Radiometric and Geometric Calibrations

Question 1

Geometric Distortion types and causes

Answer 1

Size, shape, and scale distortions
Systematic or random causes

Question 2

Systematic Distortions/Errors

Answer 2

Earths curvature
Earths rotation
Atmospheric refraction
topographic effects
Relief displacement

Question 3

Random Distortions/Errors

Answer 3

Changes in flight altitude
Changes in flight attitude (pitch/roll/yaw)
Changes in velocity

Question 4

Orthophoto definition

Answer 4

a corrected aerial photo

Question 5

Relief Displacement definition

Answer 5

Tall objects are displaced away from the center of the air photo

Question 6

Roll definition and image impact

Answer 6

rotation on the x-axis
The up and down of the wings
Compress/expand along right and left of image

Question 7

Pitch definition and image impact

Answer 7

Rotation on the y-axis
The up and down of the nose of the plane/fuselage
Compress/expand along top and bottom of image

Question 8

Yaw definition and image impact

Answer 8

rotation on z-axis
plane rotates/turns while staying level
Impacts field of imagery

Question 9

Geometric Correction definition

Answer 9

putting pixels in their proper planimetric (x, y) map locations
We did a lap for this
This creates orthophotos
AKA georeferencing, georectification, geometric transformation

Question 10

4 steps to geometric correction

Answer 10

1. Choose a source - scientifically reliable, real world reference, ie GEP
2. Select Ground Control Points (GCP) - fixed points, evenly dispersed, minimum of 3
3. Image Transformation - Software transforms image pixels based on GCPs (rectify in ArcMap)
4. Accuracy Assessment - RMSE

Question 11

4 basic image transformations

Answer 11

Rotation - turn from fixed point
Skewing - distort or slant an unrefed image
Translation - shift to new location
Scaling - resize

Question 12

Geometric Correction Accuracy Assessment

Answer 12

Root Mean Square Error (RMSE)
the lower the overall RMSE the better the fit

Question 13

Radiance and Digital Numbers

Answer 13

Radiance has a perfect linear relationship with DNs
DNs represent average radiance measured over the ground area corresponding to that pixel

Question 14

Radiance in remote sensors

Answer 14

Radiance is the most important physical quantity in RS
This is what sensors are measuring and converting to Digital Numbers
This is used to calculate reflectance

Question 15

Radiance and Reflectance relationship

Answer 15

Radiance and incoming solar radiation and angle are collected by the DLS
Those are used to calculate reflectance

Question 16

Empirical Line Calibration Method (ELC) Definition and use

Answer 16

Requires at least one dark piece and one light piece
Establishes control points of reflectance for a simple linear regression equation that is applied to the rest of the DNs to convert to surface reflectance

Question 17

ELC assumptions

Answer 17

Assumes the darkest object in an image reflects NO radiation, DN=0
Assumes brightest object wont saturate DNs, is within valid range
Assumes perfect positive linear relationship between sensor’s radiance measurements and surface reflectance