Digital Image Processing

Image Enhancement

Image Rectification

Image Classification

1.Radiometric Corrections

2.Geometric Corrections

3.Atmospheric Correction

Image Rectification

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 :

i. Line-Dropouts

ii. De-Striping

iii. Random Noise

Radiometric Corrections

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