required for both. Before one can formulate what is possible, one must have a 
grasp of what is present. Then, once it is established what is possible, information 
is required on the best way to achieve it. Finally, having set some Management 
policies and practices in motion, or having failed to do so, the manager needs 
information to assess how well or how badly they are working. 
Remote sensing plays an important role in efficient collection of the needed 
information, in assessing the success or failure of policies and practices, as well as 
in the observation of natural phenomena largely beyond the control of man. 
We have established that monitoring is an old endeavour where the most 
important changes have been brought about by new methods and technologies which 
have greatly widened the scope of possible observations and analyses. A modern 
monitoring system requires the establishment of a baseline, as well as the 
systematic measurement of changes from this point of departure. Monitoring is too 
often confused with mapping and with the up-dating of maps. Mapping has a role to 
play in the establishment of baselines, but often the best approach to monitoring is 
through a network of permanent sample points; the advantages of this approach 
are overwhelming if the purpose is to keep track of changes over a long period of 
time. 
The strongest arguments for a permanent sampling network come from 
statistical theory. The requirements for such a network include a clear definition 
of purpose, a sound sampling design, permanent sample locations, and the main- 
tenance of standards and procedures for long periods. Also there is the very 
practical requirement that the system must be able to absorb data from a great 
variety of sources. 
The most promising and important contribution of remote sensing to moni- 
toring are where large and relatively inaccessible areas are involved, or where 
present information is scarce. Remote sensing finds application in global moni- 
toring programs, such as those in forestry and agriculture, as well as in the 
monitoring of oceans, the Arctic and the tropical rain forest zones. The highest 
immediate priority in monitoring programs lie in the general area of land use with 
special attention to points of contact between competing uses of valuable or 
unique, ecologically sensitive zones. The most urgent needs for monitoring exist at 
the interface between agriculture and forestry, between agriculture and urban 
development, and in the coastal zones of the world — generally where man's 
activities encroach or invade. River pollution is an unfortunate legacy of this 
century and another area where monitoring can help in the solution of problems 
(Schneider, 1972). The magnitude of the problem and the sources of pollution are 
well known. Let us hope that the main contribution of remote sensing will not be in 
problem assessments, but in documenting the success of clean-up operations. 
In all applications of remote sensing it is important to distinguish between 
methods that are proved to be reliable, and potentially promising developments. 
Aerial photography is still the most reliable technique, although applications and 
methods have undergone great changes in the last two decades. Monitoring can 
today rely upon conventional approaches, as well as upon special systems employing 
very large and very small scales. Satellites are, of course, a vital, reliable and 
operational part of the meteorological monitoring systems, and we can look 
forward to programs such as Seasat, the Heat Capacity Mapping Mission Satellite 
and the experiments of the Space Shuttle. Landsat has already proved its 
capabilities for the monitoring of floods and fires and the results of experiments in 
thematic mapping of agricultural lands, forests and wildlands are sufficiently 
promising to ensure that no large monitoring program in these fields will again be 
undertaken without considering Landsat.