scholarly journals Improved calibration procedures for the EM27/SUN spectrometers of the COllaborative Carbon Column Observing Network (COCCON)

2021 ◽  
Author(s):  
Carlos Alberti ◽  
Frank Hase ◽  
Matthias Frey ◽  
Darko Dubravica ◽  
Thomas Blumenstock ◽  
...  

Abstract. In this study, an extension on the previously reported status of the COllaborative Carbon Column Observing Network’s (COCCON) calibration procedures incorporating refined methods is presented. COCCON is a global network of portable Bruker EM27/SUN FTIR spectrometers for deriving column-averaged atmospheric abundances of greenhouse gases. The original laboratory open-path lamp measurements for deriving the instrumental line shape (ILS) of the spectrometer from water vapour lines have been refined and extended to the secondary detector channel incorporated in the EM27/SUN spectrometer for detection of carbon monoxide (CO). The refinements encompass improved spectroscopic line lists for the relevant water lines and a revision of the laboratory pressure measurements used for the analysis of the spectra. The new results are found to be in good agreement with those reported by Frey et al. (2019), and discussed in detail. In addition, a new calibration cell for ILS measurements was designed, constructed and put into service. Spectrometers calibrated since January 2020 were tested using both methods for ILS characterisation, open path (OP) and cell measurements. We demonstrate that both methods can detect the small variations of ILS characteristics between different spectrometers, but the results of the cell method indicate a systematic bias of the OP method. Finally, a revision and extension of the COCCON network instrument-to-instrument calibration factors for XCO2, XCO, and XCH4 is presented, incorporating 47 new spectrometers (of 83 in total by now). This calibration is based on the reference EM27/SUN spectrometer operated by the Karlsruhe Institute of Technology (KIT) and spectra collected by the collocated TCCON station Karlsruhe. Variations in the instrumental characteristics of the reference EM27/SUN during 2014 to 2017 were detected probably arising from realignment and the dual-channel upgrade performed in early 2018. These variations are considered in the evaluation of the instrument-specific calibration factors in order to keep all tabulated calibration results consistent.

2015 ◽  
Vol 8 (2) ◽  
pp. 941-963 ◽  
Author(s):  
T. Vlemmix ◽  
F. Hendrick ◽  
G. Pinardi ◽  
I. De Smedt ◽  
C. Fayt ◽  
...  

Abstract. A 4-year data set of MAX-DOAS observations in the Beijing area (2008–2012) is analysed with a focus on NO2, HCHO and aerosols. Two very different retrieval methods are applied. Method A describes the tropospheric profile with 13 layers and makes use of the optimal estimation method. Method B uses 2–4 parameters to describe the tropospheric profile and an inversion based on a least-squares fit. For each constituent (NO2, HCHO and aerosols) the retrieval outcomes are compared in terms of tropospheric column densities, surface concentrations and "characteristic profile heights" (i.e. the height below which 75% of the vertically integrated tropospheric column density resides). We find best agreement between the two methods for tropospheric NO2 column densities, with a standard deviation of relative differences below 10%, a correlation of 0.99 and a linear regression with a slope of 1.03. For tropospheric HCHO column densities we find a similar slope, but also a systematic bias of almost 10% which is likely related to differences in profile height. Aerosol optical depths (AODs) retrieved with method B are 20% high compared to method A. They are more in agreement with AERONET measurements, which are on average only 5% lower, however with considerable relative differences (standard deviation ~ 25%). With respect to near-surface volume mixing ratios and aerosol extinction we find considerably larger relative differences: 10 ± 30, −23 ± 28 and −8 ± 33% for aerosols, HCHO and NO2 respectively. The frequency distributions of these near-surface concentrations show however a quite good agreement, and this indicates that near-surface concentrations derived from MAX-DOAS are certainly useful in a climatological sense. A major difference between the two methods is the dynamic range of retrieved characteristic profile heights which is larger for method B than for method A. This effect is most pronounced for HCHO, where retrieved profile shapes with method A are very close to the a priori, and moderate for NO2 and aerosol extinction which on average show quite good agreement for characteristic profile heights below 1.5 km. One of the main advantages of method A is the stability, even under suboptimal conditions (e.g. in the presence of clouds). Method B is generally more unstable and this explains probably a substantial part of the quite large relative differences between the two methods. However, despite a relatively low precision for individual profile retrievals it appears as if seasonally averaged profile heights retrieved with method B are less biased towards a priori assumptions than those retrieved with method A. This gives confidence in the result obtained with method B, namely that aerosol extinction profiles tend on average to be higher than NO2 profiles in spring and summer, whereas they seem on average to be of the same height in winter, a result which is especially relevant in relation to the validation of satellite retrievals.


