Page 107 - Digital Analysis of Remotely Sensed Imagery

78 Cha pte r T w o

FIGURE 2.14 Scanning of multiple photographs faces the problem of artifi cial
variation in image radiometry caused by varying development in the dark
room. See also color insert.

• First, the solar radiation may have changed during photo-
graphy. This can be minimized by reducing the number of
flights and shortening the duration of photography, or taking
photographs when the solar radiation is the most stable (e.g.,
around noon).
• Second, not all photographs are submerged in the chemicals
for the same duration during development and fixing in the
darkroom.
How to minimize the tonal discrepancy and unify the radiometric
properties of all photographs will be covered in Sec. 6.2. In addition
to radiometric inconsistency, scanned photographs may also suffer
from geometric problems. Recorded on paper, aerial photographs
may be stretched or worn after extensive use. As a result, their
geometry may have degraded despite the high geometric fidelity of
the original photographs. Care must be taken to remove such
distortions or control them to within an acceptable level during
subsequent geometric processing.

2.8 Proper Selection of Data
Before deciding which type of remote sensing data is the most suitable
for a particular project, the user needs to evaluate its requirements
and constraints carefully by taking a number of factors into
consideration. Some of the most important ones are user needs,
seasonality, cost, and mode of data delivery.