Спектрометр для оценки содержания SO2 в вулканических выбросах

This work presents the development and implementation of an autonomous portable spectrometer DEVI (Doas Expedition Volcanic Instrument), designed to measure SO2 slant columns in volcanic plumes by remote optical method DOAS (Differential Optical Absorption Spectroscopy) in the range of 290–365 nm with a resolution of at least 1 nm. To achieve this goal, the following tasks have been solved: practical implementation of the spectrometer, including design of optical scheme; design of a spectrometer housing for reducing scattered radiation and facilitate adjustments; applying of additional sensors to record measurement conditions; laboratory measurements to determine the spectrometer's characteristics; field measurements and preliminary data processing to retrieve SO2 slant columns in volcanic plumes. During the spectrometer design phase, numerical simulation methods in the Zemax software have been used, while DOAS was applied for processing experimental data for retrieving SO2 slant columns. Our laboratory measurements showed that the DEVI spectrometer has a spectral resolution of 0.58 ± 0.5 nm and an angular field of view of 1 × 0.25°. To improve the signal-to-noise ratio, mathematical filter based on the experimentally determined noise parameters of the DEVI detector has been introduced, which allowed us to estimate the SO2 slant columns in volcanic plumes. DEVI was successfully tested during expeditions to the Kuril Islands in the periods of July – August, 2021 and 2022 (31.07–13.08.2021 and 27.07–29.08.2022). Our field measurements and data processing showed the SO2 slant column value of (7.5 ± 1.2)·1017 molecules/cm2 for the volcano Chirinkotan. Obtained estimation is consistent with known results obtained for other volcanoes.Автономный портативный спектрометр DEVI (Doas Expedition Volcanic Instrument) предназначен для полевых измерений наклонных содержаний SO2 в вулканических выбросах дистанционным оптическим методом DOAS (Differential Optical Absorption Spectroscopy) в диапазоне 290–365 нм с разрешением не хуже 1 нм. Для его разработки были решены такие задачи, как: практическая реализация спектрометра, включающая в себя разработку оптической схемы; создание корпуса спектрометра, обеспечивающего функции уменьшения рассеянного излучения и удобство юстировки; использование набора дополнительных датчиков для регистрации условий измерений; проведение серии лабораторных измерений для определения характеристик спектрометра; проведение серии натурных измерений и предварительная обработка полученных данных с целью восстановления наклонных толщ диоксида серы в вулканическом выбросе. На этапе разработки спектрометра использовались методы численного моделирования оптических систем в программной среде Zemax, на этапе обработки экспериментальных данных для восстановления наклонных содержаний диоксида серы – метод DOAS. Представлены результаты лабораторных измерений характеристик спектрометра: спектральное разрешение 0,58 ± 0,5 нм, угловое поле зрения 1 × 0,25°. Экспериментально определенные параметры шума детектора DEVI применялись для построения математического фильтра с целью увеличения отношения сигнал – шум, что позволило оценить содержание диоксида серы в вулканических выбросах. DEVI успешно опробован в ходе экспедиций на Курильские острова в периоды 31.07–13.08.2021 и 27.07–29.08.2022, в результате чего восстановлена величина наклонного содержания (7,5 ± 1,2)·1017 молекул/см2 в выбросе вулкана Чиринкотан. Полученная оценка наклонного содержания диоксида серы согласуется с результатами, полученными различными научными группами с использованием аналогичного метода для других вулканов

Алгоритм предварительной обработки данных линейки приборов с зарядовой связью на основе адаптивного фильтра Винера

