Top PDF Validation of SCIAMACHY limb NO<sub>2</sub> profiles using solar occultation measurements

Validation of SCIAMACHY limb NO<sub>2</sub> profiles using solar occultation measurements

Validation of SCIAMACHY limb NO<sub>2</sub> profiles using solar occultation measurements

Acknowledgements. We are thankful to ECMWF for providing pressure and temperature information (ECMWF Special Project SPDECDIO) for this study. Some data shown here were calculated on German HLRN (High-Performance Computer Center North). Services and support provided by the Atmospheric Chemistry Experiment (ACE), also known as SCISAT, a Canadian-led mission mainly supported by the Canadian Space Agency and the Natural Sciences and Engineering Research Council of Canada, are greatly appreciated. Our gratitude also goes to the HALOE science and data processing teams for providing the profiles used in this study. We wish to thank the NASA Langley Research Center (NASA- LaRC) and the NASA Langley Radiation and Aerosols Branch for making it possible for us to work with SAGE II data sets. This work was funded in parts by the European Commission FP7 project QUANTIFY, the DLR project SADOS (FKZ 50EE0727), by ESA through the SCIAMACHY Quality Working Group and by the University and State of Bremen.
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SCIAMACHY WFM-DOAS <i>X</i>CO<sub>2</sub>: reduction of scattering related errors

SCIAMACHY WFM-DOAS <i>X</i>CO<sub>2</sub>: reduction of scattering related errors

SCIAMACHY (SCanning Imaging Absorption spectroMe- ter for Atmospheric CHartographY) is a grating spectrome- ter and a national contribution to the atmospheric chemistry payload of ESA’s (European Space Agency) ENVISAT (EN- VIromental SATellite) (Burrows et al., 1995; Bovensmann et al., 1999). The satellite was launched in March 2002 into a sun-synchronous daytime (descending) orbit with an equa- tor crossing time of 10:00 a.m. SCIAMACHY continuously measures reflected, backscattered and transmitted solar ra- diation in six channels covering the spectral region 214– 1750 nm and in two additional channels covering the 1940– 2040 nm and the 2265–2380 nm regions. The spectral resolu- tion ranges from 0.2 to 1.4 nm. In addition to the eight main channels, seven polarisation measurement devices (PMD) measure upwelling broad band radiation polarised with re- spect to the instrumental plane with higher spatial resolution. The satellite instrument performs measurements in four different observation modes: solar and lunar occultation and limb and nadir. For this study nadir observations from chan- nel 4 (605–805 nm; for O 2 ), channel 6 (1000–1750 nm; for
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Water vapour profiles from SCIAMACHY solar occultation measurements derived with an onion peeling approach

Water vapour profiles from SCIAMACHY solar occultation measurements derived with an onion peeling approach

The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY; Bovensmann et al., 1999) is – as MIPAS and GOMOS – part of the payload of the European Environmental Satellite ENVISAT which was launched in 2002. SCIAMACHY performs spectral measurements in nadir, limb and lunar/solar occultation ge- ometry, covering almost continuously the wavelength range between about 220 and 2400 nm (Bovensmann et al., 1999). From these measurements column densities and profiles of various atmospheric constituents are derived (see e.g. Piters et al., 2006), among these also water vapour columns from nadir measurements (see e.g. No¨el et al., 2004, 2005). How- ever, up to now no water vapour profile data product from SCIAMACHY exists, although there are first successful at- tempts to derive such profiles from SCIAMACHY limb data. In this paper a new method to derive water vapour pro- files from SCIAMACHY solar occultation data is presented. Retrievals of atmospheric trace gas profiles from limb or oc- cultation measurements are often based on the optimal esti- mation (OE) method (see e.g. Rodgers, 1990). This method has proven to be appropriate for this purpose, as it in gen- eral produces reliable results which compare well with in- dependent data, see e.g. Rozanov et al. (2005, 2007), Palm et al. (2005), Meyer et al. (2005) or Amekudzi et al. (2005) for examples of (especially SCIAMACHY) retrievals using the OE method in different viewing geometries. The OE ap- proach usually involves an iterative process where radiative transfer calculations are required in each step. This makes OE methods relatively time consuming, which may become critical if large data sets – like those provided by satellites – need to be analysed. In many cases – like for limb appli- cations in the UV/Vis/NIR, where multiple scattering plays a large role – such an iterative radiative transfer scheme can not be avoided. Alternatively some retrieval methods (see e.g. K¨uhl et al., 2008) use a two-step approach which sepa- rates the derivation of slant column densities of the respec- tive absorber from the inversion. Another method used in the analysis of limb data is the Global Fit approach (Carlotti, 1988) in which a nonlinear least-squares fit is applied simul- taneously to the spectra for all tangent heights.
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Inter-comparison of stratospheric O<sub>3</sub> and NO<sub>2</sub> abundances retrieved from balloon borne direct sun observations and Envisat/SCIAMACHY limb measurements

