Investigation of ground-based microwave radiometer calibration techniques at 530 hPa

Abstract. Ground-based microwave radiometers (MWR) are becoming more and more common for remotely sensing the atmospheric temperature and humidity profile as well as path-integrated cloud liquid water content. The calibration accuracy of the state-of-the-art MWR HATPRO-G2 (Humidity And Temperature Profiler – Generation 2) was investigated during the second phase of the Radiative Heating in Underexplored Bands Campaign (RHUBC-II) in northern Chile (5320 m above mean sea level, 530 hPa) conducted by the Atmospheric Radiation Measurement (ARM) program conducted between August and October 2009. This study assesses the quality of the two frequently used liquid nitrogen and tipping curve calibrations by performing a detailed error propagation study, which exploits the unique atmospheric conditions of RHUBC-II. Both methods are known to have open issues concerning systematic offsets and calibration repeatability. For the tipping curve calibration an uncertainty of ±0.1 to ±0.2 K (K-band) and ±0.6 to ±0.7 K (V-band) is found. The uncertainty in the tipping curve calibration is mainly due to atmospheric inhomogeneities and the assumed air mass correction for the Earth curvature. For the liquid nitrogen calibration the estimated uncertainty of ±0.3 to ±1.6 K is dominated by the uncertainty of the reflectivity of the liquid nitrogen target. A direct comparison between the two calibration techniques shows that for six of the nine channels that can be calibrated with both methods, they agree within the assessed uncertainties. For the other three channels the unexplained discrepancy is below 0.5 K. Systematic offsets, which may cause the disagreement of both methods within their estimated uncertainties, are discussed.

[1]  E. Westwater.  Ground-based passive probing using the microwave spectrum of oxygen , 1965 .

[2]  G. Reesor,et al.  The Complex Dielectric Constant of Liquid Nitrogen in the Region 18 to 26 GHz , 1975 .

[3]  D. A. Boyd,et al.  Submillimeter and millimeter optical constants of liquid nitrogen , 1983 .

[4]  Hans J. Liebe,et al.  Millimeter-wave properties of the atmosphere: Laboratory studies and propagation modeling , 1987 .

[5]  P. A. Smith,et al.  The dielectric loss tangent of liquid nitrogen , 1991 .

[6]  Hans J. Liebe,et al.  Propagation Modeling of Moist Air and Suspended Water/Ice Particles at Frequencies Below 1000 GHz , 1993 .

[7]  M. Janssen.  Atmospheric Remote Sensing by Microwave Radiometry , 1993 .

[8]  T. Button,et al.  The dielectric constant of liquid nitrogen over the frequency range 0.5 to 10.4 GHz , 1993 .

[9]  Marco A. Janssen.  An Introduction to the Passive Microwave Remote Sensing of Atmospheres , 1993 .

[10]  S. Schwartz,et al.  The Atmospheric Radiation Measurement (ARM) Program: Programmatic Background and Design of the Cloud and Radiation Test Bed , 1994 .

[11]  P. Rosenkranz.  Water vapor microwave continuum absorption: A comparison of measurements and models , 1998 .

[12]  Yong Han,et al.  Analysis and improvement of tipping calibration for ground-based microwave radiometers , 2000, IEEE Trans. Geosci. Remote. Sens..

[13]  Roland Span,et al.  A Reference Equation of State for the Thermodynamic Properties of Nitrogen for Temperatures from 63.151 to 1000 K and Pressures to 2200 MPa , 2000 .

[14]  J. Güldner,et al.  Remote Sensing of the Thermodynamic State of the Atmospheric Boundary Layer by Ground-Based Microwave Radiometry , 2001 .

[15]  Tim J. Hewison,et al.  Measuring the Accuracy of MARSS—An Airborne Microwave Radiometer , 2001 .

[16]  Jean M. Rüeger,et al.  Refractive Index Formulae for Radio Waves , 2002 .

[17]  David K. Walker,et al.  Errors due to the reflectivity of calibration targets , 2004, IGARSS 2004. 2004 IEEE International Geoscience and Remote Sensing Symposium.

[18]  Clemens Simmer,et al.  A network suitable microwave radiometer for operational monitoring of the cloudy atmosphere , 2005 .

[19]  Domenico Cimini,et al.  Validating clear air absorption models using ground-based microwave radiometers and vice-versa , 2006 .

[20]  Tim J. Hewison,et al.  1D-VAR Retrieval of Temperature and Humidity Profiles From a Ground-Based Microwave Radiometer , 2007, IEEE Transactions on Geoscience and Remote Sensing.

[21]  Shepard A. Clough,et al.  Effect of the Oxygen Line-Parameter Modeling on Temperature and Humidity Retrievals From Ground-Based Microwave Radiometers , 2007, IEEE Transactions on Geoscience and Remote Sensing.

[22]  E. Mlawer,et al.  The Radiative Heating in Underexplored Bands Campaigns , 2010 .

[23]  U. Löhnert,et al.  Assessing the potential of passive microwave radiometers for continuous temperature profile retrieval using a three year data set from Payerne , 2011 .

[24]  A. V. Uvarov,et al.  Measurement of the reflector antenna absorption at terahertz frequencies by the method of a balanced radiometer , 2011 .

[25]  Luca Palchetti,et al.  Ground‐based high spectral resolution observations of the entire terrestrial spectrum under extremely dry conditions , 2012 .

[26]  Ulrich Löhnert,et al.  Operational profiling of temperature using ground-based microwave radiometry at Payerne: prospects and challenges , 2012 .