AMTAtmospheric Measurement TechniquesAMTAtmos. Meas. Tech.1867-8548Copernicus PublicationsGöttingen, Germany10.5194/amt-11-4757-2018A large-area blackbody for in-flight calibration of an infrared interferometer deployed on board a long-duration balloon for stratospheric researchA balloon-borne blackbody for in-flight calibration of an infrared interferometerOlschewskiFriedhelmolsch@uni-wuppertal.deMonteChristianAdibekyanAlbertReinigerMaxGutschwagerBerndtHollandtJoergKoppmannRalfInstitute for Atmospheric and Environmental Research at the University of Wuppertal, 42097 Wuppertal, GermanyPhysikalisch-Technische Bundesanstalt, 10587 Berlin, GermanyFriedhelm Olschewski (olsch@uni-wuppertal.de)14August20181184757476220November201713March20189July201824July2018This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/This article is available from https://amt.copernicus.org/articles/11/4757/2018/amt-11-4757-2018.htmlThe full text article is available as a PDF file from https://amt.copernicus.org/articles/11/4757/2018/amt-11-4757-2018.pdf
The deployment of the imaging Fourier Transform Spectrometer
GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) on
board a long-duration balloon for stratospheric research requires a blackbody
for in-flight calibration in order to provide traceability to the
International Temperature Scale (ITS-90) to ensure comparability with the
results of other experiments and over time. GLORIA, which has been deployed
onboard various research aircraft such as the Russian M55 Geophysica or the
German HALO in the past, shall also be used for detailed atmospheric
measurements in the stratosphere up to 40 km altitude. The instrument
uses a two-dimensional detector array and an imaging optics with a large
aperture diameter of 36 mm and an opening angle of
4.07∘× 4.07∘ for infrared limb observations. To
overfill the field of view (FOV) of the instrument, a large-area blackbody
radiation sources (125 mm× 125 mm) is required for
in-flight calibration.
In order to meet the requirements regarding the scientific goals of the
GLORIA missions, the radiance temperature of the blackbody calibration source
has to be determined to better than 100 mK and the spatial
temperature uniformity shall be better than 150 mK. As electrical
resources on board a stratospheric balloon are very limited, the latent heat
of the phase change of a eutectic material is utilized for temperature
stabilization of the calibration source, such that the blackbody has a
constant temperature of about -32 ∘C corresponding to a
typical temperature observed in the stratosphere.
The Institute for Atmospheric and Environmental Research at the University of
Wuppertal designed and manufactured a prototype of the large-area blackbody
for in-flight calibration of an infrared interferometer deployed on board a
long-duration balloon for stratospheric research. This newly developed
calibration source was tested under lab conditions as well as in a climatic
and environmental test chamber in order to verify its performance especially
under flight conditions. At the PTB (Physikalisch-Technische Bundesanstalt), the
German national metrology institute, the spatial radiance distribution of the
blackbody was determined and traceability to the International Temperature
Scale (ITS-90) has been assured. In this paper the design and performance of
the balloon-borne blackbody (BBB) is presented.
Introduction
The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA)
is an imaging Fourier Transform Spectrometer (FTS) developed for trace gas
measurements in the atmosphere. GLORIA utilizes a two-dimensional MCT
detector array with a large aperture optical system for detailed infrared
limb observations . In the past, GLORIA
participated in various international research campaigns
(e.g., TACTS 2012, , POLSTRACC
2015, , STRATO-CLIM 2016, , WISE 2017)
deployed on board the research aircraft Geophysica and HALO. It is planned to
install GLORIA on board a stratospheric balloon in order to perform long-term
measurements at altitudes up to 40 km for several weeks.
