Geometric Distortion in Remote Sensing Images

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Questions and Answers

What is the leading cause of geometric distortion in vertical aerial photography?

Curvature and rotation of the Earth

Relief displacement (correct)

Perspective of the sensor optics

Motion of the scanning system

Why are objects directly below the center of the camera lens affected in aerial photography?

Due to the curvature and rotation of the Earth

Because they lean away from the center of the photo (correct)

Because their tops are visible

Due to platform altitude

What role does terrain relief play in causing geometric distortion?

It influences the motion of the scanning system

It contributes to geometric distortion (correct)

It causes objects to lean towards the center of the photo

It affects platform altitude

In aerial photography, why are objects at the nadir position only showing their tops?

Due to relief displacement Signup and view all the answers

Which factor influences objects appearing to lean away from the center of an aerial photograph?

Terrain relief Signup and view all the answers

How do framing systems like cameras used for aerial photography capture images?

By producing 'snapshot' views from directly overhead Signup and view all the answers

What type of distortion results in the compression of image features at points away from the nadir?

Tangential Scale Distortion Signup and view all the answers

Which scanning system distortion causes the sweep of scanning systems to cover an area slightly to the west of each previous scan?

Skew Distortion Signup and view all the answers

Which platform type helps alleviate geometric distortions by providing relatively stable orbits?

Satellite platforms Signup and view all the answers

Which factor influences geometric distortions caused by variations in platform stability?

Changes in speed, altitude, and attitude Signup and view all the answers

What causes imagery obtained from satellite multispectral scanners to exhibit skew distortion?

Eastward rotation of the Earth during a satellite orbit Signup and view all the answers

How are geometric distortions and positional errors affected by the distance of objects from the center of a photo?

They increase Signup and view all the answers

What is the primary purpose of geometric correction in digital images?

To compensate for distortions introduced by various factors Signup and view all the answers

Why are raw digital images usually not suitable for direct use as a map base?

Because they contain significant geometric distortions Signup and view all the answers

Which of the following is NOT a source of geometric distortions in digital images?

Sensor resolution Signup and view all the answers

What is the role of image data providers in the context of geometric correction?

They automatically perform all necessary corrections Signup and view all the answers

How are systematic distortions typically corrected in digital images?

By applying mathematical formulas derived from modeling the sources of distortions Signup and view all the answers

What is the key consideration before attempting to make measurements or extract further information from digital images?

The necessity of considering and addressing errors in the images Signup and view all the answers

What is the purpose of least-squares regression analysis in the context of the given text?

To determine coefficients for transformation functions. Signup and view all the answers

Which equations are used to interrelate geometrically correct (map) coordinates and distorted-image coordinates?

$x = f1 (X,Y) y = f2 (X,Y)$ Signup and view all the answers

How are the distorted-image coordinates of any map position estimated?

By determining coefficients for transformation equations. Signup and view all the answers

What does the process of 'resampling' involve in the context of the text?

Assigning intensity values based on transformed positions. Signup and view all the answers

What determines the intensity value or digital number assigned to a cell in the output matrix during resampling?

The pixel values surrounding its transformed position. Signup and view all the answers

In general, why does a cell in the output matrix not directly overlay a pixel in the input matrix during resampling?

To account for pixel values from surrounding positions. Signup and view all the answers

What is the purpose of image registration?

To map one image onto another using a perfect transformation Signup and view all the answers

What is the role of feature detection in image registration?

To extract key features and distinctive objects from images Signup and view all the answers

How do area-based methods differ from feature-based methods in feature matching?

Feature-based methods estimate control points for perfect matches, while area-based methods match predefined size. Signup and view all the answers

What does the mapping function do in the image registration process?

Reconstructs the sensed image Signup and view all the answers

In what manner is a sensed image typically registered in transformation and resampling?

Forward transformation Signup and view all the answers

What is the main objective of comparing reference and sensed images with control points in image registration?

To significantly influence the registration process Signup and view all the answers

Study Notes

Remote sensing images acquired from various platforms/sensors have inherent geometric distortions due to factors like sensor optics, platform motion, altitude, and Earth's curvature.
Aerial photography systems like cameras can cause relief displacement, where objects away from the camera's center appear distorted in vertical aerial photography.
Across-track scanning systems exhibit tangential scale distortion compressing features away from the nadir and skew distortion due to the eastward rotation of the Earth.
Geometric correction is essential to compensate for distortions in raw digital images caused by factors like platform variations, earth curvature, and atmospheric effects.
Systematic distortions are easily corrected using mathematical formulas and regression analysis to transform distorted-image coordinates into map coordinates.
Resampling is a process used to determine pixel values in the output matrix from the original image matrix during geometric correction.
Image registration involves mapping one image onto another using a perfect transformation, including feature detection, matching, designing mapping functions, and transformation/resampling processes.

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Description

Learn about the geometric distortions present in remote sensing images captured through satellite, aircraft, or other sensor platforms. Understand how these distortions affect the representation of Earth's surface in a two-dimensional image.