Non-photographic Remote Sensing, Digital Data Acquisition ...

Non-photographic Remote Sensing,
Digital Data Acquisition
And
Landsat Satellite Imagery
March 17, 2015

NON-PHOTOGRAPHIC SYSTEMS

• Remote Sensors

– “all instruments that detect and measure reflected
and/or emitted electromagnetic energy from a
distance” (recording device is NOT in contact with
the objects under study)

• Imaging Systems

– collect remotely sensed data from which two-
dimensional pictorial representations of the objects
under study can be made

• photographic camera and film

• non-photographic:

– multispectral scanners (passive)

– passive microwave

– RADAR and LIDAR (active)

– Sonar (active)

ELECTROMAGNETIC RADIATION

interactions with the atmosphere

CLASSIFICATION OF NONPHOTOGRAPHIC
REMOTE SENSORS

PASSIVE ACTIVE

CLASSIFICATION OF NONPHOTOGRAPHIC
REMOTE SENSORS

PASSIVE ACTIVE

DIGITAL VIDEO MULTI- MICROWAVE SAR LASER
CAMERA CAMERA SPECTRAL (Lidar)
SCANNERS
(Radar)

THERMAL VISIBLE & NIR HYPERSPECTRAL
(e.g. TIMS) (e.g. AVIRIS)

ACROSS TRACK ALONG TRACK
(sweep) (push)

e.g. Landsat 5 e.g. SPOT, Landsat
(TM), AVHRR 8 (OLI)

PHOTOGRAPHIC VS.
NON-PHOTOGRAPHIC

not a photograph!

Digital Image Sources

• Use of digital raster images instead of
photographs

• sources of digital photographs:
– digitized photographs and orthophotos
– digital cameras
– electro-optical scanners (e.g., multispectral
scanners)
– Other digital satellite imagery (thermal,
Radar, Lidar

Digital Satellite Image Aerial Photograph scan
(Landsat) digitized

National
Agriculture
Imagery
Program
(NAIP)
Ortho-
Photography
Leaf-on 2007
1 meter
resolution

U. Maine
Campus

http://datagateway.nrcs.usda.gov/

NON-PHOTOGRAPHIC SYSTEMS

• Digital Cameras
– use camera body and lens but the image is
recorded by a Charged Coupled Detector
(CCD) array rather than film
– electronic signals are stored digitally (pixel
by pixel, band by band) on computer disks or
other digital media
– sometimes called “digital photography” but
not photography in the traditional sense (e.g.
using film). Small format usually 35mm or
70mm.
– B/W or color
– example: Kodak Professional DCS 460
ADAR System 5000

Photographic Film vs. Digital Images

• Ground area covered in a digital image, from a digital camera,
depends on sensor flying height, the instantaneous field of view
(related to beta angle of optical system) and on the size of the two-
dimensional array (number of rows and columns of pixels) and
pixel resolution

• No single number can represent the number of “pixels” a
photographic image would have, if it had pixels

• the pixels in a CCD array are uniform in size and shape and are
arranged in a systematic geometric pattern (2-D array)

• Silver halide grains in a photographic image are random in size,
shape, and spatial distribution

• Generally, images on photographic film have been more detailed
than digital images; although digital cameras are approaching the
resolution of photographic film

• For every two-fold increase in resolution, there is a four-fold
increase in the data storage capacity required

(H – h)

Instantaneo
us Field Of
View (IFOV)

DIGITAL IMAGING - Some Advantages

• Even though they usually offer poorer resolution and are more
complex (and hence more expensive), non-photographic imaging
systems offer several advantages over photographic cameras:
– operate in portions of the EMS within and beyond the
wavelength sensitivities of photographic film
– digital output signal can be transmitted via radio
telemetry and computer links and stored on magnetic tape
and computer disks
– renewable detection process (in contrast to photographic
systems in which film is both detector and storage
medium)
– CCD elements have a wider dynamic range than film
emulsion (better able to sense subtle scene radiance
changes)
– digital data readily available for digital processing,
manipulation, and integration with GIS and other
computer-based tools

Digital Image
Acquisition

sensor’s instantaneous
field of view

As the sensor sweeps across the track of the satellite,
energy is recorded as a series of pixels along a scan line.

• A digital image is composed of pixels geographically
ordered and adjacent to one another. The pixels provide a
continuous representation of the earth’s surface.

• Each pixel represents a certain surface area on the ground,
and provides a measure of the intensity of spectral response
recorded over that unit of surface area – the spectral
response is recorded as a numeric value (a digital number or
‘DN’).

Relationship of digital numbers and brightness levels on
an eight bit, black and white or gray scale image

MULTISPECTRAL SATELLITE IMAGERY

• A multispectral image is composed of 'n' rows and 'n' columns of
pixels in each of two or more spectral bands. There are in reality
more than one "data set" which makes up one image.

• These different data sets are referred to as spectral bands,
channels, or layers.

