Remote Sensing Digital Image Processing and Sensor Resolution

Remote Sensing Digital Image Acquisition

The process of obtaining digital images from satellite sensors involves capturing electromagnetic radiation reflected or emitted from the Earth's surface.

Characteristics of Digital Images

Digital images are composed of a grid of small units called pixels. Each pixel represents the minimum area detected on the ground and corresponds to a specific intensity value, which determines its shade of gray.

Sensor Resolution Capabilities

Resolution measures a sensor's ability to discriminate detail. There are four primary types of resolution:

• Spatial Resolution: The pixel size, representing the smallest area that can be distinguished from its surroundings. This is highly variable.
• Temporal Resolution: The frequency of data updates for a sensor, ranging from minutes to days.
• Radiometric Resolution: The ability to discriminate changes in radiation intensity, measured by the total number of gray levels (e.g., 6 bits per pixel equals 64 shades of gray).
• Spectral Resolution: The distribution or spectrum of different wavelengths or bands a sensor can measure. Most satellites operate across specific bands.

Color Imaging Techniques

Multiband sensors allow for various combinations of three different bands to create color images:

• Natural Color (RGB 321): Band 3 is assigned to red, band 2 to green, and band 1 to blue. This combination can produce up to 16 million distinct colors.
• False Color (RGB 432): Band 4 is assigned to red, band 3 to green, and band 2 to blue. This technique enhances details, facilitating the study of vegetation vigor, mineral resources, water bodies, and urban areas.

Thermal Imaging

Thermal images are captured using sensors sensitive to infrared radiation emitted by clouds and all objects on the Earth's surface.