81 research outputs found
Satellite-based detection of volcanic sulphur dioxide from recent eruptions in Central and South America
Volcanic eruptions can emit large amounts of rock fragments and fine particles (ash) into the atmosphere, as well as several gases, including sulphur dioxide (SO<sub>2</sub>). These ejecta and emissions are a major natural hazard, not only to the local population, but also to the infrastructure in the vicinity of volcanoes and to aviation. Here, we describe a methodology to retrieve quantitative information about volcanic SO<sub>2</sub> plumes from satellite-borne measurements in the UV/Visible spectral range. The combination of a satellite-based SO<sub>2</sub> detection scheme and a state-of-the-art 3D trajectory model enables us to confirm the volcanic origin of trace gas signals and to estimate the plume height and the effective emission height. This is demonstrated by case-studies for four selected volcanic eruptions in South and Central America, using the GOME, SCIAMACHY and GOME-2 instruments
Retrieval and validation of ozone columns derived from measurements of SCIAMACHY on Envisat
International audienceThis paper describes a new ozone column retrieval algorithm and its application to SCIAMACHY measurements. The TOSOMI algorithm is based on the Differential Optical Absorption Spectroscopy (DOAS) technique and implements several improvements over older algorithms. These improvements include aspects like (i) the explicit treatment of rotational Raman scattering, (ii) an improved air-mass factor formulation which is based on a simulation of the reflectivity spectrum and a subsequent DOAS fit of this simulated spectrum, (iii) the use of an improved ozone climatology and a column dependent air-mass factor, (iv) the use of daily varying ECMWF temperature profile analyses. The results of three validation exercises are reported. The TOSOMI columns are compared with an extensive set of ground-based observations (Brewer, Dobson) for the years 2003 and 2004. Secondly, a direct comparison for January?June 2003 with two new GOME retrievals, GDP Version 4 and TOGOMI, is presented. Third, data assimilation is used to study the dependence of the TOSOMI columns with retrieval parameters such as the viewing angle, cloud fraction and geographical location. These comparisons show a good consistency on the percent level between the GOME and SCIAMACHY algorithms. The present TOSOMI implementation (v0.32) shows an offset of about ?1.5% with respect to ground-based observations and the GOME retrievals
The 1997 El Niño impact on clouds, water vapour, aerosols and reactive trace gases in the troposphere, as measured by the Global Ozone Monitoring Experiment
The El Niño event of 1997/1998 caused dry conditions over the Indonesian area that were followed by large scale forest and savannah fires over Kalimantan, Sumatra, Java, and parts of Irian Jaya. Biomass burning was most intense between August and October 1997, and large amounts of ozone precursors, such as nitrogen oxides, carbon monoxide and hydrocarbons were emitted into the atmosphere. In this work, we use satellite measurements from the Global Ozone Monitoring Experiment (GOME) sensor to study the teleconnections between the El Niño event of 1997 and the Indonesian fires, clouds, water vapour, aerosols and reactive trace gases (nitrogen dioxide, formaldehyde and ozone) in the troposphere
Geophysical validation and long-term consistency between GOME-2/MetOp-A total ozone column and measurements from the sensors GOME/ERS-2, SCIAMACHY/ENVISAT and OMI/Aura
The main aim of the paper is to assess the consistency of five years of Global Ozone Monitoring Experiment-2/Metop-A [GOME-2] total ozone columns and the long-term total ozone satellite monitoring database already in existence through an extensive inter-comparison and validation exercise using as reference Brewer and Dobson ground-based measurements. The behaviour of the GOME-2 measurements is being weighed against that of GOME (1995–2011), Ozone Monitoring Experiment [OMI] (since 2004) and the Scanning Imaging Absorption spectroMeter for Atmospheric CartograpHY [SCIAMACHY] (since 2002) total ozone column products. Over the background truth of the ground-based measurements, the total ozone columns are inter-evaluated using a suite of established validation techniques; the GOME-2 time series follow the same patterns as those observed by the other satellite sensors. In particular, on average, GOME-2 data underestimate GOME data by about 0.80%, and underestimate SCIAMACHY data by 0.37% with no seasonal dependence of the differences between GOME-2, GOME and SCIAMACHY. The latter is expected since the three datasets are based on similar DOAS