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What is the time frame of the project and its results?

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The time frame of the project and its results will affect the temporal resolution required and can also affect the choice of using an active or a passive sensor. Land-use and land-cover information required immediately for decision-making will often be based upon readily available archived imagery, so that the user does not have to wait for new imagery to be collected and processed. Using archived imagery is viable as long as the date of imagery capture is not so distant as to make the imagery obsolete. Conversely, disaster response requires immediate postevent imagery that shows the extent and impact of the disaster. Similarly, imagery used for weather prediction must be up to date so that weather models can be run from current weather conditions. Obviously, mapping troop and military equipment movements also requires high-temporal-resolution imagery. Mapping perpetually clouded areas such as Central America can force the use of radar imagery, which can penetrate through the clouds, rather than waiting for a cloud-free period to capture optical imagery. Figure 4.1 shows different applications plotted against their general temporal and spatial-resolution requirements—the requirements that tend to most influence imagery choices.


Figure 4.1. Comparison of required spatial and temporal resolutions of different mapping applications

Imagery and GIS

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