A fast SWIR imager for observations of transient features in OH airglow

Hannawald, Patrick; Schmidt, Carsten; Wüst, Sabine; Bittner, Michael

doi:10.5194/amt-9-1461-2016

Cited by 26 publications

(39 citation statements)

References 30 publications

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“…FAIM 3 is the second version of the Fast Airglow Imagers established at DLR (Hannawald et al, 2016). It is based on the SWIR camera CHEETAH CL developed by Xenics nv.…”

Section: Instrumentationmentioning

confidence: 99%

“…As reported by Hannawald et al (2016), the infrared imaging system FAIM (Fast Airglow Imager) is currently being operated by the German Aerospace Center (DLR) in order to continuously observe gravity waves in the OH airglow each night with a temporal resolution of 0.5 s. Obtaining a mean spatial resolution of 200 m pixel −1 , smallscale gravity wave structures with wavelengths down to 2 km have already been observed. Such instruments are currently operated at the Sonnblick Observatory (47.05 • N, 12.97 • E) in Austria (FAIM 1) as well as at Oberpfaffenhofen (48.09 • N, 11.28 • E), Germany (FAIM 4), for routine observations within the international Network for the Detection of Mesospheric Chance (NDMC, http://wdc.dlr.de/ndmc).…”

Section: Introductionmentioning

confidence: 99%

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High-resolution observations of small-scale gravity waves and turbulence features in the OH airglow layer

et al. 2016

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A new version of the Fast Airglow Imager (FAIM) for the detection of atmospheric waves in the OH airglow layer has been set up at the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) at Oberpfaffenhofen (48.09 • N, 11.28 • E), Germany. The spatial resolution of the instrument is 17 m pixel −1 in zenith direction with a field of view (FOV) of 11.1 km × 9.0 km at the OH layer height of ca. 87 km. Since November 2015, the system has been in operation in two different setups (zenith angles 46 and 0 • ) with a temporal resolution of 2.5 to 2.8 s.In a first case study we present observations of two small wave-like features that might be attributed to gravity wave instabilities. In order to spectrally analyse harmonic structures even on small spatial scales down to 550 m horizontal wavelength, we made use of the maximum entropy method (MEM) since this method exhibits an excellent wavelength resolution. MEM further allows analysing relatively short data series, which considerably helps to reduce problems such as stationarity of the underlying data series from a statistical point of view. We present an observation of the subsequent decay of well-organized wave fronts into eddies, which we tentatively interpret in terms of an indication for the onset of turbulence.Another remarkable event which demonstrates the technical capabilities of the instrument was observed during the night of 4-5 April 2016. It reveals the disintegration of a rather homogenous brightness variation into several filaments moving in different directions and with different speeds. It resembles the formation of a vortex with a horizontal axis of rotation likely related to a vertical wind shear. This case shows a notable similarity to what is expected from theoretical modelling of Kelvin-Helmholtz instabilities (KHIs).The comparatively high spatial resolution of the presented new version of the FAIM provides new insights into the structure of atmospheric wave instability and turbulent processes. Infrared imaging of wave dynamics on the subkilometre scale in the airglow layer supports the findings of theoretical simulations and modellings.

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“…FAIM 3 is the second version of the Fast Airglow Imagers established at DLR (Hannawald et al, 2016). It is based on the SWIR camera CHEETAH CL developed by Xenics nv.…”

Section: Instrumentationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High-resolution observations of small-scale gravity waves and turbulence features in the OH airglow layer

et al. 2016

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“…Tang et al (2014) and Wachter et al 10 (2015), e.g., find horizontal phase speeds of up to 160-180 m/s. The horizontal wavelengths cannot easily be compared since many authors focus on smaller horizontal scales (see, for example, Tang et al, 2014;Taylor et al, 2009;Hannawald et al, 2016;Sedlak et al, 2016). However, Reid (1986) presents in his fig.…”

