Diurnal effects in limb scatter observations McLinden, Chris A.; Haley, Craig S.; Sioris, Christopher E.
Journal of Geophysical Research - Atmospheres,
27 July 2006, Letnik:
111, Številka:
D14
Journal Article
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Instruments that measure UV/visible scattered light from the Earth's limb are emerging as an important class of sensors capable of providing high‐quality profiles of aerosols and trace gases from the ...upper troposphere to the mesosphere. Critical to the inversion of limb scatter observations is the forward radiative transfer model. A fast and accurate radiative transfer model, VECTOR (Vector Orders‐of‐scattering Radiative transfer model), is presented that is able to account for the diurnal variation of species such as NO2 and BrO along the observing line of sight and the incoming solar beam. VECTOR has been used to quantify for the first time diurnal effect errors in NO2 and BrO with application to OSIRIS (Optical Spectrograph and Infra‐Red Imager System) and SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography), two limb viewing satellite instruments. For a solar zenith angle near 90° at the tangent point, errors can exceed 50% for NO2 and 100% for BrO in the lower stratosphere, with the largest errors generally occurring when viewing across, and at large angles to, the terminator. These results applied to OSIRIS NO2 and SCIAMACHY BrO reveal that diurnal effect errors are generally small (<10%). Yet 1 out of every 6 OSIRIS NO2 profiles experiences large (10–35%) errors and 1 out of every 11 SCIAMACHY BrO profiles experiences large (10–100%, or larger) errors in the lower stratosphere.
This paper presents the validation study of stratospheric NO2 profiles retrieved from Odin/OSIRIS measurements of limb‐scattered sunlight (version 2.4). The Optical Spectrograph and Infrared Imager ...System (OSIRIS) NO2 data set is compared to coincident solar occultation measurements by the Halogen Occultation Experiment (HALOE), Stratospheric Aerosol and Gas Experiment (SAGE) II, SAGE III, and Polar Ozone and Aerosol Measurement (POAM) III during the 2002–2004 period. Comparisons with seven Systeme d'Analyse par Observation Zenithal (SAOZ) balloon measurements are also presented. All comparisons show good agreement, with differences, both random and systematic, of less than 20% between 25 km and 35 km. Inconsistencies with SAGE III below 25 km are found to be caused primarily by diurnal effects from varying NO2 concentrations along the SAGE III line‐of‐sight. On the basis of the differences, the OSIRIS random uncertainty is estimated to be 16% between 15 km and 25 km, 6% between 25 km and 35 km, and 9% between 35 km and 40 km. The estimated systematic uncertainty is about 22% between 15 and 25 km, 11–21% between 25 km and 35 km, and 11–31% between 35 km and 40 km. The uncertainties for AM (sunrise) profiles are generally largest and systematic deviations are found to be larger at equatorial latitudes. The results of this validation study show that the OSIRIS NO2 profiles are well behaved, with reasonable uncertainty estimates between 15 km and 40 km. This unique NO2 data set, with more than hemispheric coverage and high vertical resolution will be of particular interest for studies of nitrogen chemistry in the middle atmosphere, which is closely linked to ozone depletion.
This paper describes the status of the stratospheric ozone and nitrogen dioxide data products from the Optical Spectrograph and InfraRed Imager System (OSIRIS) instrument on the Odin satellite. The ...current version of the data products is 3.0, covering the period from November 2001 to the present. The O
3
and NO
2
retrieval methods are reviewed along with an overview of the error analyses and geophysical validation status.
