PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
February 2020
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Chapter 2: Sensors and Platforms
INTRODUCTION
Remote sensing technologies have proliferated greatly in recent
years. Unprecedented develop-ments in sensing technologies
and platforms have resulted in information-rich geospatial data
ac-quisition, which, in turn, has driven applications by extending
remote sensing performance as well as by creating new application
fields from ground through space. The performance level and
the application space of the sensors in terms of spatial, spectral
and temporal sensing abilities have ex-panded far beyond the
conventional boundaries of remote sensing. This chapter is dedicated
to sensors and platforms that generally are not separable.
Sensors used for mapping Earth and Space observations generally fall
into two major categories: active and passive. While technological
developments are equally strong in both groups, active sen-sors
often get more attention for two reasons. First, they generally
provide direct three-dimensional (3D) observations, resulting in
more robust surface and shape extraction. Second, active sensors
are usually less dependent on environmental circumstances of the
observation space, such as not need-ing ambient light, and they
may have certain penetration capabilities through vegetation and/
or cloud cover. Radio Detection and Ranging (Radar) sensors are
used for imaging larger geographic areas, acquiring data from high-
altitude flights and space. In contrast, Light Detection and Ranging
(LiDAR) has a local character, allowing dense data acquisition of
smaller areas, and acquiring aero-sol measurements from space.
Passive sensors have a long history and produce the largest volume
of remotely sensed data. Op-tical imaging has seen remarkable
developments in both spatial and spectral resolution capabilities.
Digital cameras can produce images easily in the billion pixel
range (Gpix) by either single sensors, such as a 400 megapixel
(Mpix) single sensor; or, by using multiple sensors and/or camera
heads. Spectral capabilities continue to improve in both single
channel radiometric performance and in the number of spectral
bands. Multispectral sensing is becoming ubiquitous, and the use
of hyper-spectral imaging is growing rapidly. With the explosion
of smartphones and consumer cameras, the amount of imagery
acquired is skyrocketing, and crowd-sensing technologies add
a totally new ap-proach for observations at large scale.
Airborne and satellite systems represent traditional remote sensing
platforms and these technolo-gies have shown little development
in recent years. In the past decade, however, major changes
have appeared that simply redefine the field of remote sensing
platforms from ground through space. First, Unmanned Airborne
Systems (UAS) have grown from “hobby-level uses”, to perfor-
mance levels that offer viable alternatives between airborne
and ground vehicle-based platforms. UAS provides unmatched
maneuverability with easy deployment, and small optical cameras
and/or other sensors can collect high spatial and spectral resolution
data. Given the extremely small ground sampling distance (GSD)
of UAS-based optical remote sensing systems, accurate point
clouds can be generated easily by using dense image matching.
Recent developments in satellite platforms are similarly significant
to the introduction of UAS. First, the use of agile sensors has
become general on high-end satellite systems, allowing better
im-age acquisition rates as well as in-track stereo capabilities.
Next, to decrease revisit time, satellite constellations have been
introduced, bringing down the revisit time to a matter of days, or less.
Meanwhile, commercially available image resolution has continued
to improve, standing currently at 30-50cm. Finally, the introduction
of micro- and nano-satellites is probably the most noteworthy recent
development. Deployed in clusters on the same orbit in multi-
Chapter 1: Fundamentals of Electromagnetic Radiation
SCIENTIFIC BASIS FOR 21ST CENTURY REMOTE SENSING
Remote Sensing, its component sciences, technologies, and
applications are all governed by the universal physics of energy
interacting with matter at scales from subatomic to galactic. MRS-
1, -2, and -3 describe hardware, software, and data processing
developments for an exploding suite of airborne and space-borne
platforms and sensors; and the resulting array of Earth and planetary
sci-ence applications. These editions are overwhelmingly Earth-
oriented to monitor Earth’s environ-ments across spatial and
temporal time-scales; and to develop methodologies for measuring
and monitoring local-to-global phenomena. To maximize these
capabilities, it has proven necessary for communities-of-practice to
work within a broad framework that includes engineering designs
that integrate environmental engineering, scientific, economic,
human, and social considerations that, together, define the suite of
remote sensing technologies. MRS-4 concentrates on state-of-the-
art platforms, sensors, processing technologies and applications
since the turn of the 2nd Millennium. Chapter 1 addresses basic
matter and energy relationships as mathematical expressions; and
where possible, as illustrated in animated and interactive graphics
from the World Wide Web. However, much of the graphical
material from the Web is limited to screen resolution (72dpi).
The term
remote sensing
was coined in the United States by
Evelyn Pruitt at the U.S. Office of Naval Research (ONR) to
describe processes for identifying, observing, and measuring
radiation from objects on the Earth’s surface (Graham, 1999;
see
).
Secret activities were in use in the 1950s in the form of Corona
imagery obtained from high altitude U-2 flights over the Soviet
Union and the downing of one flight piloted by Francis Gary
Powers on May 1, 1960. For a concise picto-rial history of early
high altitude and space-based imaging programs see Baumann
(2009) (
RS%20History%20II/RS-History-Part-2.html. Advances in these
technologies over the subsequent five-to-six decades are the basis
for the first three editions of the
Manual of Remote Sensing
.
