scholarly journals Impact of satellite viewing swath width on global and regional aerosol optical thickness statistics and trends

2013 ◽  
Vol 6 (6) ◽  
pp. 10117-10163 ◽  
Author(s):  
P. R. Colarco ◽  
R. A. Kahn ◽  
L. A. Remer ◽  
R. C. Levy
Keyword(s):  
Optical Thickness ◽  
Statistical Significance ◽  
Sampling Strategy ◽  
Aerosol Optical Thickness ◽  
Mean Values ◽  
Sampling Artifacts ◽  
Aerosol Loading ◽  
Decadal Scale ◽  
Along Track ◽  
The Impact

Abstract. We use the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite aerosol optical thickness (AOT) product to assess the impact of reduced swath width on global and regional AOT statistics and trends. Ten different sampling strategies are employed, in which the full MODIS dataset is sub-sampled with various narrow-swath (~400–800 km) and curtain-like (~10 km) along-track configurations. Although view-angle artifacts in the MODIS AOT retrieval confound direct comparisons between averages derived from different sub-samples, careful analysis shows that with many portions of the Earth essentially unobserved, the AOT statistics of these sub-samples exhibit significant regional and seasonal biases. These AOT spatial sampling artifacts comprise up to 60% of the full-swath AOT value under moderate aerosol loading, and can be as large as 0.1 in some regions under high aerosol loading. Compared to full-swath observations, narrower swaths exhibit a reduced ability to detect AOT trends with statistical significance, and for curtain-like sampling we do not find any statistically significant decadal-scale trends at all. An across-track sampling strategy obviates the MODIS view angle artifact, and its mean AOT converges to the full-swath mean values for sufficiently coarse spatial and temporal aggregation. Nevertheless, across-track sampling has significant seasonal-regional sampling artifacts, leading to biases comparable to the curtain-like along-track sampling, lacks sufficient coverage to assign statistical significance to aerosol trends, and is not achievable with an actual narrow-swath or curtain-like instrument. These results suggest that future aerosol satellite missions having significantly less than full-swath viewing are unlikely to sample the true AOT distribution well enough to determine decadal-scale trends or to obtain the statistics needed to reduce uncertainty in aerosol direct forcing of climate.

scholarly journals Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends

2014 ◽  
Vol 7 (7) ◽  
pp. 2313-2335 ◽  
Author(s):  
P. R. Colarco ◽  
R. A. Kahn ◽  
L. A. Remer ◽  
R. C. Levy
Keyword(s):  
Optical Thickness ◽  
Radiative Forcing ◽  
Aerosol Optical Thickness ◽  
Spatial Sampling ◽  
Sampling Strategies ◽  
Data Set ◽  
Modis Data ◽  
Aerosol Loading ◽  
The Impact ◽  
Single Pixel

Abstract. We use the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite aerosol optical thickness (AOT) product to assess the impact of reduced swath width on global and regional AOT statistics and trends. Along-track and across-track sampling strategies are employed, in which the full MODIS data set is sub-sampled with various narrow-swath (~ 400–800 km) and single pixel width (~ 10 km) configurations. Although view-angle artifacts in the MODIS AOT retrieval confound direct comparisons between averages derived from different sub-samples, careful analysis shows that with many portions of the Earth essentially unobserved, spatial sampling introduces uncertainty in the derived seasonal–regional mean AOT. These AOT spatial sampling artifacts comprise up to 60% of the full-swath AOT value under moderate aerosol loading, and can be as large as 0.1 in some regions under high aerosol loading. Compared to full-swath observations, narrower swath and single pixel width sampling exhibits a reduced ability to detect AOT trends with statistical significance. On the other hand, estimates of the global, annual mean AOT do not vary significantly from the full-swath values as spatial sampling is reduced. Aggregation of the MODIS data at coarse grid scales (10°) shows consistency in the aerosol trends across sampling strategies, with increased statistical confidence, but quantitative errors in the derived trends are found even for the full-swath data when compared to high spatial resolution (0.5°) aggregations. Using results of a model-derived aerosol reanalysis, we find consistency in our conclusions about a seasonal–regional spatial sampling artifact in AOT. Furthermore, the model shows that reduced spatial sampling can amount to uncertainty in computed shortwave top-of-atmosphere aerosol radiative forcing of 2–3 W m−2. These artifacts are lower bounds, as possibly other unconsidered sampling strategies would perform less well. These results suggest that future aerosol satellite missions having significantly less than full-swath viewing are unlikely to sample the true AOT distribution well enough to obtain the statistics needed to reduce uncertainty in aerosol direct forcing of climate.

