SPOT-3: 26 Sept. 1993 (lost after a period of good operation, 
due to a technical failure) 
SPOT 4: 24 March 1998 
SPOT 4 has a 5-year designed lifespan, and has been in 
operation since 26 May, 1998. It has a registration of the 10 m. 
resolution band (P) with XS 1 and XS 3 (20m), by calibrating 
XS 2 to 10 in. resolution. Recording capacity has been 
increased from 22 to 40 minutes per recorder (2 recorders on 
board). It also carries a wide-angle vegetation monitoring 
instrument with resolution of 1 km, daily global coverage, in 
operation since and of June 1998. SPOT 4 also has an 
additional Middle IR band. The recording instruments on SPOT 
1,2 and 3 are referred to as the HRV (High Resolution Visible) 
instruments (two on board each satellite); those on SPOT 4 are 
referred to as HRVIR instruments (High Resolution Visible and 
Infrared) 
SPOT is a French satellite system; images and information : 
http://www.spotimage.fr/ 
address: 5 rue des Satellites, F 31030 Toulouse cedex, France 
tel+ 33 (0) 562 19 40 40 
fax:+ 33(0) 562 19 40 11 
- New features w.r.t. Landsat: 
SPOT(l,2 and 3) operate in two modes: a multispectral, three- 
band (XS)mode with ground resolution of 20 m, and a 
panchromatic (P) [thus black/white] mode with 10 x 10 m. 
ground resolution. 
Push-broom scanner: All pixels are simultaneously depicted on 
the detector array so there is 1 detector per pixel; 6000 in P 
mode , 3000 x 3 for XS. Total, per HRV: 15000 detectors. 
Two independent HRVs. 
Linear array detectors; calibration between arrays is critical. No 
moving parts; no jittering between startpoints of lines. Dwelling 
time on the ground, per pixel is theoretically 3000 times longer 
than with an optical-mechanical scanner. Hence the ground 
resolution can be much better (10 m sampling interval in P, 20 
m in XS). • 
Orbit 830 km; inclination 98.7 degr; local sun time descending 
node at equator: 10.30 a.m 
Area of ground scene 60 x 60 (81.5) km. 
Repeat cycle 26 days ; 369 orbits per full cycle. 
Pointing capability HRV - 27 deg to + 27 deg .(+ is East 
looking) 
1 mirror step is 0.6 degr. 
step 0 is 27 degr. west, 
step 48 is vertical (nadir view), 
step 93 is 27 degr. east, 
step values increase from W to E. 
The resulting stereoscopic possibilities are a major 
improvement w.r.t. Landsat. * 
* The Indian Remote Sensing Satellites (IRS) 
The Indian satellite program started with two satellites that 
provide data comparable to Landsat MSS, now the IRS 1-C is 
in orbit. The orbit, at around 900 km, is sun-synchronous like 
those of Landsat and SPOT. Also its successor, IRS 1-D, with 
similar specifications, is now delivering data. 
The satellite provides panchromatic (500-750 nm) data at 5.8 m 
resolution, and with a sidelook capability (26 degr. east to west) 
to provide stereo imagery. 
Multispectral data comes at 25 m. ground resolution (520- 590 
nm- green, 620-680 red, 770-860 (near IR) and 1500-1700 nm 
(shortwave IR). 
Furthermore, wide-field data at 188 m. resolution and a swath 
width of 774 km is collected by IRS 1-C. 
Throughout the IRS program, push-broom scanners have bneen 
used (LISS = Linear Imaging Selfscanning Sensor). 
Ground receiving stations are in India (Shadnagar), USA 
(Norma, Oklahoma), and Germany (Neustrelitz). On-board 
recorders provide data outside the reach of these ground 
stations. More ground receiving stations are being readied. 
IRS 1-A and 1-B have no recorders on board and were intended 
to serve the Indian ground receiving facility directly; 1-B is 
now also received in the USA station. 
After the loss of Landsat 6, Eosat Company have acquired 
distribution rights for IRS data. Archiving started in March 
1996. 
Since then, the company has been taken overn by Space 
Imaging Co, at Thornton, Colorado 
Information on data availability and ordering procedures, on e- 
mail: info@spaceimage.com 
The website: http://www.spaceimage.com 
During the experimental and proof-of-concept period, prior to 
1985, we have become aware of the potential of aero-space 
remote sensing, as a data collection tool. 
* A third premise is, that earth observation from space, as 
under discussion here, should not be considered in isolation.The 
strength of its application is greatly enhanced by combining it 
with other techniques of data collection by remote sensing 
including aerial photography, and with data from other sources. 
The combination and merger of information derived from a 
variety of sources of remotely sensed data holds a strong 
application potential especially where access to remote areas is 
difficult, and where other data sources may be scarce. 
In other words: the current trend of amalgamating RS data and 
Geographic Information Systems (GIS) packs a great 
application potential for development planning. 
* My fourth and final premise is, that a decision to use this 
more or less sophisticated technology for operational purposes, 
like in local administration, regional planning etc. is pointless if 
not an in-depth investment in human resources is made at 
the same time. There is great need of expertise to extract the 
information packed in remotely sensed data, for application in 
specific domains. 
2. REMOTELY SENSED DATA AND INFORMATION 
EXTRACTION 
If RS data is considered as a bidimensional array of digital 
numbers, or as analog imagery, then that is the raw data from 
which to start our considerations. 
* Thematic Information 
is extracted from this primary source data by ordering and 
processing the data, subjecting it to specific treatment, so as to