SPOT High Resolution Visible and Near Infrared Image Data and Descriptions of LEVEL 1 Products from SPOT IMAGE of Toulouse, France

SPOT has two similar instrument on each bus; SPOT 1 launched in
February 1986 , SPOT 2 launched in January 1990 and SPOT3 launched in
September 93. The High Resolution Visible Imaging System (HRV) on
board SPOT consists of push broom instruments. Each instrument has two
spectral modes: 1) panchromatic (P), black and white from 510-730
nanometers; and 2) multispectral (XS), color with three spectral
bands, from 500-590, 610-680 and 790-890 nanometers. The resolution in
P mode is 10 meters while the resolution in XS mode is 20 meters. The
P mode number of pixels per line can vary from 6000 to 10400 and the
number of lines per scene from 6000 to 9800 depending on the surveying
method (vertical or oblique) and the prepocessing level (note, for
LEVEL 2, scenes are aligned with true North and resampled
accordingly). The volume of data per scene can therefore vary from 36
to 100 Mbytes. In XS mode, the number of pixels per lines varies from
3000 to 5200 and the number of lines per scenes from 300 to 4900 for
each of the three spectral bands. The total volume of data can
therefore vary from 27 to 76.5 Mbytes. Each SPOT scene acquired in P
or XS mode covers an area of 60 X 60 km2 in near-vertical viewing, and
up to 60 x 80 km2 in oblique viewing at viewing angles up to 27
degrees either side of the vertical. The oblique viewing offers two
possibilities: 1) to increase the revisiting capability up to five
times per 26 days; and 2) to acquire stereoscopic pairs by imaging the
same portion of landscape from two different revolutions. SPOT circles
the Earth 14 and 5/26 times each day at an altitude of 830 km in a
sun-synchronous (polar) orbit.

All scenes are nominally centered in latitude on the J rows of the
SPOT Grid Reference System (GRS). By opting for a SAT
(Shift-Along-Track) scene, rather than a standard scene, the customer
can, however, obtain scenes that are, as the name implies, shifted
along the satellite track. The center of a SAT scene lies on a line
parallel to the satellite track at a latitude corresponding to a
whole-number multiple of one-tenth of the standard scene length
(i.e. 6 km) relative to the GRS (K,J) position. These positions are
numbered from 0 to 9, from North to South, between a given (K,J)and
the next (K,J) to the South.

The LEVEL 1A product is the raw data level with the only prepocessing
being the normalization of CCD detector response in each spectral
band. Inter-band relative sensitivity coefficients are also supplied
and geometric corrections are not performed. This preprocessing level
is normally selected by users requiring scene data with minimum
processing and is used in particular for detailed radiometric and
geometric studies. These products are supplied on CCTs, and on special
requests the positive films with the auxilary attitude data are
supplied on a standard CCT without the image file.

The LEVEL 1AP product has been developed specially for use with
digital stereoplotters. Relative to LEVEL 1A, the main characteristics
of LEVEL 1AP are as follows: 1) oversampling to produce pixels 8.75 m
on a side for the P mode and 17.50 m for the XS mode. The image scale
is thus 1:350000 for a standard film measuring 241 mm x 241 mm and
including eight fiducial marks; and 2) anamorphotic distortion applied
in the image 'scanline' direction to compensate for oblique viewing;
texture enhancement by digital filtering; and photographic
specifications meeting aerial photography standards. These products
are supplied as positive film with the auxilary data on a standard CCT
without the image file. On special request the image can also be
supplied on CCT.

The LEVEL 1B includes the radiometric corrections mentioned above and
geometric corrections associated with systematic distortion introduced
by the system (Earth rotation, panoramic effect, striping effect,
viewing angle). Absolute location accuracy is 800 m (rms error) for
vertical viewing, while internal distortion is aroud 10 (-3). This is
the basic level for photo-interpretation and thematic analysis.

The GEOSPOT PRODUCTS including SPOT view basic, SPOT view plus and
SPOT MAP are delivered according to the GIS_Geospot digital format
(for additional technical information about the GIS_Geospot format,
please contact : tel [phone] or fax [phone], these new
products include orthoimage, layout in raster format, digital
elevation model in raw raster format, vector files in Arc/Info Export
6.0 and digital quick look in TIFF format. One way to access to the
SPOT IMAGE Catalogue (DALI) is via the Prototype International
Directory using the 'LINK' facility.