scholarly journals Resolving ice cloud optical thickness biases between CALIOP and MODIS using infrared retrievals

2016 ◽  
Vol 16 (8) ◽  
pp. 5075-5090 ◽  
Author(s):  
Robert E. Holz ◽  
Steven Platnick ◽  
Kerry Meyer ◽  
Mark Vaughan ◽  
Andrew Heidinger ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Spatial Scales ◽  
Radiative Properties ◽  
Radiation Balance ◽  
Data Set ◽  
Mean Values ◽  
Ice Cloud ◽  
Lidar Ratio ◽  
Cloud Optical Thickness ◽  
The Impact

Abstract. Despite its importance as one of the key radiative properties that determines the impact of upper tropospheric clouds on the radiation balance, ice cloud optical thickness (IOT) has proven to be one of the more challenging properties to retrieve from space-based remote sensing measurements. In particular, optically thin upper tropospheric ice clouds (cirrus) have been especially challenging due to their tenuous nature, extensive spatial scales, and complex particle shapes and light-scattering characteristics. The lack of independent validation motivates the investigation presented in this paper, wherein systematic biases between MODIS Collection 5 (C5) and CALIOP Version 3 (V3) unconstrained retrievals of tenuous IOT (< 3) are examined using a month of collocated A-Train observations. An initial comparison revealed a factor of 2 bias between the MODIS and CALIOP IOT retrievals. This bias is investigated using an infrared (IR) radiative closure approach that compares both products with MODIS IR cirrus retrievals developed for this assessment. The analysis finds that both the MODIS C5 and the unconstrained CALIOP V3 retrievals are biased (high and low, respectively) relative to the IR IOT retrievals. Based on this finding, the MODIS and CALIOP algorithms are investigated with the goal of explaining and minimizing the biases relative to the IR. For MODIS we find that the assumed ice single-scattering properties used for the C5 retrievals are not consistent with the mean IR COT distribution. The C5 ice scattering database results in the asymmetry parameter (g) varying as a function of effective radius with mean values that are too large. The MODIS retrievals have been brought into agreement with the IR by adopting a new ice scattering model for Collection 6 (C6) consisting of a modified gamma distribution comprised of a single habit (severely roughened aggregated columns); the C6 ice cloud optical property models have a constant g ≈ 0.75 in the mid-visible spectrum, 5–15 % smaller than C5. For CALIOP, the assumed lidar ratio for unconstrained retrievals is fixed at 25 sr for the V3 data products. This value is found to be inconsistent with the constrained (predominantly nighttime) CALIOP retrievals. An experimental data set was produced using a modified lidar ratio of 32 sr for the unconstrained retrievals (an increase of 28 %), selected to provide consistency with the constrained V3 results. These modifications greatly improve the agreement with the IR and provide consistency between the MODIS and CALIOP products. Based on these results the recently released MODIS C6 optical products use the single-habit distribution given above, while the upcoming CALIOP V4 unconstrained algorithm will use higher lidar ratios for unconstrained retrievals.

scholarly journals Obesity is associated with heavy menstruation that may be due to delayed endometrial repair

