X-SAR Geocoded Ellipsoid Corrected Data Product (GEC, held at DLR/DFD)Entry ID: DFD-X-SAR.SAR.GEC
Abstract: Mission Objective:
Please see the relevant SIR-C/X-SAR Mission description contained in the
references and as Supplementary Information for "sensor"(X-SAR).
There were two Missions with the following time frame:
- Space Shuttle Mission STS-59:
- Space ... Shuttle Mission STS-68:
Worldwide coverage and map prints are available on World Wide Web (see below).
Data Set Content:
The GEC data set contains X-SAR detected images, represented in a uniform,
preselected cartographic presentation. The image axes (i.e. the row and
column direction of the pixels) are parallel to the cartographic coordinate
system used.The cartographic system used for worldwide reference is the
Universal Transversal Mercator System (UTM).
The product mentioned here can be produced for each region of the world,
which is imaged by the X-SAR sensor. Except for the cartographic references
and possibly maps for quality control test, it does not utilize data sets
outside the SAR image generation chain. Therefore, no terrain correction
is applied to this product. The SAR inherent geometric terrain distorsions
like layover and shadowing are not considered and degrade the absolute pixel
location accuracy to maps especially in hilly terrain.
Geocoded data will be available after availability of off-line processed
precision MGD products. Geocoded data sets can be used by the scientific or
commercial community which will refer the actual SAR data to
geographic/cartographic places. Ellipsoid corrected geocoded products are
intended for that area of applications or when relative geometric
accuracy can be dispensed with some purposes.
- The standard MGD product formatted in CEOS, including parameters used for
the slant to ground range projection.
- Orbit data from the PATH tape annotated in the MGD product
- Map projection constants to be applied.
The geocoding is based on the radargrammetric functions delivered by sensor
references and processing parameters. These are:
- orbit state and velocity
- precise range measurements by sensor and corresponding annotation
within the processor
- azimuth timing information within the processor (i.e. The range
line must be annotated with the zero-Doppler orbit time.)
- map projection formula, where geographic latitude and longitude are
transferred to appropriate map coordinates.
As ellipsoid reference is used, the discrete transformation formula will
only be computed for a mesh of discrete points. Bilinear interpolation is
performed within this grid. Oversampling is applied to avoid aliasing when
resampling to map grid. The standard resampling procedure is cubic convolution.
Equivalent no. of looks
in azimuth 1.5 - 2.5
in range 1 - 3
Geometric representation cartographic UTM
ellipsoid use WG584
Data representation detected, amplitude
pixel quantization 16 bit, signed integer
Ground area covered
azimuth > 100 km
range < 62.5 km
Spatial Resolution 25 m (determined by the MGD product)
Absolute location error < 150 m (if tiepoints can be applied
and for flat terrain)
northing 12.5 m
easting 12.5 m
Number of pixels
northing 8000 ... 8960
easting 4000 ... 8960
Image data volume up to 160 MBytes
Access to the data:
On-line access to data and information as well to digital quicklook DQL
or browse data is provided by the Intelligent Satellite Data Information
System (ISIS), developed by DLR as a client / server configuration.
It represents the interface of DLR-DFD to users, providing easy access to
catalogue-, inventory-, browse- and general textual information.
ISIS can be accessed with World Wide Web by URL:
and clicking on `Information Services (ISIS)` or `Accessing ISIS` (telnet).
ISIS can also be accessed by telnet directly:
input: telnet isis.dfd.dlr.de
Other procedures (modem or X-25) to access ISIS are described as 'Supplemen-
tary Information' for data centers (keyword 'ISIS'. Access presumes the in-
stallation of the client software (available free of charge) which can be
easily done by users (supplied by DLR/DFD).
Digital and photographic products may be ordered at DFD - Help Desk,see Data
There is also available on CD-ROM and on Web a set of image sample products
as well as general and specific information about the X-SAR missions. This
'user-kit' can be accessed via Web with URL:
(Click for Interactive Map)
Start Date: 1994-04-09Stop Date: 1994-10-11
Latitude Resolution: 25m
Longitude Resolution: 25m
Distribution Media: Online
Distribution Size: 21 MB
Fees: No fees
Role: TECHNICAL CONTACT
Email: ekc at iagt.org
199 Franklin Street, Suite 30
Province or State: NY
Postal Code: 28801-5001
Role: SERF AUTHOR
Phone: (301) 614-6898
Email: Tyler.B.Stevens at nasa.gov
NASA Goddard Space Flight Center Global Change Master Directory
Province or State: MD
Postal Code: 20771
Creation and Review Dates