The ESPO archives contain ASCII data files and image files. The image files have standard image file formats like PNG and JPEG, whereas the ASCII data files are written in one of nine "standard" file formats. The ASCII data file formats were developed at Ames Research Center in 1990 to standardize the file formats used for in-the-field data exchange during aircraft field experiments.

Each ASCII data file consists of a file header, followed by the data records. The file header describes the data and the origin of the file. The data are conceptually divided into Independent Variables and Dependent Variables. The Dependent Variables are further divided into Primary and Auxiliary Variables.

Auxiliary Variables are considered to be single-valued functions of the Independent Variable with the largest index; 1 if there is only one Independent Variable, 2 if there are two, etc. Primary Variables are considered as single-valued functions of all Independent Variables. Thus, all Independent Variables must be monotonic.

A complete description of the ASCII data file formats is contained in either of the following documents:

• formatspec_2_0 (HTML)
• formatspec_2_0 (PDF)

For historical purposes, the old version of the format specification can be found in formatspec_1_3.txt.

Format Extensions

Version 2 of the format specification introduces some backward-compatible extensions to the original specification, which can be used to facilitate automated processing of the data files. The extensions do not alter the file format, but they do alter the file content by standardizing the way metadata are recorded in the files. A primary goal is to uniquely specify geophysical parameters and their associated geolocation coordinates, and eliminate multiple definitions for the same parameter. Toward that goal, selections from several tables are used to build the descriptions of geolocation, geophysical and platform-specific parameters. Those tables are described in the format specification document, and are also presented here in HTML and plain text formats:

HTML		Plain Text
Geolocation Subjects		Geolocation Subjects
Geolocation Qualifiers		Geolocation Qualifiers
Geophysical Subjects		Geophysical Subjects
Geophysical Qualifiers		Geophysical Qualifiers
Platform Qualifiers		Platform Qualifiers
Platforms		Platforms
Instruments		Instruments
Organizations		Organizations
Normal Comment Numeric Data		Normal Comment Numeric Data
Normal Comment String Data		Normal Comment String Data

Those tables will grow as new entries are included, and you, as a potential user, are invited to contribute to their development. The intention is to use sufficiently unique, common, or at least meaningful (sometimes with license), terms and definitions for the table entries. However, while reviewing the tables you may find that a new entry is required to describe your data, or that an existing term or definition is inaccurate or outright misleading. If so, please send a note to the curator of this site describing the problem and its solution.

Guidelines and Hints

When designing your ASCII data files, be mindful of the following hard rules:

1. Use only the printable ASCII characters in your data files, which have ASCII decimal values from 32 through 126. TABs and other control characters are not allowed.
2. The maximum number of characters in each line is 132.

and of these desirable features:

1. Use the file header variables, and comment lines if necessary, to clearly define:
   1. the originator of the file;
   2. the source of the data;
   3. the physical units used for each variable.
2. Define your numeric Independent Variables in such a way that their values can be differentiated with single precision numbers. Independent Variables must be monotonic, so by ensuring that changes in consecutive values can be resolved by single precision numbers will ensure that software tools using single precision can process your files.
3. Use compact files, especially if your files are larger than a few MB, since that speeds up the time to transfer and read your files, and requires less disk space to store them. Each character in an ASCII file (including a blank space) adds a byte to the file size, so eliminate extraneous characters.
   1. The precision of numeric data should be tailored to the accuracy of those data, i.e., if your data are accurate to three significant digits then there is seldom a benefit in recording them with more than four significant digits.
   2. Eliminate extraneous whitespace padding between numeric data. You only need one space to delimit the data values.
   3. Use the scale factors for the Dependent Variables to record real numbers as scaled integers, and thus eliminate the recording of decimal points in each numeric value.

Please contact the archivist if you would like help with casting your data into the ASCII file formats.

Images can be archived in any of the following standard image file formats: GIF, JPEG, PNG, PDF. It is important to include enough annotations in the image so that by viewing the image one can determine its subject, and readily compare it with other datasets. The annotations should also indicate the source of the data depicted in the image. Some image file formats allow for comments embedded within the file, and you are welcome to use those comments for lengthy descriptions.