algorithms. This underestimation of GOME-2 is within the uncertainty of the reference data used in the comparisons. Compared to the OMI sensor, on average GOME-2 data underestimate OMI_DOAS (collection 3) data by 1.28%, without any significant seasonal dependence of the differences between them. The lack of seasonality might be expected since both the GOME data processor [GDP] 4.4 and OMI_DOAS are DOAS-type algorithms and both consider the variability of the stratospheric temperatures in their retrievals. Compared to the OMI_TOMS (collection 3) data, no bias was found. We hence conclude that the GOME-2 total ozone columns are well suitable to continue the long-term global total ozone record with the accuracy needed for climate monitoring studies
TIME to Look for a Temporal GIS
An improved algorithm for the retrieval of total and tropospheric nitrogen dioxide (NO2) columns from the Global Ozone Monitoring Experiment-2 (GOME-2) is presented. The refined retrieval will be implemented in a future version of the GOME Data Processor (GDP) as used by the EUMETSAT Satellite Application Facility on Atmospheric Composition and UV Radiation (AC-SAF). The first main improvement is the application of an extended 425–497 nm wavelength fitting window in the differential optical absorption spectroscopy (DOAS) retrieval of the NO2 slant column density, based on which initial total NO2 columns are computed using stratospheric air mass factors (AMFs). Updated absorption cross sections and a linear offset correction are used for the large fitting window. An improved slit function treatment is applied to compensate for both long-term and in-orbit drift of the GOME-2 slit function. Compared to the current operational (GDP 4.8) dataset, the use of these new features increases the NO2 columns by ∼1–3×1014 molec cm2 and reduces the slant column error by ∼24 %. In addition, the bias between GOME-2A and GOME-2B measurements is largely reduced by adopting a new level 1b data version in the DOAS retrieval. The retrieved NO2 slant columns show good consistency with the Quality Assurance for Essential Climate Variables (QA4ECV) retrieval with a good overall quality. Second, the STRatospheric Estimation Algorithm from Mainz (STREAM), which was originally developed for the TROPOspheric Monitoring Instrument (TROPOMI) instrument, was optimised for GOME-2 measurements to determine the stratospheric NO2 column density. Applied to synthetic GOME-2 data, the estimated stratospheric NO2 columns from STREAM shows good agreement with the a priori truth. An improved latitudinal correction is introduced in STREAM to reduce the biases over the subtropics. Applied to GOME-2 measurements, STREAM largely reduces the overestimation of stratospheric NO2 columns over polluted regions in the GDP 4.8 dataset. Third, the calculation of AMF applies an updated box-air-mass factor (box-AMF) look-up table (LUT) calculated using the latest version 2.7 of the Vector-LInearized Discrete Ordinate Radiative Transfer (VLIDORT) model with an increased number of reference points and vertical layers, a new GOME-2 surface albedo climatology, and improved a priori NO2 profiles obtained from the TM5-MP chemistry transport model. A large effect (mainly enhancement in summer and reduction in winter) on the retrieved tropospheric NO2 columns by more than 10 % is found over polluted regions. To evaluate the GOME-2 tropospheric NO2 columns, an end-to-end validation is performed using ground-based multiple-axis DOAS (MAXDOAS) measurements. The validation is illustrated for six stations covering urban, suburban, and background situations. Compared to the GDP 4.8 product, the new dataset presents improved agreement with the MAXDOAS measurements for all the stations
Volcanic SO2 by UV-TIR satellite retrievals: validation by using ground-based network at Mt. Etna
Mt. Etna volcano in Italy is one of the most active degassing volcanoes worldwide, emitting a mean of 1.7 Mt/year of Sulphur Dioxide (SO2) in quiescent periods. In this work, SO2 measurements retrieved by Moderate Resolution Imaging Spectroradiometer (MODIS), hyper-spectral Infrared Atmospheric Sounding Interferometer (IASI) and the second Global Ozone Monitoring Experiment (GOME-2) data are compared with the ground-based data from the FLux Automatic MEasurement monitoring network (FLAME). Among the eighteen lava fountain episodes occurring at Mt. Etna in 2011, the 10 April
paroxysmal event has been selected as a case-study for the simultaneous observation of the SO2 cloud by satellite and ground-based sensors. For each data-set two retrieval techniques were adopted and the