Landsat 8

Landsat - 4, 5, 7, 8
Orbital Characteristics

• sun-synchronous , near
polar orbit: Landsat always
passes over same location at
same local time (8:30-
10:00)

• orbital period = 99 min.
(14.5 orbits per day)

• swath width = 185 km

• revisits the same location
every 16 days

(22 repeats per year)

Operational Land Imager (OLI)

Landsat Data Bands Wavelength Resolution
Continuity (micrometers) (meters)
Mission 30
(LDCM) Band 1 - Coastal aerosol 0.43 - 0.45 30
30
Band 2 - Blue 0.45 - 0.51 30
30
Band 3 - Green 0.53 - 0.59 30
30
Band 4 - Red 0.64 - 0.67 15
30
Band 5 - Near Infrared (NIR) 0.85 - 0.88 100
100
Band 6 - SWIR 1 1.57 - 1.65

Band 7 - SWIR 2 2.11 - 2.29

Band 8 - Panchromatic 0.50 - 0.68

Band 9 - Cirrus 1.36 - 1.38

Band 10 - Thermal Infrared (TIRS) 1 10.60 - 11.19

Band 11 - Thermal Infrared (TIRS) 2 11.50 - 12.51

Worldwide Reference System-2 (WRS-2) path/row system
Sun-synchronous orbit at an altitude of 705 km (438 mi)
233 orbit cycle; covers the entire globe every 16 days (except for the highest polar latitudes)
Inclined 98.2° (slightly retrograde)
Circles the Earth every 98.9 minutes
Equatorial crossing time: 10:00 a.m. +/- 15 minutes

OLI Bands and Spectral Response

Landsat - 4, 5, 7, 8
Image Characteristics

• Worldwide Reference System (WRS) -
8 scenes over Maine

• Imagery archived and catalogued by
USGS EROS Data Center (Sioux Falls)

• Scene location indexed by path /
row system
– Paths run roughly north/south
– Rows run roughly east/west

• Scene size is ~185 x 185 km

• Pixel size is 30 x 30 m (~1/4 acre)

Comparison ETM+(L7) to OLI/TIRS (L8)

Comparison ETM+(L7) to OLI/TIRS (L8)

NON-PHOTOGRAPHIC SYSTEMS

• Advantages of along-track (push broom) scanners
– linear arrays afford longer residence time for which to
measure energy from each ground resolution cell, resulting
in a stronger signal
– fixed relationship of CCDs along each scan line results in
improved geometric integrity
– CCDs small in size and require less power for operation
– w/o moving parts (e.g. oscillating mirrors), a linear array
system has a higher reliability and longer life expectancy

SATELLITE IMAGE INTERPRETATION

• Manual (visual) • Digital Image Processing and
Interpretation Land Cover Classification

– i.e. by a human interpreter – enhance data as a prelude to visual
interpretation
– imagery displayed in a
pictorial or photograph-type – automatically identify targets and
format, or a digital image on extract information
a computer screen
– supplement and assist the human
analyst

Landsat 8 Operational Land Imager

Band 2 (blue) Band 3 (green) Band 4 (red)

Band 5 (Near-IR) Band 6 (Mid-IR) Band 7(Mid-IR)

Red- Green – Blue = Primary colors

R+G = Yellow
RG

R+ G + B
R+B = Magenta G + B = Cyan

B

SATELLITE IMAGE INTERPRETATION
(Additive Color Theory)

• The additive primaries: red, green, and blue (physics of light)

• Characteristics:

– No single primary can be formed by a combination of the other two.
– All other colors are created by mixing these three. Equal proportion of

two primary colors gives complimentary colors (cyan, magenta, and
yellow).
– Equal proportions of the three additive primaries combine to form
white light.

LANDSAT COLOR COMPOSITES

Additive Color Theory and RGB Color Composites Simplified Interpretation

Computer Display: RED GREEN BLUE Interpretation
LAYER2 LAYER3 forest canopy
Image Color LAYER1

BLUE low low high cleared before
CYAN low high high regrow 95-97
GREEN low high low cleared before
RED high low low regrow 93-97
MAGENTA high low high cleared before
YELLOW high high low regrow 93-95
cleared 93-95
no regrow
cleared 93-95
regrow 95-97
cleared 95-97

WHITE high high high no change, hig
BLACK low low low forest
no change, low
urban, pasture

OLI band 4 Red color write function of
(visible red) computer monitor

OLI band 3 Green
(visible green) write
function
OLI band 2
(visible blue) A true color composite
(RGB-432)
Blue write
function Landsat 8 OLI

true color CIR false color
composite composite
RGB-432 RGB-543

false color Landsat 8- OLI
composite
RGB-564

1988 Landsat Thematic Mapper (RGB-453)
Same as RGB-564 color composite in Landsat 8
image

• Water, wetlands, clouds are
masked from the imagery,
and appear black

Mixed

Hardwood Softwood
dominant dominant

Harvest, 1985-1988

Harvest, 1982-1985