PACS Nos.: 07.05.Kf, 07.87.+v, 42.68.Mj, 92.60.hd, 92.60.Ta, 92.60.Vb, 92.70.Cp, 95.75.Fg, 95.75.Rs
A new technique for deriving the degree of linear polarization from limb‐scattered sunlight radiance measurements is presented and applied to Odin/OSIRIS. In this technique, the measured OSIRIS ...grating efficiency spectrum is fit to OSIRIS limb spectra using the differential optical absorption spectroscopy technique and the resultant fitting constant is shown to represent the difference in linear polarization between two tangent heights. The validity of this technique is confirmed using simulations from a vector limb radiative transfer model. OSIRIS scans of the difference in linear polarization from October 2003 are shown to be very sensitive to stratospheric and upper tropospheric aerosols, including background sulphates, clouds, and polar stratospheric clouds.
The association of organisms with particular habitats and habitat-forming organisms, can strongly influence species distributions, interactions and wider ecosystem services. At the sub-Antarctic ...Prince Edward Islands, the caridean shrimp Nauticaris marionis is a principal part of the benthic ecosystem, occurring between ca. 50m and 600m. Its role as a trophic link between the primary productivity and higher predators is established, but little is understood of its in situ habitat usage and associations or of how these structure patterns of abundance. We investigated these aspects directly using a benthic camera sled, sampling 27 stations between 50m and 500m. Substratum type was characterised, and estimates of percentage cover of the 13 main groups of habitat-forming epibenthic taxa were made, alongside absolute counts of N. marionis within ‘digital quadrats’ drawn from 300m transects. The distribution of N. marionis was influenced by depth, substratum type and overall biogenic cover, being limited to habitats between 50 and 160m depth on mud or gravel substrata only, and having > 50% biogenic cover. The presence/absence of N. marionis related to significantly different epibenthic assemblages (termed biogenic habitats), but this effect was contingent on depth. Likewise, densities of N. marionis were significantly affected by biogenic habitat type, identifying an association with two biogenic habitat groups, one dominated by red-algae, the other by structurally complex bryozoan species. These associations likely relate to the structural complexity of the two habitat groups, rather than the specific taxa involved. The apparent absence of N. marionis at depths > 160m contrasts with earlier records and poses questions about the trophic importance of the shrimp in deeper habitats.
•Optical sampling directly established habitat associations.•The shrimp Nauticaris marionis requires > 50% epibenthic cover.•Effect of substratum type superseded by presence of biogenic habitat.•Two associations identified with: nearshore red algae and deeper bryozoans.•Complex biogenic habitats may be increasingly important in deeper areas.
A climatology of stratospheric nitrogen dioxide (NO
2
), in terms of mean and standard deviation, as a function of latitude (5° bins); altitude (10-46 km in 2 km bins); local solar time (24 h); and ...month is constructed based on the Odin/OSIRIS limb-scattering data from 2002-2005. The measured profiles, given at specific local solar times, are scaled to all 24 h using a photochemical box model. The Odin orbit gives near global coverage around the equinoxes and hemispheric coverage elsewhere, due to lack of sunlight. The mean NO
2
field at a specific local solar time involves high concentrations in the polar summer, peaking at around 25 km, with a negative equatorward gradient. Distinct high levels between 40-50° latitude at 30 km in the winter/spring hemisphere are also found, associated with the so-called {Noxon-cliff}. The diurnal cycle reveals the lowest NO
2
concentrations just after sunrise and steep gradients at twilight. The 1σ standard deviation is generally quite low, around 20%, except for winter and spring high latitudes, where values are well above 50% and stretch through the entire stratosphere, a phenomenon probably related to the polar vortex. It is also found that NO
2
concentrations are log-normally distributed. Comparisons to a climatology based on data from a (REPROBUS) chemical transport model for the same time period reveal relative differences below 20% in general, which is comparable to the estimated OSIRIS systematic uncertainty. Clear exceptions are the polar regions in winter/spring throughout the atmosphere and equatorial regions below 25 km, where OSIRIS is relatively higher by 40% and more. These discrepancies are most likely attributable to limitations of the model, but this has to be investigated further.
