Types of Remote Sensing: Passive vs. Active
Remote sensing is a critical technology used in various fields, including agriculture, to gather data from a distance. Understanding the types of remote sensing—passive and active—is essential for effectively applying these technologies in agricultural practices.
What is Remote Sensing?
Remote sensing involves collecting information about an object or area from a distance, typically using satellites or aircraft. The data collected can help in monitoring crop health, soil moisture, land use changes, and more.Passive Remote Sensing
Passive remote sensing relies on natural sources of energy, primarily sunlight. Sensors collect reflected or emitted radiation from the Earth’s surface. Here are some key features:- Source of Energy: Sunlight is the primary energy source. - Data Collection: Sensors measure the intensity of reflected light across different wavelengths. - Common Instruments: Satellite imagery (e.g., Landsat, MODIS), aerial photography.
Example of Passive Remote Sensing in Agriculture
When monitoring crop health, a satellite equipped with a multispectral sensor can capture images of a field. The Normalized Difference Vegetation Index (NDVI) can then be calculated to assess plant health by analyzing the difference between near-infrared and red light reflected by the crops. Healthy vegetation reflects more near-infrared light compared to stressed crops.Active Remote Sensing
Active remote sensing, on the other hand, involves the emission of energy from the sensor itself. This technology sends out signals (e.g., radar, lidar) and measures the energy that is reflected back. Here are some key features:- Source of Energy: The sensor generates its own energy, typically in the form of laser or microwave signals. - Data Collection: Sensors measure the time it takes for the emitted signal to return, which helps in determining the distance and characteristics of the object. - Common Instruments: Synthetic Aperture Radar (SAR), Light Detection and Ranging (LiDAR).