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Measurements of trace gases by the cryogenic infrared spectrometers and telescopes for the atmosphere (CRISTA) experiment
Adv. Space Res. Vol. 19, pp. 563~%6,1997 0 1997 COSPAR Published by Elsevier Science Lid. All rights resemd printed in Great Britain 0273-l 177/97 017m + 0.00 PIE S027?4177(97)00172-5
MEASUREMENTS OF TRACE GASES BY THE CRYOGENIC INFRARED SPECTROMETERS AND TELESCOPES FOR THE ATMOSPHERE (CRISTA) EXPERIMENT M. Riese, P. Preusse, R Spang, M. Em, M. Jarisch, K. U. Grossmann and D. Offermann PhysicsDepartment,Umversityof WuppertalGauss-Strasse20,42097 WuppeTtal,Germany ABSTRACT The CRISTA experiment aboard the Shuttle Pallet Satellite (SPAS) was flown on STS 66 in early November 1994. During a free flying period of seven days measurements of atmospheric temperatures and of 15 trace gases were performed with unprecedented horizontal resolution. This paper gives a brief description of the instrument and of the observational technique. Preliminary results of ClONOs retrievals are presented and discussed in terms of atmospheric dynamics and photochemistry. 0 1997 COSPAR Publishedby Elsevia ScienceLtd
THE CRISTA INSTRUMENT CRISTA is a limb scanning experiment that measures thermal emissions (4 - 71 pm) of selected trace gases with high spatial resolution in three dimensions (Offermann, 1993). By means of the measured limb radiance fields, dynamical structures of the atmosphere with small horizontal scales (300 km) can be resolved. The vertical resolution is in the order of 2 - 3 km. The CRISTA instrument is mounted on the ASTRO-SPAS platform (Fig. 1) which is released from the Shuttle and operates at a distance of 20 - 100 km behind the Shuttle. For improved horizontal resolution CRISTA uses three telescopes that sense the atmosphere simultaneously at angles 18“ apart (Fig. 1). To achieve high measuring speed and, consequently, high spatial resolution along the track, the detectors and the optics of the instrument are cooled by cryogenic helium. The incoming limb radiance is analyzed by four grating spectrometers of the Ebert-Fastie type with a spectral resolving power of about 500. Trace gas emissions measured by CRISTA are listed in Table 1. On Nov 3, 1994 CRISTA was launched aboard the Space Shuttle Atlantis into a 300 km, 57O inclination orbit and measured about 50,000 height profiles of limb radiance spectra by using a number of different measurement modes (including scans of different altitude regions of the atmosphere) and some calibration modes. CRISTA-SPAS
carrier
I ISTA
Figure
1: CRISTA
measurement
-TELESCOPE
configuration 563
564
M. Riesertd
Trace gas co2
HF o(3p) HCI
1 Wave length 1
4.3 pm
1 Height interval 1 15-120 km
61.0 pm 63.0 pm 69.0 pm
40 - 65 km 80 - 180 km t.b.d.
I.,I
Measured by 1 scs 00.Z
SCL SCL SCL
Table 1: Trace gases measured by CRISTA. Measurements of short wavelengths spectrometers are available for the center (SCS), left (SL), and right (SR) viewing direction. In addition, the center telescope feeds a spectrometer for longer wavelengths (SCL). DATA
ANALYSIS
CRISTA raw data are uncalibrated detector output voltages, signals from tilting mirrors and gratings, and housekeeping data. These data are supplemented by spacecraft attitude and status data. The CRISTA data are converted to limb radiance spectra on an instrument sampling grid by means of calibration data derived from laboratory measurements and in-flight data. The fast measurement speed of CRISTA results in a large amount of radiance data. The radiative transfer calculations, required to retrieve atmospheric temperatures and trace gas mixing ratios, are very complex due to the large wavelengths and altitude ranges of the measurements (see Table 1). S’mce several iterations have to be performed, the quality of the retrieved data depends on the accuracy and speed of these calculations. To address the requirements of CRISTA, fast forward models are used that are based on the Bandpak library (Marshall el a1.,1994). The approach utilizes precalculated emissivity growth coefficients (see Gordley and Russell, 1981) that were generated by means of the Linepak algorithms (Gordley et cd., 1994). The CRISTA emissivity data allow to calculate complete limb radiance spectra at the spectral resolution of the instrument. To retrieve atmospheric temperatures and trace gas fields a multiple emitter onion peeling scheme is used. Fig. 2 shows a comparison of a measured and a calculated spectrum at a tangent height of about 32 km. The COs emission at 792 cm-l is used for the pressure/temperature retrieval. There are also significant contributions of 03, ClONOs and aerosol in this wavelengths region, requiring simultaneous retrieval of all emitting species. The spectral resolution of CRISTA is sufficient to retrieve mixing ratios of weakly emitting gases such as chlorine nitrate (ClONOs). Discussions of preliminary CRISTA data in this paper emphasize this trace gas. The systematic error of ClONOz in the current type of data (Bl) is estimated to be lower than 30% (20% due to uncertainties in spectral parameters and less than 20% due to the instrument). Atmospheric temperatures and ozone mixing ratios derived in the spectral range shown in Fig. 2 are presented in companion papers in this issue. DISCUSSION
OF PRELIMINARY
RESULTS
A global map of retrieved ClONOz mixing ratios is shown in Fig. 3 for Nov 6, 1994 at 24 km altitude. In general, the mixing ratios are relatively low at the equator and increase towards the poles. There is an interesting dynamical feature in the northern hemisphere, a tongue of relatively low (subtropical) ClONOz mixing ratios over the northern Atlantic. This tongue is also indicated in other CRISTA measurements and potential vorticity maps (e.g. from ECMWF).