It is common practice for balloon-borne FTS instruments to establish onboard
two-point calibration procedures using deep space as one reference point and
a temperature stabilized blackbody e.g.,. That
approach ensures the consistency of the measurements over a long period of
time in a variable environment with changing detector sensitivity due to
temperature alteration of the instrument. As the environmental conditions
at the flight altitude (35–38 km) are very different from those on
board a research aircraft, a new concept for the in-flight calibration system
had to be developed. Especially the limitation of electrical power was an
important factor in the design of the new large-area blackbody calibration
source.
The GLORIA instrument
GLORIA is a joint project of Research Center Juelich and the Karlsruhe Institute
of Technology, Germany. GLORIA is designed as an imaging FTS operating in the
thermal infrared spectral region from 770 to 1400 cm-1. The spectral resolution is adjusted to two different
measuring modes: 1.25 cm-1 for the dynamics mode and
0.1 cm-1 for the chemistry mode, respectively. A two-lens
aspherical telescope with an aperture of approximately 36 mm and a
vertical and horizontal field of view (FOV) of
4.07∘× 4.07∘ is used to image the atmosphere.
The radiation coming from the atmosphere is directly projected onto a large
two-dimensional photovoltaic MCT detector array mounted in a dewar with an
integrated Stirling cooler. GLORIA makes novel information on small-scale
atmospheric dynamics available, e.g., STE, the stratosphere–troposphere
exchange and other important phenomena
.
In order to study long-term phenomena in the stratosphere for up to 2 weeks, GLORIA shall be installed into a gondola of a stratospheric balloon. A
schematic of the balloon instrument is shown in Fig. . The
GLORIA balloon instrument utilizes a rotatable mirror for line-of-sight
stabilization during measurement. This mirror is also used to adjust the
line-of-sight to the blackbody calibration source and to view deep space.
Schematic of the GLORIA balloon instrument.
Calibration concept and requirements
In order to retrieve temperature and trace gas concentrations in the
atmosphere, the measured detector signals need to be converted into
atmospheric infrared radiance spectra with very small uncertainties. Assuming
that the measurement system has a linear response, the required high accuracy
can be achieved by a two point calibration in the range of the observed
atmospheric radiance . Deep space as an ideal blackbody
with a very uniform temperature of 2.7 K is a perfect calibration
source for the detector. By looking at different sectors of the sky, the
influence of star light can be subtracted. As second calibration source a
large-area blackbody at a temperature of about 240 K with high
temperature homogeneity of better than 0.15 K shall be used.
As the uncertainties in spectral radiance of the blackbody calibration
source influence the uncertainties in the measured atmospheric radiances,
radiometric calibration of the instrument with an uncertainty of less than
1 % is necessary . This requires a very high
emissivity of greater than 0.99 and very precise temperature measurement with
a temperature uncertainty of less than 0.1 K. For the technical
realization of the radiometric accuracy, the large-area blackbody calibration
source has to fulfill the requirements listed in
Table .
Requirements for the large-area blackbody calibration source
Optical surface125 mm× 125 mmTemperature range-30 to -35 ∘CTemperature uncertainty< 0.1 KEffective emissivity (7–13 µm)> 0.99Spatial temperature uniformity< 0.15 KShort-term temperature stability< 25 mKmin-1Design of the GLORIA balloon blackbody
The GLORIA in-flight calibration system uses a high-precision blackbody
radiation source, which is operated at a temperature of about 240 K.
The optical surface of this balloon blackbody (BBB) consists of a wire-eroded
aluminum plate with an array of 225 small pyramids, which are varnished with
NEXTEL-Velvet Coating (see Fig. ). Integrated in a housing
with outer dimensions of
140 mm× 140 mm× 200 mm, the
optical surface has an effective emissivity of ϵ> 0.997. In
order to verify the thermal uniformity, ten thermally cycled and calibrated
platinum resistance thermometers (PRTs) are installed in the aluminum plate.
Optical surface of large-area blackbody with wire-eroded pyramid
array. Size of a single pyramid:
base = 5 mm× 5 mm;
height = 9 mm.