2021 ◽  
Vol 249 (2) ◽  
pp. 71-82
Author(s):  
Jane J Reavey ◽  
Catherine Walker ◽  
Alison A Murray ◽  
Savita Brito-Mutunayagam ◽  
Sheona Sweeney ◽  
...  
Keyword(s):  
Blood Loss ◽  
High Fat Diet ◽  
Statistical Significance ◽  
Surrogate Marker ◽  
Menstrual Blood ◽  
Menstrual Blood Loss ◽  
High Fat ◽  
Mean Values ◽  
Diet Induced Obesity ◽  
The Impact

Heavy menstrual bleeding is common and debilitating but the causes remain ill defined. Rates of obesity in women are increasing and its impact on menstrual blood loss (MBL) is unknown. Therefore, we quantified BMI and MBL in women not taking hormones and with regular menstrual cycles and revealed a positive correlation. In a mouse model of simulated menstruation, diet-induced obesity also resulted in delayed endometrial repair, a surrogate marker for MBL. BrdU staining of mouse uterine tissue revealed decreased proliferation during menstruation in the luminal epithelium of mice on a high-fat diet. Menstruation is known to initiate local endometrial inflammation and endometrial hypoxia; hence, the impact of body weight on these processes was investigated. A panel of hypoxia-regulated genes (VEGF, ADM, LDHA, SLC2A1) showed consistently higher mean values in the endometrium of women with obesity and in uteri of mice with increased weight vs normal controls, although statistical significance was not reached. The inflammatory mediators, Tnf and Il6 were significantly increased in the uterus of mice on a high-fat diet, consistent with a pro-inflammatory local endometrial environment in these mice. In conclusion, obesity was associated with increased MBL in women. Mice given a high-fat diet had delayed endometrial repair at menstruation and provided a model in which to study the influence of obesity on menstrual physiology. Our results indicate that obesity results in a more pro-inflammatory local endometrial environment at menstruation, which may delay endometrial repair and increase menstrual blood loss.

scholarly journals XBAER derived aerosol optical thickness from OLCI/Sentinel-3 observation

2017 ◽  
Author(s):  
Linlu Mei ◽  
Vladimir Rozanov ◽  
Marco Vountas ◽  
John P. Burrows ◽  
Andreas Richter
Keyword(s):  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Retrieval Algorithm ◽  
Imaging Spectrometer ◽  
Medium Resolution ◽  
New Instrument ◽  
Resolution Imaging ◽  
Haze Episode ◽  
The Impact ◽  
First Time

Abstract. A prolonged pollution haze event occurred in the northeast part of China during December 16–21, 2016. To assess the impact of such events, the amounts and distribution of aerosol particles formed in such events need to be quantified. The newly launched Ocean Land Color Instrument (OLCI) onboard Sentinel-3 is the successor of the MEdium Resolution Imaging Spectrometer (MERIS). It provides measurements of the radiance and reflectance at the top of the atmosphere which can be used to retrieve the Aerosol Optical Thickness (AOT) on both synoptic to global scales. In this paper, the recently developed AOT retrieval algorithm – eXtensible Bremen AErosol Retrieval (XBAER) has been applied to data from the OLCI instrument for the first time to inlustrate the feasibility of transferring XBAER to new instrument. The first global retrieval results show similar patterns as MODIS and MISR aerosol products. The AOT retrieved from OLCI is validated by comparison with AERONET observations and a correlation coefficient of 0.819 and bias (root mean square) of 0.115 is obtained. The haze episode is well-captured by the OLCI-derived AOT product. XBAER is shown to retrieve AOT from the observations of MERIS and OLCI.

scholarly journals XBAER-derived aerosol optical thickness from OLCI/Sentinel-3 observation

2018 ◽  
Vol 18 (4) ◽  
pp. 2511-2523 ◽  
Author(s):  
Linlu Mei ◽  
Vladimir Rozanov ◽  
Marco Vountas ◽  
John P. Burrows ◽  
Andreas Richter
Keyword(s):  
Spatial Variability ◽  
Optical Thickness ◽  
Threshold Value ◽  
Aerosol Optical Thickness ◽  
Retrieval Algorithm ◽  
Identification Algorithm ◽  
New Instrument ◽  
Visible Wavelengths ◽  
Cloud Mask ◽  
The Impact

