NDLI: Impact of the Local Oscillator Calibration Rate on the SMOS Measurements and Retrieved Salinities

Content Provider	IEEE Xplore Digital Library
Author	Gabarro, C. Gonzalez-Gambau, V. Corbella, I. Torres, F. Martinez, J. Portabella, M. Font, J.
Copyright Year	1980
Abstract	The local oscillators (LOs) of the Soil Moisture and Ocean Salinity mission payload are used to shift the operating frequency of the 72 receivers to an optimal intermediate frequency needed for the signal processing. The LO temperature variations produce phase errors in the visibility, which result in a blurring of the reconstructed brightness temperature (Tb) image. At the end of the commissioning phase, it was decided to calibrate the LO every 10 min while waiting for a more in-depth analysis. During short periods of time, the LO calibration has been performed every 2 min to assess the impact of a higher calibration rate on the quality of the data. In this paper, by means of a decimation experiment, the relative errors of 6- and 10-min calibration interval data sets are estimated using the 2 min as a reference. A noticeable systematic across- and along-track pattern of amplitude ±0.3 K is observed for Tb differences between 10 and 2 min, whereas this is reduced between 6 and 2 min. A simulation experiment confirms that the nature of such systematic pattern is due to the visibility phase errors induced by the LO calibration rate. Such pattern is propagated into the sea surface salinity (SSS) retrievals. Overall, the SSS error increase (relative to the 2 min SSS data) is about 0.39 and 0.14 psu for the 10- and 6-min data sets, respectively. This paper shows that a LO calibration rate of at least 6 min would noticeably improve the SSS retrievals.
Sponsorship	IEEE Geoscience and Remote Sensing Society IEEE URSI
Starting Page	4633
Ending Page	4642
Page Count	10
File Size	1933956
File Format	PDF
ISSN	01962892
Volume Number	51
Issue Number	9
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2013-09-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Calibration Noise Thermal noise Receivers Temperature measurement Sea measurements Soil Moisture and Ocean Salinity (SMOS) Brightness temperature calibration interferometry Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) radiometer salinity
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Electrical and Electronic Engineering

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Impact of the Local Oscillator Calibration Rate on the SMOS Measurements and Retrieved Salinities

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