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There are 3 primary product levels:
L1A products contain the raw radiance counts from all bands as well as
spacecraft and instrument telemetry. L1A data are used as input for
geolocation, calibration, and processing.
L1B products result from applying sensor calibration to the L1A data. The
resulting product consists of calibrated, top-of-atmosphere (TOA) radiances.
L2 products are generated from a corresponding Level-1[A|B] product. The L2
products consists of geophysical values for each pixel, derived from the
Level-1A raw radiance counts by applying the sensor calibration, atmospheric
corrections, and bio-optical algorithms. Each L2 product corresponds
exactly in geographical coverage (scan-line and pixel extent) to that of its
parent L1A product.
Binned data: Each L3 binned data product consists of the accumulated data
for all L2 products, for the specified instrument and resolution, corresponding
to a period of one day, 8 days, a calendar month, or a calendar year that has not
been masked. Information about the individual flags and masks can be found
The data are stored in a representation of a global, equal-area grid grid cells or "bins".
Standard Mapped Images: The L3 standard mapped image (SMI) products are
image representations of binned data products. This image is a byte-valued,
(16-bit for SST) two-dimensional array of an Equidistant Cylindrical projection
of the globe. The original SMI definition was a ~9km resolution product.
For MODIS, we also produce a 4km product.
What is the difference between SMI and Binned products?
The SMI format is an 8 (or 16) bit image format, thus it lacks the full
precision of the original retrieval. Also, the SMI format presents the data in
an equi-rectangular grid, which means the spatial resolution varies with
latitude. In contrast, the binned products maintain the data in an equal-area
projection. Generally speaking, it is recommended that you use the binned
products when doing detailed, quantitative analysis, and you use the SMI
products when you just want easy access to a global image.
A description of the various levels of data processing can be found at
GAC, LAC, MLAC, HRPT
GAC - Global Area Coverage, typically ~4km resolution.
LAC - Local Area Coverage, ~1km resolution
SeaWiFS ground stations (HRPT - High-Resolution Picture Transmission)
produce LAC resolution products.
MLAC - a 'Merged LAC' dataset, where duplicate HRPT/LAC coverage is merged
into a single dataset on a per orbit basis.
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