Modern Surveying Technologies MCQ with answer and solution

Concept

Satellites are classified by the type of sensors they carry, such as optical or microwave sensors. Microwave satellites use long-wavelength signals that can see through clouds and work at night.

Step-by-step solution

1. Identify the satellites mentioned: ERS (European Remote Sensing), Envisat, Sentinel-1, and RISAT (Radar Imaging Satellite). 2. Check the sensors used by these satellites: They all carry Synthetic Aperture Radar (SAR). 3. SAR operates in the microwave region of the electromagnetic spectrum (wavelengths from 1 mm to 1 m). 4. Unlike optical satellites that need sunlight, these microwave satellites provide their own energy or detect microwave radiation. 5. Therefore, these are classified as microwave satellites. Answer: (D) Microwave

Explanation

ERS, Envisat, Sentinel-1, and RISAT use radar technology to map the Earth. Radar uses microwave signals which can pass through clouds, smoke, and rain. This makes them very useful for monitoring floods or forests in any weather, day or night.

Why the other options are wrong

A: Optical satellites use visible light and cannot see through clouds. B: Passive satellites only receive naturally available energy; many of these (like RISAT) are active radar systems. C: Thermal satellites detect heat (Infrared) emitted by objects, not microwave signals.

Shortcut

Remember 'RISAT' stands for Radar Imaging Satellite; Radar always works on Microwave frequencies.

Common mistake

Students often think all imaging satellites are 'Optical' because they produce pictures, but radar pictures are 'Microwave' data.