Airborne G-Band (183 GHz) Water Vapor Radiometer

ProSensing Inc. has developed a G-band (183 GHz, 1.5 mm wavelength) Water Vapor Radiometer (GVR) for measuring low concentrations of atmospheric water vapor and liquid water. Using four double-sideband receiver channels, the instrument measures brightness temperature at 183.31 +-1, +-3, +-7 and +-14 GHz. An airborne version of the instrument, shown below, is packaged and wired to operate from a standard PMS probe canister. The airborne instrument is participating in the CloudSat validation experiment onboard the NRC Canada Convair-580 aircraft through March 2007.

Airborne GVR, packaged and wired to operate from a standard PMS probe canister. A sampling rate of about 10 Hz is interrupted with 0.5 sec duration calibration gaps every 3 seconds. Instrument weighs 22 lb; 38 lb total as shown with canister.

Key System Parameters:

• Frequency: 183.31 ±1, ±3, ±7 and ±14 GHz
• Bandwidth: 0.5 (1), 1.0 (3), 1.4 (7) and 2.0 (14) GHz
• Delta T: 0.2 K @ 200 ms integration (5 Hz data rate)
• TRec: 1750 K (1), 1610 K (3), 1600 K (7) and 2170 K (14)
• Allan STD: 0.05 K @ 1000 seconds
• Data Rate: 0.1-20 Hz with periodic calibration
• Antenna: 4" offset reflector, 2 degree beamwidth
• Radome: Surface matched TPX window
• Weight: 22 lb (38 lb with canister)
• Power: 28 W AC, 126 W max. (~50 W ave.) 28 VDC

In September 2006 the Airborne GVR was installed in the NRC Canada Convair-580 Aircraft to participate in the CloudSat validation flights through March 2007.

Example Data: On October 26, 2006 the NRC Canada Convair aircraft descended into a liquid cloud for a 50 minute level flight leg, then ascended out of the cloud layer. The recoded Zenith brightness temperature from the four receiver channels are shown below in Figure 1 and the corresponding retreived Precipitable Water Vapor (PWV) and Liquid Water Path (LWP) are shown in Figure 2.

Figure 1 : Data collected with the Airborne GVR during a CloudSat validation flight near Ottawa, Canada on October 26, 2006. Zenith brightness temperature data is shown from the four double sideband receiver channels: Black=183.31 +-1 GHz, Red=+-3 GHz, Green=+-7 GHz and Blue=+-14 GHz.

Figure 2: Precipitable Water Vapor (PWV) and Liquid Water Path (LWP) estimated using a neural network algorithm from the measured brightness temperature data of Figure 3 and flight level air temperature. The neural network was trained with a combined multi-year radosonde data-set from Albany, New York and Barrow, Alaska. The sounding data was processed to a data set of brightness temperatures at the four radiometer frequencies, air temperature at the instrument and corresponding PWV and LWP. This simulated data set was used to train and test the neural network.

Ground-Based G-Band (183 GHz) Water Vapor Radiometer for Arid Environments

ProSensing, Inc. has developed a G-band (183 GHz) Water Vapor Radiometer (GVR) for long-term, unattended measurements of low concentrations of atmospheric water vapor and liquid water. Precipitable water vapor and liquid water path are estimated from zenith brightness temperatures, measured using four double-sideband receiver channels, centered at 183.31 GHz. A prototype ground-based version of the instrument was deployed at the DOE ARM Program's North Slope of Alaska site near Barrow, AK in April 2005, where it is in its second year of continuous data collection. This ground based system was the predecessor of the compact, airborne version of the same instrument.