For thermal decoupling of the blackbody calibration source from the GLORIA
balloon instrument, Glass-Fiber Reinforced Plastic (GFRP) parts are used. In
order to reduce the adverse influence of the thermal environment, the BBB is
covered with polystyrene foam sheets (see Fig. ).
Design of balloon blackbody (a) with electronics and heat
exchangers for pre-cooling (b).
Lab test of the melting plateau at an ambient pressure of about
1013 hPa and an ambient temperature of about
23 ∘C(a); and a thermal-vacuum test of the BBB at
ambient pressure of 10 hPa and ambient temperature of about
-22 ∘C(b).
(a) The Reduced Background Calibration Facility (RBCF) at
PTB and (b) the large-area balloon blackbody inside the source
chamber of the RBCF.
For temperature stabilization of the airborne GLORIA Blackbodies (GBBs)
thermo-electric coolers (TECs) are used cf.. This
concept is not feasible for the balloon-borne instrument because the power
consumption is too high and there is not sufficient air for cooling the heat
exchangers at flight altitude. Therefore, a different design concept is
realized. The phase change of a eutectic material is used to stabilize the
temperature of the optical surface at about -32 ∘C.
Six commercial cooling pads from Va-Q-tec are used for thermal stabilization
(https://www.va-q-tec.com/de/produkte/kaelte-und-waermespeicher/va-q-accu-32g.html,
last access: 10 August 2018). Table gives the properties of
the PCM (phase change material) cooling pads. Two cooling pads are used for
temperature control of the optical surface while one each will control the
temperature of the four walls of the housing.
In order to get the PCM into the solid state, pre-cooling with a chiller or
with liquid nitrogen is needed. Therefore, the PCM cooling pads are equipped
with heat exchangers made of aluminum shown in Fig. b.
Lab tests and test in a thermal vacuum chamber
In order to study the thermal behavior of the BBB, thermal tests were
performed in the lab and in the thermal vacuum chamber of Research Centre
Juelich. It was the goal of these tests to measure the progression of the
phase change and to estimate the possible operating time on a balloon mission
in the stratosphere. Figure a shows the thermal behavior
during a lab test while the aperture was closed with a polystyrene foam
sheet. The pre-cooling of the PCM cooling pads was achieved by storing the
complete device in a cooling box for 12 h. The progression of the phase
change lasted 7 h with a very small temperature change of
35 mKh-1. In the thermal vacuum chamber the most realistic
condition of a balloon flight was simulated. The chamber pressure was set to
10 hPa and the temperature to -22 ∘C, respectively.
The complete temperature evolution over time is shown in
Fig. b. Unfortunately, the test had to be discontinued after
320 h for organizational reasons. At the beginning of the test, the mean BBB
temperature was about -33.5 ∘C. The phase change started
nearly a week later and was still ongoing when the test ended. As the
temperature trend in the solid state was very small, calibrating the GLORIA
instrument before the onset of the phase change during a balloon flight will
also be possible.
Properties of the PCM cooling pads
“va-Q-accu-32G”.
The radiometric characterization of the large-area blackbody was performed
inside the Reduced Background Calibration Facility (RBCF)
of the Physikalisch-Technische Bundesanstalt (PTB)
as shown in Fig. . The pressure inside the RBCF was set to
10 hPa corresponding to the ambient pressure expected in the
stratosphere. The heat exchangers of the blackbody calibration source were
connected to an external chiller. By adjusting the temperature of the
coolant, the PCM elements were taken to the solid state first and then the
chiller thermostat was set slightly above the melting point. Due to its large
optical surface, the blackbody faces a thermally non-uniform environment
inside the RBCF with temperatures in the range between -120 and
23 ∘C. The cooled optical pathway suppressing the background
radiation from the wall and surrounding the field of view of the VIRST along
its line of sight is a sequence of cooled apertures and tubes. This aperture
system (beamline) extends into the source chamber and has there an outer
diameter of 40 mm. As the opening of the balloon blackbody is
100 mm by 100 mm, only a part of this aperture sees the
cooled beamline (-120 ∘C) while the remaining aperture of
the blackbody receives radiation from the inner walls of the source chamber,
which are at room temperature. Therefore, the radiation exchange with the
environment through the aperture is neither identical to the operating
conditions in the stratosphere nor to the measurement setup in the
thermal-vacuum chamber. In spite of this drawback, a phase change time
(melting-plateau) of more than 8 h could be reached. During this
phase change period the radiance temperature and its lateral distribution was
measured.