measurements of SO2 mass and flux with their respective uncertainty were obtained. With respect to the FLAME SO2 mass of 4.5 Gg, MODIS, IASI and GOME-2 differ by about 10%, 15% and 30%, respectively. The SO2 flux correlation coefficient between MODIS and FLAME is 0.84. All the retrievals within the respective errors are in agreement with the ground-based measurements supporting the validity of these space measurements
Monitoring and assimilation tests with TROPOMI data in the CAMS system: near-real-time total column ozone
The TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5
Precursor (S5P) satellite launched in October 2017 yields a wealth of
atmospheric composition data, including retrievals of total column ozone
(TCO3) that are provided in near-real-time (NRT) and off-line. The NRT TCO3
retrievals (v1.0.0–v1.1.2) have been included in the data assimilation
system of the Copernicus Atmosphere Monitoring Service (CAMS), and tests to
monitor the data and to carry out first assimilation experiments with them
have been performed for the period 26 November 2017 to 30 November 2018. The
TROPOMI TCO3 data agree to within 2 % with the CAMS analysis over large
parts of the globe between 60∘ N and 60∘ S and also with
TCO3 retrievals from the Ozone Monitoring Instrument (OMI) and the Global
Ozone Monitoring Experiment-2 (GOME-2) that are routinely assimilated by
CAMS. However, the TCO3 NRT data from TROPOMI show some retrieval anomalies
at high latitudes, at low solar elevations and over snow/ice (e.g. Antarctica
and snow-covered land areas in the Northern Hemisphere), where the
differences with the CAMS analysis and the other data sets are larger. These
differences are particularly pronounced over land in the NH during winter and
spring (when they can reach up to 40 DU) and come mainly from the surface
albedo climatology that is used in the NRT TROPOMI TCO3 retrieval. This
climatology has a coarser horizontal resolution than the TROPOMI TCO3 data,
which leads to problems in areas where there are large changes in
reflectivity from pixel to pixel, e.g. pixels covered by snow/ice or not. The
differences between TROPOMI and the CAMS analysis also show some dependency
on scan position.
The assimilation of TROPOMI TCO3 has been tested in the CAMS system for data
between 60∘ N and 60∘ S and for solar elevations greater
than 10∘ and is found to have a small positive impact on the ozone
analysis compared to Brewer TCO3 data and an improved fit to ozone sondes in
the tropical troposphere and to IAGOS aircraft profiles at West African
airports. The impact of the TROPOMI data is relatively small because the CAMS
analysis is already well constrained by several other ozone retrievals that
are routinely assimilated. When averaged over the periods February–April and
September–October 2018, differences between experiments with and without
assimilation of TROPOMI data are less than 2 % for TCO3 and less than
3 % in the vertical for seasonal mean zonal mean O3 mixing
ratios, with the largest relative differences found in the troposphere.</p
Ground-based validation of the MetOp-A and MetOp-B GOME-2 OClO measurements
This paper reports on ground-based validation of the atmospheric OClO data record produced within the framework of EUMETSAT's Satellite Application Facility on Atmospheric Chemistry Monitoring (AC SAF) using the Global Ozone Monitoring Experiment (GOME)-2A and GOME-2B instrument measurements, covering the 2007–2016 and 2013–2016 periods, respectively. OClO slant column densities are compared to correlative measurements collected from nine Zenith-Scattered-Light Differential Optical Absorption Spectroscopy (ZSL-DOAS) instruments from the Network for the Detection of Atmospheric Composition Change (NDACC) distributed in both the Arctic and Antarctic. Sensitivity tests are performed on the ground-based data to estimate the impact of the different OClO DOAS analysis settings. On this basis, we infer systematic uncertainties of about 25 % (i.e., about 3.75×10^13 molec. cm−2) between the different ground-based data analyses, reaching total uncertainties ranging from about 26 % to 33 % for the different stations (i.e., around 4 to 5×10^13 molec. cm−2). Time series at the different sites show good agreement between satellite and ground-based data for both the inter-annual variability and the overall OClO seasonal behavior. GOME-2A results are found to be noisier than those of GOME-2B, especially after 2011, probably due to instrumental degradation effects. Daily linear regression analysis for OClO-activated periods yield correlation coefficients of 0.8 for GOME-2A and 0.87 for GOME-2B, with slopes with respect to the ground-based data ensemble of 0.64 and 0.72, respectively. Satellite minus ground-based offsets are within 8×10^13 molec. cm−2, with some differences between GOME-2A and GOME-2B depending on the station. Overall, considering all the stations, a median offset of about -2.2×10^13 molec. cm−2 is found for both GOME-2 instruments
