APPENDIX C: SYNOPSIS OF SENSOR TECHNOLOGY NEEDS,
STATE OF KNOWLEDGE, STRENGTHS, AND WEAKNESSES
SENSOR TECHNOLOGY NEEDS
wavelengths allows liquid-water content to be
1. Establish sensing needs for phenomena to be
retrieved.
sensed, including range and resolution.
8.
Millimeter-wavelength radars most suited for
2. Develop inversion theory to determine most
cloud-water sensing.
appropriate technologies for sensing 3-D spatial
9.
Wider ranges of drop sizes in precipitating clouds
structure of liquid-water content, drop-size spec-
increase the need for a multiple-wavelength (more
tra, and temperature ahead of aircraft.
than two) radar system.
3. Develop prototype hardware for testing theory
10.
Differential attenuation techniques may require
for each selected component of remote-sensing
droplet temperature for accurate assessment of
system.
liquid-water content.
4. Select test bed for proving concepts developed
11.
Gossett and Sauvageot (1992) theoretically
in theory, develop test plans, and test.
demonstrated that 3.2-cm (X) and 0.87-cm (Ka)
5. Develop airborne prototype system component
bands are the best for detecting water in clouds,
prototypes.
but that other wavelength pairs are possible,
6. Test airborne prototypes on flight platform and
depending upon desired range and the existence
verify capabilities.
of hydrometeors.
7. Develop integrated system comprising all compo-
12.
Millimeter-wavelength radars are suited to air-
nents, with processing and display system com-
borne cloud studies because of their small size,
patible with onboard systems and protocol.
low ground-clutter susceptibility, high resolution,
8. Test integrated prototype system on civilian and
and sensitivity to small hydrometeors.
military flight platforms.
13.
It may not be possible to uniquely define cloud
9. Certify system.
drop-size distributions with radar. Only parame-
ters of a distribution may be available.
STATE OF KNOWLEDGE
Passive radiometers
Radar
1. Operationally used to measure zenith and nadir
1. Ground (vertical scanning) and airborne (hori-
temperature profiles, with thermal and spatial reso-
zontal scanning) systems are technically possible.
lution decreasing with distance from radiometer.
2. Range-resolved liquid water measurements have
2. Integrated liquid-water path sensed in vertical at
31.6 GHz with scanning possible.
been acquired from clouds.
3. Integrated liquid water might be sensed in hori-
3. Polarization techniques can be used to detect ice
zontal to provide integrated water that an aircraft
vs. water.
could intercept.
4. Doppler techniques to detect droplet sizes may
4. Modeling and experiments needed at test beds.
not be possible with horizontally scanning sys-
5. Precipitation can cause difficulties--modeling is
tems.
needed.
5. Longer wavelengths (lower frequencies) cannot
6. Cloud phase may be possible with polarimetry.
detect smaller droplets but have longer range and
7. Scanning liquid-water radiometer under devel-
can operate within Rayleigh regime to larger drop
opment provides range resolution.
sizes. Useful for detecting precipitation.
8. Passive technology advantage for cost, size,
6. Shorter wavelengths (higher frequencies) detect
weight, power, general aviation, and military ap-
smaller drop sizes but have shorter range and
plications.
cannot operate within Rayleigh regime in larger
9. Model with RADTRAN or its successors.
drops.
10. Radiometer scanning is slow.
7. Differential attenuation of two or more radar
65
To Contents
Previous Page
