Chair: Peter Bauer

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Research Working Group
Chair Peter Bauer Rapporteur Joerg
Schulz Participants Geoff Pegram Arthur
Hou Carlos Angelis Christian Mitrescu Francisco
J Tapiador Steven Miller Ben Jou Christian
Kummerow Bizzarro Bizzarri Michael Goodman Kyle
Hilburn Eric Smith Shannon Brown Amy
Doherty Tristan LEcuyer Una OKeeffe
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Issues
I. There is an ongoing uncertainty in
quantitative precipitation estimation,
quantitative precipitation forecast and the
monitoring of precipitation trends on a
climatological scale. Radars in space have
provided the impetus for most recent advances in
rainfall remote sensing. To that end this panel
recommends the deployment of next generation
space radar systems (e.g., dual frequency and
increased sensitivity) such as those proposed for
GPM and EGPM for improved understanding of
precipitation physics and enhancement of existing
radiometer measurements. II. At mid to high
latitudes snowfall constitutes an important part
of the hydrological cycle. The currently
available sensors are inadequate for snowfall
detection and quantification over land surfaces.
The new space-borne radars and radiometers (e.g.
sounding frequencies on EGPM) are needed to
continue improvement of the understanding of
solid precipitation.
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Topics
The working group identified the following topics
as crucial for the adequate use of existing and
future space-borne observations I. Open
rainfall retrieval algorithm architecture II. Com
bining MW-IR-models III. Transportable rainfall
estimation techniques IV. General
Recommendations
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I. Open rainfall retrieval algorithm architecture

• From the requirement of across-sensor/satellite
  consistent estimates and internal physical
  consistency we recommend an open rainfall
  retrieval algorithm structure.
• To combine the strengths of research groups in
  the international community.
• b) We recommend that this structure be used for
  the monitoring of the rainfall environment and
  rainfall generation processes. Processes and
  environment are critical to further improve our
  knowledge of precipitation physics and to
  constrain precipitation retrieval algorithms
  (frozen precipitation, light rain, precipitation
  in complex terrain, warm rain etc.).