Abstract. A cloud identification algorithm used for cloud masking, which is based on the spatial variability of reflectances at the top of the atmosphere in visible wavelengths, has been developed for the retrieval of aerosol properties by MODIS. It is shown that the spatial pattern of cloud reflectance, as observed from space, is very different from that of aerosols. Clouds show a high spatial variability in the scale of a hundred metres to a few kilometres, whereas aerosols in general are homogeneous. The concept of spatial variability of reflectances at the top of the atmosphere is mainly applicable over the ocean, where the surface background is sufficiently homogeneous for the separation between aerosols and clouds. Aerosol retrievals require a sufficiently accurate cloud identification to be able to mask these ground scenes. However, a conservative mask will exclude strong aerosol episodes and a less conservative mask could introduce cloud contamination that biases the retrieved aerosol optical properties (e.g. aerosol optical depth and effective radii). A detailed study on the effect of cloud contamination on aerosol retrievals has been performed and parameters are established determining the threshold value for the MODIS aerosol cloud mask (3×3-STD) over the ocean. The 3×3-STD algorithm discussed in this paper is the operational cloud mask used for MODIS aerosol retrievals over the ocean. A prolonged pollution haze event occurred in the northeast part of China during the period 16–21 December 2016. To assess the impact of such events, the amounts and distribution of aerosol particles, formed in such events, need to be quantified. The newly launched Ocean Land Colour Instrument (OLCI) onboard Sentinel-3 is the successor of the MEdium Resolution Imaging Spectrometer (MERIS). It provides measurements of the radiance and reflectance at the top of the atmosphere, which can be used to retrieve the aerosol optical thickness (AOT) from synoptic to global scales. In this study, the recently developed AOT retrieval algorithm eXtensible Bremen AErosol Retrieval (XBAER) has been applied to data from the OLCI instrument for the first time to illustrate the feasibility of applying XBAER to the data from this new instrument. The first global retrieval results show similar patterns of aerosol optical thickness, AOT, to those from MODIS and MISR aerosol products. The AOT retrieved from OLCI is validated by comparison with AERONET observations and a correlation coefficient of 0.819 and bias (root mean square) of 0.115 is obtained. The haze episode is well captured by the OLCI-derived AOT product. XBAER is shown to retrieve AOT well from the observations of MERIS and OLCI.

scholarly journals Retrieving aerosol height from the oxygen A band: a fast forward operator and sensitivity study concerning spectral resolution, instrumental noise, and surface inhomogeneity

2013 ◽  
Vol 6 (6) ◽  
pp. 10511-10550 ◽  
Author(s):  
A. Hollstein ◽  
J. Fischer
Keyword(s):  
Spectral Resolution ◽  
Optical Thickness ◽  
Principal Component ◽  
Linear Interpolation ◽  
Sensitivity Study ◽  
Aerosol Optical Thickness ◽  
Lookup Table ◽  
The Impact ◽  
Forward Operator ◽  
Aerosol Type

Abstract. Hyperspectral radiance measurements in the oxygen A band are sensitive to the vertical distribution of atmospheric scatterers, which in principle allows to retrieve aerosol height from future instruments like TROPOMI, OCO2, FLEX, and CarbonSat. Discussed in this paper is a fast and flexible forward operator for the simulation of hyperspectral radiances in the oxygen A band and, based on this scheme, a sensitivity study about the inversion quality of aerosol optical thickness, aerosol mean height, and aerosol type. The forward operator is based on a lookup table with efficient data compression based on principal component analysis. Linear interpolation and computation of partial derivatives is performed in the much smaller space of expansion coefficients rather then wavelength. Thus, this approach is computationally fast and at the same time memory efficient. The sensitivity study explores the impact of instrument design on the retrieval of aerosol optical thickness and aerosol height. Considered are signal to noise ratio, spectral resolution, and spectral sampling. Also taken into account are surface inhomogeneities and variations of the aerosol type.

