Acquiring the ISAMS L3A data held at the BADC

This file contains background information to help you get the ISAMS L3A data held at the BADC.

  1. ISAMS L3A Data held at the BADC
  2. Checking and Transferring Data from the BADC
  3. Converting the data to binary on your machine
  4. Reading the files

1. ISAMS L3A Data held at the BADC

The ISAMS data was supplied to the BADC in VMS binary files. To enable transfer of the data to a wide variety of machines we have converted it into ASCII (plain text). To speed up transfer of the ASCII files, we have compressed them using the GNU gzip program.

Therefore, you will need gzip installed on your local system to uncompress the data files and software packages - the source code is available from software archives. You will also need to know how to use gzip and tar once you have the files on your system and how to transfer files via FTP (File Transfer Protocol)

The ASCII files are purely an intermediate form for data transfer. We supply software to convert the ASCII files back into binaries on your local machine, enabling you to use software that reads the data files as binary. We also supply an example read program to read the binary data, and 3rd party software written by other users of the data, which we do not support.

Since the dataset is public, it is available anonymously by FTP and can also be acquired through the WWW.

2. Checking and Transferring Data from the BADC

All data and software is located beneath the directory /badc/isamsl3. Here you will find a README file and the following subdirectories

Check whether the data you require is available by browsing the ISAMS L3 data directories.

3. Converting the data to binary on your machine

3.1 Unzipping the files

Unzipping the compressed ASCII files (using the gzip -d command) will typically change the size from about 2-2.5 Mbytes per file to around 10-15 Mbytes. Make sure you have sufficient disk space before unzipping the files. Note that when you convert the ascii file to a binary on your machine it will be substantially reduced in size.

3.2 Building the software

The ASCII to binary conversion program - asc2bin (and the read example) is supplied in a gzipped tar archive, or as individual source files. A makefile and README file are supplied to help you build the code. The README file explains the small changes required to adapt the code to suit your local operating system.

3.3 Running the software

The conversion program will produce binary data files for your machine. If you have problems, refer to the README file or contact the BADC team. The resulting binary files are considerably smaller than the intermediate ASCII files. Once the conversion is successfully completed you can remove the ASCII files.

4. Reading the data files

4.1 The file structure

There are 4 level 3A files for each ISAMS species per day - one for each of the file classes 3AT, 3AL, 3TP, 3LP. The structure of the files is outlined below, but users should refer to the level 3A file format document for more detailed information.

The level 3AT files are a time ordered sequence of records each containing one profile, together with information on the position of the profile. The associated parameter file contains data on the operation conditions of ISAMS which are not allowed by the level 3AT file definition. There is a one-to-one correspondence between records in the 3AT and 3TP files.

The 3AL products have a similar structure, but in this case, each record corresponds to a profile interpolated onto standard 4 deg. latitude intervals at positions defined by the intersection of the tangent track with a latitude circle.

4.2 The Access Routines

A set of user-callable FORTRAN subroutines is available from the BADC to read the original data files. These should compile on most platforms with minor changes to the open statements.

4.3 Third Party Software

In the software directories for the ISAMS data, there is a subdirectory for 3rd Party software. If you develop software to use with the ISAMS data, then we encourage you to let us have a copy so that we can make it available to other researchers.