The change of radiance temperature and of contact temperature over time is
shown in Fig. together with the set temperature of the
external chiller for thermalizing the heat exchangers. The collinearity of
radiance temperature and contact temperature is obvious. The slightly higher
radiance temperature results from the thermal gradient between sensor and
emitting surface due to the thermal conductivities of the aluminium and the
coating and the non-ideal emissivity of the BBB. Due to the latter, a part of
the radiation from the surrounding (1 – emissivity) contributes to the
apparent radiance temperature and leads to higher apparent temperatures when
the BBB is operated below room temperature.
Change of radiance temperature and of contact temperature in the
backplane of the GLORIA balloon blackbody over time during phase change in
PCM cooling pads.
Figure demonstrates the very high spatial uniformity of
the radiance temperature of better than 100 mK (peak-to-peak) over
the used area of the aperture of the blackbody. The sampling of the radiating
surface of the blackbody was performed by the calibrated broad band radiation
thermometer VIRST (8–14 µm) . These results
show the suitability of the large-area blackbody BBB for the radiometric
traceability of balloon-borne imaging spectrometers as GLORIA.
Lateral radiance temperature distribution of the large-area
blackbody, recorded during phase change, featuring a non-uniformity of less
than 100 mK (peak-to-peak).
The blackbody should not be considered as reference blackbody operating at a
fixed temperature given by the melting plateau of the PCM material. Rather,
the PCM material should be considered as a reservoir for latent heat only,
enabling the operation of the blackbody with very low energy consumption. By
using well characterized PTR sensors in the backplane which are absolutely
calibrated with low uncertainties, the momentary temperature of the backplane
can be determined (cf. Fig. ) and the corresponding radiance
temperature is given as well by the characterization with VIRST. Additional
radiometric characterizations of the lateral distribution of the radiance
temperature in the liquid and frozen state revealed also a very good
uniformity. This would permit the use of the blackbody even under these
conditions.
Summary and conclusions
The Institute for Atmospheric and Environmental Research at the University of
Wuppertal developed a large-area calibration source based on phase change
material for deployment on board stratospheric balloons. The newly designed
blackbody can be used for precise in-flight calibration of hyperspectral
cameras which are assigned for remote sensing of the atmosphere. The use of
phase change material enables a long-lasting temperature stability without
any power consumption, which is essential for long duration balloon flights.
The radiometric characterization at PTB showed that the requirement regarding
the uncertainty in radiance temperature and its uniformity across the
aperture below 100 mK can be reached. So atmospheric measurements
employing this blackbody will become traceable to the International
Temperature Scale (ITS-90) with low uncertainties.
Data are presented throughout the text. Test results can be
found directly in Figs. , , and
.
The authors declare that they have no conflict of
interest.
Acknowledgements
Part of this work has been supported by the European Metrology Research
Programme (EMRP) within the joint research project Metrology for Earth
Observation and Climate (MetEOC2). The EMRP is jointly funded by the EMRP
of the participating countries within EURAMET and the EU.
