Pointing errors in solar absorption spectrometry – correction scheme and its validation

Reichert, Andreas; Hausmann, Petra; Sussmann, Ralf

doi:10.5194/amt-8-3715-2015

Cited by 8 publications

(14 citation statements)

References 34 publications

(37 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At lower wavenumber values, thermal emission from the instrument itself becomes non-negligible. Therefore, alternative methods such as the widely used method introduced by Revercomb et al (1988) are more suitable for calibration in this spectral range. The proposed new method can, however, be implemented with minor changes in the spectral range beyond 7800 cm −1 .…”

Section: Discussionmentioning

confidence: 99%

“…As outlined above, the use of a single blackbody calibration source is suitable for solar FTIR measurements in the NIR, contrary, e.g., to the Atmospheric Emitted Radiance Interferometer (AERI) (Knuteson et al, 2004) that achieves radiometric calibration in the FIR and MIR via the method proposed by Revercomb et al (1988) using two blackbody sources at different cavity temperatures. This is mainly due to the negligible influence of thermal emission by the instru-ment on the measured radiance in the NIR (see Sect.…”

Section: Discussionmentioning

confidence: 99%

“…In the far-and mid-infrared spectral range, a calibration method for high-resolution spectral radiance measurements based on the observation of two blackbody sources at different temperatures is well established (Revercomb et al, 1988). However, there is currently no standard calibration scheme available for the NIR spectral range.…”

mentioning

confidence: 99%

See 2 more Smart Citations

The Zugspitze radiative closure experiment for quantifying water vapor absorption over the terrestrial and solar infrared – Part 2: Accurate calibration of high spectral-resolution infrared measurements of surface solar radiation

2016

View full text Add to dashboard Cite

Abstract. Quantitative knowledge of water vapor absorption is crucial for accurate climate simulations. An open science question in this context concerns the strength of the water vapor continuum in the near infrared (NIR) at atmospheric temperatures, which is still to be quantified by measurements. This issue can be addressed with radiative closure experiments using solar absorption spectra. However, the spectra used for water vapor continuum quantification have to be radiometrically calibrated. We present for the first time a method that yields sufficient calibration accuracy for NIR water vapor continuum quantification in an atmospheric closure experiment. Our method combines the Langley method with spectral radiance measurements of a high-temperature blackbody calibration source (<  2000 K). The calibration scheme is demonstrated in the spectral range 2500 to 7800 cm−1, but minor modifications to the method enable calibration also throughout the remainder of the NIR spectral range. The resulting uncertainty (2σ) excluding the contribution due to inaccuracies in the extra-atmospheric solar spectrum (ESS) is below 1 % in window regions and up to 1.7 % within absorption bands. The overall radiometric accuracy of the calibration depends on the ESS uncertainty, on which at present no firm consensus has been reached in the NIR. However, as is shown in the companion publication Reichert and Sussmann (2016), ESS uncertainty is only of minor importance for the specific aim of this study, i.e., the quantification of the water vapor continuum in a closure experiment. The calibration uncertainty estimate is substantiated by the investigation of calibration self-consistency, which yields compatible results within the estimated errors for 91.1 % of the 2500 to 7800 cm−1 range. Additionally, a comparison of a set of calibrated spectra to radiative transfer model calculations yields consistent results within the estimated errors for 97.7 % of the spectral range.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

The Zugspitze radiative closure experiment for quantifying water vapor absorption over the terrestrial and solar infrared – Part 2: Accurate calibration of high spectral-resolution infrared measurements of surface solar radiation

2016

View full text Add to dashboard Cite

show abstract

“…On average, we obtain DOFS = 2.1 (Zugspitze) and DOFS = 1.8 (Lauder) for methane retrievals, while for ethane retrievals DOFS = 1.6 (Zugspitze) and DOFS = 1.2 (Lauder) is reached. Solar tracker inaccuracies and resulting total column errors during a short period of the Zugspitze long-time record are accounted for using the pointing error correction scheme developed by Reichert et al (2015). To obtain column-averaged dry-air mole fractions, the retrieved total columns of methane and ethane are divided by the corresponding dry pressure column, which is derived from ground pressure measurements and four times daily pressure-temperature-humidity profiles from the National Center for Environmental Prediction (NCEP) interpolated to FTIR measurement time.…”

Section: P Hausmann Et Almentioning

confidence: 99%

Contribution of oil and natural gas production to renewed increase in atmospheric methane (2007–2014): top–down estimate from ethane and methane column observations

