Remote Sensing Sensors:

Remote sensors collect data by detecting the energy that is reflected from Earth. These sensors can be on satellites or mounted on aircraft. Remote sensors can be either passive or active.

Types of Sensors:

Two types of remote sensing sensors, one is Imaging Sensor and another is Non-Imaging Sensors. Imaging sensors are divided in two part as passive sensors and active sensors.

Imaging Sensors:

• Passive sensors : collect electromagnetic radiation in the visible and infra-red part of the spectrum:

• Photographic Camera
• The Optical Scanners
• Across Track Scanners
• Along Track Scanners
• The Thermal Scanner

Figure 1: Passive sensors

• Active sensors : generate their own radiation:

• Air-borne RADAR (Radio Detection and Ranging)
• Space borne RADAR: RISAT-1, RADARSAT
• Lidar (Light Detection and Ranging)

Figure 2: Active sensors

Non-Imaging Sensors:

• Passive sensors : Spectro-radiometers

• Active sensors : 
• Laser Distance Meter
• Laser Water Depth Meter
• Microwave Altimeter

Across Track Multispectral Scanning:

• Whisk broom scanning.
• Scan the Earth in a series of lines.
• The lines are oriented perpendicular to the direction of motion of the sensor platform (i.e. across the swath).
• Data are collected within an arc below the system typically of some 90º to 120º.

• Multispectral scanner (MSS) and thematic mapper (TM) of LANDSAT, and Advanced Very High Resolution Radiometer (AVHRR) of NOAA are the examples of Whisk Broom scanners.

 

Figure 3: Across Track Multispectral Scanning

Along Track Multispectral Scanning:

•  Push broom scanning
•  Scan the Earth in a series of lines.
•  This also use the forward motion of the platform to record successive scan lines and build up a two dimensional image, perpendicular to the flight direction.
•  Linear arrays normally consist of numerous charge-coupled devices (CCDs) positioned end to end.

•  Linear imaging self scanning (LISS) and Wide Fielf Sensor (WiFS) of IRS Series, and High Resolution Visible (HRV) of SPOT-1 are the examples of Push broom scanners.

 

Figure 4: Along Track Multispectral Scanning

Instantaneous field of view (IFOV): 

It is defined the solid angle through which a detector is sensitive to radiation (units is mrad). It is defined as angular substance at a given instant of the limiting detector aperture at the second principal point of the system. IFOV is both a linear and angular quantity.

            IFOV = D/F radian

            GRE = (D/F) x H meter

   Where,

            D=detector dimension, F=focal length, and H=flying height

Figure 5: Instantaneous field of view (IFOV) and Field of view (FOV)

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