Edited by: Alyn Lambert Reviewed by: two anonymous referees
ReferencesFriedl-Vallon, F.: Five Years of GLORIA Flights: Results and Lessons Learnt,
in: Light, Energy and the Environment, p. FM3E.3, Opt. Soc. Am.,
10.1364/FTS.2016.FM3E.3, 2016.Friedl-Vallon, F., Maucher, G., Seefeldner, M., Trieschmann, O., Kleinert,
A.,
Lengel, A., Keim, C., Oelhaf, H., and Fischer, H.: Design and
characterization of the balloon-borne Michelson Interferometer for Passive
Atmospheric Sounding (MIPAS-B2), Appl. Opt., 43, 3335–3355,
10.1364/AO.43.003335,
2004.Friedl-Vallon, F., Riese, M., Maucher, G., Lengel, A., Hase, F., Preusse, P.,
and Spang, R.: Instrument concept and preliminary performance analysis of
GLORIA, Adv. Space Res., 37, 2287–2291,
10.1016/j.asr.2005.07.075, 2006.Friedl-Vallon, F., Gulde, T., Hase, F., Kleinert, A., Kulessa, T., Maucher,
G.,
Neubert, T., Olschewski, F., Piesch, C., Preusse, P., Rongen, H., Sartorius,
C., Schneider, H., Schönfeld, A., Tan, V., Bayer, N., Blank, J., Dapp, R.,
Ebersoldt, A., Fischer, H., Graf, F., Guggenmoser, T., Höpfner, M.,
Kaufmann, M., Kretschmer, E., Latzko, T., Nordmeyer, H., Oelhaf, H., Orphal,
J., Riese, M., Schardt, G., Schillings, J., Sha, M. K., Suminska-Ebersoldt,
O., and Ungermann, J.: Instrument concept of the imaging Fourier transform
spectrometer GLORIA, Atmos. Meas. Tech., 7, 3565–3577,
10.5194/amt-7-3565-2014,
2014.Gutschwager, B., Hollandt, J., Jankowski, T., and Gaertner, R.: A Vacuum
Infrared Standard Radiation Thermometer at the PTB, Int. J. Thermophys., 29,
330–340, 10.1007/s10765-007-0349-x, 2008.
Hollandt, J., Friedrich, R., Gutschwager, B., Taubert, D., and Hartmann, J.:
High-accuracy Radiation Thermometry at the National Metrology Institute of
Germany – the PTB, High Temperatures – High Pressures, 35/36, 379–415,
2003/2004.
Johansson, S., Friedl-Vallon, F., Höpfner, M., Ungermann, J., Vogel, B.,
Grooß, J., Müller, R., Diekmann, C., Schröter, J., Ruhnke, R., Orphal, J.,
and the GLORIA Team: 2-d chemical sampling of a tropopause fold over the
Mediterranean: Observations by the IR limb-imager GLORIA and calculations by
chemistry-transport models, in: Geophysical Research Abstracts Vol. 19,
EGU2017-12140, 2017.Kaufmann, M., Blank, J., Guggenmoser, T., Ungermann, J., Engel, A., Ern, M.,
Friedl-Vallon, F., Gerber, D., Grooß, J. U., Guenther, G., Höpfner, M.,
Kleinert, A., Kretschmer, E., Latzko, T., Maucher, G., Neubert, T.,
Nordmeyer, H., Oelhaf, H., Olschewski, F., Orphal, J., Preusse, P., Schlager,
H., Schneider, H., Schuettemeyer, D., Stroh, F., Suminska-Ebersoldt, O.,
Vogel, B., M. Volk, C., Woiwode, W., and Riese, M.: Retrieval of
three-dimensional small-scale structures in
upper-tropospheric/lower-stratospheric composition as measured by GLORIA,
Atmos. Meas. Tech., 8, 81–95, 10.5194/amt-8-81-2015,
2015.Kleinert, A., Friedl-Vallon, F., Guggenmoser, T., Höpfner, M., Neubert, T.,
Ribalda, R., Sha, M. K., Ungermann, J., Blank, J., Ebersoldt, A., Kretschmer,
E., Latzko, T., Oelhaf, H., Olschewski, F., and Preusse, P.: Level 0 to 1
