Remotely sensed data must usually be
calibrated in two distinct ways:
1) It should be geometrically (x,y,z) and
radiometrically (e.g, to percent reflectance)
calibrated so that remotely sensed data
obtained on different dates can be compared
with one another.
2) The remotely sensed data must usually be
calibrated (compared) with what is on the
ground in terms of biophysical (e.g., leaf-areaindex,
biomass) or cultural characteristics
(e.g., land use/cover, population density).
Fieldwork is necessary to achieve both of
these objectives . Thus, a person who
understands how to collect meaningful field
data about the phenomena under
investigation is much more likely to use the
remote sensing science wisely