| The fan-beam ASCAT scatterometer provides
radar backscatter measurements at 6 azimuth angles and a diversity of incidence angles.
The wide swath and frequent overflights permit generation of a wide variety
of ASCAT Image products. For highest possible spatial resolution, multiple
orbit passes are combined. These are the 'all pass' images. Since generally
orbit passes of a given point on the Earth occur at nearly the same time
of day, time-of-day studies are facilitated by computing images from ascending
(morning) passes only, and descending (evening) passes only.
For improved temporal resolution in the polar regions, daily
local-time-of-day images have been generated. In non-polar regions
ascending/descending images are produced. To ensure adequate spatial coverage
and overlap to enable B image estimation, except at the poles, generally
multiple days are combined.
Images are made from ASCAT L1B SZF files which are analogous to
SeaWinds "slice" measurements.
Further information is available in the ASCAT
Enhanced Resolution Image Users Notes.
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. Data over the
ocean is generally not useful. However the distributed images are not land
masked. .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.
Two date, three different ASCAT sensors (ASCAT-a, ASCAT-b, and
ASCAT-c) have flown. Inititally after the launch of ASCAT-b, separate -a and -b
products were made. To differentiate between the sensors, the 4th letter of
the file name was either 'a' or 'b'. Shortly after the retirement of
ASCAT-a, we ceased making separate products and only made a combined (tandem)
product of -b and -c products. For this product 't' is used for the 4th
letter combined product. In the data directories (accessed via the url
https://ftp.scp.byu.edu/data/ascat) each of the different products can be
individually accessed. The ASCAT webpages do not currently show all the
separately available products. Instead, see notes in the data directories.
|
Available Image Classes
SZF-based Images
| |
V Pol |
| all passes |
msfa |
| ascending passes only+ |
mafa |
| descending passes only+ |
mdfa |
morning passes** |
mmfa |
| mid-day passes*** |
mnfa |
| evening passes** |
mefa |
+ Non-polar regions only
* Only Ant, Arc, and Grn regions
** Only Ant region
*** Only Arc and Grn regions
| 