Inter-comparison of stratospheric O<sub>3</sub> and NO<sub>2</sub> abundances retrieved from balloon borne direct sun observations and Envisat/SCIAMACHY limb measurements

strumental and retrieval related shortcomings of either tech- nique. The LPMA Fourier Transform spectrometer inher- ently exhibits smaller signal-to-noise-ratio (SNR≃10 2 ) than the grating spectrometers operated by DOAS (SNR≃10 4 ) causing significantly smaller detection limit and higher pre- cision of the DOAS measurements. In the visible spectral range where the Sun’s intensity peaks the typical integra- tion time for individual spectra is less than 1 s, whereas in the IR it takes about 50 s to record a single interferogram. Hence, the DOAS instruments sample the atmosphere with a much higher rate than the LPMA FT-IR. Taking into ac- count the respective errors of the considered trace gases it is evident that altitude resolution is significantly better for the DOAS observations. When the apparent size of the so- lar disk becomes large during solar occultation the smaller field of view of the FT-IR (FOV≃0.2 ◦ ) partly compensates the high integration times and large errors compared to the DOAS measurements (FOV≃0.53 ◦ ). On the other hand the small field of view of the FT-IR renders the intensity of the measured interferograms very sensitive to small pointing er-
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Improvements to the retrieval of tropospheric NO<sub>2</sub> from satellite &ndash; stratospheric correction using SCIAMACHY limb/nadir matching and comparison to Oslo CTM2 simulations

Improvements to the retrieval of tropospheric NO<sub>2</sub> from satellite &ndash; stratospheric correction using SCIAMACHY limb/nadir matching and comparison to Oslo CTM2 simulations

As for correction scheme (c), SCIAMACHY is the first in- strument to combine limb- and nadir-mode measurements of approximately the same air mass, taken within 15 min of each other (Bovensmann et al., 1999). This offers the unique op- portunity to use independent measurements done by the same instrument to investigate the stratospheric contribution to the total signal. In nadir geometry, SCIAMACHY looks down towards the Earth’s surface, and it measures total trace gas columns. In limb geometry, however, the instrument operates forward-looking and scans the atmosphere from the surface to a tangent height of 92 km (Gottwald and Bovensmann, 2011), thereby allowing for the retrieval of vertical absorber profiles using scattered light only. This limb/nadir matching has been exemplarily investigated in several studies (Sierk et al., 2006; Sioris et al., 2004). Beirle et al. (2010) have gone further and created a standard data product of strato- spheric NO 2 for the extraction of the tropospheric NO 2 field
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Retrieval of tropospheric column densities of NO<sub>2</sub> from combined SCIAMACHY nadir/limb measurements

Retrieval of tropospheric column densities of NO<sub>2</sub> from combined SCIAMACHY nadir/limb measurements

SCIAMACHY measures Earthshine spectra from the UV to the NIR with a spectral resolution of 0.22–1.48 nm. It is operated in different viewing geometries, including nadir, limb, and solar/lunar occultation. In nadir geometry (i.e. di- rected vertically, perpendicular to the Earth’s surface), the instrument performs an across-track scan of about ±32 ◦ , equivalent to a swath-width of 960 km. The footprint of a sin- gle nadir observation is typically 30 × 60 km 2 . Global cover of nadir measurements is achieved after 6 days. In limb ge- ometry (i.e. directed horizontally, tangential to the Earth’s surface), the instrument performs scans in flight direction with elevation steps of approx. 3.3 km at the tangent point. The cross-track swath is 960 km, as for the nadir measure- ments, and consists of up to 4 pixels. The field of view at the
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Technical Note: Feasibility of CO<sub>2</sub> profile retrieval from limb viewing solar occultation made by the ACE-FTS instrument

