**Semiannual Report on JHT Project entitled:**

Real-Time Dissemination of Hurricane Wind Fields Determined

from Airborne Doppler Radar Data

**P.I.: John F. Gamache, Hurricane Research Division (HRD)**

**Accomplishments**:

1)  PI became familiar with HRD radar software used to access raw
    information recorded by the P3 radar systems.

2)  Software developed to remove the reflection of radar power by the
    sea surface. The preliminary testing has indicated success in this
    task.

3)  Software developed to remove speckles of data that may be near the
    signal to noise ratio, and yet have an inordinate effect upon the
    radar analysis.

4)  Several minor bugs that affect the single-ray de-aliasing software
    in HRD code were discovered and repaired. This has helped the
    automatic de-aliasing somewhat.

5)  Development of two-dimensional de-aliasing software has just begun.

**Discussion**:

The goal of this JHT project is to provide information to the National
Weather Service regarding winds in three dimensions near the core of the
storm using the airborne Doppler radar. The expertise to synthesize
quality-controlled Doppler measurements into three-dimensional analyses
is already well developed at HRD; however, the means to quality control
has always been from using "black box" software from NCAR, and doing
much of the quality control manually, using people qualified to make
judgments about which data are actually artifacts or will contribute to
errors in the analysis. The analyses are also completed over a period
that may span months or years, affording the analyst the luxury to mull
over the data. Thus the analyses are performed in a laboratory using
computers on the ground. Consequently, the major tasks to be
accomplished to provide real-time data are 1) automatic quality control,
2) production of analyses aboard the aircraft, 3) successfully
transmitting "superobs", (useful intelligent averages of the data that
can be utilized by model assimilations) from the aircraft, and 4)
transmitting and depicting the analyses conveniently for the very busy
hurricane specialist.

For the P.I., the first major task was becoming familiar with the
software that is employed regularly to ingest airborne radar data into
analysis and depiction programs. Previously most of this software was
not used for airborne Doppler analysis research, and instead the
NCAR/ATD SOLO package was used to prepare data for ingestion into the
Doppler radar interpolation. SOLO is a research tool, but is not
designed for real-time quality control, nor is it software presently
understood completely by HRD scientists and programmers. Since SOLO was
not developed at HRD, it was decided that the best plan was to modify
HRD software that could directly read data written by the onboard
AOC/SIGMET radar-data collecting software. Software written to ingest
this data stream would be modified to include automatic quality control,
and then the three-dimensional analysis code would be modified to ingest
the result of the quality control software and produce an analysis, as
well as superobs.

The first software developed was to remove the reflection of radar data
by the sea surface. This reflection will contaminate the analysis of
precipitation intensity, since the reflectivity of the rough sea surface
can be much higher than the precipitation above it. Also the motion of
the capillary waves on the sea surface is much closer to zero than to
the wind motion directly above, and thus the returned velocities are
also a contaminant in the wind analysis. Software employed by Mr. Peter
Dodge (HRD), developed originally by Jacques Testud of CNRS/CETP,
France, and Wen-Chau Lee of NCAR/ATD to detect the ocean surface along
each radar radial, was modified to remove the data from the surface and
at all radii beyond. Since data in a given radar radial include scatter
from objects located somewhat off the center of the beam, it was
necessary to compare observations immediately above the detected surface
to ensure that they were not still contaminated by sea-surface
reflectivity. Also included in surface-reflection artifacts are
reflections of the side lobes off the sea surface. These appear as an
annulus of artifacts approximately 2 km wide with a radius equal to the
height of the aircraft above the sea surface. These are also removed in
the new software. This software was developed and has been tested on two
cases thus far. This addresses one of milestones in the project
timeline.

In most airborne Doppler scans there are also data that are not
continuous, but usually represent data collected at not much above the
signal-to-noise ratio. These "speckles," if not removed, can reduce the
effectiveness of the automatic Doppler de-aliasing ("unfolding")
software and should be removed. First cuts at adding speckle removal
look promising for the analysis. This addresses the same milestone as
the tasks in the paragraph above.

Another milestone is to modify the three-dimensional software to ingest
the automatically quality-controlled data stream. This is necessary in
real time, and also for testing the quality control on a number of
differing tropical-cyclone data sets. The ingestion has been tested on
data obtained in Hurricane Humberto of 2001, and appears to be
functioning properly.

For now the development of software to compress HRD wind analyses for
transmittal over satellite data link has been postponed. It is possible
that easily available software like "gzip" will be sufficient. Unless
eventually desired by specialists, full analyses at many different
levels will not be sent from the aircraft.

In the late winter and spring of 2004, the next major step in quality
control is de-aliasing of the phase ambiguity in the airborne Doppler
observations. To determine the relative velocity of airborne scatterers,
the Doppler radar effectively compares the phase of reflected pulses
with the expected return phase and determines a Doppler phase shift. In
most past data sets, a phase shift of 180 degrees represented a relative
motion of 12.88 m/s. Only phase shifts from --180 to 180 degrees can be
measured unambiguously. Thus greater phase shifts from velocities higher
than 12.88 m/s will be misinterpreted. The goal of the Doppler-analysis
software is to prevent these misinterpretations. The high winds in the
tropical cyclone, and the even faster motion of the aircraft, require an
accurate "unfolding" of this phase ambiguity. Well established methods
exist that can remove most of the ambiguity, but some remains. Methods
will be tested in the coming months that require two-dimensional wind
continuity in a contiguous portion of data within a radar sweep. These
contiguous regions will be compared to the expected wind structure and
intensity to ensure that these otherwise self-consistent regions are
also consistent with the expected wind field. On the third page of this
document analysis of data with the real-time quality-control software in
its present state is compared to an analysis performed on data that was
quality controlled manually by the PI. Some dealiasing errors can be
seen particularly to the west of the circulation center, but the overall
qualtity of the analysis is encouraging.

The integration of this software on HRD's airborne workstations will
occur in the spring. The software will then be tested during the
hurricane season. Analyses will be produced aboard the aircraft, but it
is not expected that they will be made available in real time to the
specialists until the 2005 hurricane season. Thus IT support to allow
these analyses to be seen by the specialists on their equipment is not
needed in the 2004 season, nor are they likely to be available online.

**Next tasks:**

1)  Develop two-dimensional de-aliasing software

2)  Begin discussions with EMC on how to make superobs most useful to
    them, including determining how to determine the best estimate of
    data error covariance for assimilation into numerical models

3)  Migrate new software to airborne workstation

**Future tasks:**

1.  Produce test Doppler-wind analyses aboard aircraft

2.  Send a prototype superob from the aircraft by Oct 31

3.  Develop capability to display analysis easily for hurricane
    specialist

**Note**: A possible adjustment to the 2004 hurricane-season timeline
may be necessary if the software changes to the onboard radar data
system by AOC are made without sufficient time for HRD to adjust.

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