PACS Nos.: 92.60.hd, 95.75.Rs, 95.55.Fw, 95.40.+s
Scientific studies of the major environmental questions of global warming and ozone depletion require global data sets of atmospheric constituents with relevant temporal and spatial resolution. In ...this paper, global number density profiles of O3 and NO2 are retrieved from Odin Optical Spectrograph and Infrared Imager System (Odin/OSIRIS) limb‐scattered sunlight measurements, using the maximum a posteriori estimator. Differential optical absorption spectroscopy is applied to OSIRIS radiances as an intermediate step, using the wavelength windows 571–617 nm for O3 and 435–451 nm for NO2. The method is computationally efficient for processing OSIRIS data on an operational basis. Results show that a 2–3 km height resolution is generally achievable between about 12 km and 45 km for O3 with an estimated accuracy of 13% at the peak and between about 15 km and 40 km for NO2 with an estimated accuracy of 10% at the peak. First validations of the retrieved data indicate a good agreement both with other retrieval techniques applied to OSIRIS measurements and with the results of other instruments. Once the validation has reached a confident level, the retrieved data will be used to study important stratospheric processes relevant to global environmental problems. The unique NO2 data set will be of particular interest for studies of nitrogen chemistry in the middle atmosphere.
Vertical profiles of nitrogen dioxide in the 19–40 km altitude range are successfully retrieved over the globe from Optical Spectrograph and Infrared Imager System (OSIRIS) limb scatter observations ...in late 2001 and early 2002. The inclusion of multiple scattering in the radiative transfer model used in the inversion algorithm allows for the retrieval of NO2 down to 19 km. The slant column densities, which represent the observations in the inversion, are obtained by fitting the fine structure in normalized radiance spectra over the 435–449 nm range, where NO2 electronic absorption is readily observable because of long light paths through stratospheric layers rich in this constituent. Details of the spectral fitting and inversion algorithm are discussed, including the discovery of a pseudo‐absorber associated with pixelated detectors and a new method to verify altitude registration. Comparisons are made with spatially and temporally coincident profile measurements of this photochemically active trace gas. Better than 20% agreement is obtained with all correlative measurements over the common retrieval altitude range, confirming the validity of OSIRIS NO2 profiles. Systematic biases in the number densities are not observed at any altitude. A “snapshot” meridional cross section between 40°N and 70°S is shown from observations during a fraction of an orbit.
Stratospheric NO
2
and O
3
retrieved from measurements of limb-scattered sunlight made by the Optical Spectrograph and InfraRed Imager System (OSIRIS) are compared with like observations made by a ...ground-based infrared Fourier Transform Spectrometer at the Toronto Atmospheric Observatory (TAO-FTS). Two different versions of OSIRIS NO
2
are compared (DOAS version 3.0 and MART version 2.0) with partial column concentrations retrieved from the TAO-FTS. Two OSIRIS O
3
versions are also compared (Triplet version 3.0 and MART version 2.0) with O
3
retrieved from the TAO-FTS. To accommodate the most coincidences, comparisons are based on monthly mean stratospheric partial columns covering 16-50 km. All coincident monthly means display high correlations: 0.82-0.97. The monthly mean NO
2
at TAO compared with the monthly mean NO
2
from OSIRIS shows an average difference of less than ~3% with standard deviations up to 6%. The OSIRIS NO
2
observations show a multiplicative bias of ~0.8-0.9 and a systematic difference of 5-10% greater then those of the TAO-FTS. O
3
differences are less than 5%, on average, with standard deviations ranging from 2% to 2.8%. There is a pronounced multiplicative bias of OSIRIS compared with the TAO-FTS ranging from 0.55 to 0.73. The systematic O
3
differences are less than 5% larger for OSIRIS. These small differences meet the standards outlined in the Integrated Global Observing Strategy and confirm the quality of the OSIRIS data for studying stratospheric ozone and nitrogen chemistry.PACS{ 92.60.hd, 92.60.Ry, 92.70.Cp, 93.30.Hf
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