MODIS Collection 5 Improvements Summary
Last Update: May 23, 2006
The MODIS Science Team has begun a reprocessing campaign with improved
versions of Level 1 science algorithms, to be called Collection 5 (C5).
The reprocessing of five years of MODIS/Terra began in March 2005, and
almost three years of MODIS/Aqua will follow soon. Both reprocessing
campaigns are expected to be completed by March 2007. Parallel forward
processing using the current Collection 4 algorithms will continue through
the end of August 2005 to allow users to move over to the C5 products in an
orderly fashion. The MODIS Land, Ocean and Atmosphere discipline
reprocessing are being done on a different schedule. A number of important
changes for C5 are summarized below.
Level 1B Calibrated Reflectance and Radiance
For MODIS/Terra C5 the Thermal Emissive Bands (TEB) Response vs. Scan angle
(RVS), which is based on the Terra Deep Space Maneuver (DSM), will be
applied for the entire mission. The updated RVS has been applied to the TEB
starting in March 2004 (V4.3.0.5). The algorithm was changed to allow the
Shortwave Infrared (SWIR) Out-of-band (OOB) correction to be performed using
alternative detectors if the detector that would normally be used is noisy
or non-functional. The algorithm was also changed to distinguish the two
mirror sides when processing band 21, just like the other TEBs. To more
accurately describe the mapping between the finer-resolution image data and
geolocation data, new HDF file attributes were added
(HDF_EOS_FractionalOffset*) and the 250 meter HDF-EOS DimensionMap offsets
were corrected.
Level 1A and Geolocation
The long-term geolocation trend for MODIS Terra and Aqua was updated based
on the each mission's entire data set. An algorithm was added to perform a
correction to instrument orientation that depends upon the solar "elevation"
angle and a corresponding set of coefficients was provided for MODIS/Terra
to correct for a measured within-orbit bias. The C5 geolocation algorithm
will use a MODIS-derived land-water mask and a more accurate SRTM derived
digital elevation model. The software now uses a list of planned/actual
maneuvers to set a scan-level quality flag when maneuvers occur.
Cloud Mask
Significant improvements have been made to the MODIS cloud mask (MOD35) in
preparation for C5. Most of the modifications are realized for nighttime
scenes where polar and oceanic regions will see marked improvement. For
polar night scenes, two new spectral tests using the 7.2 um water vapor
absorption band have been added as well as updates to the 3.9-12 um and
11-12 um cloud tests. More non-MODIS ancillary data has been added for
nighttime processing. Land and sea surface temperature maps provide crucial
information for middle and low-level cloud detection and lessen dependence
on ocean brightness temperature variability tests. Sun-glint areas are also
improved by use of sea surface temperatures to aid in resolving observations
with conflicting cloud vs. clear-sky signals, where visible and NIR
reflectances are high, but infrared brightness temperatures are relatively
warm.
Further details and examples of improvements can be found on the
MODIS Atmosphere
website.
Atmospheric Profiles
The Atmospheric Profiles product (MOD07) is now updated with changes to the
training data used to create the regression coefficients, including more
profiles and better characterization of the surface. Training data and
retrievals are now also partitioned into separate land and ocean classes,
and new BT zones are used. In addition, destriping is performed on the L1B
data before performing the retrievals, and updated radiance bias values are
used.
These changes reduced the moist bias for dry cases and improved moisture
retrievals in the tropics. We reduced the along-track noise and across-track
striping. The polar ozone was significantly improved and prior
overestimates reduced. Total predictable water retrievals now compare more
favorably to surface measurements at the SGP CART site, with RMS errors in
TPW reduced to around 3 mm.
Further details and examples of improvements can be found on the
MODIS Atmosphere
website.
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