scholarly journals On Aethalometer measurement uncertainties and an instrument correction factor for the Arctic

2017 ◽  
Vol 10 (12) ◽  
pp. 5039-5062 ◽  
Author(s):  
John Backman ◽  
Lauren Schmeisser ◽  
Aki Virkkula ◽  
John A. Ogren ◽  
Eija Asmi ◽  
...  
Keyword(s):  
Detection Limit ◽  
Temporal Resolution ◽  
Correction Factor ◽  
Light Absorption ◽  
The Arctic ◽  
Electronic Noise ◽  
Relative Uncertainty ◽  
Post Processing ◽  
Absorption Coefficients ◽  
Additional Advantage

Abstract. Several types of filter-based instruments are used to estimate aerosol light absorption coefficients. Two significant results are presented based on Aethalometer measurements at six Arctic stations from 2012 to 2014. First, an alternative method of post-processing the Aethalometer data is presented, which reduces measurement noise and lowers the detection limit of the instrument more effectively than boxcar averaging. The biggest benefit of this approach can be achieved if instrument drift is minimised. Moreover, by using an attenuation threshold criterion for data post-processing, the relative uncertainty from the electronic noise of the instrument is kept constant. This approach results in a time series with a variable collection time (Δt) but with a constant relative uncertainty with regard to electronic noise in the instrument. An additional advantage of this method is that the detection limit of the instrument will be lowered at small aerosol concentrations at the expense of temporal resolution, whereas there is little to no loss in temporal resolution at high aerosol concentrations ( >  2.1–6.7 Mm−1 as measured by the Aethalometers). At high aerosol concentrations, minimising the detection limit of the instrument is less critical. Additionally, utilising co-located filter-based absorption photometers, a correction factor is presented for the Arctic that can be used in Aethalometer corrections available in literature. The correction factor of 3.45 was calculated for low-elevation Arctic stations. This correction factor harmonises Aethalometer attenuation coefficients with light absorption coefficients as measured by the co-located light absorption photometers. Using one correction factor for Arctic Aethalometers has the advantage that measurements between stations become more inter-comparable.

scholarly journals On Aethalometer measurement uncertainties and multiple scattering enhancement in the Arctic

2016 ◽  
Author(s):  
John Backman ◽  
Lauren Schmeisser ◽  
Aki Virkkula ◽  
John A. Ogren ◽  
Eija Asmi ◽  
...  
Keyword(s):  
Detection Limit ◽  
Temporal Resolution ◽  
The Arctic ◽  
Electronic Noise ◽  
Relative Uncertainty ◽  
Post Processing ◽  
Additional Advantage ◽  
Aerosol Absorption ◽  
Threshold Criterion ◽  
Small Aerosol

Abstract. Several types of filter-based instruments are used to estimate aerosol light absorption coefficients.Two significant results are presented based on Aethalometer measurements at six Arctic station from 2012–2014. First, an alternative method of post-processing the Aethalometer data is presented which reduces measurement noise and lowers the detection limit of the instrument more effectively than boxcar averaging. The biggest benefit of this approach can be achieved if instrument drift is minimized. Moreover, by using an attenuation threshold criterion for data post-processing, the relative uncertainty from the electronic noise the instrument is kept constant. This approach results in a time series with a variable collection time (Δt), but with a constant relative uncertainty with regard to electronic noise in the instrument. An additional advantage of this method is that the detection limit of the instrument will be lowered at small aerosol concentrations at the expense of temporal resolution, whereas there is little to no loss in temporal resolution at high aerosol concentrations (>2.1–6.7 Mm−1 as measured by the Aethalometers). At high aerosol concentrations, minimizing the detection limit of the instrument is less critical. Second, utilizing co-located reference methods of aerosol absorption, a multiple cattering enhancement factor (Cref) of 3.10 specific to low elevation Arctic stations is found. Cref is a fundamental part of most of the Aethalometer corrections available in literature, and this is the first time a Cref value has been obtained for the Arctic.

