A Strategy for Active Remote Sensing Amid Increased Demand for Radio Spectrum (2015) / Chapter Skim
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8 Radio-Frequency Interference Issues for Active Sensing Instruments
8 Radio-Frequency Interference Issues for Active Sensing Instruments
Pages 161-188
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From page 161... ...
. This is the interference from other radio services impacting the performance of active science sensors.
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From page 162... ...
The sensitivity of a given sensor to RFI is also a function of the specific nature of the RFI experi enced. The existence of a wide range of active sensor techniques, as well as a wide variety of RFI environments encountered globally, conspire to make it difficult to characterize the RFI problem and the associated solutions.
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From page 163... ...
The bottom image shows same scene after RFI mitigation is employed, in this case largely successfully because of the narrow-band nature of the interference encountered. SOURCE: Courtesy of NASA/JPL-Caltech.
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From page 164... ...
Although it might be possible to locate some types of science measurements in sufficiently remote locations, this may be impractical for most airborne systems, and even more difficult for spaceborne systems. • Frequency avoidance.
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From page 165... ...
In some circumstances, it may be possible for science sensors to operate cooperatively with other services. For instance, a ground radar or communication system may agree to turn off or switch frequency when a science sensor is known to be present.
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From page 166... ...
This understanding can be a very difficult objective to achieve given the varied and evolving RF environment around the world today. SCIENCE SENSOR TRANSMIT RESTRICTIONS Through the spectrum regulatory process, operational restrictions are often imposed upon active science sensors so that they do not interfere with incumbent radio services.
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From page 167... ...
, aeronautical receive frequency radio navigation RS.1282: avoid FM pulsed wind profiler radars RS.1749: mitigation techniques to share with radiolocation and radio navigation radar systems L-band 1215-1300 Primary Radiolocation, RNSS, RS.1280: processing amateur (secondary) gain of search radars RS.1347: increase in loop SNR of RNSS receiver S-band 3100-3300 Secondary Radiolocation RS.1280: processing gain of search radars C-band 5250-5460 Primary Radiolocation (active RS.1280: processing and secondary)
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From page 168... ...
to share with radiolocation radars, compatibility with fixed service W-band 78000-79000 Primary Radiolocation, amateur, amateur-satellite, space research (space-to-Earth) W-band 94000-94100 Primary Radiolocation RS.1261: mitigation technique to protect radio astronomy in 86-92 GHz, feasible to share with radiolocation, limit band to cloud profile radars mm-band 133500-134000 Primary Radiolocation mm-band 237900-238000 Primary Radiolocation NOTE: Acronyms are defined in Appendix D
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From page 169... ...
Much of the resource material for this section came from an active sensing RFI workshop held at the Jet Propulsion Laboratory (JPL) on November 8, 2013, under the auspices of the committee.1 HF and VHF Bands Band Usage The IEEE Standard Letter Designations for Radio-Frequency Bands defines the HF band as between 3 and 30 MHz and the VHF band as being between 30 and 300 MHz.
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From page 170... ...
For airborne radar sounders exploring the depths of polar ice sheets and glaciers, no report of significant deleterious interference from external sources has come to the attention of the committee. Transmit Restrictions for Active Sensors at the HF/VHF Bands HF radars used for sensing ocean currents have encountered some issues with operational restrictions, but among other science operating sensors, no significant operational restrictions have come to the attention of the committee.
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From page 171... ...
algorithm, which is frequently used to remove the often-encountered narrowband interference present in science measurements at UHF. The AirMOSS project reports that, in the instances where a limited number of narrowband interferers is observed to degrade the image, the LMS RFI removal technique is very successful at cleaning up the data to allow their specific science requirements to be met.
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From page 172... ...
Transmit Restrictions for Active Sensors at the UHF Band/P-Band In general, airborne active sensors have been allowed to operate in the UHF band but are subject to some severe restrictions. The GeoSAR system is a case in point.
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From page 173... ...
