The AmeriFlux Data Archive at the Carbon Dioxide Information Analysis
Center offers several different product levels reflecting the data origin
and level of processing, adjustment, and evaluation.

The following lists and defines briefly the AmeriFlux product levels,
most of which are available directly from this FTP area.  For further
details, please contact Tom Boden (bodenta@ornl.gov, 1 865 241 4842)

Level 0 - Original/Raw Data
----------------------------

Original data (e.g., voltages from the data logger, measurements
before processing into 30 min values) are not archived at CDIAC.
Users interested in obtaining raw data need to contact the investigators
at the individual AmeriFlux sites.

Level 1 - Processed Data Provided by the Site Investigators
-----------------------------------------------------------

These 30 min or 1 hr data are available here from the CDIAC anonymous
area.  Please note that the data files and documentation have not
been standardized and remain in the original format submitted by
the investigators.  Some investigators provide gap-filled records.
The data are organized by site.  Please refer to the AmeriFlux fair-use
data agreement (see ReadMe_First_AmeriFlux_Fair_Use_Policy.txt) before
using these data.

Level 2 - Data Checked & Formatted by CDIAC
-------------------------------------------

CDIAC checks data received from individual sites and attempts to
build a network-wide AmeriFlux database with consistent units, naming
conventions, and reporting intervals.  These data are available for
graphing, querying, viewing, and downloading from a web-based interface
(http://public.ornl.gov/ameriflux/data-access-select.shtml) requiring
user registration.  Data may be queried by site, measurement period,
or parameter. 

CDIAC also offers standardized ASCII data files (derived from the same
network-wide database described above) here from the CDIAC anonymous ftp
server.  These files contain core AmeriFlux measurements arranged by site,
year, and whether the records contain gaps or not.  These standardized
files are intended to help satisfy data requirements for modeling and
synthesis efforts.

Level 3 - Processed Data With Quality Flags Assigned
----------------------------------------------------

AmeriFlux Level 2 standardized files are kindly processed by the
European flux data activity to produce Level 3 and 4 files identical to
the European regional network.  Typically, Level 2 standardized files
from the "with_gaps" subdirectory are used by the Europeans to produce
the Level 3 and 4 data products, however, there are a few sites where
"hybrid" files are provided.  These "hybrid" files contain gap-filled
meterological records and flux records containing gaps. Users will find a
"hybrid" subdirectory only for those sites where the hybrid files were
furnished to produce the Level 3 and 4 files.  Level 3 files contain
the same values as Level 2 files but with quality flags assigned and
NEE calculated using standardized techniques.

Level 4 - Gap-filled & Adjusted Data Files with GEP & Re Estimates
------------------------------------------------------------------

Level 4 files contain gap-filled (ANN and MDS techniques) and ustar
filtered records, complete with calculated gross productivity and
respiration terms.  Flags with information regarding the quality of the
original and gap-filled data are added.

Select synthesis data sets, like the daily soil respiration data set
compiled by Hibbard et al. (2005) for Northern Hemisphere sites, are
available in the /synthesis-data subdirectory.