Impact of the local oscillator calibration rate on the SMOS measurements and retrieved salinities
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hdl:2117/86692
Tipus de documentArticle
Data publicació2013-09-02
EditorInstitute of Electrical and Electronics Engineers (IEEE)
Condicions d'accésAccés restringit per política de l'editorial
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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 LOcalibration 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 2min 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.
CitacióGabarro, C., Gonzalez, V., Corbella, I., Torres, F. Impact of the local oscillator calibration rate on the SMOS measurements and retrieved salinities. "IEEE transactions on geoscience and remote sensing", 02 Setembre 2013, vol. 51, núm. 9, p. 4633-4642.
ISSN0196-2892
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