UPSC Prelims 2024 Q34: Uses of Radar — Weather, Wildlife, Airports
Consider the following activities:
1. Identification of narcotics on passengers at airports or in aircraft
2. Monitoring of precipitation
3. Tracking the migration of animals
In how many of the above activities can the radars be used?
- Only one
- Only two
- All three
- None
Answer: (b) Only two
Statement-wise explanation
- 1: incorrect — Radar sends out radio waves and reads the echoes that bounce back from objects. That tells it where something is, how far away and how fast it moves. It cannot tell what chemical a substance is made of, so it cannot pick out a drug hidden on a passenger. Airports find narcotics with trace detectors based on ion mobility spectrometry, X-ray baggage scanners, physical searches and sniffer dogs.
- 2: correct — Monitoring precipitation is the main job of weather radar. The India Meteorological Department (IMD) runs a network of Doppler Weather Radars that update every few minutes. Dual-polarisation radars can tell rain from hail and drizzle, estimate how much rain is falling, and support nowcasts of heavy rain up to a few hours ahead.
- 3: correct — Flying birds, bats and insects return radar echoes just as raindrops do. The US NEXRAD network of about 160 Doppler weather radars is used to map bird migration, including its timing, direction, speed and stopover sites. The field is called radar ornithology, or radar aeroecology. Small tracking radars are also used to follow individual insects such as bees.
How to eliminate
You can solve this from what radar physically does. Radar detects objects, measures their distance and tracks their movement. It does not tell you what a substance is made of. Raindrops and migrating flocks are moving objects in the air, so statements 2 and 3 fit. Statement 2 is basic knowledge (Doppler Weather Radar), which already rules out the option 'None'. Statement 1 asks radar to identify a chemical (narcotics) on a person, and that needs chemical sensing such as trace detectors, X-ray or sniffer dogs. Don't be misled by the airport setting: airports use radar for air traffic control, but not to screen passengers for drugs. The rule to remember is that radar answers 'where, how far, how fast' and never 'what substance'.
Know more
RADAR stands for RAdio Detection And Ranging. A transmitter sends pulses of radio or microwave energy. Anything in the beam (a raindrop, an aircraft, a bird) scatters some energy back. The time the echo takes gives the distance. The strength of the echo gives the size or number of targets. A Doppler radar also measures the change in frequency of the echo, which gives the speed of the target towards or away from the radar.
Weather radar in India. IMD runs Doppler Weather Radars (DWRs) in three bands:
| Band | Wavelength | Typical use |
|---|---|---|
| S-band | ~10 cm | Long range (~500 km); cyclones on the coast |
| C-band | ~5 cm | Medium range; most inland stations |
| X-band | ~3 cm | Short range; hills, cities, local storms |
Dual-polarisation radars send both horizontal and vertical pulses. From the shape of the echo they can tell rain from hail or snow and estimate rainfall more accurately.
What radar can and cannot do
| Can | Cannot |
|---|---|
| Track aircraft, ships and missiles (air traffic control, AEW&C systems such as Netra) | Identify chemicals or drugs |
| Track rain, hail and cyclones | See through good conductors such as metal |
| Track bird, bat and insect migration | Detect things hidden underground beyond a few metres (ground-penetrating radar is the limit) |
| Image the Earth through cloud (Synthetic Aperture Radar, e.g. NISAR, RISAT) |
Satellite tags and GPS collars also track animals, but they work by the animal carrying a transmitter. Radar needs nothing on the animal.
NCERT Concepts to Revise
- Precipitation: Statement 2 is about monitoring precipitation. Knowing what counts as precipitation (rain, snow, hail) shows what a radar would have to detect.
- India Meteorological Department: IMD is the agency that runs India's weather radar network, which is the official setting for statement 2.
- Weather forecasting: Weather forecasting, especially short-range nowcasting, is the main reason weather radar networks exist.
- NISAR: NISAR is a radar satellite. It shows radar being used well beyond airports and helps frame what radar can and cannot sense.