Data Access and Services

1
SORCE Data Product Use of HDF5
James Johnson and Suraiya Ahmad NASA Goddard
Space Flight Center, Code 902 Goddard Earth
Sciences Distributed Active Archive
Center Greenbelt, MD 20771 jjohnson_at_daac.gsfc.na
sa.gov
SORCE Level 3 Data Products
Overview
All of the SORCE level 3 data products are
available in the new HDF5 file format. The data
are stored in HDF5 datasets using the compound
datatype, i.e. they represent a table. The solar
spectral irradiance products contain four tables,
while the total solar irradiance files contain
just a single table. Each file contains a set of
file level attributes, and each table dataset
also includes a set of attributes. And because
the SORCE data are in tabular format, one may
also use the H5lite library to read the data.
Users need easy access to the data without
worrying about details of file formats (ASCII is
often preferred).
The Solar Radiation and Climate Experiment
(SORCE) launched successfully on January 25, 2003
aboard a Pegasus XL rocket into a 645 km altitude
and 40 inclined orbit. SORCE is a key element
in NASAs Earth Observing System (EOS) with the
aim of measuring the solar radiation incident on
the Earths upper atmosphere. Management of the
SORCE mission is provided by the Laboratory for
Atmospheric and Space Physics (LASP), at the
University of Colorado in Boulder. The SORCE
principle investigator is Dr. Gary Rottman. The
LASP facility is responsible for spacecraft
mission operations support, and the processing,
analysis and validation of all science data
products. The standard data products are then
delivered to the NASA Goddard Earth Sciences
Distributed Active Archive Center (GES DAAC),
located at the Goddard Space Flight Center, for
permanent archiving and distribution to the
public. The primary science goals of SORCE are
to provide precise daily measurements of the
total solar irradiance (TSI), and solar spectral
irradiance (SSI) across the ultraviolet, visible
and near-infrared regions. Long-term
observations of solar radiation are crucial in
understanding solar activity and solar events,
and the role of solar variability on the upper
atmospheric chemistry, dynamics, and climate
change. Variations of TSI over the 11 year solar
cycle are on the order of 0.1, but show greater
variations due to short-term solar activities
(flares, solar storms, sunspots). Changes in
solar irradiance by as little as 0.25 per
century can have profound effects on the planets
climate. As an example, the late 17th century
cooling referred to as the little ice age is
believed to have occurred in Europe due to
minimum sunspot activity (no sunspots recorded
from 1650-1715, known as the Maunder Minimum)
and minimum total solar radiance. SORCE will
provide the data to improve our understanding of
long-term climate change, natural variability and
climate prediction. For more information on the
SORCE mission, please see the LASP SORCE web site
at http//lasp.colorado.edu/sorce. The SORCE
spacecraft includes four instruments the Total
Irradiance Monitor (TIM), Solar Stellar
Irradiance Comparison Experiment (SOLSTICE),
Spectral Irradiance Monitor (SIM), and the soft
X-ray Ultraviolet Photometer System (XPS). These
instruments use state-of-the-art technology to
provide more accurate spectral and total solar
irradiance measurements compared to precursor
sensors.
An IDL session using its H5_BROWSER showing a
plot of the daily averaged total solar irradiance
corrected for all known instrument and
operational effects and reported at a standard
distance of 1 A.U. By importing the data into
IDL, one can then manipulate the data and produce
plots specific to ones needs, or save the data to
any number of output formats for later use. HDF5
wrapper calls are also available for more
experienced users. IDL is a very powerful tool
and used widely throughout the science community.
Example using NCSA HDFView to see contents of
SORCE solar spectral irradiance file. Tool is
free and allows users to see contents of data
files and save to ASCII. Useful non-graphical
tools include NCSA h5dump and h5ls.
Data Access and Services
EOS Data Gateway http//eos.nasa.gov/imswelcome
The EOS Data Gateway (EDG) is the interface for
all Earth science data available in NASAs Earth
Observing System Data Information System and
related data centers. Through the EDG one can
search for and acquire various Earth science data
products from the EOS instruments, such as MODIS,
MISR and SORCE, as well as from other
instruments, such as TRMM, Landsat, etc.
DAAC Search and Order http//daac.gsfc.nasa.gov/d
ata All of the SORCE level 3 and eventually any
level 4 data products will be made available
through the GES DAAC Search and Order
interface. The GES DAAC interface utilizes a
simple point-and-click approach for searching and
ordering both on-line and near-line data products
that are archived locally. The data are
organized using a hierarchical design into tables
according to different Views (e.g. by data set,
data product, parameter). For certain products
one may use spatial, temporal, orbital, or other
attribute search features to narrow your search
to exactly what you want.

• Data Pool ftp//g0dps01u.ecs.nasa.gov/
• The ECS data pool maintained at the GES DAAC is a
  new large (50 TB capacity) online anonymous ftp
  server that allows users quick access to specific
  data holdings. Due to its relatively small size,
  the entire set of SORCE level 3 data products
  will always be available from the data pool to
  download.
• Tools and Services
• The GES DAAC will provide C, Fortran and IDL
  tools for reading and displaying the SORCE HDF5
  data files. Online documentation, guides and
  FAQs, describing these data will also be
  available. For information describing the new
  HDF5 file format and access to the libraries,
  please see the web site http//hdf.ncsa.uiuc.edu/h
  df5. HDF5 is maintained by the National Center
  for Supercomputing Applications (NCSA), located
  at the University of Illinois, at Champaign.
• Users with questions concerning data orders or
  questions about DAAC holdings should contact the
  user help desk. Users should also contact the
  help desk when requesting hardcopy documentation
  or posters. Contact information for the GES DAAC
  help desk is listed below
• e-mail help_at_daac.gsfc.nasa.gov
• telephone [phone] (local),
  1-877-422-1222 (toll free)
• fax [phone]

http//daac.gsfc.nasa.gov