Laboratory 5, Part 1

Weather Radar

Resources: Class Handouts, Simplified Radar Equation

1. The WSR-88D transmits pulses of energy rather than a continuous stream so target _______ can be determined.

a. range
b. shape
c. reflectivity
d. composition

(a) . For the WSR-88D, individual pulses of E-M energy are transmitted at constant, discrete time intervals which results in a listening period for the radar. This allows for target ranging.

2. The beam of the WSR-88D is a volume bounded by the points where the power ______ to ______ the peak power.

a. increases, one-half
b. increases, one-third
c. decreases, one-half
d. decreases, one-third

(c) Beamwidth is bounded by that region of the transmitted beam where the power decreases to 1/2 (or -3 dB) the peak power transmitted along the beam centerline.

3. Increased sensitivity of the WSR-88D at close ranges, as compared to distant ranges, is the result of __________ at close ranges.

a. more power transmitted
b. more attenuation
c. greater power density
d. less ground clutter contamination

(c) Power density is dependent on beam width and will decrease with range as the beam spreads.

4. Two sample volumes are located at 50 nm and 70 nm from a radar. They contain the same number and size particles. The power returned from 70 nm will be _______ from 50 nm. The reflectivity from 50 nm will be _______ from 70 nm.

a. greater than, less than
b. less than, greater than
c. greater than, the same as
d. less than, the same as

(d) Since reflectivity is range normalized, identical targets at differing ranges would have the same reflectivity. However, returned power and reflectivity have important differences. All things being equal (e.g. complete beam filling), two targets at different ranges with the same drop-size distribution will return different power levels to the radar with more (less) power from the close (distant) target.

5. The amount of power returned to a WSR-88D radar is _______ related to the power transmitted and _______ related to the target range.

See handout.

a. directly, directly
b. directly, inversely
c. inversely, directly
d. inversely, inversely

(b) The greater the power transmitted, the greater the power returned, which is a direct relationship. Also, as target range increases, returned power decreases, which is an inverse relationship.

6. The beamwidth for WSR-88D radars varies between 0.87° and 0.96° and is a function of the transmission wavelength and antenna diameter. If a radar has an antenna dish diameter of 28 ft and transmits at a frequency of 2800 MHZ, the beam width is approximately _______.

a. 0.88°
b. 0.90°
c. 0.92°
d. 0.96°

(c) See work.

7. Incomplete beam filling will result in the WSR-88D displaying reflectivity values _________ what the actual drop-size distribution would produce.

See handout.

a. higher than
b. lower than
c. identical to
d. comparable to

(b) Valid reflectivity estimates are dependent on complete beam filling. If a target does not fill the beam, the returned power will be underestimated, as will the reflectivity.

8. If Rmax = 250 nm and a target actually located at 275 nm was detected by the WSR-88D, the target would be displayed at ______ nm range on a 250 nm range Base Reflectivity Product.

a. 25
b. 27
c. 248
d. 275

(a) Rmax in this example is 250 nm which means that a target actually located at 275 nm is 25 nm beyond Rmax. The apparent range of the target is then 25 nm.