Radar/Radio Altimeters (RADALT) Flashcards
Radio Altimeter
Transmitter sends signals to the ground and waits for the reflection
This time taken is used to calculated the height AGL
Accuracy is to +/- 200ft
Not suitable for low level
Continuous Wave Radio Altimeters
Used for low level operations (up to 2500ft)
Radio Altimeter Accuracy
To within +/- 5% maximum error
Effect of Terrain on Radio Altimeters
Water is the best surface due to less attenuation
Weather Radar
Generally use the X band which is a SHF transmission of 9350 MHz
Some use the C band for better penetration
Consists of a flat plate or parabolic dish antennae
Weather Radar Range Resolution
The pulse length determines the minimum range as the device can only transmit or receive
Pulse length also determines the ability to distinguish between targets at the smae altitude and bearing but different distances
Pulse Repetition Frequency (PRF)
Pulses per second
Determines the maximum range as adequate time must be allowed for returns before next pulse transmitted or antenna moved to next sweep position
Range Attenuation
The power of the transmitter slightly affects the range but not much due to attenuation
Precipitation Attenuation
Suffers from heavy attenuation through storm cells, disguising/masking bad weather
Rain absorbs and weakens radar returns and image can bear little resemblance to the real storm
Atmospheric Attenuation
Absorbed by dust/pollutants
Azimuth Resolution
Unable to distinguish two targets separated by less than a beam width at the same distance
Weather Radar Antenna
Produces a 3 degree diameter beam
Size determines beam width and how narrow the Radar can focus
A large dish produces a narrow beam and increases the azimuth resolution
Antenna Tilt Angle
+/- 15 degrees
Relative to the Earth’s horizon not the aircraft pitch
Beam Width Formula
Beam-width (ft) = Range (nm) x 300
Radar Shapes
Fingers/nodules = hail
Scallops = severe turbulence
Hooks = tornadoes
