FINAL REPORT - Stakeholders - Ofcom

modern civil aircraft to determine the start of the flare procedure, or as inputs to the
Ground Proximity Warning System (GPWS). For these applications, both of which have
high ‘safety-of-life’ criticality, good performance and low interference are vital. The use of
a wide frequency band (200 MHz) is an essential feature in achieving high orders of
interference rejection, particularly in densely populated areas. ICAO Doc 9718 states
although studies in 1990 reported that accuracy requirements may be met with less than
200 MHz bandwidth, it now appears that future requirements may require more than 200
MHz.
No substitutes exist for this technology – it has a unique role in the modern aviation
operational concept.
Standards for radar altimeters have been in existence since the mid-70s (RTCA MOPS
for radar altimeters and GPWS – DO-155 and DO-161A).
Issues
Although use of the band is exclusively reserved for airborne radio altimeters (and the
associated transponders on the ground), passive sensing in the earth exploration-satellite
and space research services is allocated on a secondary basis. Research has been ongoing
since 1998 into the issues of band-sharing with space-based passive earth
sensors. Studies have recommended that the use and development of ARNS should be
unconstrained by EESS, and that no protection can be claimed by EESS. As the power
differential is reasonably large in favour of radar altimeters, interference from EESS is
minimal. The issue is therefore whether ARNS requires such a large bandwidth. As
mentioned above, ICAO believes it is an essential feature in ensuring the performance
and accuracy of the safety-of-life critical ARNS, and therefore should be maintained.
As radar altimeters experience interference in proportion to the density of surrounding
traffic (particularly above or below), it is likely that performance will be degraded in the
future as traffic density increases. Therefore, proposals have been developed to allocate
further bandwidth to ARNS – this may be debated at WRC2007.
3.4.13 Note on Mobile Navigation Aids – Airborne Radar
Airborne Doppler Radar operates in the bands 8.750 – 8.850 GHz and 13.25-13.4 GHz.
Airborne Weather Radar operates in the band 5.350 – 5.470 GHz. These allocations
apply to all three ICAO regions. Other uses of the same band for earth explorationsatellite
and space research do so as long as they cause no interference with, or
constrain, the aeronautical use.
Doppler navigation systems are widely used for specialised applications such as
identification of ground speed and flight track control.
Current weather surveillance is based on an onboard weather radar system capable of
detecting convective activity, precipitation density and turbulence in the aircraft vicinity.
The purpose is linked directly to the safety of flight by providing a means of avoiding
potentially harmful weather conditions. It also supports greater flight efficiency and
passenger comfort.
The main advance is expected to be the progressive introduction of predictive windshear
facilitated by the advance in the Doppler systems employed by weather radar. Wind shear
is a sudden change in wind direction or velocity, often found around thunderstorms or in
unstable atmospheric conditions. Its worst representation are the so called microbursts,
vertical columns of air rapidly descending towards the ground, and extremely dangerous
because they may be capable of overcoming the maximum climbing performance of the
aircraft.
Local weather conditions (including fog, smoke, wind and lightening activity) can be
obtained via voice communications from the ground or other aircraft.
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