Technical Note: Feasibility of CO<sub>2</sub> profile retrieval from limb viewing solar occultation made by the ACE-FTS instrument

metres for profiles, which is much better than currently flying or planned nadir sounding instruments can achieve. In this paper, we analyse the feasibility of obtaining CO 2 ver- tical profiles in the 5–25 km altitude range from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS, launched in August 2003), high spectral resolution solar occultation measurements. Two main difficulties must be overcome: (i)

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Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O<sub>2</sub> A-band

Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O<sub>2</sub> A-band

the measured light is mainly direct sunlight which is either scattered at the tangent point in the SCIAMACHY view- ing direction, or reflected at the Earth surface and subse- quently scattered in the instrument’s line of sight (see Fig. 1). Here the light can be scattered either by air molecules or stratospheric aerosols. At 500 nm atmospheric absorption by ozone is weak and thus its effect on the measurement is small. The Libyan desert is located around 23 ◦ north- ern latitudes and so, the solar zenith angle varies between 27 ◦ in summer and 70 ◦ in winter at the time of the SCIA- MACHY observation. For the limb viewing geometry of SCIAMACHY this causes a variation of the scattering an- gle of singly scattered light at the tangent point between 55 ◦ in winter and 100 ◦ in summer. It means that in winter the single scattering geometry is closer to the forward peak of the scattering phase function than in summer. As a result the SCIAMACHY limb radiance varies seasonally as depicted in Fig. 2 for a tangent height of 25 km. To illustrate the different effects of aerosol scattering, Rayleigh scattering, and surface reflection on the measurement, the figure shows different limb radiance simulations for the corresponding
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First quantitative bias estimates for tropospheric NO<sub>2</sub> columns retrieved from SCIAMACHY, OMI, and GOME-2 using a common standard

First quantitative bias estimates for tropospheric NO<sub>2</sub> columns retrieved from SCIAMACHY, OMI, and GOME-2 using a common standard

in the NO 2 data has been reported for various locations over the world (Boersma et al., 2008). However, the diurnal cycle observed by SCIAMACHY and OMI has been val- idated only over the Middle East, a region with highly active photochemistry (Boersma et al., 2009). The observations of the diurnal variation are expected to provide addi- tional constraints to improve models, beyond a single VCD data set at a specific local

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Retrieval of tropospheric column-averaged CH<sub>4</sub> mole fraction by solar absorption FTIR-spectrometry using N<sub>2</sub>O as a proxy

Retrieval of tropospheric column-averaged CH<sub>4</sub> mole fraction by solar absorption FTIR-spectrometry using N<sub>2</sub>O as a proxy

columns directly retrieved from the spectra include errors arising from spectroscopy im- perfections and instrumental effects. The final TCCON products are the dry air column averaged mole fraction X CH 4 , X N2O and X HF , which have been corrected by airmass in- dependent and airmass dependent calibration factors to account for such errors. These corrections should be taken into account for this work. For the strategy explicitly using

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Profiles of CH<sub>4</sub>, HDO, H<sub>2</sub>O, and N<sub>2</sub>O with improved lower tropospheric vertical resolution from Aura TES radiances

Profiles of CH<sub>4</sub>, HDO, H<sub>2</sub>O, and N<sub>2</sub>O with improved lower tropospheric vertical resolution from Aura TES radiances

the HDO/H 2 O ratio are given in per mil and have been corrected for the estimated TES bias discussed in the previous section (Worden et al., 2011). Only data in which the DOFS for the HDO estimate is larger than 1 and where the cloud optical depth is less than 0.4 are shown. Note that even though the DOFS can be approximately one, the HDO/H 2 O profile can still distinguish boundary layer variability from free tropospheric

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The 2011 Nabro eruption, a SO<sub>2</sub> plume height analysis using IASI measurements

