IEEE Geoscience and Remote Sensing Magazine - March 2016 - 40

Technical committees
MICHAEL SPENCER ANd FAWWAZ ULABY

Spectrum Issues Faced by Active Remote Sensing
Radio frequency interference and operational restrictions

Message from FARS Technical Committee Chairs
Sidharth Misra and Paolo de Matthaeis
One of the main objectives of the Frequency Allocations in
Remote Sensing (FARS) Technical Committee (TC) has been to
inform IEEE Geoscience and Remote Sensing Society members of
the increasing spectrum challenges faced by the remote sensing
community. In the June 2014 issue of IEEE Geoscience and
Remote Sensing Magazine, we presented an overview of spectrum allocations and radio frequency interference management
techniques for passive remote sensing. This article, prepared
by FARS-TC members, summarizes the impact of interference on
active remote sensing systems. If you are interested in contributing or learning about issues such as these, please contact the
chairs of the FARS-TC.

T

he scientific users of radio frequencies must contend with the fact that the spectrum is becoming
increasingly crowded, which is in large measure due
to the advent of advanced affordable electronics and
mobile wireless technology. The growing demand for
bandwidth has sparked increased discussions in the
microwave remote sensing community of how to respond to this crowded spectrum environment and how
to deal with the consequent issues of radio frequency
interference (RFI). The National Research Council
(NRC) published a study in 2010, "Spectrum Management for Science in the 21st Century" [1], that examined the increasing difficulties encountered by passive microwave measurements in the presence of the
expanding worldwide commercial and governmental occupancy of the radio spectrum. The challenges
faced by passive sensors also have been summarized
in a 2014 IEEE Geoscience and Remote Sensing Magazine
Digital Object Identifier 10.1109/MGRS.2016.2517410
Date of publication: 15 April 2016

40

0274-6638/16©2016IEEE

article [2]. Recognizing that active microwave sensors
also face spectrum-related issues, NASA later commissioned the NRC to perform a similar study, "A Strategy
for Active Remote Sensing Amid Increased Demand
for Radio Spectrum," which was recently published in
July 2015 [3]. (In this article, the report will be abbreviated as the NRC Active Sensing Report.) This report
addresses the spectrum issues faced by active science
sensors, primarily radars, and makes recommendations to government, industry, and the remote sensing
community going forward. The report considers multiple types of active sensors including ground-based
operational weather radars, ionospheric sensing radar,
and radar astronomy. This article focuses on spectrum
topics related primarily to Earth remote sensing from
aircraft and spacecraft.
THE USE OF THE RADIO SPECTRUM
BY ACTIVE SENSORS
Active remote sensing-with its unique ability to investigate geophysical phenomena by exploiting the
amplitude, range delay, Doppler shift, and phase
changes in the reflected signal-is employed in a variety of earth science disciplines by a growing number of nations. These disciplines include atmospheric
science, weather prediction, oceanography, climate
studies, cryospheric monitoring, terrestrial ecology,
hydrology, seismology, as well as disaster assessment
applications. The choice of frequency for a given medium to be sensed (i.e., land, water, or atmosphere) is
dictated by the nature of the wave-medium interaction associated with the target as well as the transmission properties of any intervening medium, such as
the atmosphere for land remote sensing. Active Earth
remote sensing is currently employed at frequencies
as low as a few megahertz and as high as hundreds
of gigahertz and at many frequencies in between. For
example, low RF frequencies (i.e., long wavelengths)
ieee Geoscience and remote sensing magazine

march 2016



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