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Chang C.-I.,University of Maryland Baltimore County | Chang C.-I.,National Chung Hsing University | Wu C.-C.,Innovim | Lo C.-S.,National formosa University | And 2 more authors.
IEEE Transactions on Geoscience and Remote Sensing | Year: 2010

The simplex growing algorithm (SGA) was recently developed as an alternative to the N-finder algorithm (N-FINDR) and shown to be a promising endmember extraction technique. This paper further extends the SGA to a versatile real-time (RT) processing algorithm, referred to as RT SGA, which can effectively address the following four major issues arising in the practical implementation for N-FINDR: 1) use of random initial endmembers which causes inconsistent final results; 2) high computational complexity which results from an exhaustive search for finding all endmembers simultaneously; 3) requirement of dimensionality reduction because of large data volumes; and 4) lack of RT capability. In addition to the aforementioned advantages, the proposed RT SGA can also be implemented by various criteria in endmember extraction other than the maximum simplex volume. © 2009 IEEE.

Ziemke J.R.,Morgan State University | Ziemke J.R.,NASA | Olsen M.A.,Morgan State University | Olsen M.A.,NASA | And 15 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2014

Measurements from the Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS), both on board the Aura spacecraft, have been used to produce daily global maps of column and profile ozone since August 2004. Here we compare and evaluate three strategies to obtain daily maps of tropospheric and stratospheric ozone from OMI and MLS measurements: trajectory mapping, direct profile retrieval, and data assimilation. Evaluation is based on an assessment that includes validation using ozonesondes and comparisons with the Global Modeling Initiative (GMI) chemical transport model. We investigate applications of the three ozone data products from near-decadal and interannual time scales to day-to-day case studies. Interannual changes in zonal mean tropospheric ozone from all of the products in any latitude range are of the order 1-2 Dobson units while changes (increases) over the 8 year Aura record investigated vary by 2-4 Dobson units. It is demonstrated that all of the ozone products can measure and monitor exceptional tropospheric ozone events including major forest fire and pollution transport events. Stratospheric ozone during the Aura record has several anomalous interannual events including split stratospheric warmings in the Northern Hemisphere extratropics that are well captured using the data assimilation ozone profile product. Data assimilation with continuous daily global coverage and vertical ozone profile information is the best of the three strategies at generating a global tropospheric and stratospheric ozone product for science applications. ©2014. American Geophysical Union. All Rights Reserved.

Harris N.R.P.,University of Cambridge | Hassler B.,University of Colorado at Boulder | Hassler B.,National Oceanic and Atmospheric Administration | Tummon F.,ETH Zurich | And 41 more authors.
Atmospheric Chemistry and Physics | Year: 2015

Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine - EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (∼ 45 km, 4 hPa) are found to be -5 to -10 % per decade at mid-latitudes and closer to -5 % per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and ground-based records have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ∼ 2 % per decade in mid-latitudes and ∼ 3 % per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties. © Author(s) 2015.

Wu X.,The Center for Satellite Applications and Research | Liu Q.,University of Maryland University College | Zeng J.,The Center for Satellite Applications and Research | Grotenhuis M.,The Center for Satellite Applications and Research | And 18 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2014

This paper evaluates the first 15 months of the Ozone Mapping and Profiler Suite (OMPS) Sensor Data Record (SDR) acquired by the nadir sensors and processed by the National Oceanic and Atmospheric Administration Interface Data Processing Segment. The evaluation consists of an inter-comparison with a similar satellite instrument, an analysis using a radiative transfer model, and an assessment of product stability. This is in addition to the evaluation of sensor calibration and the Environment Data Record product that are also reported in this Special Issue. All these are parts of synergetic effort to provide comprehensive assessment at every level of the products to ensure its quality. It is found that the OMPS nadir SDR quality is satisfactory for the current Provisional maturity. Methods used in the evaluation are being further refined, developed, and expanded, in collaboration with international community through the Global Space-based Inter-Calibration System, to support the upcoming long-term monitoring. ©2014. American Geophysical Union. All Rights Reserved.

Olsen M.A.,Morgan State University | Olsen M.A.,NASA | Douglass A.R.,NASA | Kaplan T.B.,INNOVIM
Journal of Geophysical Research: Atmospheres | Year: 2013

