Important information on the
Doppler Radar data files
Warning
The radar reflectivity in the three-dimensional wind files should be used
with great caution. We recommend you do not use the reflectivity data
quantitatively, but only to describe the precipitation
qualitatively
. Erroneous radar calibrations, and severe intervening attenuation can
affect the analysis of reflectivity which comes from power returned in
the reflected radar pulse. The same sorts of errors do not apply to the
wind data, which come from measuring the radar pusle phase, rather than
the reflected power.
The airborne Doppler radar data presented at this site have been
automatically quality controlled. Quality controlling airborne
Doppler data is inherently difficult to do, because of a number of problems,
including different beam volumes at different radii from the radar, wind shear
within a beam volume, occasional lower sensitivity of the radar, and velocity
aliasing. Velocity aliasing is a particularly difficult problem that generally
requires human intervention to do nearly perfectly.
Even when the data are quality controlled as well as is humanly possible
(manual QC instead of automatic), errors in the position, motion and attitude
of the aircraft, evolution of the system being observed during the period of
observation, and random noise in the observations reduce the accuracy and
precision of the resulting analyses. In the few remaining locations where
there may have been an error in the automatic de-aliasing, errors in the wind
field analysis could be as much as 20 or 30 m/s, but these are generally
noticeable to the human eye. In all other areas, errors may be as high as
10 m/s; however, generally the errors at each grid point are expected to be
approximately 5 m/s. The overall bias is expected to be less. The analyses
do appear to do a very good job of describing the overall three-dimensional
structure and intensity of the hurricane wind field. Further discussion of a
comparison between dropsondes and airborne Doppler analyses will be posted at
this site in the next few months.
It should also be noted that all winds shown here, including radial winds, are
relative to the storm as though it were not moving (i.e. relative to the point
on the earth where the storm was located). They are not relative to the moving
storm.
The ASCII 3D Doppler Analyses
The three-dimensional analyses used to generate the graphics have the
suffix .ascii and can be read with the accompanying
fortran software. The software is commented to help the user read
the files.
The Doppler Radial Text Files
The Doppler radials data have been stored in text files with the
suffix .txt and can be read with the accompanying
fortran software. The software is commented to help the user read
the files.
The quality-controlled Doppler radials are stored in the following format
The first record has three 2 digit integers, followed by a space, followed by
a 3 digit integer. The values are IYEAR, IMONTH, IDAY, and MAXI,
- IYEAR - is the year. (04)
- IMONTH - is the month. (09)
- IDAY - is the day of the month. (22)
- MAXI - is the number of radial bins in the radial. (0414)
The next records list the radii from the aircraft of all MAXI bins in km
in separate records of 8 variables each (10 characters per variable allowed).
If a radius is 1000, then all data at that radial bin have been flagged.
The following records contain :
- time in seconds past midnight of the day the flight started
- radar (aircraft) latitude in degrees (negative means south latitude)
- radar (aircraft) longitude (negative means west longitude)
- radar (aircraft) altitude in meters
- earth relative azimuth (mathematical angles) in degrees
- earth relative elevation from horizontal in degrees
- the Doppler radial velocities bins in m/s.
By mathematical angles we mean the eastward direction
is an angle of 0, and angles are then measured counterclockwise from east
(thus 0 = eastward, 90 = northward,
180 [-180] = westward, and 270 [-90] = southward).
If any records contain a value of -1 for time, then this indicates an operator
has caused a change in the radial resolution. The next line is then a 3-digit
integer containing the new number of radial bins.
The reading then continues as above by reading a record containing time,
latitude, longitude, radar altitude, azimuth, elevation, and Doppler
velocities, until another change in radial resolution, or the end of the file.
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