Scatterometer Climate Record Pathfinder
SeaWinds Enhanced Resolution Image Product Users Notes
This page is designed as a dynamic repository of relevant information to aid
users of SeaWinds enhanced resolution image products.
SeaWinds-on-ADEOS-II (ADEOS-II is also known as Midori-2) operated
for 9 months in 2003 before a spacecraft power system failure resulted
in the premature end of mission. By JPL convention, this sensor is
known as "SeaWinds" while the SeaWinds sensor on QuikSCAT is termed
"QuikSCAT".
Enhanced resolution images made from SeaWinds data use two
different forms of single-variate the Scatterometer Image
Reconstruction (SIR) algorithm: for egg sigma-0 measurements the SIR
algorithm is used while for slice sigma-0 measurements, the SIR with
filtering (SIRF) algorithm is used. For egg measurements the full
antenna/processing spatial response is used while a simplified
spatial response function in which the spatial response is assumed
to be 1 over the footprint and 0 elsewhere is used for slice
measurements. Unlike SASS, ERS-1/2 and NSCAT, Seawinds observations are at
(essentially) a single incidence angle for each beam so no incidence
angle dependence (B) estimates are made. The SIR algorithm with eggs
makes images of A (in this case, sigma-0 at the measurement
incidence angle) on an 4.5 km pixel grid. The effective resolution
varies depending on region and sampling conditions but is estimated
to be 8-10 km in most areas. The SIRF algorithm with slices makes A
images at 2.225 km pixel spacing with an estimated effective
resolution of 6-8 km. Slice measurements are much noisier than egg
measurements. Multiple passes of the spacecraft are combined to
produce a higher spatial resolution (at a cost of reduced temporal
resolution).
SeaWinds is a dual-pencil-beam conically scanning scatterometer
with the outer beam V pol and the inner beam H pol. The operation
frequency is 13.4 GHz. In combining the multiple passes, sigma-0 is
assumed to be independent of azimuth angle. While true for most
areas, some azimuth dependence in sigma-0 has been observed in
Antarctic firn, presumably due to sastrugi or snow dunes.
SeaWinds data was obtained from SeaWinds L1B data archived at the PO.DAAC.
No recalibration has been applied.
Images are produced in the BYU .SIR file
format, using the standard naming
scheme. The files are gzipped to minimize storage and transfer
requirements. The standard images are designed for land and ice
observation and so are landmasked. However, .SIR format land mask
files (containing 0 for ocean and 1 for land) are available for each
standard region. .SIR format images containing "images" of the
latitude and longitude of each pixel for each region are also
available.
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