Full text: Remote sensing for resources development and environmental management (Volume 3)

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There may be scope for a third type of resource 
satellite, catering for resource mapping at scales 
in the order of 1:250,000 to 1:500,000. While main 
taining the multispectral and stereoscopic capaci 
ties of the first type already mentioned, lower 
spatial resolution and the coverage of a larger 
surface area per frame should be aimed at, possibly 
in combination with a higher temporal resolution. 
Thorough exploration of the market for such products 
should precede future developments in this area. 
In addition to these three main types, satellites 
serving specific areas may prove viable, such as the 
Tropical Earth Resources (TERS) satellite concept 
studied by Indonesia and The Netherlands for appli 
cations in equatorial countries. 
In the overview on current trends in remote sen 
sing and programmes underway, the Earth Observation 
Programme of the European Space Agency should be 
mentioned. During the opening session European co 
operation in the field of remote sensing from space 
has been highlighted as a paramount example of suc 
cessful international programmes. European countries 
together with Canada decided to develop the ERS-1 
programme. The objectives are to transfer experimen 
tal use of microwave techniques to operational use 
for applications in global ocean and ice monitoring. 
This programme offers a challenge for both global 
climate research, sea state forecasting and near 
future operational and commercial applications. In 
this respect data continuity is an essential condi 
tion. After ERS-1 (to be launched in 1990) with an 
expected lifetime of three years, the duration of 
the mission will be expended by the launch of ERS-2 
in 1993. 
The ESA Earth Observation Preparatory Programme 
which started this year will define future missions 
dedicated to meteorology, land observation, ocean 
and ice observation and solid earth studies. 
With regard to land observation a major contribu 
tion is expected from the acquisition of synthetic 
aperture data on a regular basis. The ERS-1 program 
me will offer a first opportunity to collect SAR 
images in C-band overland, with the constraints 
related to regional coverage over Europe and North 
America and its experimental character. A possible 
future land-oriented mission can provide usin the 
90-ties with a capability for frequent observation 
by means of an advanced SAR system suited to develop 
operational use of polar orbiting platforms for 
monitoring of agriculture and land use. 
Although the imagery provided by the first gener 
ation satellites has to some extent put also to use 
in small-scale topographic mapping and for map re 
vision, most photogrammetrists have shown only a 
limited interest in the imagery produced because the 
limited spatial resolution and the absence of 
stereoscopic relief rendered this material unsuit 
able for most of their work. Mention should be made, 
however, of the mapping of (parts of) the moon 
making use of the stereoscopy provided first by the 
libration of that celestial body and later by lunar 
mapping systems such as on lunar orbiter and Apollo. 
The situation has changed drastically in recent 
years with the availability of high-resolution 
stereoscopic pictures of the metric camera, and 
large format camera experiments. Stereoscopy for 
them is even more crucial than for earth scientists. 
The question is: will the photogrammetrists evolve 
into "imagegrammetrists" as photo-interpreters in 
past years became image interpreters? Doubtless the 
field of photogrammetry is changing and widening 
with the introduction of new kinds of imagery. The 
use of radar imagery restitution and of digital 
cameras in close range applications are good exam 
ple. Corrections for Earth curvature became impor 
tant when satellite imagery came into use. Although 
the photogrammetric potential of SPOT imagery and 
of future satellites of this type is undeniable, it 
is likely that also in the future a substantial 
part of large scale (e.g. cadastral) photogram 
metric mapping will be done on the basis of photo 
graphic imagery using aircraft as a platform. The 
answer to the question thus is —at least in part— 
"no", even though digital analysis techniques will 
increasingly be applied. 
An interesting change in the relationships be 
tween photogrammetric and resource surveyors is 
noteworthy, however: The common interest of both in 
the past was aerial photography with the resource 
surveyor gradually devoting part of his attention 
to satellite imagery. The field of common interest 
in the future will be high-resolution satellite 
imagery. In addition, the image interpreter will 
use low-resolution imagery and may occasionally 
look at an aerial photograph for very detailed 
work. The photogrammetrist will continue to pay a 
substantial part of his attention to aerial 
photography, as will be explained below. 
The increase in spatial resolution of satellite 
imagery has been spectacularly rapid. For continu 
ously operating systems the following data can be 
Meteo satellites 1960 > 1000 m 
Landsat MSS 1972 80 m 
Landsat TM 1982 30 m 
SPOT-1 1986 10/20 m 
Non-continuously operating optical systems based on 
recoverable film or electro-optical systems based on 
recoverable tapes (MOMS) perform even better: 
Soyuz/Salyut Zeiss Jena MKF-6 camera 
(20 m photographic) 1970 8m pixel 
Metric camera (20 m photographic) 
1983 8 m pixel 
Large format camera (NASA/Itek) 
1984 5 m pixel 
MOMS (line array) FRG 1983 20 m pixel 
MEOSS FRG 1987? 50 m pixel 
Metric camera reflight 1990 3 m pixel 
The spatial detail visible on these photographic 
images is high. The fact that these systems func 
tion only at irregular intervals is a drawback, 
not so much for photogrammetry and cartography, but 
particularly for resource surveying and monitoring. 
The vertical accuracy of satellite images has 
also risen to levels that become photogrammetrical- 
ly interesting. Where occasional Landsat images 
provide stereo in the sidelap zone of adjacent 
passes, the stereo threshold is at best in the 
order of 100 meters. Experiments with the metric 
camera and the LFC have shown that, where good 
ground control is available, approximately 15-20 
meters vertical precision is possible. In the ab 
sence of adequate ground control, 40 meters is the 
maximum obtainable accuracy. For SPOT, a stereo 
capacity of 5 meters is claimed in height and 3 m 
in planimetry. 
Three main facts emerge from these data: 
1. Satellite imagery suits the needs for photo 
grammetric mapping in scales of 1:100,000 and in 
the near future even 1:50,000. 
2. The high resolution obtainable by long focal 
length cameras, particularly when operating from 
lower altitudes (space shuttle: 250-300 km) 
compared to orbiting satellites (SPOT: 
approximately 800 km), make optical (photographic) 
systems an interesting alternative not withstanding 
the lack of continuity. 
3. The second generation of satellite images do 
not meet the high horizontal/vertical precision 
required for detailed photogrammetic mapping car 
ried out for, e.g., cadastral work. Aerial photo 
graphy remains a necessity in this area. 
Some photogrammetrists at present still have

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