NASA Ames Format for Data Exchange

Quick links to
FFI Summary
3 tables summarising the nine NASA Ames Format styles and displaying all possible file headers.
Annotated Excel templates of FFIs 1001 and 1020
Including examples and instructions on Excel to NASA Ames conversion.
Note: The BADC recommends NASA-Ames format version 1.3.

Contents

Emergence and general characteristics

The NASA Ames Format for Data Exchange, often referred to as NASA Ames Format, grew out of NASA aircraft campaigns and was first formalised at the Ames Research Centre, California, during the 1987 Stratosphere Troposphere Exchange Project (STEP), when uniform rules to record data were needed to facilitate the data exchange between the participants and allow shared use of a minimised amount of software to analyse and display different datasets. The issue was that the adopted data format should meet the following requirements: The first and third requirements implied the adoption of a text format (namely ASCII). The second condition was met by including in each data file a header containing the descriptive information (metadata).

Very well suited to field campaigns involving several teams that need to share their observations, the NASA Ames Format is not well adapted to very voluminous datasets. In this case, although less portable, a binary format is recommended.

NASA Ames Format: for which type of data?

Any set of functions of 1 to 4 variables can be recorded using the NASA Ames format, which makes it particularly suitable for atmospheric datasets, whether modelled or observed. Some NASA Ames file format indices (see below) are better adapted to airborne platforms (balloons, aircraft).

The number of values taken by one (and only one) of the independent variables is not defined a priori in the data file – so that the data provider does not need to know in advance how many values it takes. This single independent variable is called unbounded, although it is bounded in a mathematical sense. All other independent variables, if they exist, are bounded, meaning that the number of values they take is explicitly defined in the data file – and implying that the data provider has determined these numbers before formatting the data.

The NASA Ames Format nomenclature distinguishes between
up to four independent variables (usually but not necessarily time and/or space) – in most cases, real numbers, one FFI allowing the use of one alphanumeric independent variable (i.e. a piece of text);
the primary dependent variables (functions of the former) – real numbers;
the auxiliary dependent variables (depending solely on the unbounded independent variable) – real numbers or character strings.
The fact that dependent variables are functions of the independent variables implies that only one dependent variable value is associated to one given set of values of the independent variables. For real numbers, this means that the independent variable values can be ordered in strictly increasing or decreasing order (the variable is monotonic), which is indeed a requirement of the NASA Ames format. There is always a way to order a finite number of objects, so that this is a condition that can always be met (if necessary, by choosing an appropriate independent variable such as a subset of the integers).
Except in a few instances, auxiliary variables are optional.

Archive concept

The underlying philosophy is that data are stored in a file-based system, a dataset being formed out of a series of numbered files. Typically, files belonging to a same dataset share some common feature such as the people who issued the data, the experiment, the platform,... This, however, is not a requirement and it is up to the data provider to organise the data files into datasets (possibilities ranging from one single dataset including all files to one file per dataset). The number of files of the dataset and the number of the file within the data set are two elements of information that appear in the file header.

File names

Whilst the first definitions of NASA Ames Format included rules regarding file names, these have been dropped from most recent versions, that now allow any naming convention or no convention at all. File names and their extensions may of course include elements of information on the data (e.g. site name, date, etc) or provide a way to sort them out.

File name rules have been set up for specific NERC thematic programmes Polluted Troposphere, UFAM, ACSOE, SOAPEX, UTLS-Ozone, URGENT.

File format indices (FFI)

The NASA Ames Format is actually a set of nine formats that comply with an overall common structure but make provision of different features adapted to various cases (depending on the number of independent variables, whether their values are regularly spaced out, etc). To each of the nine formats is univokely associated a File Format Index (FFI), which is a 4-digit number.

File structure

Each file is made of two parts. At the top of the file, the file header includes information on the data (metadata). The actual data are recorded in the lines that follow the header. In many cases, some of the independent variables are defined in the header and are not repeated in the data section (e.g. for a regular grid). An accurate description of each format is provided in the BADC NASA Ames FFI Summary (see Formatting your data below). Here is a brief description of the contents of the two file sections.

Header or Metadata section
The header includes, in a defined order and format, all the information needed to read and understand the data. Namely:
the number of the file within the dataset;
the number of lines in the header;
the FFI (which unambiguously defines the structure of the data section) and additional required information on the data format;
the number, nature and units of all types of variables (independent, primary and, when used, auxiliary), ordered as in the data section;
information on the source of the data (name and affiliation of data providers, experiment, instrumentation, model used, etc.);
information on the data, data processing and data quality (location, date, revision date, etc.).
Comment fields are provided at the end of the header for any type of additional information that would not fit in the predefined formatted lines.
Data section
The data proper are subdivided in a hierarchy of two-dimensional blocks, the last independent variable (which is always the unbounded variable – see NASA Ames Format: for which type of data? above) being the most slowly varying one. Note that error margins can be supplied as either primary or auxiliary variables, if needed.

Examples

Each file format index is illustrated by one or several examples.

Further reading

Format Specification for Data Exchange, Version 1.3 (Gaines and Hipskind, 1998) is the primary reference for NASA Ames formatting. As far as possible, the BADC documentation keeps the same nomenclature and notation system as in this original document.

Formatting your data

NASA Ames FFI Summary is a straightforward instrument to identify the appropriate file format index and to format your data step by step. For each FFI, it includes links to detailed descriptions of the corresponding data and metadata formats.
Makeheader.f is a self-explanatory Fortran program that generates NASA Ames file headers tailored to the user's needs. It does not require any knowledge of Fortran, only a Fortran compiler.
Many data files contain the variable time which can be expressed in several ways. Guidelines on the recommended format of the time-variable header lines, units and the data values are available.
The Excel templates of FFIs 1001 and 1020 (Excel format) also include instructions on inserting metadata in NASA Ames files and converting Excel spreadsheets to NASA Ames compliant ASCII files. Two examples of spreadsheets are given for each FFI. Their ASCII versions can be viewed here:
Dummies Guide to NASA Ames format with 1D data
Dummies Guide to NASA Ames format with 2D data
Specific additional rules apply to some NERC thematic programmes (ACSOE, SOAPEX, UTLS-Ozone, URGENT, NEU). Please refer to the Web pages of these data sets.

Checking your data files

The NASA Ames Format checker is an interactive facility provided by BADC, that allows you to check your NASA Ames formatted files online. It is based on a program written by S. Gaines, NASA Ames Research Center.

Uploading NASA Ames files to BADC

For programmes currently submitting NASA Ames formatted files, the BADC provides a Web based file uploader. In the process, files are checked for compliance with the NASA Ames standard.

Reading and understanding NASA Ames formatted data

Every File Format Index is explained line by line in the NASA Ames FFI Summary provided by BADC.
See also the source manual Gaines and Hipskind, 1998.