The Ozone and Mapping Profiler Suite (OMPS) is an instrument suite in the National Polar-orbiting Operation Environmental Satellite System (NPOESS). The OMPS instrument is designed to globally retrieve both total column ozone and ozone profiles. To do this, OMPS consists of three sensors, two Nadir Instruments and one Limb Instrument. Each OMPS sensor has an End-to-End Model (ETEM) developed using the Toolkit for Remote Sensing, Analysis, Design, Evaluation, and Simulation (TRADES), a Ball Aerospace proprietary set of software tools developed in Matlab. The end-to-end modeling activities, which includes a radiative transfer model, the ETEM, and retrieval algorithms, have three fundamental objectives: sensor performance validation, aid in algorithm development, and algorithm robustness validation. The end-to-end modeling activities are key to showing sensor performance meets the system level Environmental Data Record (EDR) requirements. To do this, the ETEM incorporates sensor data; including point spread functions, stray light, dispersion, bandpass, and focal plane array (FPA) noise parameters. The sensor model characteristics are first implemented with predictions and updated as component test data becomes available. To evaluate the system’s EDR performance, the input radiance derived from the radiative transfer model is entered into the ETEM, which outputs a simulated image. The retrieval algorithms process the simulated image to determine the ozone amount. The system level EDR performance is determined by comparing the retrieved ozone amount with the truth, which was entered into the forward model. Additionally, the ETEM aids the algorithm development by simulating the expected sensor and calibration data with the expected noise characteristics. Finally, the algorithm robustness can be validated against extreme conditions using the ETEM.
The Ozone Mapping and Profiler Suite (OMPS) nadir sensor and algorithms for the United States National Polar-orbiting Operational Environmental Satellite System (NPOESS) comprise a system to map ozone total column globally in 24 hours and to measure the altitude distribution of ozone in the upper stratosphere (30-50 km). The sensor consists of a wide field (110 degree) telescope and two spectrometers: an imager covering 300 to 380 nm with a 50 km nadir footprint for mapping total column ozone across a 2800 km swath, and a 250 to 310 nm spectrometer with a single 250 km footprint to provide ozone profile data with SBUV/2 heritage. Both spectrometers provide 1 nm resolution (full-width at half-maximum, FWHM) spectra. The sensitivity of the OMPS total column algorithm to sensor random and systematic errors is analyzed, and a preliminary evaluation of the potential for deriving concentrations of other trace gases from the calibrated spectral radiances is provided.
One of the objectives of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) program is to continue the long-term data set of total column ozone measurements from the Total Ozone Mapping Spectromenter (TOMS) systems while providing the increased accuracy and precision required by the NPOESS Integrated Program Office (IPO). In developing an Ozone Mapping and Profiler Suite (OMPS) sensor-algorithm system to meet the NPOESS requirements, we systematically analyzed the performance of the TOMS system and determined that it provided a strong starting point for the design of the OMPS system. In fact, our analysis showed that modern TOMS systems meet the NPOESS accuracy requirements for retrievals below 475 Dobson Units (DU). However, the NPOESS precision requirements are met only for retrievals below 225 DU. In order to meet the NPOESS accuracy and, particularly, precision requirements for all total column ozone amounts, we identified areas where improvements in the heritage design lead to the improved performance needed for the OMPS system. Simulations performed using the OMPS system design confirm that the algorithm enhancements, coupled with improvements contained in the OMPS sensor, provide performance that meets the NPOESS IPO requirements.
We evaluate the effects of possible enhancements of the current (version 1) TOMS surface UV irradiance algorithm. The major enhancements include more detailed treatment of tropospheric aerosols, effects of diurnal variation of cloudiness and improved treatment of snow/ice. The emphasis is on the comparison between the results of the version 1 TOMS UV algorithm and each of the changes proposed. TOMS UV algorithm does not discriminate between nonabsorbing aerosols and clouds. Absorbing aerosols are corrected by using the TOMS aerosol index data. The treatment of aerosol attenuation might have been improved by using newly derived TOMS products: optical depths and the single-scattering albedo for dust, smoke, and sulfate aerosols. We evaluate different approaches for improved treatment of pixel average cloud attenuation, with and without snow/ice on the ground. In addition to treating clouds based only on the measurements at the local time of the TOMS observations, the results from other satellites and weather assimilation models can be used to estimate attenuation of the UV irradiance throughout the day. The improved (version 2) algorithm will be applied to reprocess the existing TOMS UV data record (since 1978) and to the future satellite sensors (e.g., Quik/TOMS, GOME, OMI on EOS/Aura and Triana/EPIC).
The Total Ozone Mapping Spectrometer (TOMS) ozone measurement is derived by comparing measured backscattered ultraviolet (BUV) radiances with theoretical radiances which are pre- computed using standard climatological ozone profiles and stored in a look-up table. Profile shape errors occur in this algorithm at high latitudes (or more specifically, high optical path lengths) when the actual vertical ozone distribution differs significantly from the standard profile used in constructing the tables. These errors are estimated using sensitivities derived from radiative transfer calculations and measurements of the actual ozone profile from Solar Backscatter Ultraviolet (SBUV) and Balloonsonde. These estimates include a short term uncertainty with a standard deviation of 10% in total column ozone amount as well as a systematic error in the long-term trend at very high solar zenith angles. At the maximum retrieval solar zenith angle of 88 degrees, these calculations indicate that TOMS long-term ozone depletions are over-estimated by 5%/decade.