An overview of the Cooperative Institute for Meteorological Satellite Studies' FIRE research activities is presented. Emphasis is on the analysis of the High-Resolution Interferometer Sounder (HIS) made from the ER-2 as well as ground based measurements made by the Atmospheric Emitted Radiance Interferometer (AERI) prototype

Ackerman, S. A.

Knuteson, R. O.

Ma, X. L.

Revercomb, H. E.

Smith, W. L.

English

NASA Technical Reports Server

"_//-4-'_/7 /_ N94: 2 o7
CIMSS FIRE RESEARCH ACTIVITIES
W. L. Smith, S. A. Ackerman R. O. Knuteson, X. L. Ma, and H. E. Rcvercomb,
Cooperative Institute for Meteorological Satellite Studies
ABSTRACT
f This paper presents an overview of the Cooperative Institute for Meteorological Satellite Studies'
FIRE research activities. The paper focuses on analysis of the High-resolution Interferometer Sounder
(HIS) made from the ER-2 as well as ground based measurements made by the Atmospheric Emitted
Radiance Interferometer (AERI) prototype. Details are covered in companion papers.
ER-2 HIS OBSERVATIONS
The HIS aircraft instrument (Smith et al 1989) is a Michelson interferometer with a spectral
resolving power (X/hX) of approximately 2000 covering the spectral range from approximately 3.5-16.7 tx
m. The HIS spectra have an unapodized resolution of approximately 0.35 cm" 1 from 600-1100 cm" 1, and
0.7 cm" 1 resolution from 1100-2700 cm" 1. A cycle of HIS interferograms consists of four cold blackbody
views, four hot blackbody views and 12 earth views. The on board high emissiviff,, temperature controlled
reference blackbody views are used for the calibration of the earth views. The HIS has a noise equivalent
temperature and reproducibility, of about 0.1-0.2°C over much of the spectrum (Revercomb et al., 1988).
Recent upgrades to the HIS have significantly improved instrument performance in the 3.5-5.0 p.m
spectral region.
The HIS flew aboard the NASA ER-2 during FIRE Phase I (Oct-Nov 1986). The most
significant result of these observation was that cirrus clouds do not emit radiation like blackbodies,
irregardless fo their optical thickness. Figure 1 has become an historical example of the FIRE I HIS
finding that the spectral variation of the radiating temperature of cirrus has a large spectral variation
across the climatolically important 8-12 p.m "window" region of the thermal infrared.
Another very important finding from FIRE-I HIS radiance spectra was that the water phase of
clouds could be diagnosed from simultaneous infraed window measurements at 8, 11 and 12 p.m (Smith et
al 1988, Ackerman et al 1990). Figure 2 shows a time sequence of 8.3, 11.1 and 12.0 p.m HIS brightness
temperature together with simultaneous Lidar cloud backscatter observations with the CALS (Spinhirne,
1990). It can be seen that for the case of ice particle cirrus (high altitudebackscatter) the 8.3 p.m
brightness temperature is significantly larger than the 11 and 12 p.m brightness temperature whereas for
the case of liquid water droplet lower clouds (low altitude backscatter) both the 8 and 11 p.m brightness
temperature are larger than 12 p.m These results correspond to the different spectral absorption
properteis of ice and water (Figure 3).
For FIRE II, HIS data analysis has focused on the determination of the radiative and
microphysical properties of cirrus clouds. Table 1 below lists the days and times of available HIS data
during FIRE II. Our research objectives under the FIRE Phase II program include: 1) to improve our
understanding of the relationship between the microphysical and radiative propeities of cirrus clouds; 2)
to quantify the capabilities and limitations of various cirrus cloud satellite retrieval techniques; and 3) to
improve our capabilities of describing Cirrus cloud properties utilizing passive radiometric observations.
Since the last FIRE team meeting, we have focused our activities on objectives 1) and 3).
A doubling/adding model has been deveioped to simulate high-spectral resolution measurements
from ground and ER-2 aircraft. This model has been used to study the sensitivity of the spectral
