Observations of Microwave Brightness Temperature Contamination: A Global Perspective

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Observations of Microwave Brightness Temperature
ContaminationA Global Perspective

• January 7, 2005
• David Kunkee

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Outline

• C-band Missions SMMR, AMSR-E
• X-band Missions SMMR, TMI, AMSR-E
• RFI
• Europe
• North America
• Far East
• Oceans
• Summary

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C-Band Measurements

• Scanning Multichannel Microwave Radiometer
• Joint project involving Goddard Space Flight
  Center (GSFC) and Jet Propulsion Laboratory (JPL)
• Launched October 1978 Nimbus 7
• 6 GHz Channel 6.6 GHz and 250 MHz RF BW DSB
• 10 GHz Channel 10.69 GHz and 250 MHz RF BW DSB
• TB Data was reprocessed to improve calibration
  after the mission terminated
• Data for this study was obtained from the
  National Snow and Ice Data Center (NSIDC)
• Advanced Microwave Scanning Radiometer (AMSR) - E
• Built by Mitsubishi for NASDA (JAXA)
• Launched May 2002 NASA EOS Aqua
• 6 GHz Channel 6.9 GHz and 350 MHz BW
• 10 GHz Channel 10.65 GHz and 100 MHz BW

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SMMR Characteristics
From http//nsidc.org/data/docs/daac/nsidc0036_smm
r_pathfinder_tbs.gd.html
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Europe at 6 GHz
SMMR
6.6 GHz
AMSR-E
6.9 GHz
2003
1979
2004
1987
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6 GHz Over Europe

• SMMR Data over Europe
• Large area of saturation centered over Berlin
  area
• Likely originated from tropo-scatter system(s)
  that are no longer in operation
• Radio link between W. Germany and Berlin
• SMMR Data over North Atlantic (not shown)
• Investigators noted anomalies in SST retrievals
  over the North Atlantic using AMSR data
• Up to gt20 K perturbations in SST
• Attributed to RFI not seen in AMSR data
• AMSR Data over Europe
• Several smaller areas of saturation appear
• Appear as point sources affecting a smaller
  region
• Contamination appears in several locations over
  mainland Europe but not in the area of Berlin

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North America at 6 GHz
SMMR
6.6 GHz
AMSR-E
6.9 GHz
2003
1979
2004
1987
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Far East at 6 GHz
SMMR
6.6 GHz
AMSR-E
6.9 GHz
2003
1979
2004
1987
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Far East at 6 GHz

• SMMR Data
• Indicates a region of saturated Brightness
  temperature near Vladivostok
• Japan is relatively interference free
• AMSR Data
• No interference near Vladivostok
• Several prominent areas of brightness temperature
  contamination over Japan
• Notes on 6 GHz Overall
• Many differences in interference regions could be
  attributable to different observation frequencies
  of SMMR and AMSR
• Does not explain differences between SMMR-AMSR
  data over North America
• Development of radio service occurred between
  1987 and 2002
• 6.4 7.1 GHz Region allocated to Fixed Service
  (FS) and Mobile Service (MS)

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X-Band Measurements

• Scanning Multichannel Microwave Radiometer (SMMR)
• GSFC and JPL
• Launched October 1978 Nimbus 7
• 10 GHz Channel 10.69 GHz and 250 MHz RF BW DSB
• Tropical Rainfall Measuring Mission (TRMM)
  Microwave Imager (TMI)
• Built by Hughes Space and Communications (Now
  Boeing Satellite Systems)
• Launched November 1997 from Tanaga-shima Japan
  into a 35 incl. orbit
• 10 GHz Channel 10.65 and 100 MHz BW
• Advanced Microwave Scanning Radiometer (AMSR) - E
• Built by Mitsubishi for NASDA (Now JAXA)
• Launched May 2002 NASA EOS Aqua
• 10 GHz Channel 10.65 GHz and 100 MHz BW

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Europe at 10 GHz
SMMR
10.69 GHz
AMSR-E
10.65 GHz
2003
1979
2004
1987
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10 GHz over Europe

• SMMR Data
• No apparent RFI
• AMSR Data
• Several points of contamination over UK and Italy
• A few additional isolated points over other
  countries
• RFI at 10 GHz in Europe was not seen by TMI
  before AMSR-E operation
• TMI Orbit limited to 35 latitude
• AMSR and TMI passbands are the same 10.6 10.7
• Notes
• A radio service was apparently implemented in UK
  and Italy between 1987 and 2002 but not in France
  or Germany
• 10 GHz RFI over UK and Italy appears to be more
  severe than 6 GHz RFI
• Even with EESS allocation at 10 GHz and no
  Allocation at 6 GHz

