TheImprovement ofTropical and Subtropical Rangelands

90 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS
FIGURE ~-3b AD. example of ..rial photOl1'aphy acquired iu northwestern
Montaaa usm, a 35 mm camera ",nem. Not. th. "v- Ihaped reference target
(both photOi coune.,. ECON Ecololical Coanltm, 8e"ice, Helena, Montaaa).
mapping unite defined at higher levell. Ultimate verification is p~
vided by ground sampling. This multiple Itrata sampling echeme is
called the multistage approach to remote sensing (figure 4-5). The
multistage approach is used with all types of remote sensing data but
is especially effective when satellite images are being used.
PhDtD Samplin, Several other types of information must be gathered
during the reeource UBeI8IDent that are not normally mapped
by remote sensing (including human population, herd sizes and composition,
and detailed land 11M). Although much of this information
might be gathered through ground sampling or interviews, other
techniques have been developed for using large-scale (larger than
1:1,000) 35 mm photography as a supplement for ground sampling.
For example, a rich methodology has evolved for the use of low-level
photography for Itudying rangeland and large animals in East Africa
(International Livestock Centre for Africa, 1981). These systems use
the aerial photograph as a sample point in a systematic sampling
echeme. Detailed interpre\ations of the photographs are used to develop
accurate estimates of the mes of domes\ic and wild animal
[ 1.)ltIZ ,d byCoogIe