Active remote sensing and passive remote sensing are two primary approaches used in remote sensing systems to capture information about the Earth’s surface. These methods differ in their mode of operation, energy source, and data acquisition techniques. The following table presents a comparison between active remote sensing and passive remote sensing systems:
| Feature | Active Remote Sensing | Passive Remote Sensing |
|---|---|---|
| Energy Source | Emits its own energy or signal towards the target and measures the reflected or backscattered energy | Measures the naturally occurring energy or radiation emitted or reflected by the target itself |
| System Components | Consists of a transmitter and a receiver, with the transmitter emitting energy and the receiver detecting the energy that returns from the target | Comprises a sensor or instrument that captures the naturally emitted or reflected energy from the target |
| Data Acquisition | Captures both the emitted energy and the energy reflected or backscattered by the target, providing direct control over the energy source and its parameters | Collects only the naturally occurring energy emitted or reflected by the target, without active manipulation of the energy source |
| Examples of Systems | Synthetic Aperture Radar (SAR), LIDAR (Light Detection and Ranging) | Passive optical sensors, such as multispectral or hyperspectral sensors, thermal sensors, or radiometers |
| Data Characteristics | Provides information on the time delay between the emitted signal and the return signal, which can be used to infer properties such as distance, surface roughness, or topography | Measures the intensity and spectral characteristics of the reflected or emitted energy to derive information about surface properties, composition, or temperature |
| Application Examples | Used for mapping topography, measuring atmospheric properties, assessing vegetation structure, detecting changes in surface elevation, or studying ocean currents | Applied in land cover classification, vegetation analysis, urban monitoring, mineral exploration, climate studies, or environmental monitoring |
| Advantages | Offers active control over the energy source, allowing for precise timing and control of data acquisition, and providing information on target properties not available in passive systems | Provides a wide range of data from the natural energy emitted or reflected by the target, allowing for the study of the target’s inherent characteristics |
| Limitations | Requires more complex systems and data processing techniques due to the need for signal transmission and reception | Limited to the availability and quality of the naturally emitted or reflected energy, which can be influenced by external factors such as atmospheric conditions or surface properties |
| Data Interpretation | Analyzes the characteristics of the returned or backscattered energy to extract information about target properties and features | Analyzes the spectral and radiometric properties of the captured energy to derive information about target composition, temperature, or other properties |
| Data Resolution | Provides high-resolution data due to the ability to control the energy source and perform accurate measurements of the return signal | Resolution depends on the capabilities of the passive sensor or instrument used, which may vary in spatial, spectral, or radiometric resolution |
Conclusion: Active remote sensing and passive remote sensing are two distinct approaches used in remote sensing systems. Active remote sensing systems emit their own energy towards the target and measure the reflected or backscattered energy, while passive remote sensing systems capture the naturally occurring energy emitted or reflected by the target. Both approaches have unique advantages and applications, with active remote sensing offering precise control over the energy source and the ability to derive additional information not available in passive systems, while passive remote sensing provides a wide range of data reflecting the target’s inherent characteristics. The choice between active and passive remote sensing depends on the specific objectives, target properties, and data requirements of the application.