1999 ◽  
Vol 89 (4) ◽  
pp. 989-1003 ◽  
Author(s):  
István Bondár ◽  
Robert G. North ◽  
Gregory Beall

Abstract The prototype International Data Center (PIDC) in Arlington, Virginia, has been developing and testing software and procedures for use in the verification of the Comprehensive Test Ban Treaty. After three years of operation with a global network of array and three-component stations, it has been possible to characterize various systematic biases of those stations that are designated in the Treaty as part of the International Monitoring System (IMS). These biases include deviations of azimuth and slowness measurements from predicted values, caused largely by lateral heterogeneity. For events recorded by few stations, azimuth and slowness are used in addition to arrival-time data for location by the PIDC. Corrections to teleseismic azimuth and slowness observations have been empirically determined for most IMS stations providing data to the PIDC. Application of these corrections is shown to improve signal association and event location. At some stations an overall systematic bias can be ascribed to local crustal structure or to unreported instrumental problems. The corrections have been applied in routine operation of the PIDC since February 1998.


2018 ◽  
Vol 11 (4) ◽  
pp. 2523-2536 ◽  
Author(s):  
Astrid Lampert ◽  
Jörg Hartmann ◽  
Falk Pätzold ◽  
Lennart Lobitz ◽  
Peter Hecker ◽  
...  

Abstract. To investigate if the LI-COR humidity sensor can be used as a replacement of the Lyman-alpha sensor for airborne applications, the measurement data of the Lyman-alpha and several LI-COR sensors are analysed in direct intercomparison flights on different airborne platforms. One vibration isolated closed-path and two non-isolated open-path LI-COR sensors were installed on a Dornier 128 twin engine turbo-prop aircraft. The closed-path sensor provided absolute values and fluctuations of the water vapour mixing ratio in good agreement with the Lyman-alpha. The signals of the two open-path sensors showed considerable high-frequency noise, and the absolute value of the mixing ratio was observed to drift with time in this vibrational environment. On the helicopter-towed sensor system Helipod, with very low vibration levels, the open-path LI-COR sensor agreed very well with the Lyman-alpha sensor over the entire frequency range up to 3 Hz. The results show that the LI-COR sensors are well suited for airborne measurements of humidity fluctuations, provided that a vibrationless environment is given, and this turns out to be more important than close sensor spacing.


2014 ◽  
Vol 14 (5) ◽  
pp. 2571-2589 ◽  
Author(s):  
E. Eckert ◽  
T. von Clarmann ◽  
M. Kiefer ◽  
G. P. Stiller ◽  
S. Lossow ◽  
...  

Abstract. Drifts, trends and periodic variations were calculated from monthly zonally averaged ozone profiles. The ozone profiles were derived from level-1b data of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) by means of the scientific level-2 processor run by the Karlsruhe Institute of Technology (KIT), Institute for Meteorology and Climate Research (IMK). All trend and drift analyses were performed using a multilinear parametric trend model which includes a linear term, several harmonics with period lengths from 3 to 24 months and the quasi-biennial oscillation (QBO). Drifts at 2-sigma significance level were mainly negative for ozone relative to Aura MLS and Odin OSIRIS and negative or near zero for most of the comparisons to lidar measurements. Lidar stations used here include those at Hohenpeissenberg (47.8° N, 11.0° E), Lauder (45.0° S, 169.7° E), Mauna Loa (19.5° N, 155.6° W), Observatoire Haute Provence (43.9° N, 5.7° E) and Table Mountain (34.4° N, 117.7° W). Drifts against the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) were found to be mostly insignificant. The assessed MIPAS ozone trends cover the time period of July 2002 to April 2012 and range from −0.56 ppmv decade−1 to +0.48 ppmv decade−1 (−0.52 ppmv decade−1 to +0.47 ppmv decade−1 when displayed on pressure coordinates) depending on altitude/pressure and latitude. From the empirical drift analyses we conclude that the real ozone trends might be slightly more positive/less negative than those calculated from the MIPAS data, by conceding the possibility of MIPAS having a very small (approximately within −0.3 ppmv decade−1) negative drift for ozone. This leads to drift-corrected trends of −0.41 ppmv decade−1 to +0.55 ppmv decade−1 (−0.38 ppmv decade−1 to +0.53 ppmv decade−1 when displayed on pressure coordinates) for the time period covered by MIPAS Envisat measurements, with very few negative and large areas of positive trends at mid-latitudes for both hemispheres around and above 30 km (~10 hPa). Negative trends are found in the tropics around 25 and 35 km (~25 and 5 hPa), while an area of positive trends is located right above the tropical tropopause. These findings are in good agreement with the recent literature. Differences of the trends compared with the recent literature could be explained by a possible shift of the subtropical mixing barriers. Results for the altitude–latitude distribution of amplitudes of the quasi-biennial, annual and the semi-annual oscillation are overall in very good agreement with recent findings.


