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
sensed, including range and resolution.
Millimeter-wavelength radars most suited for
2. Develop inversion theory to determine most
appropriate technologies for sensing 3-D spatial
Wider ranges of drop sizes in precipitating clouds
structure of liquid-water content, drop-size spec-
tra, and temperature ahead of aircraft.
than two) radar system.
3. Develop prototype hardware for testing theory
for each selected component of remote-sensing
droplet temperature for accurate assessment of
4. Select test bed for proving concepts developed
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,
but that other wavelength pairs are possible,
6. Test airborne prototypes on flight platform and
depending upon desired range and the existence
7. Develop integrated system comprising all compo-
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
military flight platforms.
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
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-
zontal to provide integrated water that an aircraft
4. Doppler techniques to detect droplet sizes may
4. Modeling and experiments needed at test beds.
not be possible with horizontally scanning sys-
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.
8. Passive technology advantage for cost, size,
weight, power, general aviation, and military ap-
smaller drop sizes but have shorter range and
cannot operate within Rayleigh regime in larger
9. Model with RADTRAN or its successors.
10. Radiometer scanning is slow.