It will be necessary to read or seek to that point in the file. The byte column contains the size in byte of the previous section. The remaining sections are fixed in size. The Phoenix header will contain the actual length of the Phoenix and native CDF header in bytes. The native header of the CDF file is of variable length and can contain characters, integers, and floating-point numbers.
There are eight sections in the CDF file. The Phoenix file has the same sections plus a variable length Phoenix header at the beginning. The files are organized as in the example below. The Phoenix files were written with the Sun Floating point standard. The phase history values in the CDF files and Phoenix files are complex floating-point numbers. The phase history blocks also contain a Phoenix header describing the data. The phase history data block was extracted with 221 frequency and 79 azimuth points. The data was down-sampled in frequency and in azimuth from ½ ft x ½ ft range and cross range resolution to 1 ft x 1 ft resolution. The phase history blocks contain down-sampled segments of the phase history data at a specific polarization and aspect. This Phoenix header allows the Phoenix tools to be used to extract data from the file. The main difference is the Phoenix version contains a Phoenix header that describes the file in an ASCII format. The Phoenix files are very similar to the CDF files. Finally, the channel section states which polarization was used for each part of the data collected. The header section contains comments about the factors of the collection.
The cal_add and cal_mult sections describe the calibration of the radar system for each sample. The azimuth is available at three nominal depression angles. The frequency and azimuth sections contain the frequency of the radar system and target orientation. The frequency domain contains the actual phase history data for the target. The data segments of the phase history CDF files include: frequency_domain (phase history), frequency, azimuth, cal_add, cal_mult, header, and channel. The header data can be accessed with an inquiry from Matlab using the mexcdf routine described later. The native header of the CDF file contains all the necessary information to access the data segments of the file. The CDF file format is useful due to the fact that it contains several data groups of different data types and dimensions. The data is also available in phase history blocks that include sections of the available phase history accessible by Matlab. There is a Phoenix version of the data available that can be accessed with the normal Phoenix tools. The original data is stored in a CDF file that is available and accessible with mexcdf routines for Matlab. GTRI Turntable Phase History data is available in several different formats.
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