सुदूर संवेदन प्रणाली जी नैसर्गिकरित्या उपलब्ध असलेल्या उर्जेचे मापन करते. त्याला ______ म्हणतात.

The correct answer is Option C (Passive sensors).

Key Points:
• Remote Sensing Sensor Classifications:
• Passive Sensors: These remote sensing instruments measure naturally available electromagnetic radiation that is reflected or emitted by objects on the Earth's surface. The Sun is the primary natural external source of illumination (e.g., optical multispectral sensors, thermal infrared sensors, radiometers).
• Active Sensors: These sensors emit their own electromagnetic energy pulses towards the target and measure the portion of energy reflected back (e.g., RADAR, LiDAR, SONAR).
• Passive remote sensing is constrained by day/night cycles and atmospheric cloud cover, whereas active systems operate independently of sunlight.
• Hence, systems measuring naturally available ambient energy are defined as Passive Sensors.
• Key Takeaway: Sensors measuring natural ambient/solar energy = Passive Sensors; sensors providing their own energy = Active Sensors.