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North America at 10 GHz
SMMR
10.69 GHz
AMSR-E
10.65 GHz
2003
1979
2004
1987
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Far East at 10 GHz
SMMR
10.69 GHz
AMSR-E
10.65 GHz
2003
1979
2004
1987
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Observations of RFI from TMI (10.65 V)
1998
RF interference with TMI for first several months
of operation. Black circles are to enhance the
visibility of the interference and do not
represent the actual extent of the interference.
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6 GHz RFI Over Ocean SMMR
Several regions were found where retrieved
SST standard deviation exceeded 15 C
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10 GHz RFI Over Ocean WindSAT
Geostationary Broadcast Satellite believed to be
operating near 10.71 GHz

• WindSat
• Built by the US Naval
• Research Laboratory
• Launched 06-Jan-2003
• 10 GHz Channel
• 10.55 to 10.8 GHz

The location and amplitude of RFI depends on
viewing geometry Impacts Sea Surface Winds
Sea Surface Temperature
Courtesy RSS Inc.
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Summary of Initial Observations

• SMMR and AMSR data show different regions of RFI
• Areas of contamination have changed over time
• 1987 Germany and Vladivostok
• 2003 UK, Italy, USA and Japan
• Monotonic increase in use of the radio spectrum
  is not necessarily the case for all parts of the
  spectrum
• Utilization of radio services and the services
  themselves change over time
• Some services may be phased out or replaced by
  different technology
• New radio services may be built and put into
  widespread service quickly
• Some differences may be explained by sensor
  characteristics
• SMMR and AMSR 6 and 10 GHz passbands are slightly
  different
• May explain some differences observed for
  isolated points of RFI
• Not likely to explain differences in areas
  showing general contamination such as NA at 6 GHz
  and UK and Italy at 10 GHz
• Frequency allocations are generally consistent
  across the range of observing frequencies of each
  sensor for each band

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Perspective

• Vulnerability of EESS Passive Users is
  Illustrated By C-band History
• What appears to be open spectrum can undergo
  widespread changes
• In contrast to the RF environment at 6-GHz, a
  better situation exists near 10.6 GHz for EESS.
  However
• EESS Allocation at 10.6 10.68 is shared with
  other services
• Frequency management has apparently kept this
  spectrum clear for EESS in N/A
• Observations at X-band over Europe suggest the
  impacts of frequency management on a per
  country basis.
• EESS should strive to obtain good neighbors
• Frequency managers need to be aware of special
  needs of passive users
• EESS users and scientists need to be aware of
  radio services operating in areas that may affect
  their measurements
• 10 GHz Illustrates the impact of Frequency
  Management
• EESS Operation in L- C- and X-band Poses
  Challenges ahead
• 3 Major EESS Missions are currently planned for
  L-band (1.400 1.427)

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Sources of RFI Are Very Different Each Band

• L-band
• Highly utilized area of the spectrum
• Protected band
• RFI to EESS due to spurious and out-of-band
  emissions, possibly including harmonics from many
  legally operating emitters
• radars, communications links, harmonics from UHF
  TV
• Some RFI may be very hard to track down passive
  inter-modulation
• C-band
• Highly utilized area of spectrum
• No EESS allocation
• RFI due to continuously operating
  communications/data links over land
• Easy to find the sources of RFI there are just
  too many of them
• X-band
• Highly utilized area of the spectrum
• RFI Highly variable globally over land

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What is Next?
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What is Next?

• Ultrawideband
• Approved for use from 3.1 to 10.6 GHz
• Standards controversy use the entire spectrum or
  a portion
• Applications expected to increase rapidly in the
  coming years
• 24 GHz Short Range Radar
• Collision avoidance
• May become also become widespread and ubiquitous

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• Back Up Slides

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Observations of RFI from TMI (10.65 H)
1997
RF interference with TMI for first several months
of operation. Black circles are to enhance the
visibility of the interference and do not
represent the actual extent of the interference.
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EMI produces very high measurements at 19 GHz for
both polarizations
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Anomalous polarization difference at 19 GHz
identifies EMI at 19 GHz between Julian day
204 and 238
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Anomalous frequency difference between 19 and 22
GHz identifies EMI at 22 GHz between Julian
days 236-238.