The key difference between active and passive satellite sensors lies in their source of energy for detecting and measuring objects on Earth. Active sensors provide their own source of energy, while passive sensors rely on natural energy sources.
Here's a more detailed breakdown:
Active Sensors
- Energy Source: Active sensors emit their own energy signal (e.g., radar, laser) towards the target.
- Operation: They measure the energy reflected or backscattered from the target.
- Independence: They do not rely on external sources like sunlight, allowing for data collection at any time of day or night, and even through cloud cover.
- Examples:
- Radar: Uses radio waves to penetrate clouds and darkness.
- Lidar: Uses laser light to measure distances and create 3D models of the Earth's surface.
- Synthetic Aperture Radar (SAR): A type of radar that creates high-resolution images.
Passive Sensors
- Energy Source: Passive sensors detect and measure naturally occurring energy, such as sunlight reflected from the Earth's surface, or thermal radiation emitted by objects.
- Operation: They measure the intensity of the received energy within specific wavelengths.
- Dependence: They depend on external sources of energy (primarily solar radiation) and are often limited by weather conditions (e.g., clouds obstructing the view).
- Examples:
- Multispectral Scanners: Record energy in multiple bands of the electromagnetic spectrum.
- Radiometers: Measure the intensity of electromagnetic radiation.
- Cameras: Capture visible light images.
- Thermal Infrared Sensors: Detect heat emitted from objects.
Table Summarizing the Differences
| Feature | Active Sensor | Passive Sensor |
|---|---|---|
| Energy Source | Emits its own energy signal | Detects naturally occurring energy |
| Dependency | Independent of external energy sources | Dependent on external energy sources |
| Time of Day | Can operate day or night | Typically limited to daylight hours |
| Weather | Can penetrate clouds (some types) | Affected by cloud cover and atmospheric conditions |
| Examples | Radar, Lidar, SAR | Multispectral scanners, radiometers, cameras, thermal infrared sensors |
In summary, active sensors actively emit energy to analyze targets, providing independence from external sources, while passive sensors passively receive naturally available energy, limiting their operation based on available light and weather.
