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Liu X.,University of Maryland, Baltimore | Liu X.,Harvard - Smithsonian Center for Astrophysics | Liu X.,NASA | Bhartia P.K.,NASA | And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2010

Ozone profiles from the surface to about 60 km are retrieved from Ozone Monitoring Instrument (OMI) ultraviolet radiances using the optimal estimation technique. OMI provides daily ozone profiles for the entire sunlit portion of the earth at a horizontal resolution of 13 km×48 km for the nadir position. The retrieved profiles have sufficient accuracy in the troposphere to see ozone perturbations caused by convection, biomass burning and anthropogenic pollution, and to track their spatiotemporal transport. However, to achieve such accuracy it has been necessary to calibrate OMI radiances carefully (using two days of Aura/Microwave Limb Sounder data taken in the tropics). The retrieved profiles contain ∼6-7 degrees of freedom for signal, with 5-7 in the stratosphere and 0-1.5 in the troposphere. Vertical resolution varies from 7-11 km in the stratosphere to 10-14 km in the troposphere. Retrieval precisions range from 1% in the middle stratosphere to 10% in the lower stratosphere and troposphere. Solution errors (i.e., root sum square of precisions and smoothing errors) vary from 1-6% in the middle stratosphere to 6-35% in the troposphere, and are dominated by smoothing errors. Total, stratospheric, and tropospheric ozone columns can be retrieved with solution errors typically in the few Dobson unit range at solar zenith angles less than 80°.

Efremenko D.S.,German Aerospace Center | Loyola D.G.,German Aerospace Center | Doicu A.,German Aerospace Center | Spurr R.J.D.,RT Solutions Inc.
Computer Physics Communications | Year: 2014

The operational processing of remote sensing data usually requires high-performance radiative transfer model (RTM) simulations. To date, multi-core CPUs and also Graphical Processing Units (GPUs) have been used for highly intensive parallel computations. In this paper, we have compared multi-core and GPU implementations of an RTM based on the discrete ordinate solution method. To implement GPUs, the original CPU code has been redesigned using the C-oriented Compute Unified Device Architecture (CUDA) developed by NVIDIA. GPU memory management is a crucial issue regarding the performance. To cope with limitations of GPU registers, we have adapted an RTM based on the matrix operator technique together with the interaction principle for multilayer atmospheric systems. The speed-up of such an implementation depends on the number of discrete ordinates used in the RTM. To reduce the CPU/GPU communication overhead, we have exploited the asynchronous data transfer between host and device. To obtain optimal performance, we have also used overlapping of CPU and GPU computations by distributing the workload between them. With GPUs, we have achieved a 20x-40x speed-up for the multi-stream RTM, and 50x speed-up for the two-stream RTM with respect to the original single-threaded CPU codes. Based on these performance tests, an optimal workload distribution scheme between GPU and CPU is proposed. Additionally, CPU/GPU benchmark tests regarding basic matrix operations are given. Finally, we discuss the performance obtained with the multi-core-CPU and GPU implementations of the RTM. © 2014 Elsevier B.V.

Liu X.,University of Maryland, Baltimore | Liu X.,Harvard - Smithsonian Center for Astrophysics | Liu X.,NASA | Bhartia P.K.,NASA | And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2010

We validate OMI ozone profiles between 0.22-215 hPa and stratospheric ozone columns down to 215 hPa (SOC215) against v2.2 MLS data from 2006. The validation demonstrates convincingly that SOC can be derived accurately from OMI data alone, with errors comparable to or smaller than those from current MLS retrievals, and it demonstrates implicitly that tropospheric ozone column can be retrieved accurately from OMI or similar nadir-viewing ultraviolet measurements alone. The global mean biases are within 2.5% above 100 hPa and 5-10% below 100 hPa; the standard deviations of the differences (1Ï) are 3.5-5% between 1-50 hPa, 6-9% above 1 hPa and 8-15% below 50 hPa. OMI shows some latitude and solar zenith angle dependent biases, but the mean biases are mostly within 5% and the standard deviations are mostly within 2-5% except for low altitudes and high latitudes. The excellent agreement with MLS data shows that OMI retrievals can be used to augment the validation of MLS and other stratospheric ozone measurements made with even higher vertical resolution than that for OMI. OMI SOC215 shows a small bias of 0.6% with a standard deviation of 2.8%. When compared as a function of latitude and solar zenith angle, the mean biases are within 2% and the standard deviations range from 2.1 to 3.4%. Assuming 2% precision for MLS SOC215, we deduce that the upper limits of random-noise and smoothing errors for OMI SOC215 range from 0.6% in the southern tropics to 2.8% at northern middle latitudes.

Vasilkov A.,Science Systems And Applications Inc. | Joiner J.,NASA | Spurr R.,RT Solutions Inc.
Atmospheric Measurement Techniques | Year: 2013

Quantifying the impact of rotational-Raman scattering (RRS) on the O 2 A- and B-bands is important as these bands can be used for cloud and aerosol characterization for trace-gas retrievals including CO2 and CH4. In this paper, we simulate the spectral effects of RRS for various viewing geometries and instruments with different spectral resolutions. We also examine how aerosols affect the amount of RRS filling-in. We show that the filling-in effects of RRS are relatively small, but not negligible, in these O2absorption bands, particularly for high-spectral-resolution instruments. For comparison, we also compare and contrast the spectral signatures of RRS with those of terrestrial chlorophyll fluorescence. © Author(s) 2013.

Rault D.F.,NASA | Spurrb R.,RT Solutions Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

An alternative algorithm is being developed to retrieve ozone vertical distribution information from the OMPS/LP sensor which will be manifested on the upcoming NPOESS Preparatory Project (NPP) platform in late 2011. In contrast to most limb sensors retrieval methods, the proposed algorithm will forgo the spherical symmetry assumption for the atmospheric structure, and will attempt to simultaneously retrieve the ozone distribution in both the vertical and the along-track directions. The paper describes the two-dimensional forward model as well as the methods which have been developed to simultaneously retrieve a whole orbit of data. Sample retrieval results are shown to illustrate the technique.© 2010 SPIE.

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