Abstract.Measurements of e-folding depth, nadir reflectivity and stratigraphy of the snowpack around Concordia station (Dome C, 75.10 • S, 123.31 • E) were undertaken to determine wavelength dependent coefficients (350 nm to 550 nm) for light scattering and absorption and to calculate potential fluxes (depth-integrated production rates) of nitrogen dioxide (NO 2 ) from the snowpack due to nitrate photolysis within the snowpack. The stratigraphy of the top 80 cm of Dome C snowpack generally consists of three main layers:-a surface of soft windpack (not ubiquitous), a hard windpack, and a hoar-like layer beneath the windpack(s). The e-folding depths are ∼10 cm for the two windpack layers and ∼20 cm for the hoar-like layer for solar radiation at a wavelength of 400 nm; about a factor 2-4 larger than previous model estimates for South Pole. The absorption cross-section due to impurities in each snowpack layer are consistent with a combination of absorption due to black carbon and HULIS (HUmic LIke Substances), with amounts of 1-2 ng g −1 of black carbon for the surface snow layers. Depth-integrated photochemical production rates of NO 2 in the Dome C snowpack were calculated as 5. using the TUV-snow radiative-transfer model. Depending upon the snowpack stratigraphy, a minimum of 85 % of the NO 2 may originate from the top 20 cm of the Dome C snowpack. It is found that on a multi-annual time-scale photolysis can remove up to 80 % of nitrate from surface snow, confirming independent isotopic evidence that photolysis is an important driver of nitrate loss occurring in the EAIS (East Antarctic Ice Sheet) snowpack. However, the model cannot completely account for the total observed nitrate loss of 90-95 % or the shape of the observed nitrate concentration depth profile. A more complete model will need to include also physical processes such as evaporation, re-deposition or diffusion between the quasi-liquid layer on snow grains and firn air to account for the discrepancies.

[1] Photolytic production rates of NO, NO 2 and OH radicals in snow and the total absorption spectrum due to impurities in snowpack have been calculated for the Ocean-Atmosphere-Sea-Ice-Snowpack (OASIS) campaign during Spring 2009 at Barrow, Alaska. The photolytic production rate and snowpack absorption cross-sections were calculated from measurements of snowpack stratigraphy, light penetration depths (e-folding depths), nadir reflectivity (350-700 nm) and UV broadband atmospheric radiation. Maximum NO x fluxes calculated during the campaign owing to combined nitrate and nitrite photolysis were calculated as 72 nmol m À2 h À1 for the inland snowpack and 44 nmol m À2 h À1 for the snow on sea-ice and snowpack around the Barrow Arctic Research Center (BARC). Depth-integrated photochemical production rates of OH radicals were calculated giving maximum OH depth-integrated production rates of $160 nmol m À2 h À1 for the inland snowpack and $110-120 nmol m À2 h À1 for the snow around BARC and snow on sea-ice. Light penetration (e-folding) depths at a wavelength of 400 nm measured for snowpack in the vicinity of Barrow and snow on sea-ice are $9 cm and 14 cm for snow 15 km inland. Fitting scaled HULIS (HUmic-LIke Substances) and black carbon absorption cross-sections to the determined snow impurity absorption cross-sections show a "humic-like" component to snowpack absorption, with typical concentrations of 1.2-1.5 mgC g À1 . Estimates of black carbon concentrations for the four snowpacks are $40 to 70 ng g À1 for the terrestrial Arctic snowpacks and $90 ng g À1 for snow on sea-ice.Citation: France, J. L., H. J. Reay, M. D. King, D. Voisin, H. W. Jacobi, F. Domine, H. Beine, C. Anastasio, A. MacArthur, and J. Lee-Taylor (2012), Hydroxyl radical and NO x production rates, black carbon concentrations and light-absorbing impurities in snow from field measurements of light penetration and nadir reflectivity of onshore and offshore coastal Alaskan snow,

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[1] Depth-integrated production rates of OH radicals and NO 2 molecules from snowpacks in Ny-Ålesund, Svalbard, are calculated from fieldwork investigating the light penetration depth (e-folding depth) and nadir reflectivity of snowpacks during the unusually warm spring of 2006. Light penetration depths of 8.1, 11.3, 5.1, and 8.2 cm were measured for fresh, old, marine-influenced, and glacial snowpacks, respectively (wavelength 400 nm). Radiative-transfer calculations of the light penetration depths with reflectivity measurements produced scattering cross sections of 5.3, 9.5, 20, and 25.5 m 2 kg −1 and absorption cross sections of 7.7, 1.4, 3.4, and 0.5 cm 2 kg −1 for the fresh, old, marineinfluenced, and glacial snowpacks, respectively (wavelength 400 nm). Photolysis rate coefficients, J, are presented as a function of snow depth and solar zenith angle for the four snowpacks for the photolysis of H 2 O 2 and NO 3 − . Depth-integrated production rates of hydroxyl radicals are 1270, 2130, 950, and 1850 nmol m −2 h −1 (solar zenith angle of 60°) for fresh, old, marine-influenced, and glacial snowpacks, respectively. Depth-integrated production rates of NO 2 are 32, 56, 11, and 22 nmol m −2 h −1 (solar zenith angle of 60°) for the fresh, old, marine-influenced, and glacial snowpacks, respectively. The uncertainty of repeated light penetration depth measurement was determined to be ∼20%, which propagates into a 20% error in depth-integrated production rates. A very simple steady state hydroxyl radical calculation demonstrates that a pseudo first-order loss rate of OH radicals of ∼10 2 -10 4 s −1 is required in snowpack. The snowpacks around Ny-Ålesund are thick enough to be considered optically infinite.Citation: France, J. L., M. D. King, J. Lee-Taylor, H. J. Beine, A. Ianniello, F. Domine, and A. MacArthur (2011), Calculations of in-snow NO 2 and OH radical photochemical production and photolysis rates: A field and radiative-transfer study of the optical properties of Arctic (Ny-Ålesund, Svalbard) snow,

ABSTRACT:Commercial off-the-shelf (COTS) digital cameras on-board unmanned aerial vehicles (UAVs) have the potential to be used as multispectral imaging systems; however, their spectral sensitivity is usually unknown and needs to be either measured or estimated. This paper details a step by step methodology for identifying the spectral sensitivity of modified (to be response to near infra-red wavelengths) and un-modified COTS digital cameras, showing the results of its application for three different models of camera. Six digital still cameras, which are being used as imaging systems on-board different UAVs, were selected to have their spectral sensitivities measured by a monochromator. Each camera was exposed to monochromatic light ranging from 370 nm to 1100 nm in 10 nm steps, with images of each step recorded in RAW format. The RAW images were converted linearly into TIFF images using DCRaw, an open-source program, before being batch processed through ImageJ (also open-source), which calculated the mean and standard deviation values from each of the red-green-blue (RGB) channels over a fixed central region within each image. These mean values were then related to the relative spectral radiance from the monochromator and its integrating sphere, in order to obtain the relative spectral response (RSR) for each of the cameras colour channels. It was found that different un-modified camera models present very different RSR in some channels, and one of the modified cameras showed a response that was unexpected. This highlights the need to determine the RSR of a camera before using it for any quantitative studies.

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