The AirMOSS system, which operates at a much narrower bandwidth and spatial resolution, has been allowed to operate over all required science sites without notching the spectrum, but is nevertheless subject to severe transmit restrictions near government radars. The ESA BIOMASS UHF SAR radar, which operates in accordance with the EESS-Active frequency allocation of 432-438 MHz, has been denied permission to operate within line-of-sight field of view of the space object tracking radars in North America and Europe.
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From page 174... ...
Interference Environment for Active Sensors at the L-Band RFI is a well-known issue for science sensors operating at the L-band, particu larly over the world's developed population centers: North America, Europe, and East Asia (see Figure 8.4)
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types of systems. Globally, the RFI environment at the L-band has been observed to be growing steadily worse with time.
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RFI mitigation techniques have enabled JAXA science objectives to be met over most of the globe. The NASA L-band SMAP and planned NISAR missions are planning to use similar techniques for RFI mitigation.
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From page 177... ...
Although these measures can be seen as justifiable means to demonstrate that critical incumbent services will not be interfered with, the perception of many in the science community is that the criteria for interference are often ill defined, and, consequently, extreme conservatism is invoked at the expense of science measurements. (Again, it is noted that no instances or reports of L-band science sensors actually having interfered with incumbent services have come to the attention of the committee.)
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From page 178... ...
Transmit Restrictions for Active Sensors at the S-Band No ongoing difficulties with spectrum access at the S-band have come to the attention of the committee. C-Band Band Usage The IEEE Standard Letter Designations for Radio-Frequency Bands defines the C-band as between 4000 and 8000 MHz.
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From page 179... ...
. A major concern is that extension of mobile services to the 5350-5470 MHz band would eventually be applied worldwide.
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From page 180... ...
Transmit Restrictions for Active Sensors at the C-Band The ITU Radio Regulations have several footnotes at the C-band stating that the EESS-Active shall not claim protection from the radiolocation service in the 5250-5350 MHz band and that the EESS-Active shall not cause harmful interfer
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From page 181... ...
X-band science sensors share the band with terrestrial radio navigation radars and radiolocation tracking radars operating between 9300-9900 MHz. Interference Environment for Active Sensors at the X-Band Although some anecdotal discussion of RFI observed by X-band SAR came to the attention of the committee, this has not been reported to be much of a current problem.
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From page 182... ...
Although there has been interest in creating new allocations for EESS-Active in other regions of the spectrum, this proposal at the X-band represents perhaps the most significant near-term effort to expand the EESS-Active allocation rather than simply defend it. Ku-Band and K-Band Band Usage The IEEE Standard Letter Designations for Radio-Frequency Bands defines the Ku-band as between 12000 and 18000 MHz.
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From page 183... ...
in the EESS-Active band 13.25-13.4 GHz. These services represent a potential threat to science sensors either as future interference sources or as future spectral co-occupants that could impose transmit restrictions on active science systems.
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From page 184... ...
As with the Ku-band, it is currently difficult to assess the prospects of future measurements with respect to RFI. Transmit Restrictions for Active Sensors at the Ka-Band There are some restrictions on transmitted signals for science sensors at the Ka-band.
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From page 185... ...
Transmit Restrictions for Active Sensors at the W-Band There are restrictions on spectral access for science sensors in the W-band related to possible interference with radio astronomy (a passive radio science technique)
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Transmit Restrictions for Active Sensors at the Millimeter-Band There are restrictions on spectral access for science sensors in the mm-band. The lower mm-band at 133.5-134.0 GHz falls into the 130-134 GHz band, where the radio astronomy service has a primary allocation.
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From page 187... ...
Restrictions imposed in the lower-frequency UHF and L-bands are increasing with time. Finding 8.3: Whereas active science sensors routinely report interference from other nonscience sources, science sensors appear to rarely interfere with other services.
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data mining of currently operating science sensors. To the extent possible, this effort should be a collaborative one with other space and science agencies of the world.
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