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| Titel |
A Wing Pod-based Millimeter Wave Cloud Radar on HIAPER |
| VerfasserIn |
Jothiram Vivekanandan, Peisang Tsai, Scott Ellis, Eric Loew, Wen-Chau Lee, Jonathan Emmett |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093660
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| Publikation (Nr.) |
 EGU/EGU2014-8593.pdf |
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| Zusammenfassung |
| One of the attractive features of a millimeter wave radar system is its ability to detect
micron-sized particles that constitute clouds with lower than 0.1 g m-3 liquid or ice water
content. Scanning or vertically-pointing ground-based millimeter wavelength radars are used
to study stratocumulus (Vali et al. 1998; Kollias and Albrecht 2000) and fair-weather cumulus
(Kollias et al. 2001). Airborne millimeter wavelength radars have been used for atmospheric
remote sensing since the early 1990s (Pazmany et al. 1995). Airborne millimeter wavelength
radar systems, such as the University of Wyoming King Air Cloud Radar (WCR) and the
NASA ER-2 Cloud Radar System (CRS), have added mobility to observe clouds in remote
regions and over oceans.
Scientific requirements of millimeter wavelength radar are mainly driven by climate and
cloud initiation studies. Survey results from the cloud radar user community indicated a
common preference for a narrow beam W-band radar with polarimetric and Doppler
capabilities for airborne remote sensing of clouds. For detecting small amounts of liquid and
ice, it is desired to have -30 dBZ sensitivity at a 10 km range. Additional desired capabilities
included a second wavelength and/or dual-Doppler winds. Modern radar technology offers
various options (e.g., dual-polarization and dual-wavelength). Even though a basic fixed
beam Doppler radar system with a sensitivity of -30 dBZ at 10 km is capable of
satisfying cloud detection requirements, the above-mentioned additional options,
namely dual-wavelength, and dual-polarization, significantly extend the measurement
capabilities to further reduce any uncertainty in radar-based retrievals of cloud
properties.
This paper describes a novel, airborne pod-based millimeter wave radar, preliminary radar
measurements and corresponding derived scientific products. Since some of the primary
engineering requirements of this millimeter wave radar are that it should be deployable on an
airborne platform, occupy minimum cabin space and maximize scan coverage, a pod-based
configuration was adopted. Currently, the radar system is capable of collecting observations
between zenith and nadir in a fixed scanning mode. Measurements are corrected for aircraft
attitude changes. The near-nadir and zenith pointing observations minimize the cross-track
Doppler contamination in the radial velocity measurements. An extensive engineering
monitoring mechanism is built into the recording system status such as temperature,
pressure, various electronic components’ status and receiver characteristics. Status
parameters are used for real-time system stability estimates and correcting radar system
parameters. The pod based radar system is mounted on a modified Gulfstream V
aircraft, which is operated and maintained by the National Center for Atmospheric
Research (NCAR) on behalf of the National Science Foundation (NSF). The aircraft is
called the High-Performance Instrumented Airborne Platform for Environmental
Research (HIAPER) (Laursen et al., 2006). It is also instrumented with high spectral
resolution lidar (HSRL) and an array of in situ and remote sensors for atmospheric
research.
As part of the instrument suite for HIAPER, the NSF funded the development of the
HIAPER Cloud Radar (HCR). The HCR is an airborne, millimeter-wavelength,
dual-polarization, Doppler radar that serves the atmospheric science community by providing
cloud remote sensing capabilities for the NSF/NCAR G-V (HIAPER) aircraft. An optimal
radar configuration that is capable of maximizing the accuracy of both qualitative and
quantitative estimated cloud microphysical and dynamical properties is the most attractive
option to the research community. The Technical specifications of cloud radar are optimized
for realizing the desired scientific performance for the pod-based configuration. The radar
was both ground and flight tested and preliminary measurements of Doppler and polarization
measurements were collected. HCR observed sensitivity as low as -37 dBZ at 1 km range and
resolved linear depolarization ratio (LDR) signature better than -29 dB during its latest test
flights.
References:
Kollias, P., and B. A. Albrecht, 2000: The turbulence structure in a continental
stratocumulus cloud from millimeter wavelength radar observation. J. Atmos. Sci., 57,
2417-2434.
Kollias, P., B.A. Albrecht, R. Lhermitte, and A. Savtchenko, 2001: Radar observations of
updrafts, downdrafts, and turbulence in fair weather cumuli. J. Atmos. Sci. 58,
1750-1766.
Laursen, K. K., D. P. Jorgensen, G. P. Brasseur, S. L. Ustin, and J. Hunning, 2006:
HIAPER: The next generation NSF/NCAR research aircraft. Bulletin of the American
Meteorological Society, 87, 896–909.
Pazmany, A. L., R. E. McIntosh, R. Kelly, and V. G., 1994: An airborne 95-GHz
dual-polarized radar for cloud studies. IEEE Trans. Geosci. Remote Sens., 32, 731–739.
Vali, G., Kelly, R.D., French, J., Haimov, S., Leon, D., McIntosh, R., Pazmany, A., 1998.
Fine-scale structure and microphysics of coastal stratus. J. Atmos. Sci. 55, 3540–3564. |
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