scholarly journals Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods

2019 ◽  
Vol 19 (13) ◽  
pp. 8817-8830 ◽  
Author(s):  
Nishit J. Shetty ◽  
Apoorva Pandey ◽  
Stephen Baker ◽  
Wei Min Hao ◽  
Rajan K. Chakrabarty
Keyword(s):  
Solvent Extraction ◽  
Correction Factor ◽  
Light Absorption ◽  
Radiative Forcing ◽  
Total Carbon ◽  
Particle Phase ◽  
Absorption Coefficients ◽  
Scaling Factors ◽  
Phase Measurements ◽  
Solvent Phase

Abstract. Recent studies have shown that organic aerosol (OA) could have a nontrivial role in atmospheric light absorption at shorter visible wavelengths. Good estimates of OA light absorption are therefore necessary to better estimate radiative forcing due to these aerosols in climate models. One of the common techniques used to measure OA light absorption is the solvent extraction technique from filter samples which involves the use of a spectrophotometer to measure bulk absorbance by the solvent-soluble organic fraction of particulate matter. Measured solvent-phase absorbance is subsequently converted to particle-phase absorption coefficient using scaling factors. The conventional view is to apply a correction factor of 2 to absorption coefficients obtained from solvent-extracted OA based on Mie calculations. The appropriate scaling factors are a function of biases due to incomplete extraction of organic carbon (OC) by solvents and size-dependent absorption properties of OA. The range for these biases along with their potential dependence on burn conditions is an unexplored area of research. Here, we performed a comprehensive laboratory study involving three solvents (water, methanol, and acetone) to investigate the bias in absorption coefficients obtained from solvent-extraction-based photometry techniques as compared to in situ particle-phase absorption for freshly emitted OA from biomass burning. We correlated the bias with OC∕TC (total carbon) mass ratio and single scattering albedo (SSA) and observed that the conventionally used correction factor of 2 for water and methanol-extracted OA might not be extensible to all systems, and we suggest caution while using such correction factors to estimate particle-phase OA absorption coefficients. Furthermore, a linear correlation between SSA and the OC∕TC ratio was also established. Finally, from the spectroscopic data, we analyzed the differences in absorption Ångström exponents (AÅE) obtained from solution- and particulate-phase measurements. We noted that AÅE from solvent-phase measurements could deviate significantly from their OA counterparts.

scholarly journals A synthesis of light absorption properties of the Pan-Arctic Ocean: application to semi-analytical estimates of dissolved organic carbon concentrations from space

2013 ◽  
Vol 10 (11) ◽  
pp. 17071-17115 ◽  
Author(s):  
A. Matsuoka ◽  
M. Babin ◽  
D. Doxaran ◽  
S. B. Hooker ◽  
B. G. Mitchell ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Arctic Ocean ◽  
Light Absorption ◽  
Ocean Color ◽  
The Arctic ◽  
Absorption Coefficients ◽  
Absorption Properties ◽  
Chl A ◽  
Color Data

Abstract. The light absorption coefficients of particulate and dissolved materials are the main factors determining the light propagation of the visible part of the spectrum and are, thus, important for developing ocean color algorithms. While these absorption properties have recently been documented by a few studies for the Arctic Ocean (e.g., Matsuoka et al., 2007, 2011; Ben Mustapha et al., 2012), the datasets used in the literature were sparse and individually insufficient to draw a general view of the basin-wide spatial and temporal variations in absorption. To achieve such a task, we built a large absorption database at the pan-Arctic scale by pooling the majority of published datasets and merging new datasets. Our results showed that the total non-water absorption coefficients measured in the Eastern Arctic Ocean (EAO; Siberian side) are significantly higher than in the Western Arctic Ocean (WAO; North American side). This higher absorption is explained by higher concentration of colored dissolved organic matter (CDOM) in watersheds on the Siberian side, which contains a large amount of dissolved organic carbon (DOC) compared to waters off North America. In contrast, the relationship between the phytoplankton absorption (aφ(λ)) and chlorophyll a (chl a) concentration in the EAO was not significantly different from that in the WAO. Because our semi-analytical CDOM absorption algorithm is based on chl a-specific aφ(λ) values (Matsuoka et al., 2013), this result indirectly suggests that CDOM absorption can be appropriately derived not only for the WAO but also for the EAO using ocean color data. Derived CDOM absorption values were reasonable compared to in situ measurements. By combining this algorithm with empirical DOC vs. CDOM relationships, a semi-analytical algorithm for estimating DOC concentrations for coastal waters at the Pan-Arctic scale is presented and applied to satellite ocean color data.

