Important information on the Doppler Radar data files

(This documentation downloaded from http://www.aoml.noaa.gov/hrd/Storm_pages/Doppler.html). The data were downloaded from http://www.aoml.noaa.gov/hrd/data_sub/hurr2005.html by clicking on Radar for the storm of interest.

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 (readwindascii.f). 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 readradials.f). 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,

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 :

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.