Work has been primarily focussed on three tasks: (1) comparison of wind fields produced at MSFC with the CO2 autowind/autoeditor system newly installed in NESDIS operations; (2) evaluation of techniques for improved tracer selection through use of cloud classification predictors; and (3) development of height assignment algorithm with water vapor channel radiances. The contract goal is to improve the CIMSS wind system by developing new techniques and assimilating better existing techniques. The work reported here was done in collaboration with the NESDIS scientists working on the operational winds software, so that NASA funded research can benefit NESDIS operational algorithms

Hayden, Kit

Menzel, Paul

Nieman, Steve

Velden, Chris

English

NASA Technical Reports Server

N93-20094
Investigation of Cloud/Water Vapor Motion
Winds from Geostationary Satellite
Steve Nieman, Chris Velden, Kit Hayden, and Paul Menzel
Cooperative Institute for Meteorological Satellite Studies
University of Wisconsin-Madison
Work has been primarily focussed on three tasks: (A) comparison of wind fields
produced at MSFC with the CO2 autowind/autoeditor system newly installed in
NESDIS operations, (B) evaluation of techniques for improved tracer selection
through use of cloud classification predictors, and (C) development of height
assignment algorithm with water vapor channel radiances. The contract goal is
to improve the CIMSS wind system by developing new techniques and assimilating
better exisitng techniques. The work reported here was done in collaboration
with the NESDIS scientists working on the operational winds software, so that
NASA funded research can benefit NESDIS operational algorithms.
(A) Comparison of A Wind Set Produced by MSFC with the New Operational CO2
Autowind/Autoeditor (C. Hayden, NOAA/NESDIS, C. Velden, CIMSS)
In the early spring of 1990 a team from the Cooperative Institute for
Satellite Studies (CIMSS) joined with the NESDIS Interactive Processing Branch
and the Satellite Analysis Branch in introducing and testing at the VAS Data
Utilization Center a new software system for automated cloud motion winds with
pressure altitude assignment using the CO 2 slicing method. Wind vectors
generated during this demonstration were given to the NMC to investigate
forecast impact. One of the highlights of this effort occurred on April 24
and 25 when the new pressure assignment method succeeded in correctly locating
the altitude of thin cirrus tracers off the coast of California associated
with a shortwave which would later affect the weather over the U.S.
(Merrill,et al. 1991). The success of this venture breathed new life into
applied research for improving the vectors obtainable from satellite imagery,
and one consequence was an agreement with Marshall Space Flight Center (MSFC)
that they use the April test case with their vector generating software for
comparison with the new NESDIS system, the eventual goal being the
amalgamation of better aspects of the two methods. MSFC agreed to this task,
and subsequently delivered a data set to CIMSS which included vectors from
visible, infrared window, and water vapor (6.7 micrometer) imagery for April
25, 00 UT. CIMSS evaluation of these data was conducted under this contract
and the results are briefly highlighted here.
CIMSS has developed a system for objective quality control of the winds
generated from tracers. This quality control includes both pressure altitude
reassignment by objective assimilation with other data and ojective editing
(Hayden, 1991; Hayden and Velden, 1991). It is a part of the new wind
generating system which became operational at NESDIS on February 12, 1992.
The MSFC wind data were evaluated by this quality control system.
The principal conclusion from examination of the MSFC data set is that NESDIS
should be paying more attention to visible data to improve vector coverage. A
second conclusion is that MSFC seems to have a superior technique for
obtaining targets in the water vapor imagery. Certainly their density is much
higher. Finally, the NESDIS assimilation system was quite successful in
blending the MSFC winds into the analysis, despite the deficiencies of the
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initial height assignment. Although an obvious bias to the NMC forecast is
enforced by the reassignment, the end result in comparison to rawinsondes
shows an rms improvement over the forecast.
Hayden, C. M. and C. S. Velden, 1991: Quality control and assimilation
experiments with satellite-derived wind estimates. Preprint Volume, 9th
Conference on Numerical Weather Prediction, Denver, CO. Amer. Meteor. Soc.,
19-23 October.
Hayden, C. M. 1991: Research leading to operational methods for wind
extraction. Proceedings of the Workshop on Wind Extraction from Operational
Meteorological Satellite Data, Washington, DC, 17-19 September, Eumetsat ISBN
92-9110-007-2.
Merrill, R. T., W P. Menzel, W. Baker, J. Lynch, and E. Legg, 1991. A report
on the recent demonstration of NOAA's upgraded capability to derive cloud
motion satellite winds. Bull. Amer. Meteor. Soc., 72, 372-376.
(B) Use of Cloud Classification Predictors for Cloud Tracer Selection in
Operational Winds Algorithms (C. Moeller, CIMSS)
