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8/10/2019 Prey Ent Are
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The ionosphere, an area of the atmosphere which extends from ~80 to ~1000 km, can
significantly affect the propagation of radio frequency (R! signals which pass through it or are
reflected "y it [Cannon, 1##$a% Cannon, 1##$"&' The effects are aried "ut include a"sorption,
refraction, retardation and scintillation' )t frequencies a"oe ~1 *+, the lower D region causes
a"sorption and the higher E and F regions cause a ariety of other effects' These effects, which
include refraction, signal group delay, signal phase adance, pulse "roadening and araday
rotation of the polarisation ector, all follow an inerse power law and are generally only
significant up to a frequency of ~- .+' /elow ~1 *+ radio systems "ounce their signals from
the tenuous D region% consequently although the height of the layer is important for system
operation, a"sorption is not an issue'igure 1' ystems affected "y the ionosphere
The dierse set of affected systems (igure 1! include groundground high frequency (+!
communications, groundspace communications, .2 (.lo"al 2aigation atellite ystems!,
such as .3 (.lo"al 3ositioning ystem! and .alileo 4 particularly singlefrequency systems,
+ oerthehorion radars, satellite altimeters and space"ased radars [Goodman and Aarons,
1##0&' + communications and radar systems rely on the ionosphere for their operation "ut also
hae to contend with its effects' *ost other systems are degraded "y the ionosphere and its
aria"ility "ut for certain specialist applications this aria"ility can "e exploited' 5oss of phase
lock and range errors in .2 are examples of such deleterious effects'
6f the ionospheric enironment were isotropic and sta"le in time, it would "e relatiely easy to
determine its effects on the propagation of R waes' 7nfortunately, this is not the case' The
spatial scales of inhomogeneities ary from thousands of kilometres to tur"ulence with scale siesof a less than a metre' 5ikewise, the temporal scales ary oer many orders of magnitude from
many years (solar cycle effects on ionospheric propagation! to hours or een minutes (the scale of weather phenomena!' )s a consequence of this aria"ility, timely and relia"le strategies are
required to "oth specify and accurately forecast the enironment and to assess the attendant
impact on the operational performance of the R systems' These strategies can "e used to
automatically apply corrections to a systems operating parameters or, ia a decision aid, adise
the user on a course of action that will improe a systems functionality [Cannon et al ', 1##&'
Satellite Altimetry
EQUATORIAL
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