Though research and development may be accom-
1973). The NOAA wind profilers are capable of meas-
plished through partnering, purchasing, and in-house
uring temperature accurately in horizontal and vertical
work, managers must acquire expertise to understand
wind by averaging over a long time period, about 6
and properly direct activities. They must have the under-
min, and by using multiple acoustic sources. Vertical
standing, focus, and comprehensive vision to complete
wind errors have been experimentally reduced to as low
as 0.1C using 6-min averaging times (Angevine and
the project.
Adapt means to take technology and skills and adapt
Ecklund 1994). Overall RASS accuracies are compar-
it to needs (Deffeyes 1996). A full understanding of the
able to radiosondes, with overall error consistently about
1C rms, with altitudes of 3.5 km agl reached 50% of
needs, operations, environment, and technologies avail-
able allows developers to adapt existing or developing
the time (Westwater 1997). Experimentally, RASS
technologies and techniques to the requirements of the
measurements have been made to 15 km altitude and
product. This means, for example, adapting microwave
more (Matuura et al. 1986).
radiometers or differential attenuation radar to operate
RASS is certainly a viable technique for sensing tem-
on aircraft with other sensors as a system to satisfy the
perature from the ground during icing conditions around
icing information needs of operators and pilots.
airports. Its only limitation at airports may be an occa-
Adopt means to acquire new ways of thinking and
sional inability to reach needed altitudes. Use of RASS
of doing business (Deffeyes 1996). This will be neces-
in airborne applications, especially sensing ahead of
sary for system developers, as well as for regulatory
the aircraft, has been assessed to be impractical because
bodies, manufacturers, operators, and pilots. Adopting
of problems with aircraft pitch and yaw and cross winds
new techniques may improve efficiency and safety, but
causing loss of signal (Mead et al. 1998).
it requires willingness to change. For example, FAR
25, Appendix C, has been the standard for aircraft design
5.6.4 Raman lidar
criteria in icing conditions. As new information is
Raman lidar techniques, discussed above, are also
acquired characterizing the icing environment, users of
used to measure atmospheric temperature profiles (Gill
Appendix C may be required to change the range of
et al. 1979, Evans et al. 1997). Raman lidar uses a variety
of wavelengths, with examples at 0.55 and 0.35 m
conditions for certifying aircraft for flight in icing con-
ditions.
(Evans et al. 1997, Vaughan et al. 1993). Raman lidar
A logical initial location to provide icing protection
is typically operated only at night because the signal is
using remote-sensing technology is at airports. The need
overwhelmed by solar radiation. Long integration times
for ice protection is greatest in the approach and depar-
of 10 min are often necessary to obtain accurate temper-
ture phases of flight because aircraft are operating at
atures (Evans et al. 1997). In addition, it suffers from
lower altitudes, lingering in conditions for longer
the typical extinction problems suffered by all lidars in
periods at slower speeds, and operating closer to maneu-
clouds. As a result, Raman lidar would not be practical
vering limits. Protecting airports would also provide
for ground or aircraft-mounted remote sensing in icing
the greatest benefit for the least cost.
conditions.
The ability to sense cloud microphysical properties
There are few known remote temperature-measuring
remotely from the earth's surface is mature in some
methods suitable for operation from airborne platforms
technology areas. For example, RASS is a mature tech-
in icing conditions. The best possibilities lie with scan-
nology for measuring temperature profiles in the lower
ning microwave radiometers, but they scan slowly and
atmosphere. Passive microwave radiometers are mature,
may be difficult to use from a moving platform. Lidar
but have less resolution than RASS for measuring tem-
methods are not practical, and infrared radiometers
operated in the 3.8- to 16.8-m region have a short range
perature profiles from the surface to midtroposphere
altitudes. Integrated liquid-water measurements may be
in clouds because of reduced optical depth. For ground-
made from the earth's surface using microwave radio-
based systems, RASS and radiometers are proven and
meters, and the technology is mature. Liquid water may
thus offer the best prospects of success.
be distributed among clouds with lidar ceilometers used
to determine cloud base and Ka- or W-band radar to
6.0 RECOMMENDATIONS
determine cloud base and top locations, the locations
Development of a remote-sensing system to detect
of multiple cloud layers, and, if needed, cloud phase,
icing potential requires developers and users to be adept,
or the new radiometer that profiles temperature, water
to adapt, and to adopt (Deffeyes 1996). Adept means that
vapor, and cloud liquid water may be a viable option. A
developers have a sufficient understanding of the oper-
system composed of this hardware, driven by expert
ational, meteorological, and sensor technology issues
system logic, and perhaps supplemented with satellite
to develop a coherent product that addresses user needs.
information, would make a usable prototype airport-
46
To Contents
Previous Page
