Spacecraft inertial pointing and star tracker data are combined with spacecraft and GHz antenna structural/thermal data and scan mechanism encoder data to estimate the boresight angles for each radiometer. The software collects and generates ancillary data (e.g., tangent point location, local solar time, local solar zenith angle, flags for bright objects in the field of view) that are needed in Level 2 processing. A log file is produced that summarizes instrument performance and outputs.