Digital Image Processing Image Enhancement Image Rectification Image Classification
1. Instruments used to record the data
2. From the effect of the atmosphere
Radiometric Corrections
Radiometric Corrections are carried out when an image
data is recorded by the sensors they contain errors in the
measured brightness values of the pixels. These errorsare referred as radiometric errors and can result from the :
Geometric Corrections
Raw digital images often contain serious geometricaldistortions that arise from earth curvature, platformmotion, relief displacement, non-linearities in scanningmotion. The distortions involved are of two types:
1. Non-systematic Distortion 2. Systematic Distortions
Non-Systematic Distortions
These distortions are caused due to variations in spacecraft variables.
Distortion Evaluated from Tracking Data:
Non-Systematic Distortions
Distortion Evaluated from Ground Control :
Altitude Variation
Pitch RollYaw
1. Locating Ground Control Points
2. Resampling Methods
• Nearest Neighbor
• Bilinear Interpolation
• Cubic Convolution
3. Image Correction using Mapping Polynomial
Correction Process for Non-systematic Distortions :
Non-Systematic Distortions
Systematic Distortions
1. Scan Skew
Geometric systematic distortions are those effects that are constant and can be predicted in advance. These are of three types:
3. Cross Track Distortion
2. Known Mirror Velocity Variation
Systematic Distortions
Atmospheric Corrections
Effect Of The Atmosphere on Radiation
Need for Atmospheric Correction
• Derive ratios in 2 bands of multi spectral image since the effect ofatmospheric scattering depends on the wavelength, the two channels will beunequally affected and the computed ratio will not accurately reflect the trueratio leaving the earth's surface
• When land surface reflectance or sea surface temperature is to bedetermined.
• When two images taken at different times and needed to be compared ormosaic the images .
Correction Methods
• Ignore the atmosphere• Collecting the ground truth measurements of target temperature, reflectance
etc and calibrating these values or quantities on the ground and the radiancevalues by the sensor.
• Modeling the absorption or scattering effects for the measurement of thecomposition and temperature profile of the atmosphere.
• Utilizing the information about the atmosphere inherent to remotely senseddata i.e. use the image to correct itself.
Correcting For Atmospheric Scattering
Atmospheric Corrections