Ground-Based Scanning Radiometer (GSR)
NOAA/ETL has designed a multi-frequency scanning radiometer operating
from 50 to 380 GHz. The radiometers are installed into a scanning
drum scanhead which is mechanically and electrically compatible with the
NOAA aircraft instrument, the Polarimetric Scanning Radiometer (PSR).
The PSR system has operated in more than 15 experiments and has over 600
flight hours of successful operation observing the Earth's surface and
atmospheric parameters. The ground-based instrument, GSR, uses the
submillimeter scanhead (PSR/S) with 11-channels in the 50-56 GHz region,
a dual-polarization measurement at 89 GHz, 7-channels around the
183.31 GHz water vapor absorption line, dual-polarized channels at 340
GHz, and 3-channels at 380 GHz. It also has a 10.6 micrometer infrared
radiometer within the same scanhead. All of the radiometers are mounted
within a rotating scanhead, use lens antennas, and view two external
reference targets during the calibration cycle. New thermally stable
calibration targets with high emission coefficients have been designed
for the purpose. In addition, each of the radiometers' design includes
two internal reference points for more frequent calibration. The beam
widths of the GSR channels are 1.8° and can be averaged to given
beam-widths consistent with the ARM MWR (4.5 to 5.5°).
Schematic diagram of the GSR calibration and scanner system. The GSR
scanhead periodically moves out of the framework for zenith viewing on
a trolley system, and shares time observing the atmosphere and the two
temperature-controlled blackbody reference targets.
|
GSR in process of assembly on March 7, 2004 in Barrow, AK. This photo
shows the GSR framework with the external calibration targets and the
scanhead with the radiometers installed are shown.
|
GSR radiometers mounted on the scanning drum scanhead.
|
GSR operating in Barrow, AK, during the WVIOP04, on March-April 2004.
|
Unique features of the GSR radiometer include:
- Potential for inclusion of several important radiometric bands in a single co-aligned scanning system
- Use of two common large thermally stabilized calibration targets with up to 100-120 degrees centigrade of hot-cold temperature spread
- Complete shielding of calibration targets from vertically-falling hydrometeors
- Absence of reflecting mirrors normally used to implement scanning
- Absence of radome materials between the radiometer antennas and sky
- Horizon-to-horizon sky field of view of all radiometers
- Inclusion of co-aligned 10-um thermal IR sensor for cloud detection
The GSR was operated at Barrow, Alaska, during the Arctic Winter Water
Vapor Intensive Operating Period 2004 (WVIOP04) from March 9 to April 9,
2004. The primary purpose of the instrument was to measure temperature,
water vapor, and clouds, at cold (-20 to -55 °C) and dry
(PWV < 5 mm) conditions.
- Typical Target, continuous scan, and air-mass dwell for GSR
- GSR sample data during the WVIOP04
- Artic Winter Water Vapor IOP 2004 preliminary results
Typical Target, scan and air-mass dwell for GSR
The GSR has a flexible and software programmable angular-scanning sequence
that is repeated every two minutes. The sequence starts with the GSR being
inside the calibration house and viewing the hot calibration target for
3 seconds. During the next step, the GSR remains in the calibration house
and views the cold target, again for 3-seconds. The scanhead then moves
out of the calibration house and moves to the atmospheric-scanning
position, where it moves from air mass = 3.5 to a sequence of air mass
dwells of 2-seconds each. Between the air mass dwells the radiometer moves
continuously to the next scan position. Thus the radiometer acquires both
continuous and dwell data for the atmosphere with two-point calibration
data in between. For channels in the transparency windows, both 2-point
and tip-curve calibration methods can be used. In addition to the external
calibration, the radiometer also switches between hot and cold internal
calibration loads. The GSR basic record length is 10ms.
Calibration, dwell, and continuous scanning sequence of the GSR.
|
|
|
GSR in motion samples (mpg) from Barrow, Alaska, on March 10 2004
|
GSR sample data during the WVIOP04
Short time series of data taken on March 11, 2004, during the WVIOP. From
the channels in the 50-60 GHz Oxygen band it is possible to note that the
strongest channels from 55.5 to 56.3 GHz clearly show the presence of a
thermal inversion. Conversely, the weakest channel at 50.3 GHz will allow
tip curve calibration. For all of the channels, the time spent dwelling at
the separate air mass dwell points can be seen. From the channels around
the 183.31 GHz Water vapor line we note that the strongest channels from
183.31 ±0.5 and ±1 are close to saturation. Conversely, the
weakest channels from 183.31 ± 15, ±12, and ±7 all will
allow tip curve calibration. From the channels around the 380.2 GHz water
vapor line we note that the strongest channel at 380.2 ±4 shows the
presence of a thermal inversion.
Time series of Tb between 50 and 60 GHz.
|
Time Series of Tb for channels around the 183.31 GHz water vapor line.
|
Time series of Tb near the 380.2 GHz water vapor line.
|
Publications
-
Ed R. Westwater, Susanne Crewell and Christian Mätzler,
Surface-based Microwave and Millimeter wave Radiometric Remote Sensing of the Troposphere: a Tutorial,
IEEE Geosciences and Remote Sensing Newsletter, March 2005, 134.
-
Ed R. Westwater, Marian Klein, and Vladimir Leuski, Al Gasiewsk, Taneil Uttal, and Duane Hazen, Domenico CiminiM Vinia Mattioli, Bob L. Weber, Sally Dowlatshahi,Joe A. Shaw, Jim Liljegren ,B. M. Lesht, Bernie Zak;
The 2004 North Slope of Alaska Arctic Winter Radiometric Experiment
Proceedings Of The 14th ARM Science Team Meeting, March 22-26, 2004, Albuquerque, New Mexico.
-
E. R. Westwater, M. Klein, V. Leuski, A. J. Gasiewski, T. Uttal, D. A. Hazen, D. Cimini V. Mattioli B. L. Weber, S. Dowlatshahi, J. A. Shaw, J. S. Liljegren , B. M. Lesht, and B. D. Zak,
Initial Results from the 2004 North Slope of Alaska Arctic Winter Radiometric Experiment
Proc. IGARSS'04 (in press).
-
Ed R. Westwater, Susanne Crewell,and Christian Mätzler,
Frontiers in Surface-based Microwave and Millimeter Wavelength Radiometry
Proc. IGARSS'04 (in press).
|