Validation of the IASI FORLI/EUMETSAT ozone products using satellite (GOME-2), ground-based (Brewer–Dobson, SAOZ, FTIR) and ozonesonde measurements
This paper assesses the quality of IASI (Infrared Atmospheric Sounding Interferometer)/Metop-A (IASI-A) and
IASI/Metop-B (IASI-B) ozone (O3) products (total and partial
O3 columns) retrieved with the Fast Optimal Retrievals on Layers
for IASI Ozone (FORLI-O3; v20151001) software for 9Â years
(2008–July 2017) through an extensive intercomparison and validation
exercise using independent observations (satellite, ground-based and
ozonesonde). Compared with the previous version of FORLI-O3 (v20140922),
several improvements have been introduced in FORLI-O3 v20151001,
including absorbance look-up tables recalculated to cover a larger spectral
range, with additional numerical corrections. This leads to a change of  ∼ 4 % in the total ozone column (TOC) product, which is mainly associated
with a decrease in the retrieved O3 concentration in the middle
stratosphere (above 30 hPa/25 km). IASI-A and IASI-B TOCs are consistent,
with a global mean difference of less than 0.3 % for both daytime and
nighttime measurements; IASI-A is slightly higher than IASI-B. A global
difference of less than 2.4 % is found for the tropospheric (TROPO)
O3 column product (IASI-A is lower than IASI-B), which is partly
due to a temporary issue related to the IASI-A viewing angle in 2015. Our
validation shows that IASI-A and IASI-B TOCs are consistent with
GOME-2 (Global Ozone Monitoring Experiment-2), Dobson, Brewer, SAOZ
(Système d'Analyse par Observation
Zénithale) and FTIR (Fourier transform infrared)
TOCs, with global mean differences in the range of 0.1 %–2 %
depending on the instruments compared. The worst agreement with UV–vis
retrieved TOC (satellite and ground) is found at the southern high latitudes.
The IASI-A and ground-based TOC comparison for the period from 2008 to July
2017 shows the long-term stability of IASI-A, with insignificant or small negative
drifts of 1 %–3 % decade−1. The comparison results of IASI-A and IASI-B
against smoothed FTIR and ozonesonde partial O3 columns vary with
altitude and latitude, with the maximum standard deviation being seen for the
300–150 hPa column (20 %–40 %) due to strong ozone variability and
large total retrievals errors. Compared with ozonesonde data, the IASI-A and
IASI-B O3 TROPO column (defined as the column between the surface
and 300 hPa) is positively biased in the high latitudes (4 %–5 %)
and negatively biased in the midlatitudes and tropics (11 %–13 % and
16 %–19 %, respectively). The IASI-A-to-ozonesonde TROPO comparison
for the period from 2008 to 2016 shows a significant negative drift in the
Northern Hemisphere of −8.6±3.4 % decade−1, which is also
found in the IASI-A-to-FTIR TROPO comparison. When considering the period
from 2011 to 2016, the drift value for the TROPO column decreases and becomes
statistically insignificant. The observed negative drifts of the IASI-A TROPO
O3 product (8 %–16 % decade−1) over the 2008–2017
period might be taken into consideration when deriving trends from this
product and this time period.</p
The Diagnostic Sensitivity of Dengue Rapid Test Assays Is Significantly Enhanced by Using a Combined Antigen and Antibody Testing Approach
Dengue is a serious public health concern with around 3 billion people at risk of infection. Severe forms of the infection can be fatal and with no licensed vaccine or effective therapeutic currently available, early detection is important to assist with the clinical management of symptoms. Isolation of the virus and the detection of viral RNA using RT-PCR are commonly used methods for early diagnosis but are time-consuming, expensive and require skilled operation. Rapid immunochromatographic tests (ICT) are relatively simple, inexpensive and easy to perform at or near the point of care. Here, we report on the clinical performance of a new rapid ICT for the non-structural protein 1 (NS1) of dengue virus, a marker of acute infection. At two clinical study sites, NS1 was detected in 60–70% of laboratory-confirmed dengue cases and specificity of the test was >95%. We have also shown that a combined testing approach for both circulating NS1 antigen and antibody responses to the glycoprotein E of the virus can significantly improve diagnostic sensitivity compared to the detection of NS1 alone. Importantly, the combined antigen and antibody testing approach also provides an expanded window of detection from as early as day 1 post-onset of illness
- …