Weather Radar

Question 1

How does a weather radar receive large water droplets, cumulus and cumulus-nimbus clouds and not fine mist and small water particles?

Answer 1

At very short wavelengths fine mist, haze and clouds comprising tiny water droplets will not reflect radio waves, wheres large water drops and hail in large cumulus and cumulus-nimbus clouds are large enough to give echos

Question 2

What is the suitable wavelength and frequency for weather radar?

Answer 2

Suitable wavelength for reflection is between 3 cm and 10 cm, in the SHF between 9 an 12 GHz,

Question 3

What will happen if we use a wavelength below 3 cm?

Answer 3

Below 3cm more energy is absorbed than reflected.

Question 4

What will happen if we use a wavelength above 10 cm?

Answer 4

Above 10cm the waves are too large to be reflected

Question 5

For given amount of power, which weather radar wavelength will give best range and presentation?

Answer 5

3 cm

Question 6

What happens to the beam width at range?

Answer 6

It widens, making two targets look like one

Question 7

What wavelengths will provide a narrower beam width?

Answer 7

Shorter wavelengths

Question 8

What type of beam is used by the weather radar?

Answer 8

Conical pencil beam

Question 9

What type of antenna does newer weather radar versions use?

Answer 9

More modern versions use a flap plate which, for a given diameter and wavelength, is able to create a narrower beam.

Question 10

What type of antenna does older weather radar versions use?

Answer 10

Older versions make use of a parabolic dish containing a centre dipole

Question 11

Does a larger scanner size increase or decrease beam width?

Answer 11

The bigger the dish(bandwidth), the narrower the beam width.

Question 12

What type of beam is used for ground mapping?

Answer 12

The cosecant beam(fan shaped)

Question 13

When flying over high ground what type of error would occur?

Answer 13

Radar shadow, which is a false image which may be indicated as water.

Question 14

Normal angle of tilt used for ground mapping that will provide the best range?

Answer 14

5 degrees down from the horizontal

Question 15

Maximum range for ground mapping using the cosecant beam?

Answer 15

60nm

Question 16

Tilt limit of the dish?

Answer 16

15 degrees

Question 17

Define the MAN function?

Answer 17

Used for mapping in conjunction with tilt control. In this function the conical pencil weather beam is used, thus greater ranges are obtained than when using MAP

Question 18

Greatest range that can be obtained using the MAN function?

Answer 18

150nm

Question 19

Define the CONTOUR function?

Answer 19

This position is used on monochrome displays to examine clouds in detail by the use of an iso-echo display.

Question 20

What does the iso-echo display indicate?

Answer 20

Areas of large water drops, where severe turbulence can be expected. Clouds will appear to have black holes in them, these are the areas of strongest echoes and therefore the areas of extreme turbulence.

Question 21

How wide is the ground map(MAP) horizontally?

Answer 21

85 degrees

Question 22

What mnemonic can we use to remember the correct sequence of colours?

Answer 22

GYRM

Question 23

In weather radar the use of a cosecant beam in ‘Mapping’ mode enables:

Answer 23

scanning of a large ground zone producing echoes whose signals are practically independent of distance

Question 24

The antennae of modern airborne weather radars are stabilized by means of inputs from the aircraft’s FMS.

True or False?

Answer 24

False