of spiritual guardians of the new faith, resulting in a syncretic melding of the
Buddhist and Bon faiths. Many additional examples may be identified, and few
religious movements exist today that do not show some effects of syncretism.Remote Sensing
Geographers are keen in using fieldwork as part of their professional toolkits for under-
standing the world. Fieldwork can be quite laborious, costly, and—sometimes—
dangerous. Since the middle of the 20th century when aerial photography became
widely available, geographers have made frequent use of remote sensing.
Remote sensing is a term that refers to a set of techniques by which the environ-
ment is studied. Electromagnetic radiation is sensed by devices as it is reflected,
refracted, scattered, transmitted, and emitted by matter in the environment. Each
feature ofEarthand theatmospherehas a “spectral signature,” that is, the interaction
of the various electromagnetic wavelengths with that feature. Thus, we are able to
identify, measure, and model features that are not in physical contact with the features
under study. There are many measurement devices that are in direct contact with what
they are measuring and so, by definition, arenotremote sensing devices. A thermom-
eter isnota remote sensing device for air temperature because its temperature
readings are dependent on the collision ofatmospheric molecules with the device. A
thermal radiometer, however, can be mounted in a satellite and measure the tempera-
ture in the atmosphere it is not touching. Table 3 illustrates the types of remote sensing
commonly used by geographers, primary wavelengths involved, and typical uses.
The most well-known and commonly used form of remote sensing is photogra-
phy. A camera contains film sensitive to light. The film is kept in the dark until the
lens is opened to expose the film. The image is made permanent by developing it
with chemicals. Aerial photography is of oblique and vertical types. Oblique pho-
tography is the perspective we see looking out of an aircraft window. Much more
useful to the geographer is vertical photography in which the camera is pointed
underneath the aircraft and features can be mapped and measured.
Color infrared photography is sometimes mistaken for thermal infrared sensing.
Color infrared photography uses color film sensitive to most visible wavelengths
but also sensitive to the shorter (non-thermal) infrared wavelengths that are plenti-
ful in Earth’s environment. These near or reflective infrared wavelengths cannot be
perceived by humans. In color infrared film emulsions, reds are assigned to strong
near infrared reflectivities. Living green vegetation is very reflective in the near
infrared and appears very red on color infrared film. Water absorbs near infrared
wavelengths so that lakes, streams, and soil moisture appear dark.284 Remote Sensing