RAS question
Synthetic Aperture Radar (SAR) satellite can image Earth's surface:
Correct answer: (C) In all weather conditions, day and night.
A Synthetic Aperture Radar satellite can image Earth's surface in all weather conditions, day and night.
Explanation
SAR is not limited by the two main constraints of optical imaging: sunlight and clear skies. It sends its own microwave radar signals towards the surface, so it can work after sunset as well as during the day. NASA's NISAR mission concept explains that synthetic aperture radar produces high-resolution images and that radar penetrates clouds and darkness, allowing data collection day and night in any weather. This is why the all-weather, day-and-night option is correct. The same operating principle makes SAR useful for detecting soil moisture, floods and ship movements, and explains why Indian SAR missions such as RISAT-1, the RISAT-2 series and EOS-04 are important for Earth observation.
Why the other options are wrong
- (A) Clear weather is not required because microwave radar can penetrate clouds and rain, unlike optical sensors that depend on cloud-free views.
- (B) SAR is an Earth-observation technique for imaging the planet's surface, not a sensor restricted to ocean areas.
- (D) Daylight is not required because SAR carries its own radar source instead of relying on sunlight.
Concept
This tests the remote-sensing distinction between active microwave radar sensors and passive optical sensors. RAS repeats this idea because SAR links space technology with practical governance uses such as flood mapping, soil-moisture assessment and maritime monitoring.