ACE Level 1 data are distributed by the ACE Science Center to each of the ACE instrument teams, and are permanently archived at NASA's National Space Science Data Center (the NSSDC). Since the ACE data are non-proprietary, no authorization for release of the data to the general science community is required.
However, ACE Level 1 data requires significant further processing to make them useful for scientific studies. The experience and expertise required to perform this processing rests with the instrument teams. Therefore, it is strongly recommended that users of Level 1 data from the ACE Science Center, or the permanent NASA archive at the NSSDC, contact the responsible instrument teams regarding correct usage of the data.
The ACE Level 1 data are organized to meet the individual requirements of the nine ACE instrument teams. Several (in some cases many) data structures are defined for each instrument, and several more are defined for the spacecraft engineering data. The data structures were defined by the Science Center in consultation with each instrument team. Therefore, the degree to which the raw data is massaged during Level 1 processing varies from instrument to instrument.
The basic elements of the Level 1 data produced by the Science
Center are C data structures, each defined in their own include
file. Based on the definition of a data structure, a library of C
subroutines is created that make it quite easy to read/write that
data structure from/to
HDF format data files.
All ACE Level 1 data are formatted in HDF (Version 4.1r2).
The Level 1 and browse data structures for each instrument and for the spacecraft engineering data can be viewed by selecting the appropriate link below.
To simplify the process of converting data to HDF format, a perl program (hdfgen.pl) has been written which creates the code necessary to initialize and perform reads and writes of the HDF file, using a C structure as a template. Thus, minimal knowledge of HDF is needed to access the data in an ACE Level 1 file.
hdfgen.pl can be used to convert any data to HDF format, once one has defined a set of C data structures to contain the data. At ASC, hdfgen.pl is used to create Level 2, browse and ancillary HDF data files, as well as Level 1.
The ACE Level 1 data requires significant further processing to make it useful for scientific studies, so it is most likely that you will want to read the data and process it using your own custom software. This guide is intended to help get you started. If you are not already familiar with ACE data, we encourage you to read the previous sections of this document before reading the material below. We assume that you have already gained access to the data by contacting one of the ACE instrument teams.
Note: All ACE Level 1 data is in HDF format, so you can access the data using any of the scientific data analysis applications which support the HDF format (IDL, NOESYS, etc.). However, if you wish to take this route, be aware that the Science Center does not provide support for these applications.
The Science Center has put together a software package to enable you to access ACE Level 1, browse and ancillary HDF data files from C programs. The package contains source code and example programs which illustrate how to read most of the Level 1 data structures from a Level 1 HDF file. What follows is a step-by-step guide for obtaining, installing and using this software package.
ftp://mussel.srl.caltech.edu/pub/ace/softwareThe package is a zip-compressed archive, which unzips into a directory called "acetest". The acetest directory contains a number of subdirectories, whose contents are described in the accompanying README file. In particular, the "hdfsubs" directory contains all the low-level routines created automatically by our hdfgen.pl perl script (See the previous section, Automatic HDF Code Generation - hdfgen.pl). So, you do not need to have perl or hdfgen.pl installed on your system to use this software package.
or if this is the CD version it will be in the top directory.
The procedure is the same for other instruments. EPAM example programs are in the "epamtest" subdirectory, etc., etc.
ACE ancillary data is provided in a HDF format data file which is updated daily by the Science Center. This file may be downloaded from
ftp://mussel.srl.caltech.edu/pub/ace/ancilExamples illustrating how to access the ancillary data from C programs are in the "anciltest" subdirectory of the ACE Level 1 software package.
If you have any questions which are not answered here, please
contact an ASC staff member.
Last Updated: 30 June 2000Return to ASC Home Page