Robert Paul Loughman

Comparison of radiative transfer models for limb‐viewing scattered sunlight measurements

[1] This study compares the limb scattered radiances calculated by six radiative transfer models for a variety of viewing conditions. Atmospheres that include molecular scattering, aerosol scattering, and ozone absorption are considered. All models treat single scattering accurately in full spherical geometry. Two ‘‘approximate spherical’’ models (CDI and LIMBTRAN) rely on the plane-parallel atmosphere approximation to calculate the diffuse radiance field; the remaining four ‘‘spherical’’ models (Siro, MCC++, GSLS, and CDIPI) treat multiple scattering in a spherical atmosphere. Only three of the models (Siro, MCC++, and GSLS) have vector treatment with polarization. A brief comparison of vector radiances with the limb scattered radiances measured by the SOLSE and LORE instruments demonstrates agreement usually within 15% and always within 30%. The inclusion of polarization appears to have little effect on the level of agreement among the models (which agree to within 2% for this sample case). A more general comparison among calculated scalar radiances follows, including four solar zenith angles (20� ,6 0� , 80� , and 90� ), three relative azimuth angles (20� ,9 0� , and 160� ), and two surface albedos (0 and 0.95). The single scattered radiances agree to within 1% for almost every case. Comparisons of the total radiance show larger differences, with 2–4% spread among the results of the spherical models. The approximate spherical models show a positive radiance difference relative to the other models that increases with tangent height, reaching as much as 8% at 60 km. The rule used to divide the model atmosphere into discrete layers is shown to affect the calculated radiance, causing a height-dependent difference of up to 1% for 1 km layer thickness. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0669 Electromagnetics: Scattering and diffraction; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; KEYWORDS: radiative transfer, limb scattering, model comparison

The OMPS Limb Profiler Environmental Data Record Algorithm Theoretical Basis Document and Expected Performance

The retrieval algorithm for the Suomi National Polar-Orbiting Partnership (NPP) Ozone Mapping and Profiler Suite (OMPS) Limb Profiler is described. The goal of the OMPS Limb Profiler is to produce high quality vertical profiles of ozone in the stratosphere and upper troposphere. Additional products include aerosol extinction vertical profiles together with an estimate of the Angstrom coefficient, cloud top height and

Errors resulting from assuming opaque Lambertian clouds in TOMS ozone retrieval

\hbox{NO}_{2}

Stratospheric and upper tropospheric aerosol retrieval from limb scatter signals

column density. The ozone retrieval algorithm relies on the optimal estimation approach, and uses the Pair/Triplet methodology. Estimates of bias and random errors are presented, together with a brief description of the operational code output products and the planned validation.

Data analysis and retrieval algorithms for the Ozone Mapping and Profiler Suite / Limb Profiler instrument

Abstract Accurate remote sensing retrieval of atmospheric constituents over cloudy areas is very challenging because of insufficient knowledge of cloud parameters. Cloud treatments are highly idealized in most retrieval algorithms. Using a radiative transfer model treating clouds as scattering media, we investigate the effects of assuming opaque Lambertian clouds and employing a Partial Cloud Model (PCM) on Total Ozone Mapping Spectrometer (TOMS) ozone retrievals, especially for tropical high-reflectivity clouds. Assuming angularly independent cloud reflection is good because the Ozone Retrieval Errors (OREs) are within 1.5% of the total ozone (i.e., within TOMS retrieval precision) when Cloud Optical Depth (COD)⩾20. Because of Intra-Cloud Ozone Absorption ENhancement (ICOAEN), assuming opaque clouds can introduce large OREs even for optically thick clouds. For a water cloud of COD 40 spanning 2– 12 km with 20.8 Dobson Unit (DU) ozone homogeneously distributed in the cloud, the ORE is 17.8 DU in the nadir view. The ICOAEN effect depends greatly on solar zenith angle, view zenith angle, and intra-cloud ozone amount and distribution. The TOMS PCM is good because negative errors from the cloud fraction being underestimated partly cancel other positive errors. At COD⩽5, the TOMS algorithm retrieves approximately the correct total ozone because of compensating errors. With increasing COD up to 20–40, the overall positive ORE increases and is finally dominated by the ICOAEN effect. The ICOAEN effect is typically 5–13 DU on average over the Atlantic and Africa and 1–7 DU over the Pacific for tropical high-altitude (cloud top pressure ⩽300 hPa ) and high-reflectivity (reflectivity ⩾ 80%) clouds. Knowledge of TOMS ozone retrieval errors has important implications for remote sensing of ozone/trace gases from other satellite instruments.