2016

View full text Add to dashboard Cite

Abstract. Harmonized time series of column-averaged mole fractions of atmospheric methane and ethane over the period 1999-2014 are derived from solar Fourier transform infrared (FTIR) measurements at the Zugspitze summit (47 • N, 11 • E; 2964 m a.s.l.) and at Lauder (45 • S, 170 • E; 370 m a.s.l.). Long-term trend analysis reveals a consistent renewed methane increase since 2007 of 6. 2 [5.6, 6.9] ppb yr −1 (parts-per-billion per year) at the Zugspitze and 6.0 [5.3, 6.7] ppb yr −1 at Lauder (95 % confidence intervals). Several recent studies provide pieces of evidence that the renewed methane increase is most likely driven by two main factors: (i) increased methane emissions from tropical wetlands, followed by (ii) increased thermogenic methane emissions due to growing oil and natural gas production. Here, we quantify the magnitude of the second class of sources, using long-term measurements of atmospheric ethane as a tracer for thermogenic methane emissions. and can be assigned to thermogenic methane emissions with an ethane-to-methane ratio (EMR) of 12-19 %. We present optimized emission scenarios for 2007-2014 derived from an atmospheric two-box model. From our trend observations we infer a total ethane emission increase over the period 2007-2014 from oil and natural gas sources of 1-11 Tg yr −1 along with an overall methane emission increase of 24-45 Tg yr −1 . Based on these results, the oil and natural gas emission contribution (C) to the renewed methane increase is deduced using three different emission scenarios with dedicated EMR ranges. Reference scenario 1 assumes an oil and gas emission combination with EMR = 7.0-16.2 %, which results in a minimum contribution C > 39 % (given as lower bound of 95 % confidence interval). Beside this most plausible scenario 1, we consider two less realistic limiting cases of pure oil-related emissions (scenario 2 with EMR = 16.2-31.4 %) and pure natural gas sources (scenario 3 with EMR = 4.4-7.0 %), which result in C > 18 % and C > 73 %, respectively. Our results suggest that long-term observations of columnaveraged ethane provide a valuable constraint on the source attribution of methane emission changes and provide basic knowledge for developing effective climate change mitigation strategies.

show abstract

“…In fact, the determination of pointing accuracy is a common challenge for most types of Sun-pointing instruments, and various approaches have been presented to address this issue. For example, innovative camera-based (e.g., Gisi et al, 2011) and camera-free (e.g., Reichert et al, 2015) approaches to monitor tracking accuracy have been presented in the field of solar Fourier transform infrared (FTIR) spectrometry. While Gisi et al (2011) documents a camera setup with real-time image-evaluation and tracking software (CamTrack), Reichert et al (2015) presents an approach based on subsequent FTIR measurements with a different orientation of the solar rotation axis relative to the zenith direction, which allows us to obtain both mispointing components, the component in the zenith direction, and the component perpendicular to the solar rotation axis.…”

Section: Introductionmentioning

confidence: 99%

An automated method for the evaluation of the pointing accuracy of Sun-tracking devices

et al. 2017

View full text Add to dashboard Cite

Abstract. The accuracy of solar radiation measurements, for direct (DIR) and diffuse (DIF) radiation, depends significantly on the precision of the operational Sun-tracking device. Thus, rigid targets for instrument performance and operation have been specified for international monitoring networks, e.g., the Baseline Surface Radiation Network (BSRN) operating under the auspices of the World Climate Research Program (WCRP). Sun-tracking devices that fulfill these accuracy requirements are available from various instrument manufacturers; however, none of the commercially available systems comprise an automatic accuracy control system allowing platform operators to independently validate the pointing accuracy of Sun-tracking sensors during operation. Here we present KSO-STREAMS (KSO-SunTRackEr Accuracy Monitoring System), a fully automated, systemindependent, and cost-effective system for evaluating the pointing accuracy of Sun-tracking devices. We detail the monitoring system setup, its design and specifications, and the results from its application to the Sun-tracking system operated at the Kanzelhöhe Observatory (KSO) Austrian radiation monitoring network (ARAD) site. The results from an evaluation campaign from March to June 2015 show that the tracking accuracy of the device operated at KSO lies within BSRN specifications (i.e., 0.1 • tracking accuracy) for the vast majority of observations (99.8 %). The evaluation of manufacturer-specified active-tracking accuracies (0.02 • ), during periods with direct solar radiation exceeding 300 W m −2 , shows that these are satisfied in 72.9 % of observations. Tracking accuracies are highest during clearsky conditions and on days where prevailing clear-sky conditions are interrupted by frontal movement; in these cases, we obtain the complete fulfillment of BSRN requirements and 76.4 % of observations within manufacturer-specified active-tracking accuracies. Limitations to tracking surveillance arise during overcast conditions and periods of partial solar-limb coverage by clouds. On days with variable cloud cover, 78.1 % (99.9 %) of observations meet active-tracking (BSRN) accuracy requirements while for days with prevailing overcast conditions these numbers reduce to 64.3 % (99.5 %).

show abstract

Pointing errors in solar absorption spectrometry – correction scheme and its validation

Cited by 8 publications

References 34 publications

The Zugspitze radiative closure experiment for quantifying water vapor absorption over the terrestrial and solar infrared – Part 2: Accurate calibration of high spectral-resolution infrared measurements of surface solar radiation

The Zugspitze radiative closure experiment for quantifying water vapor absorption over the terrestrial and solar infrared – Part 2: Accurate calibration of high spectral-resolution infrared measurements of surface solar radiation

Contribution of oil and natural gas production to renewed increase in atmospheric methane (2007–2014): top–down estimate from ethane and methane column observations

An automated method for the evaluation of the pointing accuracy of Sun-tracking devices

Contact Info

Product

Resources

About