The 2011 Nabro eruption, a SO<sub>2</sub> plume height analysis using IASI measurements

measurements are for the most part, less than 2 km. It is re- markably good for plumes in the range 16–18 km, which are more often than not captured within a 1 km error bar. The largest discrepancies seems to be for plumes around 8–9 km, which are in about half of the cases put at altitudes around 10–11 km. But even for these, it is striking how well the gradient within the plumes are captured (for instance on the 18 June 3rd PM overpass). Almost no coincident plumes be- low 7 km were found in the analysis of CALIOP data, be- cause of the limited coverage of CALIOP coupled with the smaller sizes of the plumes. And even in those cases where there was a good overpass, interference of other lower tropo- spheric aerosol (e.g. desert dust) made identification of vol- canic aerosol impossible in the CALIOP data. As mentioned before however, the plumes at lower altitude are almost cer- tainly identified correctly based on their transport pathway and shorter lifetime. The CALIOP data reveals that the per- formance of the algorithm for plumes located below meteo- rological clouds, is not any worse than in cloud free scenes.
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Towards validation of ammonia (NH<sub>3</sub>) measurements from the IASI satellite

Towards validation of ammonia (NH<sub>3</sub>) measurements from the IASI satellite

measurements allowing the investigation of individual IASI observations and testing the effect of averaging different time scales. However, it is worth noting that this network provides measurements in an area (the Netherlands) that is not partic- ularly favorable for infrared remote sensing of surface pol- lution (low thermal contrast and relatively high cloud cover- age). Table 2 summarizes the results from the comparison of the IASI concentrations (columns converted to surface con- centrations as above) to those measured from the ground. The upper part presents the comparison from the linear re- gression for each individual site (slope (a) and intercept (b) of the linear regression, Pearson’s r (underlined when sig- nificant) and the number of observations (n)). We took into account only the IASI measurements covering the stations, which means that the true elliptical footprint is considered and only the observations including the LML site are kept. Six of the sites show significant correlation and for all, ex- cept for one (Valthermond, which has a negative intercept and fairly high slope), we find a very low slope (0.03–0.3) but a high intercept between 0.89 µg m − 3 (De Zilk) and 1.91
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Direct N<sub>2</sub>O<sub>5</sub> reactivity measurements at a polluted coastal site

Direct N<sub>2</sub>O<sub>5</sub> reactivity measurements at a polluted coastal site

bilities on average, showing maximum values in the early part of the study and depressions between day 260–262 and on day 269. Indeed, the parameterizations even show simi- lar day-to-day variations, except the variations are much less pronounced in the parameterizations than in the observations. The overestimates of the parameterizations are especially large during the first period of the study when particulate ni- trate loadings are low. As noted above, some of the over- estimation of the full parameterization may be caused by the assumption that chloride is internally mixed across all particles. The parameterization also has no explicit depen- dences on POM, the effects of which represent an area re- quiring more research. Similarly we neglect particle phase transitions and assume all particles are metastable solutions. Thus, if effloresced aerosol components were present in the atmosphere, then the parameterization would likely overesti- mate γ (N 2 O 5 ) given its strong dependence on particle phase
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Global distributions of C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, HCN, and PAN retrieved from MIPAS reduced spectral resolution measurements

Global distributions of C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, HCN, and PAN retrieved from MIPAS reduced spectral resolution measurements

Singh, H. B., Herlth, D., Kolyer, R., Chatfield, R., Viezee,W., Salas, L. J., Chen, Y., Bradshaw, J. D., Sandholm, S. T., Talbot, R., Gregory, G. L., Anderson, B., Sachse, G. W., Browell, E., Bachmeier, A. S., Blake, D. R., Heikes, B., Jacob, D., and H. E. Fuelberg: Impact of biomass burning emissions on the composition of the South Atlantic troposphere: Reactive nitrogen and ozone, J. Geophys. Res., 101(D19), 24203–24219, 1996. 5396, 5397, 5398, 5399

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An aircraft based three channel broadband cavity enhanced absorption spectrometer for simultaneous measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub> and NO<sub>2</sub>

An aircraft based three channel broadband cavity enhanced absorption spectrometer for simultaneous measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub> and NO<sub>2</sub>

Eq. (1). However, resultant improvements in detection limits are offset by an increase in noise associated with fewer photons arriving at the detector per unit time due to the ac- companying reduction in light intensity transmitted through the cavity which is roughly proportional to 1 − R(λ). Sensitivity can also be improved by using a more luminous light source. This is because signal increases proportionally to the number of photons

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Validation of NO<sub>2</sub> and NO from the Atmospheric Chemistry Experiment (ACE)

