A Calibration Scheme for Microwave Radiometers Using Tipping Curves and Kalman Filtering

Calibration of microwave radiometers is a critical task and remains a key issue for the accuracy of brightness-temperature measurements. The tipping-curve calibration method is a well-established technique for ground-based microwave radiometers measuring at frequencies where the opacity of the atmosphere is low. This method relies on the known relationship between the tipping angles of the radiometer and the atmospheric opacity at those angles. Atmospheric inhomogeneities slightly disturb this relationship and therefore lead to calibration errors. The calibration scheme presented in this paper uses the determined tipping-calibration accuracy and incorporates the statistical behavior of radiometer gain and system-temperature variations in a Kalman filter framework. In this paper, a calibration simulation is set up to test the capability of the proposed scheme by reconstructing simulated brightness temperatures first. Moreover, the technique is applied to experimental data. The calibration quality is evaluated with the detrended-fluctuation-analysis method. Model and experimental results show that the calibration accuracy can be increased by a factor of two or even higher. Finally, we apply the calibration technique to a microwave radiometer with internal calibration, resulting in a reduction of the calibration noise.

[1]  R. Frater,et al.  An Active "Cold" Noise Source , 1981 .

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

[3]  Axel Murk,et al.  The Fully Polarimetric Imaging Radiometer SPIRA at 91 GHz , 2008, IEEE Transactions on Geoscience and Remote Sensing.

[4]  Ed R. Westwater,et al.  The accuracy of water vapor and cloud liquid determination by dual‐frequency ground‐based microwave radiometry , 1978 .

[5]  C. Peng,et al.  Mosaic organization of DNA nucleotides. , 1994, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

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

[7]  J. C. Liljegren,et al.  Evaluating the Quality of Ground-Based Microwave Radiometer Measurements and Retrievals Using Detrended Fluctuation and Spectral Analysis Methods , 2001, physics/0108035.

[8]  Christian Mätzler,et al.  ASMUWARA, a ground-based radiometer system for tropospheric monitoring , 2006 .

[9]  Christian Mätzler,et al.  Tropospheric water and temperature retrieval for ASMUWARA , 2006 .

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

[11]  J. C. Liljegren,et al.  A multichannel radiometric profiler of temperature, humidity, and cloud liquid , 2003 .

[12]  Lorenz Martin Microwave Transmission and Emission Measurements for Tropospheric Monitoring , 2009 .

[13]  N. Kämpfer,et al.  Radiometric determination of water vapor and liquid water and its validation with other techniques , 1992 .

[14]  Christian Mätzler,et al.  Ground-based observations of atmospheric radiation at 5, 10, 21, 35, and 94 GHz , 1992 .

[15]  A. B. Vane,et al.  Atmospheric Absorption Measurements with a Microwave Radiometer , 1946 .

[16]  Arthur Gelb,et al.  Applied Optimal Estimation , 1974 .

[17]  Christian Mätzler,et al.  Refined Physical Retrieval of Integrated Water Vapor and Cloud Liquid for Microwave Radiometer Data , 2009, IEEE Transactions on Geoscience and Remote Sensing.

[18]  T. Başar,et al.  A New Approach to Linear Filtering and Prediction Problems , 2001 .

[19]  Niklaus Kämpfer,et al.  A new 22-GHz radiometer for middle atmospheric water vapor profile measurements , 2004, IEEE Transactions on Geoscience and Remote Sensing.

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