2018 ◽  
Vol 10 (5-6) ◽  
pp. 547-555 ◽  
Author(s):  
S. Ruess ◽  
K. A. Avramidis ◽  
M. Fuchs ◽  
G. Gantenbein ◽  
Z. Ioannidis ◽  
...  

Karlsruhe Institute of Technology (KIT) is doing research and development in the field of megawatt-class radio frequency (RF) sources (gyrotrons) for the Electron Cyclotron Resonance Heating (ECRH) systems of the International Thermonuclear Experimental Reactor (ITER) and the DEMOnstration Fusion Power Plant that will follow ITER. In the focus is the development and verification of the European coaxial-cavity gyrotron technology which shall lead to gyrotrons operating at an RF output power significantly larger than 1 MW CW and at an operating frequency above 200 GHz. A major step into that direction is the final verification of the European 170 GHz 2 MW coaxial-cavity pre-prototype at longer pulses up to 1 s. It bases on the upgrade of an already existing highly modular short-pulse (ms-range) pre-prototype. That pre-prototype has shown a world record output power of 2.2 MW already. This paper summarizes briefly the already achieved experimental results using the short-pulse pre-prototype and discusses in detail the design and manufacturing process of the upgrade of the pre-prototype toward longer pulses up to 1 s.


Author(s):  
S. Kudriakov ◽  
E. Studer ◽  
M. Kuznetsov ◽  
J. Grune

A set of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the LACOMECO European project is devoted to flame propagation in an obstructed large scale facility A3 (of 8 m height and 33 m3 volume) with initially vertical hydrogen concentration gradients. Almost linear positive and negative (relative to gravity) concentration gradients are created prior to ignition in the range from 4% to 13%, and the process of flame acceleration is investigated depending on hydrogen concentration gradient and ignition positions. In this paper we describe the A3 facility and analyse the experimental data obtained during the project. The results of numerical simulation performed using Europlexus code are presented together with the critical discussions and conclusions.


2014 ◽  
Vol 4 (1) ◽  
pp. 13
Author(s):  
Stefan Krebs ◽  
Sebastian Schmidt ◽  
Sven Matthiesen ◽  
Sören Hohmann

This paper presents a new mechatronics laboratory for students in the 5th semester of the mechatronics degree course at the Karlsruhe Institute of Technology. It is the aim of this teaching event to sharpen the appreciation of synergy effects in the development of mechatronic systems among the students. Despite of the great freedom in the development process, a concept has been evolved, which causes low running costs due to the combination of a model kit with rapid prototyping methods. A first pilot study of the laboratory starting in the winter term 2014 has shown that the students approach the task despite of the high level of difficulty with fun and dedication, especially because of the wide solution space which was unknown for them from previous lectures.


2016 ◽  
Vol 711 ◽  
pp. 863-870 ◽  
Author(s):  
Nico Herrmann ◽  
Harald S. Müller ◽  
Christoph Niklasch ◽  
Sylvie Michel-Ponnelle ◽  
Benoît Masson

Investigating nuclear power plant containments under accidental conditions obviously leads to the question of possible leakage through cracks of the pre-stressed concrete containment. In the last decades a number of civil engineering R&D programs dedicated to theoretical and experimental analyses have been performed. For the PACE-1450 experiment a leakage testing facility for pre-stressed curved specimen has been built in the laboratory of the Materials Testing and Research Institute (MPA Karlsruhe) at the Karlsruhe Institute of Technology (KIT). The test campaign has now been successfully finished with the evaluation of gained results still ongoing. The first half of the campaign was mainly dedicated to the cracking of the realistically reinforced specimen while the second half was focussing on the leakage behaviour of the cracked specimen. In the tests cold air, heated air and air-steam mixtures were used.


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