Instrument : G-band (183 GHz) Vapor Radiometer (GVR)

Picture of the G-band (183 GHz) Vapor Radiometer (GVR)

General Overview

The G-Band Vapor Radiometer (GVR) provides time-series measurements of brightness temperatures from four double sideband channels centered at ±1, ±3, ±7, and ±14 GHz around the 183.31-GHz water vapor line. Atmospheric emission in this spectral region is primarily due to water vapor, with some influence from liquid water. The 183.31 ±14-GHz channel is particularly sensitive to the presence of liquid water. The sensitivity to water vapor of the 183.31-GHz line is approximately 30 times higher than at the frequencies of the two-channel microwave radiometer (MWR) for a precipitable water vapor (PWV) amount of less than 2.5 mm. Measurements from this instrument are, therefore, especially useful during low-humidity conditions (PWV < 5 mm).

A detailed description of the calibration algorithm can be found in the instrument handbook. For additional details on the instrument’s design and operations the following references are available:

Pazmany, AL. 2007. “A compact 183 GHz radiometer for water vapor and liquid sensing.” IEEE Transactions on Geoscience and Remote Sensing 45(7): 2202–2207.

Cadeddu, MP, JC Liljegren, and AL Pazmany. 2007. “Measurements and retrievals from a new 183-GHz water-vapor radiometer in the arctic.” IEEE Transactions on Geoscience and Remote Sensing 45(7): 2207–2215.

Available Retrievals and Uncertainty

Neural network retrievals of precipitable water vapor are available from this instrument as value-added product in the datastream nsagvrC1.c1. The retrievals use seasonal neural network coefficients. Uncertainties in the retrieval are expressed as 1-sigma individual error bars. Details of the retrieval algorithm and uncertainty estimation can be found in the following reference:

Cadeddu, MP, DD Turner, and JC Liljegren. 2009. “A neural network for real-time retrievals of
PWV and LWP From Arctic millimeter-wave ground-based observations.” IEEE Transactions on
Geoscience and Remote Sensing 47(7): 1887–1900. A rough estimate of the retrieval uncertainty is:

Precipitable water vapor: varies between 3-4% when PWV is less than 10 mm to ~10% when PWV > 10 mm

Summary Table:

Name	Physical Quantity	Approximate Uncertainty	Datastream	Uncertainty Variable in the Datastream
Tbsky1	183.3±1 GHz brightness temperature	1.5-2 K	gvr.b1	N/A
Tbsky2	183.3±3 GHz brightness temperature	1.5-2 K	gvr.b1	N/A
Tbsky3	183.3±7 GHz brightness temperature	1.5-2 K	gvr.b1	N/A
Tbsky4	183.3±14 GHz brightness temperature	1.5-2 K	gvr.b1	N/A
pwv	Precipitable water vapor	between 3-4% (PWV < 10 mm) to ~10% (PWV > 10 mm)	gvr.c1	pwv_error