Clutter is a term used for unwanted echoes in electronic systems, particularly in reference to radars.wikipedia
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### Clutter folding

*Clutter folding
Clutter folding is a term used in describing "clutter" seen by radar systems.

Clutter is a term used for unwanted echoes in electronic systems, particularly in reference to radars. The clutter return from the volume is calculated as for the normal radar equation but the radar cross section is replaced by the product of the volume backscatter coefficient, \eta, and the clutter cell volume as derived above.

### Turbulence

turbulentturbulent flowatmospheric turbulence
Such echoes are typically returned from ground, sea, rain, animals/insects, chaff and atmospheric turbulences, and can cause serious performance issues with radar systems.

### Chaff (countermeasure)

chaffWindowchaff rocket launchers
Such echoes are typically returned from ground, sea, rain, animals/insects, chaff and atmospheric turbulences, and can cause serious performance issues with radar systems.

### Independence (probability theory)

independentstatistically independentindependence
Assume that the clutter fills the cell containing the target, that scatterers are statistically independent and that the scatterers are uniformly distributed through the volume.

The clutter return from the volume is calculated as for the normal radar equation but the radar cross section is replaced by the product of the volume backscatter coefficient, \eta, and the clutter cell volume as derived above.

### Sinc function

sinccardinal sine functionnormalized sinc function
In practice the beam shape will approximate to a sinc function which itself approximates to a Gaussian function.

### Gaussian function

Gaussianbell curvegaussian curve
In practice the beam shape will approximate to a sinc function which itself approximates to a Gaussian function.

### Beam diameter

beam widthhalf power beam widthD4σ or "second moment" width
The correction factor is found by integrating across the beam width the Gaussian approximation of the antenna.

### Antenna gain

gaindirective gaingain of an antenna
G_t = gain of the transmitting antenna

### Pulse compression

If pulse compression is used then the appropriate pulse duration to be used in the calculation is that of the compressed pulse, not the transmitted pulse.

### Antenna aperture

apertureaperture efficiencyeffective area
A_r = effective aperture (area) of the receiving antenna

### Distributed antenna system

DASdistributed antenna system (DAS)distributed-antenna systems
DAS antenna elevations are generally at or below the clutter level, and node installations are compact.

### Moving target indication

moving target indicatorground moving target indicationMTI
Moving target indication (MTI) is a mode of operation of a radar to discriminate a target against the clutter.

Continuous-wave (CW) radar uses Doppler, which renders the radar immune to interference from large stationary objects and slow moving clutter.

### Look-down/shoot-down

look downlook down shoot downlook-down
That reflection and the ensuing "cluttered" display overwhelms human operators and computing systems (see ground clutter ).

Radar signal processing benefits from STAP in areas where interference is a problem (i.e. ground clutter, jamming, etc.).

### Rockwell B-1 Lancer

B-1B-1BB-1B Lancer
This tactic greatly reduces radar detection distances through the use of terrain masking; using features of the terrain like hills and valleys, the line-of-sight from the radar to the bomber can be broken, rendering the radar (and human observers) incapable of seeing it. Additionally, radars of the era were subject to "clutter" from stray returns from the ground and other objects, which meant a minimum angle existed above the horizon where they could detect a target.

This so-called dual polarization allows the radar to distinguish between rain, hail, and snow, something the horizontally polarized radars cannot accurately do. Early trials showed that rain, ice pellets, snow, hail, birds, insects, and ground clutter all have different signatures with dual polarization, which could mark a significant improvement in forecasting winter storms and severe thunderstorms.

### Radar in World War II

This had been anticipated and was countered to some degree with a series of shorter range stations built right on the coast, known as Chain Home Low (CHL). These systems had been intended for naval gun-laying and known as Coastal Defence (CD), but their narrow beams also meant that they could sweep an area much closer to the ground without "seeing" the reflection of the ground (or water) – known as clutter.

### McDonnell Douglas F-15 Eagle

F-15F-15 EagleF-15s
The F-15 has a "look-down/shoot-down" radar that can distinguish low-flying moving targets from ground clutter.

### Air traffic control radar beacon system

Air traffic control radarMode Smode S air traffic control radar beacon system
The controllers can use the information to identify radar returns from aircraft (known as targets) and to distinguish those returns from ground clutter.