The CRISTA Experiment
h i
0.40 _._._._.
Measurement - - Simulation co,
0
2
0.30
Y
b
y
0 c .-0 u g
: .A
0.20
k
0.10
‘\
..‘.:
,-.
‘. \.
../
0.00 780
790
800
810
Wavenumbers
820
830
840
(cm-‘)
Figure 2: Comparison of a measured and a simulated spectrum for detector channel SCSG. Contributions of all main emitters are also shown.
Volume
mixing
ratio
[ppb]
ClONO, Figure 3: ClON02 distribution of Nov 6, 1994 at 24 km altitude. The map shown in this figure covers latitudes from -80” to +SOa and longitudes from -180’ to +lSO’ (East). Each data point represents a complete altitude profile of CIONO? (20 - 40 km).
M. Riese et al.
566
A comparison of daytime profiles for locations inside (profile la) and outside 4. Large differences in mixing ratios occur at altitudes below 30 km. Figure (profile
lb) and high latitude
air (profile
2b).
These
four profiles suggest
(profile 2a) the tongue is given in Fig. 4 also shows mean profiles of tropical
that the tongue
originates
from the tropics.
When the CRISTA measurements were taken, the south polar vortex was no longer centered around but elongated towards South America. The edge of the vortex can be identified in Fig. 3 by enhanced values
(see also Toon
the pole ClONOs
et al., 1989).
The ClONOs distribution of Fig. 3 contains daytime as well as nighttime values. The local time of ascending nodes is about 9 pm at the equator. Equatorial measurements at the descending nodes were performed during the day (9 am). To derive the altitude dependence of the night/day ratio, profiles from the ascending and descending portion profiles
of the orbit were separated and zonally averaged for a latitudinal band from - 10’ to + 10”. The resulting (Fig. 5) indicate that the night/day ratio increases with altitude, as expected from photochemical theory
for the considered
Figure
4:
local times
Comparison
(see e. g. Brasseur
of ClONOz
daytime
and Solomon,
1986).
Figure
5:
daytime
profiles
profiles.
Comparison
of mean
at equatorial
nighttime
and
latitudes.
ACKNOWLEDGEMENT We thank
L.L. Gordley
and T.B.
Marshall
of Gordley
Associated
Technical
of CRISTA retrieval software and algorithms. The CRISTA experiment is funded by the Bundesministerium fur Bildung Deutsche Agentur fiir Raumfahrtangelegenheiten (DARA, Bonn).
Software
for supporting
und Forschung
the development
(BMBF,
Bonn)
through
REFERENCES Brssseur,
G. and S. Solomon,
Company, Boston Gordley, L.L. and J.M.
Appl. Gordley,
Opt.,20, L.L., B.T.
Aeronomy
(1986). Russell III, Rapid
of the middle inversion
atmosphere,
(second
of limb radiance
807, (1981). Marshall, and D.A. Chu, Linepak:
Algorithms
edition),
D. Reidel
data using an emissivity for modeling
spectral
Publishing
growth
transmittance
approximation, and radiance,
JQRST Marshall,
54, 563 (1994). T.B., L.L. Gordley,
and D.A.
Chu, Bandpak:
radiance,J&RST 54, 581 (1994). Offermann, D., CRISTA: A Shuttle Shuttle
experiment
Algortithms for middle
for modeling atmosphere
broadband
transmission
small scale structures,
and
in:
E.V. Thrane et al. (editor), Coupling processes in the lower and middle atmosphere, p. 389, Kluwer Academ. Publ., Holland (1993). Toon, G.C., C. Farmer, L.L. Lowes, P.W. Schaper, J.-F. Blavier and R.H. Norton, Infrared aircraft measurements of stratospheric
composition
over Antarctica
during
September
1987,
J. Geophys.
Res., 94,16,
571 (1989).
