This software reads MLS Level 1 products — the Earth Observing System (EOS) Microwave Limb Sounder (MLS) calibrated measurements of microwave radiance products and operational meteorological data — and produces a set of estimates of atmospheric temperature and composition. The software features are driven by the instrument and its unique capabilities to measure the atmospheric temperatures and composition at the Earth's limb. By careful and judicious choice of signal bands, and by dividing the computing into chunks and phases, scientifically useful products can be produced with wide spatial and temporal coverage. The software includes a highly developed forward model algorithm and an inverse model that makes efficient use of memory.

This version improves the Level 2 data products and adds a new standard product, methanol. One existing Level 2 standard product, N2O, has been replaced by a different product derived from a surviving signal. In v3, the ozone, CO, and HNO3 showed unphysical correlation with IWC (ice water content) in regions of thick clouds, requiring complex screening to exclude. Even after screening, the prior version (v2) was recommended for many scientific uses. Now, due to an improved algorithm, v4 has become the recommended version for these products.

The software to implement the algorithm has been written in the Fortran 95 programming language, chosen because of its great suitability to handling the complex matrix and vector entities involved. The program was designed to be as flexible as possible, and is controlled by a Level 2 Configuration File that controls all aspects of the software, defining the contents of state and measurement vectors, defining the configurations of the various forward models available, reading appropriate a priori spectroscopic and calibration data, performing retrievals, post-processing results, computing diagnostics, and outputting results in appropriate files. In production mode, the software operates in a parallel form, with one instance of the program acting as a master, coordinating the work of multiple slave instances on a cluster of computers, each computing the results for individual chunks of data.

In addition to doing conventional retrieval calculations producing geophysical products, the Level 2 Configuration File can instruct the software to produce files of simulated radiances based on a state vector formed from a set of geophysical product files taken as input. Combining both the retrieval and simulation tasks in a single piece of software makes it far easier to ensure that identical forward model algorithms and parameters are used in both tasks, and dramatically reduces the complexity of the code maintenance effort.

This work was done by Nathaniel J. Livesey, William V. Snyder, William G. Read, Michael J. Schwartz, Alyn Lambert, Michelle L. Santee, Luis F. Millan, Lucien Froidevaux, Shuhui Wang, and Paul A. Wagner of Caltech; Gloria L. Manney of Northwest Research Associates; Christina Vuu of Raytheon; and Hugh C. Pumphrey of the University of Edinburgh for NASA's Jet Propulsion Laboratory. This software is available for license through the Jet Propulsion Laboratory, and you may request a license here . NPO-49802


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This article first appeared in the February, 2018 issue of Tech Briefs Magazine.

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