nal 
n, 
- 299 = 
The subjects are indicative of the objects and conditions to be remotely 
Sensed, The five earth-related fields are defined as follows: 
LIQUID EARTH : water, ice, snow; sea state, currents, tides, upwelling; 
lake/reservoir/river, water level; processes are often rapid. 
SOLID EARTH : soil, mud, sand, rock, minerals; structure/texture, 
solidness/condition; topography, acreage; processes are 
often slow. 
BUILT-UP EARTH : buildings, parks, constructions, transportation; consumption, 
waste, pollution/destruction; activities of people visible 
from space. 
flora: forest/range/crop, vigour/biomass; 
fauna: wildlife/insects/fish/cattle; processes are often 
rapid, cyclical and seasonal. 
LIVING-EARTH 
ë 
oe 
VOLATILE EARTH : atmospheric conditions/constituents; weather, climate, 
precipitation; pollution, hazards; processes are (very) 
rapi à 
It is relatively easy to compare the relative value of aerial photography 
and airborne remote sensing with that of satellite remote sensing using 
a similar matrix, if one considers the main differences between airphotos, 
non-photographic airborne remote sensing and satellite imagery. Aerial 
photography has a very high spatial resolution and provides accurate height 
information with easy to take Stereopairs. However, repetivity, for practical 
and economic reasons is restricted in most cases to an airphoto coverage 
once every few years. Hence it is very suited for mapping and inventory, 
especially of relatively slow processes. This is also the case with the 
non-photographic airborne remote sensing, which however lacks a height 
information, but which sometimes permits a better differentiation of materials, 
In contrast, satellite remote sensing, which provides synoptic views and 
high repetivity rates varying according to the systems from twice every hour 
to daily, twice monthly or several times per year. is very suited for the | 
study of rapid processes. It permits also mapping of features of large dimensions | 
escaping observation on normal aerial photography (Refs. 10, 11, 12). 
  
  
| 
| 
| 
Mapping and inventory, change detection and monitoring represent types of 
activity and are related to the action to be taken by man. They define 
requirements and specifications for methods of data collection, information 
handling and presentation (aee Refs. 2, 8, 9 for details), Reconnaissance 
Surveys and base-line surveys of resources and environment, required as a 
starting point for development planning, can be carried out in an efficient 
and cost-effective way by combining satellite remote sensing and (partial) 
aerial photography in a multistage sampling approach, whereby satellite 
imagery not only provides the synoptic overview, but also, as required, 
multispectral, multi-temporal/multi-seasonal or combined multispectral 4 
multitemporal data, essential when studying the living earth and sometimes 
useful for surveying the solid earth, The role of aerial photography becomes 
increasingly important when the stage is reached of preparation and implementatic 
of projects, requiring detailed technical and thematic maps. For change 
detection preference may be given to aerial photography and/or airborne 
remote sensing or satellite imagery or a combination of survey techniques 
depending on circumstances, such as nature and the dimensions of the phenomena, 
frequency and urgency of observations, weather and other conditions. Monitoring, 
which requires repetitive data collection, would become very dependent on 
satellite remote sensing as the only tool suited for re-visiting large areas 
at frequent intervals. Concepts and methodologies for adequate monitoring 
require innovation and development. 
Voute 4