scholarly journals Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: a multi-instrumental approach

2021 ◽  
Vol 14 (10) ◽  
pp. 6335-6355
Author(s):  
Jesús Yus-Díez ◽  
Vera Bernardoni ◽  
Griša Močnik ◽  
Andrés Alastuey ◽  
Davide Ciniglia ◽  
...  
Keyword(s):  
Multiple Scattering ◽  
Correction Factor ◽  
Aerosol Particles ◽  
Wavelength Dependence ◽  
Absorption Coefficients ◽  
Scattering Parameter ◽  
Cross Sensitivity ◽  
Scattering Correction ◽  
C Value ◽  
Factor C

Abstract. Providing reliable observations of aerosol particles' absorption properties at spatial and temporal resolutions suited to climate models is of utter importance to better understand the effects that atmospheric particles have on climate. Nowadays, one of the instruments most widely used in international monitoring networks for in situ surface measurements of light absorption properties of atmospheric aerosol particles is the multi-wavelength dual-spot Aethalometer, AE33. The AE33 derives the absorption coefficients of aerosol particles at seven different wavelengths from the measurements of the optical attenuation of light through a filter where particles are continuously collected. An accurate determination of the absorption coefficients from the AE33 instrument relies on the quantification of the non-linear processes related to the sample collection on the filter. The multiple-scattering correction factor (C), which depends on the filter tape used and on the optical properties of the collected particles, is the parameter with both the greatest uncertainty and the greatest impact on the absorption coefficients derived from the AE33 measurements. Here we present an in-depth analysis of the AE33 multiple-scattering correction factor C and its wavelength dependence for two different and widely used filter tapes, namely the old, and most referenced, TFE-coated glass, or M8020, filter tape and the currently, and most widely used, M8060 filter tape. For performing this analysis, we compared the attenuation measurements from AE33 with the absorption coefficients measured with different filter-based techniques. On-line co-located multi-angle absorption photometer (MAAP) measurements and off-line PP_UniMI polar photometer measurements were employed as reference absorption measurements for this work. To this aim, we used data from three different measurement stations located in the north-east of Spain, namely an urban background station (Barcelona, BCN), a regional background station (Montseny, MSY) and a mountaintop station (Montsec d'Ares, MSA). The median C values (at 637 nm) measured at the three stations ranged between 2.29 (at BCN and MSY, lowest 5th percentile of 1.97 and highest 95th percentile of 2.68) and 2.51 (at MSA, lowest 5th percentile of 2.06 and highest 95th percentile of 3.06). The analysis of the cross-sensitivity to scattering, for the two filter tapes considered here, revealed a large increase in the C factor when the single-scattering albedo (SSA) of the collected particles was above a given threshold, up to a 3-fold increase above the average C values. The SSA threshold appeared to be site dependent and ranged between 0.90 to 0.95 for the stations considered in the study. The results of the cross-sensitivity to scattering displayed a fitted constant multiple-scattering parameter, Cf, of 2.21 and 1.96, and a cross-sensitivity factor, ms, of 1.8 % and 3.4 % for the MSY and MSA stations, respectively, for the TFE-coated glass filter tape. For the M8060 filter tape, Cf values of 2.50, 1.96 and 1.82 and ms values of 1.6 %, 3.0 % and 4.9 % for the BCN, MSY and MSA stations, respectively, were obtained. SSA variations also influenced the spectral dependence of C, which showed an increase with wavelength when SSA was above the site-dependent threshold. Below the SSA threshold, no statistically significant dependence of C on the wavelength was observed. For the measurement stations considered here, the wavelength dependence of C was to some extent driven by the presence of dust particles during Saharan dust outbreaks that had the potential to increase the SSA above the average values. At the mountaintop station, an omission of the wavelength dependence of the C factor led to an underestimation of the absorption Ångström exponent (AAE) by up to 12 %. Differences in the absorption coefficient determined from AE33 measurements at BCN, MSY and MSA of around 35 %–40 % can be expected when using the site-dependent experimentally obtained C value instead of the nominal C value. Due to the fundamental role that the SSA of the particles collected on the filter tape has in the multiple-scattering parameter C, we present a methodology that allows the recognition of the conditions upon which the use of a constant and wavelength-independent C is feasible.