scholarly journals Implications of satellite swath width on global aerosol optical thickness statistics

2012 ◽  
Vol 5 (2) ◽  
pp. 2795-2820 ◽  
Author(s):  
P. R. Colarco ◽  
L. A. Remer ◽  
R. A. Kahn ◽  
R. C. Levy ◽  
E. J. Welton
Keyword(s):  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Temporal Scales ◽  
Spatial And Temporal Scales ◽  
Moderate Resolution ◽  
Direct Forcing ◽  
Resolution Imaging ◽  
Sun Photometer ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
The Impact

Abstract. We assess the impact of swath width on the statistics of aerosol optical thickness (AOT) retrieved by satellite, as inferred from observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS). Using collocated AERONET sun photometer observations we develop a correction to the MODIS data to account for calibration and algorithmic view angle dependency in the retrieved AOT. We sub-sample and correct the AOT data from the MODIS Aqua instrument along several candidate swaths of various widths for the years 2003–2011. We find that over ocean the global, annual mean AOT is within ± 0.01 of the full swath AOT for all of our sub-samples. Over land, however, most of our sub-samples are outside of this criterion range in the global, annual mean. Moreover, at smaller spatial and temporal scales we find wide deviation in the sub-sample AOT relative to the full swath over both land and ocean. In all, the sub-sample AOT is within ± 0.01 of the full swath value less than 25% of the time over land, and less than 50% of the time over ocean (less than 35% for all but the widest of our sub-sample swaths). These results suggest that future aerosol satellite missions having only narrow swath views may not sample the true AOT distribution sufficiently to reduce significantly the uncertainty in aerosol direct forcing of climate.

scholarly journals Impact of crossing of Svrljig pramenka with East Friesian sheep on change in milk protein content

2007 ◽  
Vol 23 (5-6-2) ◽  
pp. 153-161
Author(s):  
D. Miocinovic ◽  
Anka Kasalica ◽  
J. Miocinovic-Djerovski
Keyword(s):  
Protein Content ◽  
Milk Protein ◽  
Statistical Significance ◽  
Total Yield ◽  
Sheep Breed ◽  
Lactation Period ◽  
Mean Values ◽  
Milk Protein Content ◽  
Significant Difference ◽  
The Impact

This research paper presents the results obtained based on a study on the impact of crossing the Svrljig pramenika and East Friesian sheep breed on the milk protein content and yield in the F1 generation of crossbreeds in the course of lactation. In all the three sheep breeds, while the difference between the first and last lactation months was of exceptionally high significance. The average protein content in the milk yielded by the East Friesian sheep and crossbreeds is very similar and amounts to 5.32% and 5.37%, while in the Svrljig Pramenka it was 5.53%. Based on the statistical significance appraisal of the differences in mean values of protein content in each stated breeds for the whole lactation period a highly significant difference between the Svrljig Pramenka and East Friesian sheep (p<0.01) can be observed, as well as a significant difference between the Svrljig Pramenka and crossbreeds (p<0.05), and an insignificant difference between the East Friesian breed and crossbreeds(p>0.05). The crossing of the stated breeds had an impact on the increase in the total yield of milk protein in the half-breeds (5948.72g), which is an increase of 1755.36g compared with that in the Svrljig Pramenka, and a decrease of only 237.36g in relation to that in the East Friesian sheep breed.

scholarly journals Cluster analysis of an impact of air back-trajectories on aerosol optical properties at Hornsund, Spitsbergen

2009 ◽  
Vol 9 (4) ◽  
pp. 15423-15451
Author(s):  
A. Rozwadowska ◽  
T. Zieliński ◽  
T. Petelski ◽  
P. Sobolewski
Keyword(s):  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Hysplit Model ◽  
Local Conditions ◽  
Back Trajectories ◽  
Local Direction ◽  
The Mean ◽  
The Impact ◽  
Network Station ◽  
Average Cluster