observations to various cloud conditions and then to develop and test cloud retrieval algorithms using such
observations (Smith et al 1990,1992, 1993). A time section of cloud ice particle size and ice water
content deduced from HIS spectra from the ER-2 aircraft are shown in Figure 4. The cloud altitude and
thickness were set at the height levels observed by the CALS. The cloud ice water content varies between
2.3 g m "3 and effective radius is about 20 p.m. Cloud heights are accurately determined using HIS carbon
ldoxide channel information even for relatively low effective cloud emissivites. Improvements in cloud
properties retrieval from HIS data by incorporating the 3.7-4.0 p.m window and the 4.3 CO 2 radiances are
now being investigated.
56
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Figure 2. Time series plot of 8, 11 and 12 m brightness temperatures. CALS lidar image is
displayed below.
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Figure 3. Absorption Coefficient as a function of wavelength
57
TARGET
DATE AREA
14 Nov 91 Kansas 14:01-18:00 Cirrus
18 Nov 91 Kansas 20:56-23:30 Clear sky
22 Nov 91 Kansas 18:30-20:30 Cirrus
24 Nov 91 Gulf Mex 17:00-21:10 Cirrus
25 Nov 91 Oklahoma 16:00-20:00 Cirrus
26 Nov 91 Kansas 15:00-17:50 Cirrus
3 Dec 91 GulfMex 15:30-18:00 Cirrus
4 Dec 91 GulfMex 18:30-20:30 Corpus Christi
TIME HIS DATA
(UTC) STUDY OBJECTIVE
Gulf of Mexico
. 5 Dec 91 Kansas 15:00-19:00 Cirrus
..................................... ,--- ............. m.._..--.,--,- ................. ,---
AERI OBSERVATIONS
The AERI instrument is a goundbased IIIS system for the accurate and continuous measurement
of downwelling infrared radiation from the atmosphere. The observed spectra are being used for many
diverse functions, including identification and elimination of absolute errors in calculated spectra for
known atmospheric states" evaluation and improvement of cloud radiation calculations: characterization
of the distribution and evolution of effective cloud radiative properties: and studies of the state parameter
changes associated with cloud formation, evolution, and dissipation. Table 2. is a summary of when the
AERI prototype was operational during the DOE Spectral Radiance Experiment (SPECTRE.) in
association with FIRE II, conducted in Coffeyville, Kansas in the Fall of 1991. Ouservations of the
atmosphere were collected approximately every. 10 minutes.
Examples of cloudy brightness temperature spectra during FIRE II are shown in Figure 5. As
found with HIS aircraft observations, clouds do not behave as "blackbodies" for which the brightness
temperature would be constant in the regions between absorption lines in the atmospheric window
between 8 and 13 I.tm (770-1250 cm'l). The low cloud spectrum in the figure is close to that of a
blackbody cloud, but the middle cloud shows major deviations from that simple behavior. The deviations
from blackbody behavior are being used to estimate cloud base microphysical properties in much the same
way cloud top microphysical propeties are being estimated from ER-2 HIS spectra (Smith. et al., 1993).
The AERI data have been used to assess the capabilities of radiative transfer model results,
analyze the evolution of the boundary layer, and retrieve cloud properties. These applications are
discussed in a companion paper.
FUTURE ACTIVITIES
Ground-based interferometer observations, at a resolution similar to the aircraft HIS, were
collected at Coffeyville KS as part of FIRE II and SPECTRE. ER-2 over-flights of the site will enable
assessment of the spectral infrared effects of clouds on the radiance distribution at the ground and at the
top of the atmosphere. Cloud base properties will also be derived from the ground-based intefferometer
for comparison with the ER-2 based derived cloud top properties. This study is crucial for the
characterization of the downwelling radiance of a cloud, based on satellite observations of the upwelling
radiance as needed for use in global climate studies.
Upgrades to the HIS prior to the FIRE, II field experiment improved inst,-,tment performance in
the 2000-2700 cm "1 regime. This spectral region is also measured by the AERI. The 3.7 p.m region has