The extratropical stratosphere-troposphere exchange (STE) of ozone from 2005 to 2010 is estimated by combining Microwave Limb Sounder ozone observations and MERRA reanalysis meteorological fields in an established direct diagnostic framework. The multiyear mean ozone STE is 275 Tg yr-1 and 214 Tg yr-1 in the Northern and Southern Hemispheres, respectively. The year-to-year variability is greater in the Northern Hemisphere, where the difference between the highest and the lowest annual flux is 15% of the multiyear mean compared with 6% in the Southern Hemisphere. Variability of lower stratospheric ozone and variability of the net mass flux both contribute to interannual variability in the Northern Hemisphere ozone flux. The flux across the extratropical 380K surface determines the amount of flux across the extratropical tropopause, and the greatest seasonal variability of the 380K ozone flux occurs in the late winter/early spring, around the time of greatest flux. Both the mass flux and the ozone mixing ratios on the 380K surface show recurring spatial patterns, but interannual variability of these quantities and their alignment contribute to the ozone flux variability. The spatial and temporal variability are not well represented when zonal and/or monthly mean fields are used to calculate the ozone STE, although this results in a small high bias of the seasonal amplitude and annual magnitude. If the climatological variability over these 6 years is representative, the estimated number of years required to detect a 2-3% decade-1 trend in ozone STE using this diagnostic is 35-39 years. © 2012. American Geophysical Union.

Timofeyeva-Livezey M.,National Oceanic and Atmospheric Administration | Horsfall F.,National Oceanic and Atmospheric Administration | Hollingshead A.,Innovim | Meyers J.,National Oceanic and Atmospheric Administration | Dupigny-Giroux L.-A.,University of Vermont
Bulletin of the American Meteorological Society | Year: 2015

The National Oceanic and Atmospheric Administration (NOAA) has responded to the increased demand for local climate information by developing the Local Climate Analysis Tool (LCAT). The tool provides rapid responses to climate questions that historically required an extensive data search, research on appropriate analysis techniques, and complex graphics packages. LCAT offers easy and efficient access to scientifically sound analytical capabilities and trusted climate data. Results obtained from LCAT provide relevant climate information to local technical users, decision makers, and educators that will help build a healthy nation and create resilient communities. To ensure that LCAT responds to the articulated needs for local climate studies, a team of representatives from the NWS field offices routinely collects and ranks needs for capabilities to be incorporated into LCAT. The team also helps to design the LCAT user interface and provides training on the tool's features, methods, and usability. The LCAT framework offers analyses of climate change impacts, climate variability impacts, and correlation.

Wolfe R.E.,NASA | Nishihama M.,Sigma Space Corporation | Lin G.,Innovim | Tewari K.P.,Innovim | Montano E.,Sigma Space Corporation
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

The VIIRS instrument was launched on the NASA/NOAA Suomi NPP satellite in October 2011. This instrument is the first of a series of VIIRS instruments meant to continue the operational and long-term measurements of NASA, NOAA and DOD heritage instruments such as the MODIS instruments on the NASA EOS Terra and Aqua satellites and other. The VIIRS Sensor Data Record product recently achieved Beta Maturity in geometric and radiometric performance after the initial on-orbit instrument characterization and calibration. In this paper, we compare MODIS and VIIRS instrument's geometric characteristics and geolocation accuracy. This VIIRS geometric characterization is on-going and the product to be much more mature by the end of the year. At this time, the MODIS and VIIRS instruments have different but comparable geometric performance and that the VIIRS geometric characteristics will enable it to fulfill the mission objectives. © 2012 IEEE.

Wolfe R.E.,NASA | Lin G.,Innovim | Nishihama M.,Sigma Space Corporation | Tewari K.P.,Innovim | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor was launched 28 October 2011 on the Suomi National Polar-orbiting Partnership (SNPP) satellite. VIIRS has 22 spectral bands covering the spectrum between 0.412 μm and 12.01 μm, including 16 moderate resolution bands (M-bands) with a nominal spatial resolution of 750 m at nadir, five imaging resolution bands (I-bands) with a nominal spatial resolution of 375 m at nadir, and a day-night band (DNB) with a near-constant nominal 750 m spatial resolution throughout the scan. These bands are located in a visible and near-infrared focal plane assembly (FPA), a shortwave and midwave infrared FPA, and a long-wave infrared FPA. All bands, except the DNB, are coregistered for proper environmental data records retrievals. Observations from VIIRS instrument provide long-term measurements of biogeophysical variables for climate research and polar satellite data stream for the operational community's use in weather forecasting and disaster relief and other applications. Well Earth-located (geolocated) instrument data are important to retrieving accurate biogeophysical variables. This paper describes prelaunch pointing and alignment measurements, and the two sets of on-orbit correction of geolocation errors, the first of which corrected error from 1300 m to within 75 m (20% I-band pixel size) and the second of which fine-tuned scan-angle dependent errors, bringing VIIRS geolocation products to high maturity in one and a half years of the SNPP VIIRS on-orbit operations. Prelaunch calibration and the on-orbit characterization of sensor spatial impulse responses and band-to-band coregistration are also described. Key Points VIIRS geolocation errors are corrected by a control point matching program Sensor geometry and spatial response is characterized Geolocation of other VIIRS bands is transferred by band-to-band co-registration ©2013 The Authors. Journal of Geophysical Research: Atmospheres published by Wiley on behalf of the American Geophysical Union.

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