HIRDLS Level 1 to 2 Pre and Post Retrieval Data Processing

The HIRDLS infrared limb-scanning radiometer onboard the NASA EOS Aura satellite was launched in July of 2004. The depressurization during launch caused some kapton insulation to drape over a significant portion of the aperture. This incident caused modifications to the ground data processing system as discussed below. The HIRDLS instrument is designed to sound the upper troposphere, stratosphere, and mesosphere measuring 10 atmospheric species (O3, H2O, CH4, NO2, N2O5, HNO3, CFC11, CFC12, N2O, and ClONO2) along with temperature, pressure, geopotential height, aerosols in 4 spectral regions, and the locations of PSCs and cloud tops. The HIRDLS ground data processing system converts instrument telemetry into geophysical parameters. There are two major processing steps in going from L0 telemetry to L2 standard products: the L1 (L0 to L1) processor and the L2 (L1 to L2) processor. The L1 processor, being developed by Oxford University and the National Center for Atmospheric Research in Boulder, Colorado, converts raw counts into engineering units and calibrates and geolocates radiance signals. This processor bore a majority of the changes due to the kapton incident. Changes to the L2 were less extensive as discussed below. The L2 processor is being developed in Boulder, Colorado as a joint effort of the University of Colorado and the National Center for Atmospheric Research. The HIRDLS L2 software system converts calibrated radiances into geophysical quantities and is composed of the L2 Preprocessor and the L2 Processor, developed in C++ and Fortran90 respectively. Here we describe in more detail the subsystems of the L2 processor and the pre- and post-processing needed in standard L2 product generation. This includes the data preparation for the retrieval (geolocating ancillary data, preparation of a-priori and climatology inputs, performing the line of sight gridding, filling all data structures as required by the retrieval algorithm) and the post processing of retrieval output (transforming from a vertical altitude grid to a pressure grid as specified for Aura Level 2 products). The kapton incident resulted in the addition of GMAO data to the retrieval and changes to the line of sight gridding. This results in the final Level 2 HIRDLS product which is currently being validated.