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- Hopfner, M., et al.
(author)
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Validation of MIPAS ClONO2 measurements
- 2007
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 7, s. 257-281
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Journal article (peer-reviewed)abstract
- Altitude profiles of ClONO2 retrieved with the IMK (Institut fur Meteorologie und Klimaforschung) science-oriented data processor from MIPAS/Envisat (Michelson Interferometer for Passive Atmospheric Sounding on Envisat) mid-infrared limb emission measurements between July 2002 and March 2004 have been validated by comparison with balloon-borne (Mark IV, FIRS2, MIPAS-B), airborne (MIPAS-STR), ground-based (Spitsbergen, Thule, Kiruna, Harestua, Jungfraujoch, Izana, Wollongong, Lauder), and spaceborne (ACE-FTS) observations. With few exceptions we found very good agreement between these instruments and MIPAS with no evidence for any bias in most cases and altitude regions. For balloon-borne measurements typical absolute mean differences are below 0.05 ppbv over the whole altitude range from 10 to 39 km. In case of ACE-FTS observations mean differences are below 0.03 ppbv for observations below 26 km. Above this altitude the comparison with ACE-FTS is affected by the photochemically induced diurnal variation of ClONO2. Correction for this by use of a chemical transport model led to an overcompensation of the photochemical effect by up to 0.1 ppbv at altitudes of 30-35 km in case of MIPAS-ACE-FTS comparisons while for the balloon-borne observations no such inconsistency has been detected. The comparison of MIPAS derived total column amounts with ground-based observations revealed no significant bias in the MIPAS data. Mean differences between MIPAS and FTIR column abundances are 0.11 +/- 0.12 x 10(14) cm(-2) (1.0 +/- 1.1%) and -0.09 +/- 0.19 x 10(14) cm(-2) (-0.8 +/- 1.7%), depending on the coincidence criterion applied. chi(2) tests have been performed to assess the combined precision estimates of MIPAS and the related instruments. When no exact coincidences were available as in case of MIPAS-FTIR or MIPAS-ACE-FTS comparisons it has been necessary to take into consideration a coincidence error term to account for chi(2) deviations. From the resulting chi(2) profiles there is no evidence for a systematic over/underestimation of the MIPAS random error analysis.
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- Khosrawi, Farahnaz, et al.
(author)
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Seasonal cycle of averages of nitrous oxide and ozone in the Northern and Southern Hemisphere polar, midlatitude, and tropical regions derived from ILAS/ILAS-II and Odin/SMR observations
- 2008
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:D18, s. D18305-
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Journal article (peer-reviewed)abstract
- Northern and Southern Hemispheric monthly averages of ozone (O-3) and nitrous oxide (N2O) have been suggested as a tool for evaluating atmospheric photochemical models. An adequate data set for such an evaluation can be derived from measurements made by satellites which, in general, have a high spatial and temporal coverage. Here, we use measurements made by the Improved Limb Atmospheric Spectrometers (ILAS and ILAS-II) which use the solar occultation technique and by the Odin-Sub-Millimetre Radiometer (Odin/SMR) which passively observes thermal emissions from the Earth's limb. From ILAS/ILAS-II and Odin/SMR observations, 1-year data sets of monthly averaged O-3 and N2O, covering a full seasonal cycle, were derived for the latitude range between 60 - 90 degrees N and 60 - 90 degrees S, respectively, by partitioning the data into equal bins of altitude or potential temperature. A comparison between both data sets in this latitude region shows a good agreement and verifies that limited sampling from satellite occultation experiments does not constitute a problem for deriving such a full seasonal cycle of monthly averaged N2O and O-3. Since Odin/SMR provides measurements globally, a 1-year data set of monthly averaged N2O and O-3 is reported here for both the entire Northern and Southern Hemispheres from these measurements. Further, these hemispheric data sets from Odin/SMR are separated into data sets of monthly averaged N2O and O-3 for the low latitudes, midlatitudes, and high latitudes. The resulting families of curves help to differentiate between O-3 changes due to photochemistry from those due to transport. These 1-year hemispheric data sets of monthly averaged N2O and O-3 from Odin/SMR and ILAS/ILAS-II as well as the data sets of monthly averaged N2O and O-3 for the specific latitude regions from Odin/SMR provide a potentially important tool for the evaluation of atmospheric photochemical models. An example of how such an evaluation can be performed is given using data from two chemical transport models (CTMs), the Chemical Lagrangian Model of the Stratosphere (CLaMS) and the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA). We find a good agreement between Odin/SMR and the CTMs CLaMS and KASIMA with differences generally less than +/- 20%.
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- Burgard, W., et al.
(author)
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A Comparison of SLAM Algorithms Based on a Graph of Relations
- 2009
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In: <em>IEEE/RSJ Int. Conf. on Intelligent Robots and Systems (IROS)</em>. - : IEEE conference proceedings. ; , s. 2089-2095
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Conference paper (peer-reviewed)abstract
- In this paper, we address the problem of creating an objective benchmark for comparing SLAM approaches. We propose a framework for analyzing the results of SLAM approaches based on a metric for measuring the error of the corrected trajectory. The metric uses only relative relations between poses and does not rely on a global reference frame. The idea is related to graph-based SLAM approaches, namely to consider the energy that is needed to deform the trajectory estimated by a SLAM approach into the ground truth trajectory. Our method enables us to compare SLAM approaches that use different estimation techniques or different sensor modalities since all computations are made based on the corrected trajectory of the robot. We provide sets of relative relations needed to compute our metric for an extensive set of datasets frequently used in the SLAM community. The relations have been obtained by manually matching laser-range observations to avoid the errors caused by matching algorithms. Our benchmark framework allows the user an easy analysis and objective comparisons between different SLAM approaches.
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- Kümmerle, R., et al.
(author)
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On Measuring the Accuracy of SLAM Algorithms
- 2009
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In: Autonomous Robots. - : Springer. - 0929-5593 .- 1573-7527. ; 27:4, s. 387-407
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Journal article (peer-reviewed)abstract
- In this paper, we address the problem of creating an objective benchmark for evaluating SLAM approaches.We propose a framework for analyzing the results of a SLAM approach based on a metric for measuring the error of the corrected trajectory. This metric uses only relative relations between poses and does not rely on a global reference frame. This overcomes serious shortcomings of approaches using a global reference frame to compute the error. Our method furthermore allows us to compare SLAM approaches that use different estimation techniques or different sensor modalities since all computations are made based on the corrected trajectory of the robot. We provide sets of relative relations needed to compute our metric for an extensive set of datasets frequently used in the robotics community. The relations have been obtained by manually matching laser-range observations to avoid the errors caused by matching algorithms. Our benchmark framework allows the user to easily analyze and objectively compare different SLAM approaches.
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