Validation of NO<sub>2</sub> and NO from the Atmospheric Chemistry Experiment (ACE)

Variability is quantified more clearly in panels (d) of Figs. 36 and 37, which show the standard deviations of the distributions relative to the mean VMRs, again separately for the low- and high-altitude cases. Below 65 km, there is very good agreement between ACE-FTS and HALOE, with both instruments showing slightly increasing standard deviations above about 35 km, and more steeply increasing standard de- viations below 35 km. The standard deviations shown here reflect both instrument precision and geophysical variabil- ity in the measurements. Above 64 km (only shown from 90 km), there is substantial disagreement between the ACE- FTS and HALOE standard deviations, with ACE-FTS show- ing higher variability. It is possible that these standard devi- ation differences are due to different geophysical conditions sampled by the instruments, but this should not be a large ef- fect given the relatively tight coincidence criteria employed here. In addition, geophysical variability would not be ex- pected to result in a bias in one instrument compared to the other, since it is unlikely that one instrument would always sample geophysical conditions that were biased in the same way with respect to the conditions sampled by the other in- strument. We thus speculate that the precision of the ACE- FTS measurements is generally worse than that of HALOE above 64 km.
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Validation of TANSO-FTS/GOSAT XCO<sub>2</sub> and XCH<sub>4</sub> glint mode retrievals  using TCCON data from near-ocean sites

Validation of TANSO-FTS/GOSAT XCO<sub>2</sub> and XCH<sub>4</sub> glint mode retrievals using TCCON data from near-ocean sites

2011a). Although all the GOSAT greenhouse gases retrieval algorithms have already been validated, to some degree, via the TCCON observations (e.g. Wunch et al., 2011b; Tanaka et al., 2012; Yoshida et al., 2013; Dils et al., 2014), only the land data have been selected in these previous studies. In- oue et al. (2013, 2014) made ocean data of NIES SWIR L2 products validation by aircraft measurements. To ensure that the ocean data of GOSAT can be used to achieve a more global coverage, we compare the ocean data from different algorithms with FTIR measurements from five TCCON sites close to the ocean and near-by GOSAT land data. In Sect. 2, we introduce the GOSAT retrievals and TCCON measure- ments. The validation method is described in Sect. 3. The results and summary are presented in Sects. 4 and 5, respec- tively.
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Comparisons of continuous atmospheric CH<sub>4</sub>, CO<sub>2</sub> and N<sub>2</sub>O measurements &ndash; results from a travelling instrument campaign at Mace Head

Comparisons of continuous atmospheric CH<sub>4</sub>, CO<sub>2</sub> and N<sub>2</sub>O measurements &ndash; results from a travelling instrument campaign at Mace Head

the AGAGE network. One working standard, which is mea- sured alternately with ambient air or other samples, is used for on-site calibration. These whole air standards last for ap- proximately 8 months and are analysed at Scripps Institute of Oceanography (SIO) before and after use at Mace Head, for details see Prinn et al. (2000). New working standards are always compared on-site with the old working standards and agree well with the values assigned at the SIO on a dif- ferent instrument but applying the same non-linearity correc- tion. For more than 15 years, weekly pressure-programmed injections of the standard were used to determine the non- linearity of the ECD response. It was also compared to non- linearities measured using primary gases spanning a range of concentrations. From May 2009 onwards, the non-linearity tests were discontinued, as it was found that the non-linearity between AGAGE instruments was remarkably consistent and stable, and because the pressure-programmed non-linearity tests also introduced occasional artifacts due to the vari-
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Quantitative bias estimates for tropospheric NO<sub>2</sub> columns retrieved from SCIAMACHY, OMI, and GOME-2 using a common standard for East Asia

Quantitative bias estimates for tropospheric NO<sub>2</sub> columns retrieved from SCIAMACHY, OMI, and GOME-2 using a common standard for East Asia

three different satellite sensors (SCIAMACHY, OMI, and GOME-2), we use a common standard to quantitatively eval- uate the biases for the respective data sets. As the stan- dard, a regression analysis using a single set of collocated ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations at several sites in Japan and China from 2006–2011 is adopted. Examina- tions of various spatial coincidence criteria indicates that the slope of the regression line can be influenced by the spa- tial distribution of NO 2 over the area considered. While the
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