Instruments designed to illuminate earth surfaces using specific wavelengths or wavebands of electromagnetic radiation are designated as________________?
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Answer: C. Active sensors
Explanation
Active sensors supply their own artificial illumination source to probe target surfaces. Instruments emit specific wavelengths of electromagnetic radiation toward the Earth. Sensors then measure the intensity and timing of the resulting backscattered radiation. Radar and LiDAR represent common active remote sensing systems operating today. Active systems operate independently of natural sunlight, enabling nighttime data acquisition. Laser altimeters transmit pulses to measure precise vertical elevations of terrain features.
Foresters use active LiDAR systems to map dense tropical forest canopy structures. Radar satellites image cloud-covered tropical regions where passive optical sensors fail. Topographic mapping relies on active laser pulses to penetrate vegetation and find ground. Passive sensors rely exclusively on natural sunlight rather than emitting artificial radiation. General sensors encompass both active and passive types without specifying the illumination source. Declaring none of these ignores the correct active sensor classification category.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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