Data analysis for the Microwave Limb Sounder instrument on the EOS Aura Satellite
by
Van Snyder
Jet Propulsion Laboratory, California Institute of Technology

A brief discussion of the goals of the Microwave Limb Sounder (MLS) instrument on NASA's Earth Observing System (EOS) Aura satellite, which was launched on 15 July 2004, is followed by a discussion of the organization and mathematical methods of the software used for analysis of data received from that instrument.

The MLS instrument measures microwave thermal emission from the atmosphere by scanning the earth's limb 3500 times per day. The limb tangent altitude varies from 8 to 80 km. Roughly 600 million measurements in five spectral bands are returned every day. From these, estimates of the concentration of approximately 20 trace constituents, and temperature, are formed at 70 pressure levels on each of these scans - altogether roughly 5 million results per day. The program is organized to process "chunks" consisting of about 20 scans, with a five-scan overlap at both ends of the chunk, giving 350 chunks per day. Each chunk requires about 15 hours on a 3.6 GHz Pentium Xeon workstation. Although one chunk can be processed on a workstation, processing all of the data requires the attention of 350 such processors.

The software is an interpreter of a "little language, " as described in April 2008 Software: Practice and Experience. This confers substantial benefits for organization, development, maintenance and operation of the software. Most importantly, it separates the responsibilities, and the requirements for expertise, of the software engineers who develop and maintain the software, from the scientists who configure the software.

Mathematically, the problem consists of tracing rays through the atmosphere, roughly corresponding to limb views of the instrument. The radiative transfer equation, together with variational equations with respect to the parameters of interested, are then integrated along these rays. A Newton method is then used to solve for the parameters of interest.

Date received: April 2, 2008