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I. Open rainfall retrieval algorithm
architecture, contd
This has large implications on algorithm
development and on validation (e.g., GPM
supersites) Action Establish international
community working group for the development of an
algorithm framework and validation requirements.
(example GPM parametric algorithm development
effort, link to IPWG). (ST-LT C. Kummerow, P.
Bauer) We recommend the consideration of
NWP-type analysis techniques (such as data
assimilation) for the generation of rainfall
products from rainfall and rainfall related
observations as well as ancillary data with
different error structures. These methods can
also be used for retrieval error estimation and
the optimization of future satellite sensor
design (e.g., using observing system simulation
studies).
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I. Open rainfall retrieval algorithm
architecture, contd
IPWG 2002, Standards/Common Procedures
Recommendation Recommendation 1 Provide a
generally accessible platform on data and
algorithms for the research community Action
Define elements of algorithm transition required
for general applications. (QPE, bias/error
estimate, limits of applicability, documentation,
comprehensive bibliography, compliance with user
requirements as defined by WMO, EUMETSAT,
NASA-DAO, ESA, others - compile user requirements
w.r.t. to precipitation on the IPWG web site).
(ST Peter Bauer, Bob Adler, IPWG-O)
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I. Open rainfall retrieval algorithm
architecture, contd
IPWG 2002, Standards/Common Procedures
Recommendation Recommendation 2 Enable
co-operation and training through software
libraries Action Provision of radiative
transfer codes, algorithm codes, footprint
matching codes (e.g. to be used with direct read
out raw data, especially for developing
countries) with corresponding training tools and
documentation. (ST-MT Joerg Schulz, Ralf
Bennartz, IPWG-O) Recommendation 3 Develop new
strategies on flexible and global structures for
physical algorithm development, validation, and
data fusion. Action Establish a framework
for - (physical) algorithm development (global
and regional). (ST-LT GPM, Vincenzo Levizzani)
- a testbed for algorithm validation
(comparison data sets etc.). (ST-LT IPWG-V,
IPWG-R)
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I. Open rainfall retrieval algorithm
architecture, contd
IPWG 2002, Research Recommendation
Recommendation 1 The principal problem of
under-constrained precipitation retrievals
requires a different type of analysis/retrieval
approach. (TOR d) Recommendation 2 The
physical uncertainty modelling has to be pursued
in a similar fashion as physical algorithm
development is carried out. (TOR d) IPWG 2002,
Future Sensors Recommendation 1 From the work
of the group indications for future sensors
should emerge based on the identified scientific
outstanding areas (TOR d, e) Action Generate a
framework for the development of a
multi-frequency simulator, orbit configurations,
required to optimise future sensors w.r.t. to
different application areas. (MT-LT IPWG-R)
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II. Combining MW-IR-models
We recommend combined approaches that embody the
open and modular architecture philosophy (see
I.). For example techniques that combine the
quantitative precipitation estimate from the
microwave sensor and the temporal information on
cloud development from the IR sensor embody the
above principles. This will facilitate data
reprocessing/reanalysis. We further recommend
that merging of model data into retrieval
algorithms should be considered for certain
applications. The impact of merging procedures
on statistics of merged products (e.g.,
consistency of rain pdfs, rain occurrence
between product and ingredients, scale
discrepancies) should be considered for all
future algorithm developments.
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II. Combining MW-IR-models , contd
IPWG 2002, Standards/Common Procedures
Recommendation 3 Develop new strategies on
flexible and global structures for physical
algorithm development, validation, and data
fusion. Action Product merging and blending.
(ST-LT IPWG-O, Bob Adler, Phil Arkin, Joe Turk)
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III. Transportable rainfall estimation techniques
There is an ongoing demand for high-frequency
satellite rainfall retrievals (currently
IR-based). These IR techniques should ultimately
be replaced by microwave and sub-millimetre
sounding from geostationary satellites to provide
more direct information on precipitation physics.
High frequency observations are mainly used for
short-range meteorological and hydrological
forecasting applications. We recommend the
development of a transportable technique that
reflects the existing skill that is well
documented, tutorial, and simple to implement.
Action As part of the algorithm development
group, we will form a sub-group to implement such
an algorithm for a test location (e.g., to be
identified by D. Hinsman).
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General recommendations
Action In the short term, we recommend the
planning of a workshop dedicated to frozen
precipitation physics and observation (link to
GPCP activities). (ST Ralf Bennartz, Ralph
Ferraro) Action The initiation of a liaison
with ITWG for the coordination of common
projects. (Represent IPWG at the next ITSC in May
2005, ITWG website). (ST-LTAmy Doherty, Una
OKeeffe) CGMS to IPWG GPCP assessment is
thought to belong to the Operations WG Snowfall,
frozen precip (dedicated workshop
GPCP/IPWG) Orographic precipitation Ongoing
validation is thought to belong to the Validation
WG Formats, Level 2 Precipitation File Content
Standard, precipitation standards We support the
introduction of standards for precipitation
products, e.g., formats. We recommend the
formation of a working group under the auspices
of GPM to realize format definition.
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General recommendations , contd
IPWG 2002, Future Sensors Recommendation 1 From
the work of the group indications for future
sensors should emerge based on the identified
scientific outstanding areas (TOR d, e) Action
Definition and provision of experimental data
sets (ST Bizzarro Bizzarri) Recommendation
2 In view of future sensor development a
long-term strategy for frequency protection has
to be developed and integrated in the current
ITWG activities. (TOR e) Actions Expression of
need for frequency protection including
approximate frequency bands and their scientific
justification w.r.t. future precipitation
missions. (very ST IPWG) Demonstrate the
usefulness of chosen frequencies in order to
support the request for protection. (ST-MT
Bizzarro Bizzarri)
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General recommendations , contd
IPWG 2002, Standard/common procedures Recommendat
ion 1 Provide a generally accessible platform on
data and algorithms for the research community
(TOR a, d) Actions Define criteria of
satellite data (including meta-data) access for
research applications including data availability
(schedules), sensor specifications,
calibration/validation activities, data formats,
data accessibility (cost). (ST Ralph Ferraro,
Ralf Bennartz, IPWG-O). In the short term, the
responsible agencies have to be approached for
providing information on the following sensors
which will be used for experimental/operational
applications (Jim Purdom, CGMS) SSMIS
(DOD/NOAA), AMSR-E (NASA/NASDA), AMSR-J
(NASA/NASDA), MSMR, VIS/IR sensors. Actions Set
up an inventory of field campaign data,
co-located satellite data. (ST IPWG-V)