Retrieval of atmospheric ozone and nitrogen dioxide vertical distribution from SAGE III limb scattering measurements

Solar occultation observations made by the SAGE family of space instruments have provided a record of global stratospheric and upper tropospheric aerosols that extends over 25 years. Since the demise of SAGE II and SAGE III however, there are presently no space instruments devoted to continuing this aerosol data set. The paper aims to demonstrate that aerosol extinction profiles, together with a moment of the size distribution, can be accurately retrieved from Limb Scatter measurements. The methodology is described, and retrieval examples are presented using data from a Limb Scatter instrument, namely SAGE III. The retrieved extinction profiles are compared with SAGE II and SAGE III occultation aerosol products for a series of wavelengths. It is shown that the relative retrieval accuracy is good (less than 5%), with a relative precision on the order of 25%. Once operational, it is planned to apply the retrieval method to the data collected by the two still-operating Limb Scatter instruments (namely OSIRIS and SCIAMACHY) in order to extend the aerosol data record into the present time. In the future, the OMPS Limb Profiler instrument, which is presently manifested on NPP with a launch date of September 2009, will be used for additional stratospheric aerosol research.

Retrievals from the Limb Ozone Retrieval Experiment on STS107

Three candidate algorithms for the retrieval of ozone profile for the NPP OMPS Limb Profiler are described. The first one relies on the well established Doublet/Triplet method coupled with Optimal Estimation. The second one performs spectral fitting and uses Multiple Linear Regression. The last one is a direct application of the Optimal Estimation method on the actual CCD array measurements. The fundamentals of each technique are reviewed and their advantages/disadvantages are discussed. Sample results are given to illustrate the performance of each method.

Ozone Retrieval from SAGE III Limb Scattering measurement

The limb scattering radiances measured by SAGE III are analyzed. After accounting for instrument issues, ozone and nitrogen dioxide vertical density profiles are retrieved from the data and compared with results from other instruments. These initial results are very promising and show the potential of SAGE III to operate in this mode.

Description and sensitivity analysis of a limb scattering ozone retrieval algorithm

The Ozone Mapping Profiler Suite will produce ozone profiles using the limb scatter technique. While this technique has been used in the 1980s for mesospheric retrievals with data from the Solar Mesospheric Explorer, its use for the stratosphere and upper troposphere is relatively recent. To increase the scientific experience with this method, the Limb Ozone Retrieval Experiment LORE was flown on-board STS107 in 2003. A significant amount of data from thirteen orbits was down-linked during the mission and exists for analysis. LORE was an imaging filter radiometer, consisting of a linear diode array, five interference filters (plus a blank for dark current) and a simple telescope with color correcting optics. The wavelengths for the channels were 322, 350, 602, 675 & 1000 nm and can be viewed as a minimum set of measurements needed for ozone profiling from 50 km to 10 km. The temporal sampling of the channels, along with the shuttle orbital and attitude (e.g. pitch) motions present a challenge in retrieving precise ozone profiles. Presented are the retrieval algorithms for determination of the channels altitude scale, cloud top height and aerosol extinction. Also shown are a sub-set of flight data and the corresponding retrieved ozone profiles.

SCIAMACHY stratospheric aerosol extinction profile retrieval using the OMPS/LP algorithm

Atmospheric Ozone concentration is retrieved from SAGE III measurement of the Earth limb scattering radiation. Retrieval algorithm is described and sample data is presented