Large-scale Arctic sea ice motion from Sentinel-1 and the RADARSAT Constellation Mission

2021 ◽  
Author(s):  
Stephen Howell ◽  
Mike Brady ◽  
Alexander Komarov
Keyword(s):  
Sea Ice ◽  
Spatial Resolution ◽  
Temporal Resolution ◽  
Large Scale ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
High Temporal Resolution ◽  
Sar Images ◽  
Sea Ice Extent ◽  
Arctic Sea

<p>As the Arctic’s sea ice extent continues to decline, remote sensing observations are becoming even more vital for the monitoring and understanding of this process.  Recently, the sea ice community has entered a new era of synthetic aperture radar (SAR) satellites operating at C-band with the launch of Sentinel-1A in 2014, Sentinel-1B in 2016 and the RADARSAT Constellation Mission (RCM) in 2019. These missions represent a collection of 5 spaceborne SAR sensors that together can routinely cover Arctic sea ice with a high spatial resolution (20-90 m) but also with a high temporal resolution (1-7 days) typically associated with passive microwave sensors. Here, we used ~28,000 SAR image pairs from Sentinel-1AB together with ~15,000 SAR images pairs from RCM to generate high spatiotemporal large-scale sea ice motion products across the pan-Arctic domain for 2020. The combined Sentinel-1AB and RCM sea ice motion product provides almost complete 7-day coverage over the entire pan-Arctic domain that also includes the pole-hole. Compared to the National Snow and Ice Data Center (NSIDC) Polar Pathfinder and Ocean and Sea Ice-Satellite Application Facility (OSI-SAF) sea ice motion products, ice speed was found to be faster with the Senintel-1AB and RCM product which is attributed to the higher spatial resolution of SAR imagery. More sea ice motion vectors were detected from the Sentinel-1AB and RCM product in during the summer months and within the narrow channels and inlets compared to the NSIDC Polar Pathfinder and OSI-SAF sea ice motion products. Overall, our results demonstrate that sea ice geophysical variables across the pan-Arctic domain can now be retrieved from multi-sensor SAR images at both high spatial and temporal resolution.</p>

A Real-Time Inspection System Using a Terahertz Technique To Detect Microleak Defects in the Seal of Flexible Plastic Packages

2005 ◽  
Vol 68 (4) ◽  
pp. 833-837 ◽  
Author(s):  
YASUYUKI MORITA ◽  
ADRIAN DOBROIU ◽  
CHIKO OTANI ◽  
KODO KAWASE
Keyword(s):  
Detection Limit ◽  
Real Time ◽  
Refraction Index ◽  
Minimum Size ◽  
Inspection System ◽  
Absorption Coefficients ◽  
Polyethylene Films ◽  
Plastic Packages ◽  
Transmitted Signal ◽  
Ultrasound Inspection