processing of the imaging Fourier transform spectrometer GLORIA: generation
of radiometrically and spectrally calibrated spectra, Atmos. Meas. Tech.,
7, 4167–4184, 10.5194/amt-7-4167-2014,
2014.Krisch, I., Preusse, P., Ungermann, J., Dörnbrack, A., Eckermann, S. D.,
Ern, M., Friedl-Vallon, F., Kaufmann, M., Oelhaf, H., Rapp, M., Strube, C.,
and Riese, M.: First tomographic observations of gravity waves by the
infrared limb imager GLORIA, Atmos. Chem. Phys., 17, 14937–14953,
10.5194/acp-17-14937-2017, 2017.Monte, C., Gutschwager, B., and Hollandt, J.: The Reduced Background
Calibration Facility for Detectors and Radiators at the
Physikalisch-Technische Bundesanstalt, in: Proc. of SPIE Vol. 7474 Sensors,
Systems, and Next-Generation Satellites XIII, 747414,
10.1117/12.830454, 2009.Olschewski, F., Rolf, C., Steffens, P., Kleinert, A., Piesch, C., Ebersoldt,
A., Monte, C., Gutschwager, B., J., H., Preusse, P., Friedl-Vallon, F., and
Koppmann, R.: In-flight blackbody calibration sources for the GLORIA
interferometer, in: Proc. SPIE 8511, Infrared Remote Sensing and
Instrumentation XX, 85110I, 10.1117/12.928194, 2012.Olschewski, F., Ebersoldt, A., Friedl-Vallon, F., Gutschwager, B., Hollandt,
J., Kleinert, A., Monte, C., Piesch, C., Preusse, P., Rolf, C., Steffens, P.,
and Koppmann, R.: The in-flight blackbody calibration system for the GLORIA
interferometer on board an airborne research platform, Atmos. Meas. Tech., 6, 3067–3082, 10.5194/amt-6-3067-2013,
2013.Riese, M., Oelhaf, H., Preusse, P., Blank, J., Ern, M., Friedl-Vallon, F.,
Fischer, H., Guggenmoser, T., Höpfner, M., Hoor, P., Kaufmann, M., Orphal,
J., Plöger, F., Spang, R., Suminska-Ebersoldt, O., Ungermann, J., Vogel,
B., and Woiwode, W.: Gimballed Limb Observer for Radiance Imaging of the
Atmosphere (GLORIA) scientific objectives, Atmos. Meas. Tech., 7, 1915–1928,
10.5194/amt-7-1915-2014,
2014.Té, Y., Jeseck, P., Camy-Peyret, C., Payan, S., Perron, G., and Aubertin,
G.: Balloonborne calibrated spectroradiometer for atmospheric nadir sounding,
Appl. Optics, 41, 6431–6441, 10.1364/AO.41.006431, 2002.Ungermann, J., Blank, J., Lotz, J., Leppkes, K., Hoffmann, L., Guggenmoser,
T.,
Kaufmann, M., Preusse, P., Naumann, U., and Riese, M.: A 3-D tomographic
retrieval approach with advection compensation for the air-borne limb-imager
GLORIA, Atmos. Meas. Tech., 4, 2509–2529,
10.5194/amt-4-2509-2011, 2011.Ungermann, J., Blank, J., Dick, M., Ebersoldt, A., Friedl-Vallon, F., Giez,
A.,
Guggenmoser, T., Höpfner, M., Jurkat, T., Kaufmann, M., Kaufmann, S.,
Kleinert, A., Krämer, M., Latzko, T., Oelhaf, H., Olchewski, F., Preusse,
P., Rolf, C., Schillings, J., Suminska-Ebersoldt, O., Tan, V., Thomas, N.,
Voigt, C., Zahn, A., Zöger, M., and Riese, M.: Level 2 processing for the
imaging Fourier transform spectrometer GLORIA: derivation and validation of
temperature and trace gas volume mixing ratios from calibrated dynamics mode
spectra, Atmos. Meas. Tech., 8, 2473–2489,
10.5194/amt-8-2473-2015, 2015.