The researcher should choose the modes of recording spectra which allow to achieve the highest accuracy of spectral measurements in remote sensing systems. When registering a signal from aircraft which provide maximum coverage of the studied area, it is important to obtain a signal with the maximum signal-to- noise ratio in a minimum time, since the accumulation of spectra samples for averaging is impossible. The paper presents the experimental results of determining the noise components (readout noise, photon, electronic shot, pattern noise) for a monochrome uncooled CCD-line detector Toshiba TCD1304DG (CCD – charge-coupled devices) with various conditions of spectrum registration: detector temperature, exposition. Obtained dependences of the noise components make it possible to estimate the noise level for well-known conditions of spectra registration. The algorithm for processing CCD data based on an adaptive Wiener filter is proposed to increase the signal-to-noise ratio by using a priori information about the statistical parameters of the noise components. Such approach has allowed to increase the signal-to-noise ratio of sky spectral brightness by 4–9 dB for exposure times. The practical application of the algorithm has reduced the uncertainty in the vegetation index NDVI by 1.5 times when recording the reflection spectra of vegetation from the aircraft in the nadir measurement geometry.Для применения спектрометров в задачах дистанционного зондирования Земли исследователю необходимо выбирать режимы регистрации спектров, позволяющие добиться наивысшей точности спектральных измерений. При регистрации сигнала с борта авианосителей, обеспечивающих максимальный охват исследуемой территории, важно получить данные с максимальным отношением сигнал-шум за минимальное время, поскольку накопление выборки спектров для последующего усреднения невозможно. В работе представлены экспериментальные результаты определения компонентов шума (шума считывания; фотонного, электронного дробового и структурного шумов) для монохромной неохлаждаемой ПЗС-линейки Toshiba TCD1304DG (ПЗС – приборы с зарядовой связью) при различных условиях регистрации спектра: температуре детектора, времени экспозиции. Полученные зависимости компонентов шума позволяют оценить уровень шума для известных условий регистрации спектров. Предлагается алгоритм обработки данных ПЗС на основе адаптивного фильтра Винера с целью увеличения соотношения сигнал-шум путем использования априорной информации о статистических параметрах компонентов шума. Такой подход позволил увеличить отношение сигнал-шум спектров яркости небесной сферы на 4–9 дБ при регистрации сигнала на различных временах экспозиции. Практическое применение предлагаемого алгоритма уменьшило неопределенность расчета вегетационного индекса NDVI в 1,5 раза при регистрации спектров отражения растительности с борта самолета в надирной геометрии измерений

Inter-comparison of MAX-DOAS measurements of tropospheric HONO slant column densities and vertical profiles during the CINDI-2 campaign

We present the inter-comparison of delta slant column densities (SCDs) and vertical profiles of nitrous acid (HONO) derived from measurements of different multi-axis differential optical absorption spectroscopy (MAX-DOAS) instruments and using different inversion algorithms during the Second Cabauw Inter-comparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) in September 2016 at Cabauw, the Netherlands (51.97∘ N, 4.93∘ E). The HONO vertical profiles, vertical column densities (VCDs), and near-surface volume mixing ratios are compared between different MAX-DOAS instruments and profile inversion algorithms for the first time. Systematic and random discrepancies of the HONO results are derived from the comparisons of all data sets against their median values. Systematic discrepancies of HONO delta SCDs are observed in the range of ±0.3×1015 molec. cm−2, which is half of the typical random discrepancy of 0.6×1015 molec. cm−2. For a typical high HONO delta SCD of 2×1015 molec. cm−2, the relative systematic and random discrepancies are about 15 % and 30 %, respectively. The inter-comparison of HONO profiles shows that both systematic and random discrepancies of HONO VCDs and near-surface volume mixing ratios (VMRs) are mostly in the range of ∼±0.5×1014 molec. cm−2 and ∼±0.1 ppb (typically ∼20 %). Further we find that the discrepancies of the retrieved HONO profiles are dominated by discrepancies of the HONO delta SCDs. The profile retrievals only contribute to the discrepancies of the HONO profiles by ∼5 %. However, some data sets with substantially larger discrepancies than the typical values indicate that inappropriate implementations of profile inversion algorithms and configurations of radiative transfer models in the profile retrievals can also be an important uncertainty source. In addition, estimations of measurement uncertainties of HONO dSCDs, which can significantly impact profile retrievals using the optimal estimation method, need to consider not only DOAS fit errors, but also atmospheric variability, especially for an instrument with a DOAS fit error lower than ∼3×1014 molec. cm−2. The MAX-DOAS results during the CINDI-2 campaign indicate that the peak HONO levels (e.g. near-surface VMRs of ∼0.4 ppb) often appeared in the early morning and below 0.2 km. The near-surface VMRs retrieved from the MAX-DOAS observations are compared with those measured using a co-located long-path DOAS instrument. The systematic differences are smaller than 0.15 and 0.07 ppb during early morning and around noon, respectively. Since true HONO values at high altitudes are not known in the absence of real measurements, in order to evaluate the abilities of profile inversion algorithms to respond to different HONO profile shapes, we performed sensitivity studies using synthetic HONO delta SCDs simulated by a radiative transfer model with assumed HONO profiles. The tests indicate that the profile inversion algorithms based on the optimal estimation method with proper configurations can reproduce the different HONO profile shapes well. Therefore we conclude that the features of HONO accumulated near the surface derived from MAX-DOAS measurements are expected to represent the ambient HONO profiles well