Section: Horizontal Wavelengthsmentioning

confidence: 99%

“…Wachter et al (2015) show that the combination of three airglow spectrometers measuring under different azimuth angles allows the additional derivation of horizontal wavelengths. Due to the setup of the three instruments, their fields of view (FoV) and the data analysis technique, the retrieved wavelengths lie mostly in the range of some 100 km, the addressed wave periods range from 1 to 14 h with a maximum between 2 and 4 h. Small-scale horizontal features in the order of some 10 km or even 15 turbulent structures like they are observed with OH* cameras as shown by Sedlak et al (2016) and Hannawald et al (2016) cannot be investigated based on this approach. Schmidt et al (2017) introduce a method to additionally derive vertical wavelengths from OH* spectrometer measurements by observing two vibrational transitions, OH(3-1) and OH(4-2).…”

Section: Introductionmentioning

confidence: 99%

Derivation of horizontal and vertical wavelengths using a scanning OH(3-1) airglow spectrometer

Wüst

Offenwanger

Schmidt

et al. 2017

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For the first time, we present an approach to derive zonal, meridional and vertical wavelengths as well as periods of gravity waves based on only one OH* spectrometer addressing one vibrational-rotational transition. Knowledge of these parameters 15 is a precondition for the calculation of further information such as the wave group velocity vector.OH(3-1) spectrometer measurements allow the analysis of gravity wave periods, but spatial information cannot necessarily be deduced. We use a scanning spectrometer and the harmonic analysis to derive horizontal wavelengths at the mesopause above Oberpfaffenhofen (48.09°N, 11.28°E), Germany for 22 nights in 2015. Based on the approximation of the dispersion relation for gravity waves of low and medium frequency and additional horizontal wind information, we calculate vertical 20 wavelengths afterwards. The mesopause wind measurements nearest to Oberpfaffenhofen are conducted at Collm (51.30°N, 13.02°E), Germany, ca. 380 km northeast of Oberfpaffenhofen by a meteor radar.In order to check our results, vertical temperature profiles of TIMED-SABER (Thermosphere Ionosphere Mesosphere Energetics Dynamics, Sounding of the Atmosphere using Broadband Emission Radiometry) overpasses are analysed with respect to the dominating vertical wavelength. 25Atmos. Meas. Tech. Discuss., https://doi

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“…These perturbations can be measured and are most often caused by atmospheric gravity waves or other atmospheric wave types. Gravity wave parameters such as horizontal wavelength and observed phase speed can be derived from images of the OH airglow layer (see Peterson, 1979;Taylor et al, 1995;Hecht et al, 2000;Nakamura et al, 1999;Mukherjee et al, 2010;Pautet et al, 2014 and others).…”

Section: Introductionmentioning

confidence: 99%

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Hannawald¹

2018

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Between December 2013 and August 2017 the instrument FAIM (Fast Airglow IMager) observed the OH airglow emission at two Alpine stations. A year of measurements was performed at Oberpfaffenhofen, Germany (48.09 • N, 11.28 • E) and 2 years at Sonnblick, Austria (47.05 • N, 12.96 • E). Both stations are part of the network for the detection of mesospheric change (NDMC). The temporal resolution is two frames per second and the field-of-view is 55 km × 60 km and 75 km × 90 km at the OH layer altitude of 87 km with a spatial resolution of 200 and 280 m per pixel, respectively. This resulted in two dense data sets allowing precise derivation of horizontal gravity wave parameters. The analysis is based on a two-dimensional fast Fourier transform with fully automatic peak extraction. By combining the information of consecutive images, time-dependent parameters such as the horizontal phase speed are extracted. The instrument is mainly sensitive to high-frequency small-and medium-scale gravity waves. A clear seasonal dependency concerning the meridional propagation direction is found for these waves in summer in the direction to the summer pole. The zonal direction of propagation is eastwards in summer and westwards in winter. Investigations of the data set revealed an intra-diurnal variability, which may be related to tides. The observed horizontal phase speed and the number of wave events per observation hour are higher in summer than in winter.

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A fast SWIR imager for observations of transient features in OH airglow

Abstract: This paper introduces the instrument and compares the FAIM data with spectrally resolved GRIPS (GRound-based Infrared P-branch Spectrometer) data. In addition, a case study of a breaking gravity wave event, which we assume to be associated with Kelvin-Helmholtz instabilities, is discussed.

Cited by 26 publications

References 30 publications

High-resolution observations of small-scale gravity waves and turbulence features in the OH airglow layer

High-resolution observations of small-scale gravity waves and turbulence features in the OH airglow layer

Derivation of horizontal and vertical wavelengths using a scanning OH(3-1) airglow spectrometer

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