with a minimum of ground control points.
Results so far indicate an altitude determination
accuracy of 5 m (r m.s.) when using stereo pairs
with a base to height ratio close to 1 ( viewing
angle) and 8 m (r.m.s.) when using a vertical and
an oblique images (base to height ratio of 0.5).
This very encouraging result confirm that
mapping at a scale of 1/100 000 can easily be
performed with SPOT stereoscopic pairs when using
ordinary analytical stereoplotter. No result is
available yet with digital correlation techniques but
it is expected that similar if not better accuracy
should be obtained with this new approach.
The results of the SPOT images quality
assessment are thus very encouraging A permanent
image quality team has been established to
continuously monitor the various parameters
describing this quality, particularly the relative and
absolute calibration parameters, in order to inject
them at regular intervals in the preprocessing
software and keep the user community informed of
possible changes.
3 - Spacecraft imaging operations and ground
facilities.
After official system commissioning on May 6,
1986, the full capacity of the spacecraft was used,
and regular transmissions to both the
Toulouse/Aussaguel and the Kiruna stations took
place on the basis of an average of five passes per
day (2 passes in the real time mode and 3 passes
for recorders play-back).
From May 1st 1986 until mid August, the total
number of scenes recorded and archived in these
two stations was about 100 000. In addition 25 000
scenes had been received and archived in the
Toulouse station during the post launch assessment
phase.
The percentage of cloud-free images is about
20 %, although this percentage is significantly
higher if one considers as acceptable images where
one quadrant is cloud-covered while the other three
quadrants are cloud free.
All received images are archived and referenced
in the SPOT IMAGE Catalogue, which is remotely
accessible by users worldwide. As of mid August,
more than 50 users were already connected to the
catalogue system and were interrogating it on a
regular basis. Quick-Look images of all scenes are
also produced but the poor quality of the
Quick-Look frames (on 70 mm film) make their
reproduction difficult. A modification of the
Quick-Look production and retrieval system is
planned to improve the situation.
Preprocessing of images received in Toulouse is
made on the basis of customers orders and, when
these do not require the full production capacity,
on the basis of systematic processing of cloud free
images of selected areas. At mid August, 2 400
SPOT scenes had been processed in Toulouse, 600
of them for internal use such as quality control,
relative calibration, etc. Most of the preprocessing
is done at level 1A and IB (system correction) and
very few at level 2 (precision correction), reflecting
a relatively low level of demand for precision
processed data.
Actual production capacity gradually raised since
commissioning. In August, the average number of
processed scenes is 43, with production delays of
one week for 85 % of scenes. It is expected that
the full processing capacity of the Toulouse center
(70 scenes per day) will be achieved in September
or October.
In mid June 1986, the two Canadian stations
located in Prince Albert (Saskatchewan) and
Gatineau (Quebec) started routine operations. These
two stations read out the SPOT telemetry when the
spacecraft overflies the North American continent.
Thus, real time imagery of both Canada and the
USA (with the exception of Western Alaska and
Hawal) is collected. Scenes relative to the Canadian
territory are archived by the Canada Center for
Remote Sensing (CCRS); routine image production
should start by the end of the year.
Scenes relative to the U.S. territory are recorded
in the Canadian station, and High Density Tapes
are shiped to the SPOT IMAGE CORPORATION's
facility in Reston (Virginia). SICORP's production
system is almost completed and will start
operations in October.
Other direct read-out facilities are in the
implementation or planning stage: agreements have
been signed already with station operators in India,
China, Saudi Arabia, Bangladesh and Australia.
Other receiving stations planning to receive SPOT
telemetry are located in Brazil, Pakistan, Japan,
South Africa and in Mas Palomas (Canary Islands).
It is expected that at least three or four of these
stations will be ready to routinely receive SPOT
data in mid-1987, while the rest of them should be
ready by end of 1987 or early 1988.
4 - Data distribution and uses
The extensive network of SPOT data distributors
established by SPOT IMAGE prior to the launch has
permitted wide distribution of images soon after
commissionning: while some government-owned
distributors did not engage in any significant
marketing efforts, many other have been very
active from the start and provide an efficient
service to the users in their country. In addition,
many customers in more than 25 countries have
ordered SPOT data directly to SPOT IMAGE in
Toulouse. The market outlook after only a few
months of operations is thus very encouraging,
particularly in the areas of land survey, topographic
mapping and agriculture-related applications.
One market area which had not really been
expected to be significant is the provision of SPOT
images to the media: the availability of images of
the Chernobyl nuclear power plant in Ukraine, soon
after the accident which took place on April 26th,
raised a very high interest for civilian remote
sensing satellites data in the media circles. Both
natural disasters such as the gaseous explosion in a
volcanic crater lake in Cameroun or the extensive
forest fires in Southern France in July^ and human
activities such as the world soccer championship in
Mexico in June have indeed put a lot of pressure
on SPOT IMAGE to produce images in a very short
time at the request of the media. This had a
significant impact on production, but in a world
where the media are the fifth power, it is difficult
not to satisfy them.
One reason for such a high interest, of course,
is the high resolution of SPOT images as well as
the ability to collect data at short intervals.
Images of the forest fires in Southern France, for
example, were collected on 24th and 29th of July,
thus allowing a rapid determination of the extent
of damages as well as illustrating for the general
public the location and size of the areas destroyed
by fire.
These two principal characteristics of SPOT
images, namely high resolution and repetitive
coverage have been well taken into account by the
user community in Western Europe; this has led to
a very high level of demand for imaging requests,
leading to an unexpected number of programming
conflicts in this part of the world. Establishing a
satisfactory system for priority management of
these conflicts proved to be difficult, leading to
many requests being delayed for many weeks, if
not months. A gradual improvement of the situation
is expected once a larger archive of data will have
been collected, therefore allowing to serve more
users directly from the raw data archive instead of
having to go through the spacecraft programming
cycle.
Another very demanding program in terms of
