Ozone Mapping and Profiler Suite (OMPS)
The Ozone Mapping and Profiler Suite (OMPS) instrument will provide the long-term stratospheric ozone monitoring capability for the Joint Polar Satellite System (JPSS). It consists of two nadir-viewing instruments to provide ozone total column and low-resolution profile information, as well as a limb profiler (LP) designed to measure the ozone profile at ~2-3 km vertical resolution. The OMPS/LP will measure limb-scattered solar radiation in the wavelength range from 290 to 1000 nm to retrieve the ozone profile between the tropopause and 60 km. This data set will provide continuity for the long time-series ozone profile measurements that have been made for the past 30 years by a variety of NASA and other instruments (including POAM). OMPS-like ozone data are needed for developing and testing the extensions to global weather forecast models such as the Navy Global Ocean-Atmosphere Predictions System (NOGAPS).
CPI has been working for a number of years on alternative retrieval algorithms for the OMPS/LP, with funding from the NPOESS Internal Government Studies (IGS) program in collaboration with NRL. This effort has resulted in a completely independent research-grade Environmental Data Record (EDR) algorithm that will be used to help validate and test the operational OMPS algorithms developed by NASA. The goal is to address those areas that are not thoroughly examined and/or covered in the OMPS System Specification. These areas include: accurate aerosol inversions, minor species retrievals (NO2), stray light mitigation, and detailed retrieval characterization. The CPI algorithm has reached a significant level of maturity and has been used extensively to test combined ozone/aerosol retrievals from the LP, and their sensitivity to important error sources such as surface albedo uncertainties, altitude errors and aerosol feedback. CPI intends to use this code to process the OMPS/LP data when it becomes available, and compare results with the operational retrievals.
The OMPS/LP sensor is a six-slit prism spectrometer. Light entering each slit is dispersed by a prism and focused onto a portion of a single, two-dimensional (740×340) charged-coupled device (CCD) focal-plane array, covering a spectral range from 290 to 1000 nm and a nominal altitude range of 0 to 65 km. Stray light originating from bright regions of the LP CCD (corresponding to wavelength/altitude regions of the atmosphere with high radiance) can easily contaminate low-signal regions, with the potential to affect the quality of the data products. Stray light contamination adversely affects most pixels and is scene-dependent. It must be adequately accounted for in the data processing if the sensor is to achieve the design accuracy for the ozone environmental data record (EDR).
CPI has developed a detailed and realistic instrument model (IM) for the Limb Profiler. This model is capable of mapping a given atmospheric scene into a very realistic simulation of CCD pixel maps exactly as they will be sampled by the OMPS instrument on orbit. It has been used extensively to explore various approaches for removing instrument stray light from the OMPS data, and has also been made available to scientists at NOAA and NASA as a valuable tool in aiding the development of the operational OMPS sensor data record (SDR) algorithms. The approach models the stray light in the forward direction as part of the EDR algorithm, to fit the raw pixel counts from the OMPS detector. This is in sharp contrast to the traditional approach (used by the operational algorithms) where stray light is removed in pre-processing via deconvolution, or some other process, that is often ill-posed and unstable. The logic flow diagram below illustrates the approach. Further details can be found in the report cited below.
Eden, T. D., J. D. Lumpe, and J. S. Hornstein, 2012: An Alternative Retrieval Algorithm for the Ozone Mapping and Profiler Suite Limb Profiler, NRL Memorandum Report, Report No. NRL/MR/7220--12-9409, pp. 29, Naval Research Laboratory, Washington, DC 20375-5320.