A method to detect production faults in flexible plastic packages with the use of terahertz radiation is presented. Relying on the large difference between the absorption coefficients of plastic and water (for water-filled channel defects) and on the refraction index difference between plastic and air (for air-filled channel defects), our technique consists of focusing and scanning a terahertz beam on the sealed area of the package, followed by detection of the transmitted signal. Compared with previous methods, such as visual and ultrasound inspection, our technique can be applied to optically opaque packages and does not require immersion in a matching liquid. We tested our system on defects that we fabricated as water-filled and airfilled channels imbedded in polyethylene films, with diameters in the range of 10 to 100 μm. The detection limit (the minimum size of a detectable defect) depends on the conveying speed; this relationship was determined and analyzed. The results show that our system has the potential for application in an actual production line for real-time inspection.

scholarly journals Aerosol light absorption from attenuation measurements of PTFE-membrane filter samples: implications for particulate matter monitoring networks

2018 ◽  
Author(s):  
Apoorva Pandey ◽  
Nishit J. Shetty ◽  
Rajan K. Chakrabarty
Keyword(s):  
Light Absorption ◽  
Membrane Filter ◽  
Low Cost ◽  
Single Scattering ◽  
Carbonaceous Aerosols ◽  
Monitoring Networks ◽  
Absorption Coefficients ◽  
Ptfe Membrane ◽  
Thick Fiber ◽  
Multi Wavelength

Abstract. Mass absorption cross-section (MAC) measurements of atmospherically-relevant aerosols are required to quantify their effect on Earth’s radiative budget. Estimating aerosol light absorption from transmittance and/or reflectance measurements through filter deposits is an attractive option because of ease of deployment in field settings and low cost. These measurements suffer from artifacts that depend on a given filter measurement system and type of aerosol. Empirical correction algorithms are available for commercial instruments equipped with optically-thick fiber filters, but optically-thin filter media have not been characterized in detail. Here, we present empirical relationships between particle light absorption–measured using multi-wavelength integrated photoacoustic spectrometers and nephelometers–and attenuation measurements for polytetrafluoroethylene (PTFE) membrane filter samples of carbonaceous aerosols generated from combustion of diverse biomass fuels and kerosene (surrogate for fossil-fuel combustion). We establish a simple, wavelength-independent formulation for calculating aerosol MAC and absorption coefficients from filter attenuation measurements. We find the ratio between in-situ absorption and bulk attenuation to be inversely proportional to aerosol single scattering albedo. As a case study, we apply our formulations on 2010 attenuation datasets of the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network to quantify the overestimation in their filter-based absorption coefficients.

scholarly journals A single-beam photothermal interferometer for in situ measurements of aerosol light absorption

2020 ◽  
Vol 13 (12) ◽  
pp. 7097-7111
Author(s):  
Bradley Visser ◽  
Jannis Röhrbein ◽  
Peter Steigmeier ◽  
Luka Drinovec ◽  
Griša Močnik ◽  
...  
Keyword(s):  
Detection Limit ◽  
Cross Section ◽  
Light Absorption ◽  
Detection Limits ◽  
Field Measurements ◽  
Absorption Cross ◽  
Single Beam ◽  
Dual Beam ◽  
Set Up

Abstract. We have developed a novel single-beam photothermal interferometer and present here its application for the measurement of aerosol light absorption. The use of only a single laser beam allows for a compact optical set-up and significantly easier alignment compared to standard dual-beam photothermal interferometers, making it ideal for field measurements. Due to a unique configuration of the reference interferometer arm, light absorption by aerosols can be determined directly – even in the presence of light-absorbing gases. The instrument can be calibrated directly with light-absorbing gases, such as NO2, and can be used to calibrate other light absorption instruments. The detection limits (1σ) for absorption for 10 and 60 s averaging times were determined to be 14.6 and 7.4 Mm−1, respectively, which for a mass absorption cross section of 10 m2 g−1 leads to equivalent black carbon concentration detection limits of 1460 and 740 ng m−3, respectively. The detection limit could be reduced further by improvements to the isolation of the instrument and the signal detection and processing schemes employed.

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