Unmanned Aerial Vehicles

Unmanned Aerial Vehicles (UAVs) are remotely piloted or self-piloted aircraft that can carry cameras, sensors, communications equipment or other payloads. They have been used in a reconnaissance and intelligence-gathering role since the 1950s, and more challenging roles are envisioned, including combat missions. Since 1964 the Defense Department has developed 11 different UAVs, though due to acquisition and development problems only 3 entered production. The US Navy has studyied the feasibility of operating VTOL UAVs since the early 1960s, the QH-50 Gyrodyne torpedo-delivery drone being an early example. However, high cost and technological immaturity have precluded acquiring and fielding operational VTOL UAV systems.

By the early 1990s DOD sought UAVs to satisfy surveillance requirements in Close Range, Short Range or Endurance categories. Close Range was defined to be within 50 kilometers, Short Range was defined as within 200 kilometers and Endurance as anything beyond. By the late 1990s, the Close and Short Range categories were combined, and a separate Shipboard category emerged. The current classes of these vehicles are the Tactical UAV and the Endurance category.

Pioneer: Procured beginning in 1985 as an interim UAV capability to provide imagery intelligence for tactical commanders on land and see at ranges out to 185 kilometers. No longer in the Army inventory (returned to the US Navy in 1995).

Tactical UAV : Designed to support tactical commanders with near-real-time imagery intelligence at ranges up to 200 kilometers. Outrider Advanced Concept Technology Demonstration (ACTD) program terminated. Material solution for TUAV requirements is being pursued through a competive acquisition process with goal of contract award in DEC 99.

Joint Tactical UAV (Hunter): Developed to provide ground and maritime forces with near-real-time imagery intelligence at ranges up to 200 kilometers; extensible to 300+ kilometers by using another Hunter UAV as an airborne relay. Training base located at Fort Huachuca, with additional baseline at Fort Polk to support JRTC rotations. Operational assets based at Fort Hood (currently supporting the KFOR in Kosovo).

Medium Altitude Endurance UAV (Predator): Advanced Concept Technology Demonstration now transitioned to Low-Rate Initial Production (LRIP). Provides imagery intelligence to satisfy Joint Task Force and Theater Commanders at ranges out to 500 nautical miles. No longer in the Army inventory (transferred to the US Air Force in 1996).

High Altitude Endurance UAV (Global Hawk): Intended for missions requiring long-range deployment and wide-area surveillance (EO/IR and SAR) or long sensor dwell over the target area. Directly deployable from CONUS to the theater of operations. Advanced Concept Technology Demonstration (ACTD) managed by the US Air Force.

LIDAR

Light detection and ranging (lidar) is a technique in which
a beam of light is used to make range-resolved remote
measurements. A lidar emits a beam of light, that interacts
with the medium or object under study. Some of this light
is scattered back toward the lidar. The backscattered light
captured by the lidar’s receiver is used to determine some
property or properties of the medium in which the beam
propagated or the object that caused the scattering.
The lidar technique operates on the same principle
as radar; in fact, it is sometimes called laser radar.
The principal difference between lidar and radar is the
wavelength of the radiation used. Radar uses wavelengths
in the radio band whereas lidar uses light, that is
usually generated by lasers in modern lidar systems. The
wavelength or wavelengths of the light used by a lidar
depend on the type of measurements being made and may
be anywhere from the infrared through the visible and into
the ultraviolet. The different wavelengths used by radar
and lidar lead to the very different forms that the actual
instruments take.
The major scientific use of lidar is for measuring
properties of the earth’s atmosphere, and the major commercial
use of lidar is in aerial surveying and bathymetry
(water depthmeasurement). Lidar is also used extensively
in ocean research (1–5) and has several military applications,
including chemical (6–8) and biological (9–12)
agent detection. Lidar can also be used to locate, identify,
and measure the speed of vehicles (13). Hunters
and golfers use lidar-equipped binoculars for range finding
(14,15).
Atmospheric lidar relies on the interactions, scattering,
and absorption, of a beam of light with the constituents
of the atmosphere. Depending on the design of the lidar,
a variety of atmospheric parameters may be measured,
including aerosol and cloud properties, temperature, wind
velocity, and species concentration.
This article covers most aspects of lidar as it relates to
atmospheric monitoring. Particular emphasis is placed on
lidar system design and on the Rayleigh lidar technique.
There are several excellent reviews of atmospheric lidar
available, including the following:
Lidar for Atmospheric Remote Sensing (16) gives
a general introduction to lidar; it derives the lidar
equation for various forms of lidar including Raman
and differential absorption lidar (DIAL). This work
includes details of a Raman and a DIAL system
operated at NASA’s Goddard Space Flight Center.
Lidar Measurements: Atmospheric Constituents, Clouds,
and Ground Reflectance (17) focuses on the differential
absorption and DIAL techniques as well as their
application to monitoring aerosols, water vapor, and
minor species in the troposphere and lower stratosphere.
Descriptions of several systems are given, including the
results of measurement programs using these systems.
Optical and Laser Remote Sensing (18) is a compilation
of papers that review a variety of lidar techniques
and applications. Lidar Methods and Applications (19)
gives an overview of lidar that covers all areas of
atmospheric monitoring and research, and emphasizes