Aerosol profile measurements in the coastal zone of Antarctica: instrumentation and preliminary results

The IPCC has identified the indirect aerosol effect as the biggest uncertainty in the Earth's climate system. For this reason, efforts are being made to measure aerosols and the associated effect on the climate. Antarctica is often used to reveal changes in the global background. One of the characteristics enabling to separate aerosol of the local origin from the background level is the aerosol vertical profile. A MAX-DOAS technique is among the approaches that can give information on the aerosol vertical distribution. The paper presents instrumentation and preliminary results of aerosol measurements which were conducted in eastern Antarctica, near the Russian station "Progress" (69°22S 76°23E, Larsemann Hills). The aerosol measurements were performed using a MAX-DOAS instrument called MARS-B originally designed by NOMREC of BSU. The MARS-B instrument records spectra of the scattered sunlight in a range of the elevation angles of 0°–90° in the UV and visible range of 341-426 and 416-500 nm with FWHM=0.32 nm. To retrieve aerosol extinction, we used its influence on the optical depth of the collision complex O2-O2 (or O4) of the molecular oxygen O2. Aerosol extinction was obtained for the wavelengths of 370 and 458 nm. The MAX-DOAS aerosol measurements were performed in January and February, 2014, and were further compared with Cimel-CE318 solar photometer data for clear days. Features of two data series are discussed in brief

Inter-comparison of MAX-DOAS measurements of tropospheric HONO slant column densities and vertical profiles during the CINDI-2 campaign

