Active vs. Passive Remote Sensing: Key Differences

remote sensing
active sensing
passive sensing
radar
optical sensor

Active and passive remote sensing are two approaches to acquiring information about the Earth’s surface and atmosphere from a distance, and they differ in the way they capture and measure data.

What is Active Remote Sensing?

In active remote sensing, the sensor emits its own radiation (usually in the form of pulses of energy, such as radar or laser beams) towards the target, and the sensor measures the reflected or backscattered energy. The system actively interacts with the environment.

The active system provides its own energy source, which is directed towards the target. Examples include radar systems and LiDAR (Light Detection and Ranging).

The timing of data acquisition is controlled by the sensor, as it actively sends out pulses of energy and measures the return time. This allows for precise control over when and where data is collected.

Applications: Common applications include terrain mapping, surface elevation measurement, and vegetation structure analysis. Radar systems are often used in active remote sensing applications.

Examples: Radar systems (e.g., Synthetic Aperture Radar or SAR), LiDAR, and sonar are examples of active remote sensing technologies.

Remote Sensing, Passive and Active

What is Passive Remote Sensing?

In passive remote sensing, the sensor detects and records the natural radiation emitted or reflected by the Earth’s surface without emitting any energy of its own. It relies on ambient sources of radiation, such as sunlight or thermal radiation.

Passive systems rely on external sources of energy, such as the sun, to illuminate the target. Examples include optical sensors and thermal infrared sensors.

Passive sensors capture data whenever the natural radiation is available. They are dependent on external factors, such as sunlight or thermal emissions, and do not provide control over the timing of data acquisition.

Applications: Common applications include optical imagery for land cover classification, vegetation health assessment, and thermal infrared imagery for temperature mapping.

Examples: Optical sensors (e.g., cameras, multispectral sensors), thermal infrared sensors, and radiometers are examples of passive remote sensing technologies.

Difference between active and passive remote sensing

Here are the key differences between active and passive remote sensing systems.

ParametersActive Remote SensingPassive Remote Sensing
Energy sourceSensor provides its own energy e.g. radar, LiDAR etc.Relies on external sources of energy e.g. sunlight
InteractionEmits energy towards the target and measures the reflected or backscattered energyDetects and records natural radiation emitted or reflected by surface of the Earth without emitting its own energy.
Timing of data acquisitionControlled by the sensorDependent on external factors e.g. sunlight availability
Precision and controlProvides precise control over when and where data is collected.Less control over the timing of data acquisition
ExamplesRadar systems (e.g., Synthetic Aperture Radar or SAR), LiDAR, sonarOptical sensors (e.g., cameras, multispectral sensors), thermal infrared sensors, radiometers
Applications or use casesTerrain mapping, surface elevation measurement, vegetation structure analysisLand cover classification, vegetation health assessment, temperature mapping
AdvantagesCan penetrate clouds and operate in adverse weather conditions, can achieve high spatial resolutionLess energy consumption, environment friendly, simple system, very cost effective
DisadvantagesConsumes more energy, complex system, more expensiveLimited performance in cloudy or obscured conditions, Lower spatial resolution

Conclusion

In summary, the primary distinction between active and passive remote sensing lies in whether the sensor actively emits energy or relies on ambient energy sources. Both approaches have their strengths and weaknesses, and the choice between them depends on the specific goals and requirements of the remote sensing application.

Optical Sensors: Advantages and Disadvantages

Optical Sensors: Advantages and Disadvantages

Explore the benefits and drawbacks of optical sensors, including sensitivity, environmental susceptibility, cost, and applications in remote sensing.

optical sensor
sensor
remote sensing
Remote Sensing: Applications and Benefits

Remote Sensing: Applications and Benefits

Explore remote sensing: how it works, its types (active/passive), key applications in environmental monitoring, agriculture, urban planning, and more.

remote sensing
environmental monitoring
urban planning