Active sensors in remote sensing offer significant advantages, primarily the ability to collect data regardless of time of day or weather conditions and to utilize wavelengths unavailable from natural sources.
Here's a breakdown of the key benefits:
-
Independent of External Illumination: Unlike passive sensors that rely on reflected sunlight or emitted thermal radiation, active sensors emit their own energy signal. This allows them to:
- Operate day and night: They can collect data at any time, irrespective of sunlight availability.
- Function in various weather conditions: They can penetrate clouds, fog, and rain, providing data even when passive sensors are ineffective. For example, Synthetic Aperture Radar (SAR) can "see" through clouds.
-
Control Over Illumination: Active sensors give researchers and operators control over the emitted signal's:
- Wavelength: Enables the use of specific wavelengths not readily available from the sun, such as microwaves used by radar systems. This is crucial for studying specific surface characteristics.
- Intensity: Allows for optimization of the signal strength for the target being observed, improving data quality.
- Polarization: Manipulating the polarization of the emitted signal can reveal information about the target's structure and orientation.
-
Penetration Capabilities: Some active sensors, like radar, can penetrate:
- Vegetation: Providing information about underlying terrain or the structure of the vegetation canopy itself.
- Dry soil: Revealing subsurface features.
-
Precise Distance Measurements: Technologies like LiDAR (Light Detection and Ranging) actively measure the distance between the sensor and the target. This enables:
- Creation of highly accurate elevation models (DEMs).
- Detailed mapping of terrain and object heights.
Here's a table summarizing these advantages:
| Advantage | Description | Example |
|---|---|---|
| Day/Night Operation | Data collection independent of sunlight. | SAR imagery at night |
| Weather Independence | Data collection possible through clouds and other atmospheric obstructions. | SAR monitoring of flooded areas |
| Wavelength Control | Ability to use specific wavelengths not available from natural sources. | Radar mapping using microwaves |
| Target Illumination Control | Optimization of signal intensity and polarization for specific targets. | Improved image contrast in radar data |
| Penetration Capabilities | Ability to penetrate vegetation or dry soil. | Radar mapping of subsurface features |
| Precise Distance Measurement | Creation of accurate elevation models and terrain mapping. | LiDAR-based DEMs |
In conclusion, active sensors provide significant advantages in remote sensing due to their independence from external illumination, their control over the emitted signal, their penetration capabilities, and their ability to provide precise distance measurements. These capabilities make them invaluable tools for a wide range of applications, including environmental monitoring, disaster management, and resource exploration.
