February 3

Interpretation of Digital Data

Bit and ByteASCIIBinary

Image Recording Media and Formats

Geometric correctionsImage registration

Projections

Computer Basics(1)Bit and byte

1 bit 0-1 21

0 1

2 bit 0-3 22

3 bit 0-7 23

One bit in computer requires one register– a switch between 0 and 1

0 1 2 3

0 1 2 3

4 5 6 7

5 bit 0-31 25

4 bit 0-15 24

6 bit 0-63 26

7 bit 0-127 27

8 bit 0-255 28

One byte has 2 =256 combinations with 8 registers. It therefore can be used to specifyLetter, arabics and symbols up to a total of 256

Computer Basics

2. ASCII file (text file) (American Standard Code for Information Interchange)

101 102 103

201 202 202

111 112 113

12 bytes

12 bytes

12 bytes

Each digit uses one byte. One byte is required between two numbers andat the end of a line or file.

Information on an image, such as date, location, level of processing, solar zenith angle, view angle, etc., are usually contained in ASCII format i.e., header of an image file.

Computer Basics

2. binary file

101 102 103

201 202 202

111 112 113

3 bytes

3 bytes

3 bytes

Advantage of binary files: (i) less memory requirement, (ii) fast reading and saving operations

Remote sensing images are commonly stored in binary files

Disadvantage of binary files: (i) content can’t be displayed as text,

(ii) the information can not be retrieved without knowing the image format, i.e., # of bits/datum, pixels/line, # of lines

Packing Multispectral Data(1) Band interlived by pixel (BIP) : data are stored pixel by pixel for all bands

simultaneously21 86 34 28 31 89 21 ……

Band 1

Band 2

Band 3

Band 4

16 18 21 32 19 18 21 ….

08 06 04 03 06 09 10 12 …..

06 03 02 08 10 21 19 16 …..

In a binary file:

21 16 08 06 86 18 06 03 34 21 04 02 ………

Pixel (1,1) Pixel (2,1) Pixel (3,1)

Packing Multispectral Data(2) Band interlived by line (BIL): data are stored line by line for all bands

simultaneously21 86 34 28 31 89 21 ……

Band 1

Band 2

Band 3

Band 4

16 18 21 32 19 18 21 ….

08 06 04 03 06 09 10 12 …..

06 03 02 08 10 21 19 16 …..

In a binary file:

Band 1 line 1, band 2 line 1, band 3, line 1, band 4, line 1, band 1 line 2, band 2 line 2, ……

Packing Multispectral Data(3) Band sequential (BSQ) : data are stored one image (band) by one image

21 86 34 28 31 89 21 ……Band 1

Band 2

Band 3

Band 4

16 18 21 32 19 18 21 ….

08 06 04 03 06 09 10 12 …..

06 03 02 08 10 21 19 16 …..

In a binary file:

band 1, band 2, band 3, band 4

Geometric Distortions

Sources: variations in altitude and velocity of sensor platform

panoramic distortion, earth curvature, atmosphericrefraction, relief displacement, and nonlinearitiesin the swath of a sensor’s field of view (FOV)

Campbell chapter 10Lillesand-Kiefer 7.2

Geometric corrections compensate for the distortionintroduced by these factors so that the corrected images

will have geometric integrity.

Image distortions: nonsystematic

Campbell 8.7

Earth rotation Altitude variation Pitch variation

Spacecraft velocity Roll variation Yaw Variation

Distorted image Restored image

Image distortions: systematic

Cross-track distortion Mirror velocity variation Scan skew

TimeM

irror

ang

le Actualvelocity

Nominalvelocity

Image Matching

(1) Overlay of two images

(2) Registration of two images (or one image to a map)

(3) Analytical registration of two images

Campbell 10.5

Projections and re-sampling

No re-sampling

Ground control points and re-sampling

Registration

Find the same features, Ground Control Points (GCPs), on two images or on one image and a map.

GCPs can also be takenduring field experiments with

Global Positioning Systems (GPS).

GPS is a US Military satellite-based navigation systemthat uses at least three satellites to calculate a position.

Verbyla Chap. 5Campbell 12.7

Choice of Ground Control Points

From Maps and GPS

Road intersections

Rivers

Water bodies

Campbell 10.6

Image Rectification models

Verbyla Chap. 5

LinearY = AX + B

Residual Errors

X

Y

Affine Coordinate Transformations

Y’ = AX + BY + C

X’ = DX + EY + F

Polynomial Models

Y’ = A + BX + CY + DX2 + EY2 + FX3 +GY3 +...

How many GCPs?

Polynomialorder

First

Second

Third

Minimum Numberof GCPs Required

Verbyla Chap. 5

3

6

10

PCI: GCPWorks

Distorted Restored

Sabins, Chapter 8

Geometric Correction

Output Image Original Image

Campbell 10.6Lillersand-Kiefer 7.2

In general, a pixel in the output image will not directly overlay a pixel in the original image

What valueswill the pixels in

output image have?

Nearest Neighbour Bilinear Interpolation(weighted average)

Re-sampling

Campbell 10.6

Cubic Convolution(weighted average)

Re-sampling

Campbell 10.6

Most widely used

Map Projections

Campbell 10.7Verbyla Chap. 5

Satellite Images that cover large areas need map projections because of the Earth’s spherical surface.

It is impossible to project a spherical surface ontoa flat sheet without distortions to theshape, area, distance, and direction

of the surface features.

Universal Transverse Mercator Coordinates

Campbell 10.715.3-15.4

Zones of 6 degrees wide (east-west)zone 1 is at 180-174o WFrom 84o N to 80o S in latitude

Projections

Polar azimuthal (planar) Regular conic

Sabins, Chapter 8