Types of Sensor

Types of Sensor

(1) Optical sensor

Optical sensors observe visible lights and infrared rays (near infrared, intermediate infrared, thermal infrared).  There are two kinds of observation methods using optical sensors: visible/near infrared remote sensing and thermal infrared remote sensing. a)               Visible/Near Infrared Remote Sensing The observation method to acquire visible light and near infrared rays of sunlight reflected by objects on the ground. By examining the strength of reflection, we can understand a conditions of land surface, e.g., distribution of plants, forests and farm fields, rivers, lakes, urban areas. During period of darkness, This method can not be observe. Also, clouds block the reflected sunlight, so this method can not be observed areas under clouds.

b)      Thermal Infrared Remote Sensing
The observation method to acquire thermal infrared rays, which is radiated from land surface heated by sunlight. Also it can observe the high temperature areas, such as volcanic activities and fires. By examining the strength of radiation, we can understand surface temperatures of land and sea, and status of volcanic activities and forest fires. This method can observe at night when there is no cloud.

(2)   Microwave sensor

Microwave sensors receive microwaves, which is longer wavelength than visible light and infrared rays, and observation is not affected by day, night or weather.   There are two types of observation methods using microwave sensor: active and passive. a) Active type The sensor aboard earth observation satellite emits microwaves and observes microwaves reflected by land surface. It is suitable to observe mountains and valleys. b) Passive type This type observes microwaves naturally radiated from land surface. It is suitable to observe sea surface temperature, snow accumulation, thickness of ice.