been employed in cloud retrieval techniques applicable to satellite observations. Radiance in the 3.5-4.6 t.t
,m region aro-sehsitive to the particle size. shape and water phase of the cloud. We plan to enhance our
previously developed capabilities of inferring cloud microphysical characteristics_ from the 8-12 lam
spectral region using radiance from the 3.5-4.5 _tm spectral region. Inferences of the cloud particle phase
and effective size.will be based on the spectral variability, in the 3.5- 4 p.m and 8-12 gm regions.
58
REFERENCES
Ackerman. S. A., W. L. Smith, J. D. Spinhirne, and H. E. Revercomb, 1990: The 27-28 October 1986
FIRE cirrus case study: spectral properties of cirrus clouds in the 8-12 v,m window. Mon. g:ea. Rev.,
118, 2377-2388.
Revercomb. HE., H. Buijs, H.B. Howell, D.D. LaPorte, W.L. Smith, and L.A. Sromovsky, 1988:
Radiometric Calibration of IR Fourier Transform Spectrometers: Solution to a Problem with the High
Resolution Interferometer Sounder. Applied Optics, 27, 3210-3218.
Smith W. L., H. E. Revercomb, H. B. Howell, and M. -X. Lin, 1988: Multi-specwal window radiance
observations of cirrus from satellite and aircraft - November 2, 1986 "Project FIRE", .FIRE Science
Results 1988, Proceeding of a conference held in Vail, CO July 11-15, pp 89-93.
Smith W. L., H. E. Revercomb, D. D. LaPorte, H. M. Woolf, H. B. Howell, IL O. Knuteson, H. L. Huang,
L. A. Sromovsky and S. Silverman, 1989: GHIS, the Geostationary High-resolution lnterferometer
Sounder. C1MSS View, Vol. V, No.l, available from the Space Science and Engineering Center,
Uaiverstiy of Wisconsin, Madison, Wisconsin, 53706.
Smith W.L., Xia Lin Ma, S.A. Ackerman, H.E. Revercomb, and 1LO. Knuteson, 1993: Remote Sensing
Cloud Properties from High Spectral Resolution Infrared Observations. ,I. Appl. Met, in press, 1993.
Smith, W. L. and IL Frey, 1990: On cloud altitude determinations from high resqlution intefferometer
sounder (HIS) observations. J. Appl. Meteor., 29, 658-662.
Smith, W. L., and tL Frey, 1991: Altitude specification of cloud motion winds. Workshop on Wind
Extraction from Operational Meteorological Satellite Data, Washington, D.C. September 17-19.
Table2. WISCONSIN AERI INSTRUMENT OPERATIONS
......................... ,,,.. ....... - ............... ---..-.,.-.- .......... . .................................
LOCATION: COFFEYVILLE, KANSAS
YEAR: 1991
RENIARKS: (1) Observations areai ib minute interv_s between_aie, d STARI" find END times. (2)
The letter H indicates that the ER-2 HIS was overhead. (3) OP # refers to an AERI operating period.
OP # DATE TIME PERIOD CONDITIONS FROM VISUAL OBS
1 11 NOV 17:06 - 17:30 low overcast
2 12 NOV 23:26 - 02:29 cirrus
13 NOV 02:53 - 04:28 cirrus/clear
3 13 NOV 18:18 - 01:26 cirrus
14 NOV 02:13 - 03:41 thin cirrus
4 17NOV 17:58 - 21:12 mixed cirrns to clear
18 NOV 01:29 - 24:00 clear
19 NOV 00:00 - 05:57 clear/cimas/low thick cloud
5 20 NOV 17:20 - 23:33 clear
21 NOV 00:12 - 24:00 clear
22 NOV 00:00 - 19:07 cirrus/clear/rain
6 23 NOV 16:28 - 24:00 clear/mixed/overcast
24 NOV 00:47 - 23:29 overcast/clear
25 NOV 00:37 - 05:48 overcast
7 25 NOV 16:19 - 23:52 alto-cumulus/scatter citrus
26 NOV 00:29 - 24:00 clear/cirrus/mixed
8 27NOV 14:01 - 17:21 lowcloud
9 28 NOV 14:40 - 22:35 cirrus/overcast stratus
10 29 NOV 15:00 - 24:00 overcast/clear
30 NOV 00:00 - 17:34 clear/overcast
11 03 DEC 00:25- 23:08 overcast/clear/cold
04 DEC 23:55 - 06:41 clear
12 04 DEC 17:16 - 24:36 clear/aerosol
05 DEC 01:23 - 24:00 clear/cirrus
06 DEC 00:00 - 05:31 thin cirrus
06 DEC 14:52 - 20:33 mixed cirrus/alto cu
07 DEC 00:54 - 05:52 clear/aerosol/low cloud
07DEC 14:49 . 21:23 lowovereast/broken low
13
14
59
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Figure 4. HIS observation near Coffevville KS on Dec 5. 1991. (a) Cirrus ice water content and effective
particle site and (b) deduced cloucl altitude.and effective emissivity
60
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Figure 5. AERI measurements of the downwelling spectra of clouds showing deviations from black body
emission.
61


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