The Ocean Biology Processing Group collects and processes data from Earth-viewing
satellites. These data are organized in various ways reflecting different spatial,
temporal, and parameter groupings. Over the years, certain terminology has arisen
to describe these organizational conventions. Here follow some explanations of
- Level 0
Level 0 data are unprocessed instrument/payload data at full resolution.
Any artifacts of the communication (e.g. synchronization frames, communication
headers) of these data from the spacecraft to the ground station have been
removed. These data are the most raw format available, and are only provided
for a few of the missions that we support.
- Level 1A
Level 1A data are reconstructed, unprocessed instrument data at full
resolution, time-referenced and annotated with ancillary information
including radiometric and geometric calibration coefficients and georeferencing
parameters (e.g. platform ephemeris data) computed and appended but
not applied to the Level 0 data.
It is this last point that makes Level 1A the preferred archival data level.
If the sensor calibration changes, the data do not need to be
reacquired — no mean feat where large data sets are concerned.
The same is not true for Level 1B data (described below) which must be
replaced every time the sensor calibration changes.
- Level 1B
Level 1B data are Level 1A data that have had instrument/radiometric
- Level 2
Level 2 data consist of derived (by the
program) geophysical variables at the same resolution
as the source Level 1 data. These variables are grouped into a few
(e.g. OC [ocean color], SST, and SST4 for MODIS).
- Level 3
Level 3 data are derived geophysical variables that have been
aggregated/projected onto a well-defined spatial grid over a
well-defined time period. We archive two types of Level 3 data.
Each Level 3 binned data product consists of the accumulated data for
all L2 products in a product suite,
for the specified instrument and resolution, corresponding to a period
of time (e.g. daily, 8 days, monthly, etc.) and stored in a global, nearly
equal-area, integerized sinusoidal grid.
The Level 3 Standard Mapped Image (SMI) products are created from
the corresponding Level 3 binned products. Each SMI file contains a
grid of floating-point values (or scaled integer representations of the
values) for a single geophysical parameter. A color look-up table is
also provided in each file that may be used to generate an image from the data.
- Level 4
Level 4 data are model output or results from analyses of lower level data
(e.g., variables derived from multiple measurements).
is a good example of a Level 4 product.
The numerous products computed from the satellite data that we collect
often differ with respect to the flagging or masking criteria used
to characterize the quality of each retrieved pixel value. We have found
it useful to separate products with differing flagging or masking needs
into separate files whose names include a string identifying which product
suite the included parameters belong to. At Level-2, this categorization
currently separates all the ocean color ("
which share an
l2_flags data set, from sea surface
temperature products ("
SST" and "
which are classified with quality levels stored in a
Further division of the Level-2 products into additional product
suites occurs during Level-3 binning of the Level-2 products. Again, this
is driven by different masking requirements of the different products during
their aggregation into Level-3. Example product suites at Level-3 include:
A detailed description of each product suite is accessible via links provided on the Algorithm Descriptions page.
Note that as part of
Reprocessing 2014.0 the
file formats were changed
from the HDF4 mentioned in the documents below to NetCDF4.
- Level 0
- Level 1A
- Level 2
- Level 3