National Aeronautics and Space Administration

Glenn Research Center

What Are We Measuring?

As NASA’s frequency utilization for deep space and near earth are in the 2 GHz frequencies and above, the propagation effects being characterized are due primarily to contributions from the troposphere and include atmospheric attenuation, rain attenuation, gaseous absorption, and atmospheric noise temperatures. Particularly, as spectrum use progresses towards the Ka-band frequencies (26 GHz and above), increased losses due to rain attenuation and atmospheric noise temperature can degrade ground-to-space communications link margins and cause loss of signal acquisition and data return.

The primary atmospheric effects being characterized at the NASA facilities of interest include the following:

  • Rain (Snow) Fade – the contribution of rain (or snow, ice) to the total signal path attenuation
  • Gaseous Absorption – the contribution of gaseous components of the atmosphere (water vapor, clouds, oxygen, etc.) to the total signal path attenuation
  • Brightness Temperature – the contribution of the atmosphere to the increase of signal noise
  • Phase Decorrelation – the contribution of the atmosphere to the increase in phase noise (decoherence)
  • Scintillation – the phenomenon of rapid fluctuations in signal power through the atmosphere
  • Depolarization – the effect of the atmosphere on the polarization of the signal
  • Site Diversity – the improvement in system gain for spatially separated single aperture antenna systems
Table 1: List of Past and Current Propagation Measurement Campaigns Conducted by NASA and the Relevant Phenomenon Characterized
Location Satellite Used Frequency: Station Years Characterization
Fairbanks, Alaska ACTS
  • 20.2 GHz : 5 st. yrs.
  • 27.5 GHz : 5 st. yrs.
  • Gaseous Absorption (Cloud Effects)
  • Scintillation
Vancouver, British Columbia ACTS
  • 20.2 GHz : 5 st. yrs.
  • 27.5 GHz : 5 st. yrs.
  • Rain Fade
  • Scintillation
Fort Collins, Colorado ACTS
  • 20.2 GHz : 5 st. yrs.
  • 27.5 GHz : 5 st. yrs.
  • Rain Fade/Snow Fade
  • Depolarization
Tampa, Florida ACTS
  • 20.2 GHz : 5 st. yrs.
  • 27.5 GHz : 5 st. yrs.
  • Rain Fade (Subtropical Zone)
  • Site Diversity
Norman, Oklahoma ACTS
  • 20.2 GHz : 5 st. yrs.
  • 27.5 GHz : 5 st. yrs.
  • Rain Fade
  • Scintillation
Clarksburg, MD ACTS
  • 20.2 GHz : 5 st. yrs.
  • 27.5 GHz : 5 st. yrs.
  • Rain Fade
  • Scintillation
Ashburn, VA ACTS
  • 20.2 GHz : ~1 st. yr.
  • Depolarization
Humacao, Puerto Rico UFO 09
  • 20.7 GHz : 1.5 st. yrs.
  • Rain Fade (Tropical Zone)
Goldstone, California ANIK F2 

DBS

  • 20.2 GHz : ONGOING
  • 12.5 GHZ : ONGOING
  • Phase Decorrelation
Las Cruces, New Mexico ANIK F2
ACTS
  • 20.2 GHz : ONGOING
  • 27.5 GHz : 5 st. yrs.
  • Phase Decorrelation
  • Gaseous Absorption
GUAM, USA UFO 08
  • 20.7 GHz : ONGOING
  • Rain Fade/Gaseous Absorption
  • Phase Decorrelation
  • Site Diversity
Madrid, Spain DBS
  • 12.5 GHz : TBD
  • Phase Decorrelation
Canberra, Australia DBS
  • 12.5 GHz : ONGOING
  • Phase Decorrelation
Svalbard, Norway —-
  • 26.5 GHz : ONGOING
  • Gaseous Absorption
  • Brightness Temperature