Aquarius Maps: Radiometer RFI (Northern Hemisphere)

  • Radiometer RFI, September 2011

    September 2011

  • Radiometer RFI, October 2011

    October 2011

  • Radiometer RFI, November 2011

    November 2011

  • Radiometer RFI, December 2011

    December 2011

  • Radiometer RFI, January 2012

    January 2012

  • Radiometer RFI, February 2012

    February 2012

  • Radiometer RFI, March 2012

    March 2012

  • Radiometer RFI, April 2012

    April 2012

  • Radiometer RFI, May 2012

    May 2012

  • Radiometer RFI, June 2012

    June 2012

  • Radiometer RFI, July 2012

    July 2012

  • Radiometer RFI, August 2012

    August 2012

  • Radiometer RFI, September 2012

    September 2012

  • Radiometer RFI, October 2012

    October 2012

  • Radiometer RFI, November 2012

    November 2012

  • Radiometer RFI, December 2012

    December 2012

  • Radiometer RFI, January 2013

    January 2013

  • Radiometer RFI, February 2013

    February 2013

  • Radiometer RFI, March 2013

    March 2013

  • Radiometer RFI, April 2013

    April 2013

  • Radiometer RFI, May 2013

    May 2013

  • Radiometer RFI, June 2013

    June 2013

  • Radiometer RFI, July 2013

    July 2013

  • Radiometer RFI, August 2013

    August 2013

  • Radiometer RFI, September 2013

    September 2013

  • Radiometer RFI, October 2013

    October 2013

  • Radiometer RFI, November 2013

    November 2013

  • Radiometer RFI, December 2013

    December 2013

  • Radiometer RFI, January 2014

    January 2014

  • Radiometer RFI, February 2014

    February 2014

  • Radiometer RFI, March 2014

    March 2014

  • Radiometer RFI, April 2014

    April 2014

  • Radiometer RFI, May 2014

    May 2014

  • Radiometer RFI, June 2014

    June 2014

  • Radiometer RFI, July 2014

    July 2014

  • Radiometer RFI, August 2014

    August 2014

  • Radiometer RFI, September 2014

    September 2014

  • Radiometer RFI, October 2014

    October 2014

  • Radiometer RFI, November 2014

    November 2014

  • Radiometer RFI, December 2014

    December 2014

  • Radiometer RFI, January 2015

    January 2015

  • Radiometer RFI, February 2015

    February 2015

  • Radiometer RFI, March 2015

    March 2015

  • Radiometer RFI, April 2015

    April 2015

  • Radiometer RFI, May 2015

    May 2015

  • Credit
  • Credit
Slideshow: Monthly radiometer RFI at 1.413 GHz (hover over images to pause the slideshow).

Radio Frequency Interference (RFI) can cause errors in the salinity estimated by Aquarius by affecting the signal received by the microwave radiometers and the scatterometer. The images on this page show global monthly RFI for ascending/descending passes as detected by the radiometers in the Orthographic Northern Hemisphere in the 1400-1.427 GHz band, the frequency of the three Aquarius radiometers.

Each data point represents the average radiometer measurements over 1.44 seconds (the fundamental data block in Aquarius Level 2 data). The color scale indicates the percentage of radiometer measurements within this window that are identified as RFI by the RFI detection algorithm (Le Vine, et al., 2014). Measurements identified as RFI are removed from processing and not used to calculate salinity. Red colors indicate areas where over 80% of the sampled data are flagged for RFI presence. Dark blues show relatively little detected RFI, with less than about 10% of samples flagged in these regions. An additional RFI flag is used to identify locations where the measured brightness temperature over land exceeds the expected limits of surface emissivity (Soldo et al., 2017). This flag is not used to remove samples from further processing, but in generating the RFI maps, 100% RFI is assigned to data points where this flag is raised. The lighter blue areas in the polar regions are an artifact of the particular processing used to detect RFI which is based on the standard deviation of the measurements within the 1.44-second averaging window. The processor identifies as RFI samples that show a relatively large deviation from average even if they are not affected by RFI. This effect, usually referred to as false alarms, has been accounted for by using different RFI algorithm parameters on ocean and land, but it is still present on sea ice whose constantly changing extent makes a tuning of the algorithm parameters over it unpractical.

Despite the fact that the Aquarius radiometers operated within a band designated for scientific research where all radio frequency emissions are prohibited (i.e. the window at 1.413 GHz), RFI was still detected (Le Vine and de Matthaeis, 2014). This is especially true over land. Since L-band radiometers have been operational in space (e.g. SMOS, Aquarius and SMAP) many sources have been identified and mitigated. However, RFI at L-band is still a problem in many parts of the world.

Click here to view a slideshow of radiometer RFI in the southern hemisphere.

Images are provided by Paolo de Matthaeis and Yan Soldo, NASA Goddard Space Flight Center.

References
Le Vine, D.M., de Matthaeis, P., Ruf, C.S., and Chen, D.D. (2014). Aquarius RFI Detection and Mitigation Algorithm: Assessment and Examples, IEEE T. Geosci. Remote, 52 (8).
Le Vine, D. and de Matthaeis, P. (2014). Aquarius Active/Passive RFI Environment at L-band, IEEE T. Geosci. Remote Let, 11 (10), 1747-1751.
Soldo, Y., Le Vine, D.M., de Matthaeis, P. and Richaume, P., 2017. L-Band RFI Detected by SMOS and Aquarius, IEEE T. Geosci. Remote, 55 (7), 4220-4235.
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