MEASUREMENTS OF TRACE GASES BY THE CRYOGENIC INFRARED SPECTROMETERS AND TELESCOPES FOR THE ATMOSPHERE (CRISTA) EXPERIMENT M. Riese, P. Preusse, R Spang, M. Em, M. Jarisch, K. U. Grossmann and D. Offermann PhysicsDepartment,Umversityof WuppertalGauss-Strasse20,42097 WuppeTtal,Germany ABSTRACT The CRISTA experiment aboard the Shuttle Pallet Satellite (SPAS) was flown on STS 66 in early November 1994. During a free flying period of seven days measurements of atmospheric temperatures and of 15 trace gases were performed with unprecedented horizontal resolution. This paper gives a brief description of the instrument and of the observational technique. Preliminary results of ClONOs retrievals are presented and discussed in terms of atmospheric dynamics and photochemistry. 0 1997 COSPAR Publishedby Elsevia ScienceLtd
THE CRISTA INSTRUMENT CRISTA is a limb scanning experiment that measures thermal emissions (4 - 71 pm) of selected trace gases with high spatial resolution in three dimensions (Offermann, 1993). By means of the measured limb radiance fields, dynamical structures of the atmosphere with small horizontal scales (300 km) can be resolved. The vertical resolution is in the order of 2 - 3 km. The CRISTA instrument is mounted on the ASTRO-SPAS platform (Fig. 1) which is released from the Shuttle and operates at a distance of 20 - 100 km behind the Shuttle. For improved horizontal resolution CRISTA uses three telescopes that sense the atmosphere simultaneously at angles 18“ apart (Fig. 1). To achieve high measuring speed and, consequently, high spatial resolution along the track, the detectors and the optics of the instrument are cooled by cryogenic helium. The incoming limb radiance is analyzed by four grating spectrometers of the Ebert-Fastie type with a spectral resolving power of about 500. Trace gas emissions measured by CRISTA are listed in Table 1. On Nov 3, 1994 CRISTA was launched aboard the Space Shuttle Atlantis into a 300 km, 57O inclination orbit and measured about 50,000 height profiles of limb radiance spectra by using a number of different measurement modes (including scans of different altitude regions of the atmosphere) and some calibration modes. CRISTA-SPAS
carrier
I ISTA
Figure
1: CRISTA
measurement
-TELESCOPE
configuration 563
564
M. Riesertd
Trace gas co2
HF o(3p) HCI
1 Wave length 1
4.3 pm
1 Height interval 1 15-120 km
61.0 pm 63.0 pm 69.0 pm
40 - 65 km 80 - 180 km t.b.d.
I.,I
Measured by 1 scs 00.Z
SCL SCL SCL
Table 1: Trace gases measured by CRISTA. Measurements of short wavelengths spectrometers are available for the center (SCS), left (SL), and right (SR) viewing direction. In addition, the center telescope feeds a spectrometer for longer wavelengths (SCL). DATA
ANALYSIS
CRISTA raw data are uncalibrated detector output voltages, signals from tilting mirrors and gratings, and housekeeping data. These data are supplemented by spacecraft attitude and status data. The CRISTA data are converted to limb radiance spectra on an instrument sampling grid by means of calibration data derived from laboratory measurements and in-flight data. The fast measurement speed of CRISTA results in a large amount of radiance data. The radiative transfer calculations, required to retrieve atmospheric temperatures and trace gas mixing ratios, are very complex due to the large wavelengths and altitude ranges of the measurements (see Table 1). S’mce several iterations have to be performed, the quality of the retrieved data depends on the accuracy and speed of these calculations. To address the requirements of CRISTA, fast forward models are used that are based on the Bandpak library (Marshall el a1.,1994). The approach utilizes precalculated emissivity growth coefficients (see Gordley and Russell, 1981) that were generated by means of the Linepak algorithms (Gordley et cd., 1994). The CRISTA emissivity data allow to calculate complete limb radiance spectra at the spectral resolution of the instrument. To retrieve atmospheric temperatures and trace gas fields a multiple emitter onion peeling scheme is used. Fig. 2 shows a comparison of a measured and a calculated spectrum at a tangent height of about 32 km. The COs emission at 792 cm-l is used for the pressure/temperature retrieval. There are also significant contributions of 03, ClONOs and aerosol in this wavelengths region, requiring simultaneous retrieval of all emitting species. The spectral resolution of CRISTA is sufficient to retrieve mixing ratios of weakly emitting gases such as chlorine nitrate (ClONOs). Discussions of preliminary CRISTA data in this paper emphasize this trace gas. The systematic error of ClONOz in the current type of data (Bl) is estimated to be lower than 30% (20% due to uncertainties in spectral parameters and less than 20% due to the instrument). Atmospheric temperatures and ozone mixing ratios derived in the spectral range shown in Fig. 2 are presented in companion papers in this issue. DISCUSSION
OF PRELIMINARY
RESULTS
A global map of retrieved ClONOz mixing ratios is shown in Fig. 3 for Nov 6, 1994 at 24 km altitude. In general, the mixing ratios are relatively low at the equator and increase towards the poles. There is an interesting dynamical feature in the northern hemisphere, a tongue of relatively low (subtropical) ClONOz mixing ratios over the northern Atlantic. This tongue is also indicated in other CRISTA measurements and potential vorticity maps (e.g. from ECMWF).