The utility of cloud feature characteristics as additional information to the
operational automated cloud tracking wind algorithm is being investigated.
This effort is aimed at improving the quality of operationally produced cloud
tracked winds while eliminating computational time spent trying to produce
vectors from cloud targets which are not likely to yield good quality vectors.
Automated wind vectors can be improved by limiting cloud tracer selection to
tracers that are, more often than not, accurately tracked (via correlation
technique) through time. A goal of this work is to base cloud tracer
selection on cloud feature characteristics as well as the usual pixel
brightness and gradient thresholds. The characteristics for describing cloud
tracers include cloud albedo, fraction, multilayering, height of base and top,
spatial distribution and orientation, connectivity (cloud and background), and
type (Garand, 1988). These cloud characteristics are being compared to cloud
tracers and vectors produced by the operational cloud tracking procedure in an
effort to identify the conditions under which good (and bad) quality wind
vectors are produced. Those characteristics demonstrating skill in
identifying good (and bad) cloud tracers will be retained; those not
demonstrating skill will be removed from the algorithm to reduce computational
time.
Garand, L., 1988: Automated Recognition of Oceanic Cloud Patterns. Part I:
Methodology and Application to Cloud Climatology. Jour. of Clim., Vol.l,
No.l, 20-39.
(C) Compariosn of Several Techniques to Assign Heights to Cloud Tracers (S.
Nieman, CIMSS, P. Menzel, NOAA/NESDIS, J. Schmetz, ESOC)
In the current operational use of four geostationary satellites, satellite
derived cloud motion vector (CMV) production has been troubled by inaccurate
height assignment of cloud tracers, especially in thin semi-transparent
clouds. At the recent Workshop on Wind Extraction from Operational
Meteorological Satellite Data (Eumetsat, 1991) there was a consensus that the
86
present techniques for height assignment needed further review and that
greater commonality in techniques should be encouraged.
Presently heights are assigned by any of three techniques when the appropriate
spectral radiance measurementsare available. In opaque clouds, infrared
window (IRW) brightness temperatures are comparedtO forecast temperature
profiles to infer the level of best agreementwhich is taken to be the level
of the cloud. In semi-transparent clouds or sub-pixel clouds, since the
observed radiance contains conributions from below the cloud, this IRW
technique assigns the cloud to too low a level. Corrections for the semi-
transparency of the cloud are possible with the carbon dioxide (CO2) slicing
technique (Menzel, 1983) where radiances from different layers of the
atmosphere are ratioed to infer the correct height. A similar concept is used
in the water vapor (H20) intercept technique (Szejwach, 1982), where the fact
that radiances influenced by upper tropospheric moisture (H20) and IRW
radiances exhibit a linear relationship as a function of cloud amount is used
to extrapolate the correct height. These three techniques are being compared
at CIMSSthrough this contract and other NESDISsupported work.
There is an added impetus to this work. The European community is sharing one
of its satellites with the United States, METEOSAT3: understanding the
relative performance of the NESDIS(National Environmental Satellite and Data
Information Service) operational CO2 slicing heights and the ESOC(European
Satellite Operations Center) operational H20/IRWintercept heights is
necessary for the United States to begin production of CMVswith M3.
Furthermore, GMS5 will be supplementedwith a water vapor channel so that
international commonality of height assignment is closer, if viable H20/IRW
height performance can be verified.
Evaluations so far suggest that the H20/IRWintercept technique is a viable
alternative to the CO2 slicing technique for inferring the heights of semi-
transparent cloud elements. On a given day the heights from the two
approaches compare to within 60 to Ii0 mbrms; drier atmospheric conditions
tend to reduce the effectiveness of the H20/IRWintercept technique. The
infrared window channel technique consistently places the semi-transparent
cloud elements too low in the atmosphereby i00 mbor more; only in more
opaque clouds does it perform adequately. Comparisonof the heights produced
operationally at NESDIS(with the CO2 slicing technique) and ESOCwith their
version of the H20/IRWintercept technique) reveal that the cloud height
algorithms are approaching an international commonality.
EUMETSAT,1992: Workshopon wind extraction from operational meteorological
satellite data, 17-19 September1991. EUMP i0, ISBN 92-9110-007-2.
Menzel, W. P., W. L. Smith, and T. R. Stewart, 1983: Improved cloud motion
wind vector and altitude assignment using VAS. J. Clim. Appl. Meteor., 22,
377-384.
Szejwach, G., 1982: Determination of semitransparent cirrus cloud temperatures
from infrared radiances: application to METEOSAT. J. Appl. Meteor., 21, 384.
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Investigation of cloud/water vapor motion winds from geostationary satellite

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