Abstract. In this paper spectra of aerosol optical thickness from AERONET (AErosol RObotic NETwork) station at Hornsund in the southern part of Spitsbergen were employed to study the impact of air mass history on aerosol optical thickness (AOT(500)) and Angstrom coefficient. Backward trajectories computed by means of NOAA HYSPLIT model were used to trace air history. It was found that in spring changes in AOT values over the Hornsund station were influenced by the at least 8-day trajectories of air, which was advected both in free troposphere and in the boundary layer. However, the free tropospheric advection was dominating. In summer the AOT variability was created mainly by local conditions, local direction and speed of advection (1-day trajectories). During the ASTAR 2007 campaign aerosols near Hornsund showed low AOT values ranging from 0.06 to 0.09, which is lower than the mean AOT(500) for spring seasons from 2005 to 2007 (0.110±0.007; mean ± standard deviation of mean). The 9 April 2007 with AOT(500)=0.147 was an exception. Back-trajectories belonged to the clusters of low and average cluster mean AOT value. Beside the maximum AOT of the 9 April 2007, the observed AOT values were close to the means for the clusters to which they belonged or were lower than the means.

scholarly journals Resolving ice cloud optical thickness biases between CALIOP and MODIS using infrared retrievals

2015 ◽  
Vol 15 (20) ◽  
pp. 29455-29495 ◽  
Author(s):  
R. E. Holz ◽  
S. Platnick ◽  
K. Meyer ◽  
M. Vaughan ◽  
A. Heidinger ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Spatial Scales ◽  
Radiative Properties ◽  
Radiation Balance ◽  
Data Set ◽  
Mean Values ◽  
Ice Cloud ◽  
Lidar Ratio ◽  
Cloud Optical Thickness ◽  
The Impact

Abstract. Despite its importance as one of the key radiative properties that determines the impact of upper tropospheric clouds on the radiation balance, ice cloud optical thickness (IOT) has proven to be one of the more challenging properties to retrieve from space-based remote sensing measurements. In particular, optically thin upper tropospheric ice clouds (cirrus) have been especially challenging due to their tenuous nature, extensive spatial scales, and complex particle shapes and light scattering characteristics. The lack of independent validation motivates the investigation presented in this paper, wherein systematic biases between MODIS Collection 5 (C5) and CALIOP Version 3 (V3) unconstrained retrievals of tenuous IOT (< 3) are examined using a month of collocated A-Train observations. An initial comparison revealed a factor of two bias between the MODIS and CALIOP IOT retrievals. This bias is investigated using an infrared (IR) radiative closure approach that compares both products with MODIS IR cirrus retrievals developed for this assessment. The analysis finds that both the MODIS C5 and the unconstrained CALIOP V3 retrievals are biased (high and low, respectively) relative to the IR IOT retrievals. Based on this finding, the MODIS and CALIOP algorithms are investigated with the goal of explaining and minimizing the biases relative to the IR. For MODIS we find that the assumed ice single scattering properties used for the C5 retrievals are not consistent with the mean IR COT distribution. The C5 ice scattering database results in the asymmetry parameter (g) varying as a function of effective radius with mean values that are too large. The MODIS retrievals have been brought into agreement with the IR by adopting a new ice scattering model for Collection 6 (C6) consisting of a modified gamma distribution comprised of a single habit (severely roughened aggregated columns); the C6 ice cloud optical property models have a constant g ~ 0.75 in the mid-visible spectrum, 5–15 % smaller than C5. For CALIOP, the assumed lidar ratio for unconstrained retrievals is fixed at 25 sr for the V3 data products. This value is found to be inconsistent with the constrained (predominantly nighttime) CALIOP retrievals. An experimental data set was produced using a modified lidar ratio of 32 sr for the unconstrained retrievals (an increase of 28 %), selected to provide consistency with the constrained V3 results. These modifications greatly improve the agreement with the IR and provide consistency between the MODIS and CALIOP products. Based on these results the recently released MODIS C6 optical products use the single habit distribution given above, while the upcoming CALIOP V4 unconstrained algorithm will use higher lidar ratios for unconstrained retrievals.

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