What MODIS data levels are provided by the OBPG and are they customized in certain ways?
The Ocean Biology Processing Group acquires the entire onboard recorded global Level-0 archive of MODIS data in near-real-time. The Level-0 data is split into 5-minute granules (contiguous portions of sensor swath data) and immediately processed to Level-1A, Level-1B, Level-2, and Level-3. Every data level is freely and immediately available from our distribution system (see below for more details).
made to certain MODIS files distributed by the OBPG (and so these files differ from those distributed by non-OBPG sources). In a nutshell only Level-1A and Level-1B files are altered, and these ocean-specific customizations in turn affect the Level-2 and Level-3 data products. It should be noted that if SeaDAS is used to process standard MODIS data files, all customizations can be turned off in order to produce "standard" MODIS Level-1A and/or Level-1B data files. (A full description of the OBPG data processing chain is available here
The information below outlines OBPG MODIS data access and customization details for each data level.---Level-0 data
All the recorded MODIS Level-0 data (in the standard PDS format with no customizations
) is available for the entire Aqua and Terra missions via the Level 1 and 2 Browser
A rolling 60-day archive of recent Level-0 data is also available on the OBPG ftp site
.---Level-1A dataMODIS Level-1A
data for the entire Aqua and Terra missions is available from the Level 1 and 2 Browser
as single file downloads or by ordering multiple files that are staged to an ftp site. A rolling 30-day archive of recent Level-1A data is also available on the OBPG ftp site
The Level-1A data files distributed by the OBPG have been reduced by ocean-subsetting
, a process in which excess bands and data that are not utilized for ocean processing are removed. This greatly reduces file sizes (easing storage and distribution), while retaining the information needed to derive all higher-level MODIS ocean products as well as true color imagery.SeaDAS is capable of processing Level-0 files to non-ocean-subsetted standard Level-1A files containing all 36 MODIS bands.---Level-1B data
Though not available in the browser, MODIS Level-1B
files are available in the rolling 30-day data archive on the OBPG ftp site
Along with being ocean-subsetted
, OBPG MODIS Level-1B files differ from those of other data sources due to the application of custom calibration look-up tables (LUTs) for both Aqua and Terra
during Level-1A to Level-1B processing. This is done in an attempt to improve accuracy as ocean color has more stringent calibration requirements than other disciplines. For both Aqua and Terra data, other providers of Level-1B data (e.g. LAADS) will likely process their Level-1A data using the standard calibration LUTs provided by the MODIS Characterization Support Team (MCST).
The methodology of customizing Aqua's LUTs
differs in some ways from Terra's LUTs customization
. To summarize, for Aqua, the OBPG makes subtle changes to the instrument temporal calibration, and adds a correction for residual detector striping to improve the spatial and temporal stability of the Level-1B radiances. MODIS Terra LUTs have been modified by MCST for the purpose of ocean color (and provided to the OBPG) up until June 2007. (However, we currently do not encourage the use of Terra for ocean color due to Terra calibration problems described in http://oceancolor.gsfc.nasa.gov/DOCS/Publications/franz_et_al_2007_spie.pdf
So for ocean color Level-1A to Level-1B processing, we strongly encourage the use of the calibration LUTs distributed by the OBPG for both MODIS Aqua and Terra.SeaDAS includes custom ocean calibration LUTs and is also capable of processing both ocean-subsetted or non-ocean-subsetted Level-1A files to Level-1B.---Level-2 dataMODIS Level-2
data distributed by the OBPG are stored in HDF files in a custom ocean-specific OBPG format. Level-2 data for the entire Aqua and Terra missions is available from the Level 1 and 2 Browser
as single file downloads or by ordering multiple files that are staged to an ftp site. A rolling 30-day archive of recent Level-2 data is also available on the OBPG ftp site
.Though the distributed Level-2 files contain only ocean bands/products, if SeaDAS is used to process non-ocean-subsetted Level-1B data, then it is possible to create Level-2 files containing non-ocean bands and geophysical products derived from non-ocean bands (including hi-res products).---Level-3 dataMODIS Level-3
data distributed by the OBPG are stored in HDF files in two custom ocean-specific OBPG formats. Level-3 data for the entire Aqua and Terra missions is available from both the Level 3 Browser
and the OBPG ftp site
.As with the Level-2 files, SeaDAS can be used to create Level-3 files containing non-ocean bands and geophysical products derived from non-ocean bands (including hi-res products).