The CRISTA Experiment
h i
0.40 _._._._.
Measurement - - Simulation co,
0
2
0.30
Y
b
y
0 c .-0 u g
: .A
0.20
k
0.10
‘\
..‘.:
,-.
‘. \.
../
0.00 780
790
800
810
Wavenumbers
820
830
840
(cm-‘)
Figure 2: Comparison of a measured and a simulated spectrum for detector channel SCSG. Contributions of all main emitters are also shown.
Volume
mixing
ratio
[ppb]
ClONO, Figure 3: ClON02 distribution of Nov 6, 1994 at 24 km altitude. The map shown in this figure covers latitudes from -80” to +SOa and longitudes from -180’ to +lSO’ (East). Each data point represents a complete altitude profile of CIONO? (20 - 40 km).
M. Riese et al.
566
A comparison of daytime profiles for locations inside (profile la) and outside 4. Large differences in mixing ratios occur at altitudes below 30 km. Figure (profile
lb) and high latitude
air (profile
2b).
These
four profiles suggest
(profile 2a) the tongue is given in Fig. 4 also shows mean profiles of tropical
that the tongue
originates
from the tropics.
When the CRISTA measurements were taken, the south polar vortex was no longer centered around but elongated towards South America. The edge of the vortex can be identified in Fig. 3 by enhanced values
(see also Toon
the pole ClONOs
et al., 1989).
The ClONOs distribution of Fig. 3 contains daytime as well as nighttime values. The local time of ascending nodes is about 9 pm at the equator. Equatorial measurements at the descending nodes were performed during the day (9 am). To derive the altitude dependence of the night/day ratio, profiles from the ascending and descending portion profiles
of the orbit were separated and zonally averaged for a latitudinal band from - 10’ to + 10”. The resulting (Fig. 5) indicate that the night/day ratio increases with altitude, as expected from photochemical theory
for the considered
Figure
4:
local times
Comparison
(see e. g. Brasseur
of ClONOz
daytime
and Solomon,
1986).
Figure
5:
daytime
profiles
profiles.
Comparison
of mean
at equatorial
nighttime
and
latitudes.
ACKNOWLEDGEMENT We thank
L.L. Gordley
and T.B.
Marshall
of Gordley
Associated
Technical
of CRISTA retrieval software and algorithms. The CRISTA experiment is funded by the Bundesministerium fur Bildung Deutsche Agentur fiir Raumfahrtangelegenheiten (DARA, Bonn).
Software
for supporting
und Forschung
the development
(BMBF,
Bonn)
through
REFERENCES Brssseur,
G. and S. Solomon,
Company, Boston Gordley, L.L. and J.M.
Appl. Gordley,
Opt.,20, L.L., B.T.
Aeronomy
(1986). Russell III, Rapid
of the middle inversion
atmosphere,
(second
of limb radiance
807, (1981). Marshall, and D.A. Chu, Linepak:
Algorithms
edition),
D. Reidel
data using an emissivity for modeling
spectral
Publishing
growth
transmittance
approximation, and radiance,
JQRST Marshall,
54, 563 (1994). T.B., L.L. Gordley,
and D.A.
Chu, Bandpak:
radiance,J&RST 54, 581 (1994). Offermann, D., CRISTA: A Shuttle Shuttle
experiment
Algortithms for middle
for modeling atmosphere
broadband
transmission
small scale structures,
and
in:
E.V. Thrane et al. (editor), Coupling processes in the lower and middle atmosphere, p. 389, Kluwer Academ. Publ., Holland (1993). Toon, G.C., C. Farmer, L.L. Lowes, P.W. Schaper, J.-F. Blavier and R.H. Norton, Infrared aircraft measurements of stratospheric
composition
over Antarctica
during
September
1987,
J. Geophys.
Res., 94,16,
571 (1989).