We present the inter-comparison of delta slant column densities (SCDs) and vertical profiles of nitrous acid (HONO) derived from measurements of different multi-axis differential optical absorption spectroscopy (MAX-DOAS) instruments and using different inversion algorithms during the Second Cabauw Inter-comparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) in September 2016 at Cabauw, the Netherlands (51.97∘ N, 4.93∘ E). The HONO vertical profiles, vertical column densities (VCDs), and near-surface volume mixing ratios are compared between different MAX-DOAS instruments and profile inversion algorithms for the first time. Systematic and random discrepancies of the HONO results are derived from the comparisons of all data sets against their median values. Systematic discrepancies of HONO delta SCDs are observed in the range of ±0.3×1015 molec. cm−2, which is half of the typical random discrepancy of 0.6×1015 molec. cm−2. For a typical high HONO delta SCD of 2×1015 molec. cm−2, the relative systematic and random discrepancies are about 15 % and 30 %, respectively. The inter-comparison of HONO profiles shows that both systematic and random discrepancies of HONO VCDs and near-surface volume mixing ratios (VMRs) are mostly in the range of ∼±0.5×1014 molec. cm−2 and ∼±0.1 ppb (typically ∼20 %). Further we find that the discrepancies of the retrieved HONO profiles are dominated by discrepancies of the HONO delta SCDs. The profile retrievals only contribute to the discrepancies of the HONO profiles by ∼5 %. However, some data sets with substantially larger discrepancies than the typical values indicate that inappropriate implementations of profile inversion algorithms and configurations of radiative transfer models in the profile retrievals can also be an important uncertainty source. In addition, estimations of measurement uncertainties of HONO dSCDs, which can significantly impact profile retrievals using the optimal estimation method, need to consider not only DOAS fit errors, but also atmospheric variability, especially for an instrument with a DOAS fit error lower than ∼3×1014 molec. cm−2. The MAX-DOAS results during the CINDI-2 campaign indicate that the peak HONO levels (e.g. near-surface VMRs of ∼0.4 ppb) often appeared in the early morning and below 0.2 km. The near-surface VMRs retrieved from the MAX-DOAS observations are compared with those measured using a co-located long-path DOAS instrument. The systematic differences are smaller than 0.15 and 0.07 ppb during early morning and around noon, respectively. Since true HONO values at high altitudes are not known in the absence of real measurements, in order to evaluate the abilities of profile inversion algorithms to respond to different HONO profile shapes, we performed sensitivity studies using synthetic HONO delta SCDs simulated by a radiative transfer model with assumed HONO profiles. The tests indicate that the profile inversion algorithms based on the optimal estimation method with proper configurations can reproduce the different HONO profile shapes well. Therefore we conclude that the features of HONO accumulated near the surface derived from MAX-DOAS measurements are expected to represent the ambient HONO profiles well

Evaluating different methods for elevation calibration of MAX-DOAS (Multi AXis Differential Optical Absorption Spectroscopy) instruments during the CINDI-2 campaign

We present different methods for in-field elevation calibration of MAX-DOAS (Multi AXis Differential Optical Absorption Spectroscopy) instruments that were applied and inter-compared during the second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2). One necessary prerequisite of consistent MAX-DOAS retrievals is a precise and accurate calibration of the elevation angles of the different measuring systems. Therefore, different methods for this calibration were applied to several instruments during the campaign, and the results were inter-compared. This work first introduces and explains the different methods, namely far- and near-lamp measurements, white-stripe scans, horizon scans and sun scans, using data and results for only one (mainly the Max Planck Institute for Chemistry) instrument. In the second part, the far-lamp measurements and the horizon scans are examined for all participating groups. Here, the results for both methods are first inter-compared for the different instruments; secondly, the two methods are compared amongst each other. All methods turned out to be well-suited for the calibration of the elevation angles of MAX-DOAS systems, with each of them having individual advantages and drawbacks. Considering the results of this study, the systematic uncertainties of the methods can be estimated as ±0.05∘ for the far-lamp measurements and the sun scans, ±0.25∘ for the horizon scans, and around ±0.1∘ for the white-stripe and near-lamp measurements. When comparing the results of far-lamp and horizon-scan measurements, a spread of around 0.9∘ in the elevation calibrations is found between the participating instruments for both methods. This spread is of the order of a typical field of view (FOV) of a MAX-DOAS instrument and therefore affecting the retrieval results. Further, consistent (wavelength dependent) offsets of 0.32∘ and 0.40∘ between far-lamp measurements and horizon scans are found, which can be explained by the fact that, despite the flat topography around the measurement site, obstacles such as trees might mark the visible horizon during daytime. The observed wavelength dependence can be explained by surface albedo effects. Lastly, the results are discussed and recommendations for future campaigns are given

Intercomparison of NO₂, O₄, O₃ and HCHO slant column measurements by MAX-DOAS and zenith-sky UV--visible spectrometers during CINDI-2

In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17 d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97∘ N, 4.93∘ E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation. The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions. The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques