| Abstract: |
The Aquarius/SAC-D mission operated between August 2011 and June 2015 with the main goal of providing global estimates of sea surface salinity (SSS) [1, 2]. It comprised both active and passive microwave sensors operating at L-band to observe the same surface area almost simultaneously. The passive instrument, a combination of three radiometers sharing the same antenna and antenna feeds, measured the surface brightness temperature at 1,413 GHz, which over the ocean was used to retrieve SSS.
Despite the fact that the radiometers operate in the 1,400-1,427 GHz band, where all man-made emissions are prohibited by international regulation, Radio Frequency Interference (RFI) can still be seen in measurements in this band. Thus, RFI detection and mitigation were included in the data processing [3] and appear to work well, detecting most instances of interference [4]. The most serious and difficult unresolved problem is that the RFI filter can still miss low-level RFI such the one that occurs when strong RFI enters the antenna sidelobes.
A study has been performed to assess the amount of missed detection in certain ocean region where low-level interference is a problem. The work is based on estimating the statistics of RFI based on the acquired antenna temperature samples. The statistics are then used to simulate RFI and its detection by the RFI filter. The results of this simulation are compared with the RFI detected in the acquired sample to provide an estimate of the level of missed detection. The estimation of the RFI histograms is performed in two different ways, based either on a change of RFI environment over the North Atlantic Ocean in November 2013 or on a reference region assumed to be RFI-free, and the results of the two approaches are compared. The RFI filter appears to miss a large part of low-level RFI whose level is below the RFI algorithm threshold, suggesting that a threshold adjustment may be needed in some regions.
REFERENCES
[1] D.M. Le Vine, G.S.E. Lagerloef, F.R. Colomb, S.H. Yueh, and F.A. Pellerano, “Aquarius: An Instrument to Monitor Sea Surface Salinity From Space”, IEEE Transactions on Geoscience and Remote Sensing, vol. 45, no. 7, pp. 2040-2050, July 2007
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[4] D.M. Le Vine, P. de Matthaeis, C.S. Ruf, and D.D. Chen, Aquarius RFI Detection and Mitigation Algorithm: Assessment and Examples, IEEE Transactions on Geoscience and Remote Sensing, vol.52, no.8, pp.4574-4584, Aug. 2014.
[5] D.M. Le Vine and P. de Matthaeis, Aquarius Active/Passive RFI Environment at L-Band, IEEE Geoscience and Remote Sensing Letters, vol.11, no.10, pp.1747-1751, Oct. 2014. |
