الصور الفضائية والاقمار الصناعية pdf - د.علاء حمدون

Major Types of Satellite Imagery

------Using GIS--

Major Satellite Systems

•

High spatial resolution

–

Quickbird, IKONOS, OrbView-3, SPOT-5 PAN, IRS-

•

Medium spatial resolution

–

Landsat-5 TM, Landsat-7 ETM+, ASTER, SPOT

•

Low spatial resolution

–

MODIS, ENVISAT, GOES, AVHRR, MSS

Orbits

•Most of these satellites are in sun-synchronous orbit

•The satellite passes over the same part of the Earth
at roughly the same local time each day

•Its “inclination” is about 8 degrees off of polar orbit

•The fact that the earth is not perfect sphere makes
the orbital plane rotate slowly around the earth (this
would not happen if it were perfectly polar)

Orbits

Source:http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbo
ok_htmls/chapter6/chapter6.html

Orbits

•The slow motion of that orbital plane
matches the latitudinal motion of the
sun in the sky over the year

•Maintains similar sun angles along its
ground trace for all orbits

•That means that the area the sun flies
over always get the same sunlight
angle, which gives constant lighting

Source:http://hdsn.eoc.nasda.go.jp/experience/rm_kiso/sat
ellit_type_orbit_e.html

Scanners

•Pushbroom (along track) vs.
Whiskbroom (across track)

•SPOT and IKONOS: Pushbroom

•Landsat: Whiskbroom

•Pushbroom scanners generally have
higher radiometric resolution because
they have longer “dwell time” than
across-track scanners, which move
laterally across landscape as also
move forward

Source: http://www.sci-ctr.edu.sg/ssc/publication/remotesense/spot.htm

Direction of Satellite Motion

Active remote
sensing
instruments send
out a signal of
radiation at a
particular
wavelength.

Active Remote Sensing

Active remote sensing
instruments rely upon the
amount or frequency of
radiation reflected back to
the satellite instrument by
the Earth’s surface or
atmosphere.

Active Remote Sensing

Atmosphere

An example of an active
remote sensing instrument
is the CALIOP (Cloud
Aerosol LIdar with
Orthogonal Polarization)

Active Remote Sensing

Lidar (laser LIght Detection
and Ranging) instrument on
the CALIPSO satellite.

Atmosphere

Passive Remote Sensing

Passive remote
sensing instruments
either use the Sun as
the source of
radiation…

Passive Remote Sensing

… or use radiation
emitted by the Earth’s
surface or
atmosphere.

Passive Remote Sensing

Passive remote sensing
instruments rely upon the
amount or frequency of
radiation received by the
satellite instrument from
the Earth’s surface or
atmosphere.

Passive Remote Sensing

Most satellite remote
sensing instruments
rely on passive
observations.

Nadir

Horizon

Solar

Zenith

Angle

Zenith

Elevation

Angle

Orbital Geometry

The nadir FOV is
defined as directly
beneath the satellite
track, when the
satellite is overhead
(90° elevation
angle from the
horizon).

Low Earth Orbit (LEO) FOV

Direction of Satellite Motion

Horizon

Nadir

90°

The orbit is
defined as having
a

cross-track

and an

along-

track

direction.

Low Earth Orbit (LEO) FOV

Direction of Satellite Motion

Along-Track Direction

Cross-Track Direction

Instantaneous Field-of-View (IFOV)

The nadir
(downward-looking)
Instantaneous Field-
of-View (IFOV) or
footprint represents
the nadir spatial
resolution.

By stitching together a
continuous series of
push broom images, a
contiguous swath or
ribbon of data
encircling the Earth
can be achieved.

Push-Broom Sensors

In “Cross-Track Scanning,” a

scan mirror swings back and

forth along the sub-orbital track,

allowing the sensor to

sequentially observed pixels and

trace out a small swath or ribbon

of the Earth’s surface along the

direction of the satellite’s

motion.

Cross-Track Scanning Sensors

LANDSAT

• First started by NASA in
1972 but later turned over to
NOAA

• Since 1984 satellite
operation and data handling
are managed by a commercial
company EOSAT
•LANDSAT-7 launched in
1999; developed scan line
error in 2003
• Only 5 is still working;
outdated

Source: http://www.sci-ctr.edu.sg/ssc/publication/remotesense/landsat.htm

LANDSAT

•LANDSAT 4 and 5 had two types of sensors, MSS
(multi-spectral scanner) and TM (thematic mapper):

•MSS:Started on LANDSAT 1, terminated in late
1992. 80 m resolution with four spectral bands from
the visible green to the near-infrared (IR)
wavelengths. Only Landsat 3’s MSS sensor had a
fifth band in the thermal-IR.

Introduction to GIS

LANDSAT Thematic Mapper

* Mid infra red

•

Spatial and spectral resolution

•

Radiometric resolution: 8 bits (256 DNs)

•

Temporal resolution: 16 days.

LANDSAT TM

•An example:August 14, 1999 (left) and October 17, 1999 (right)
images of the Salt Lake City area

• Differences in color due to growing season

LANDSAT 7

•Uses a new sensor called
Enhanced Thematic Mapper
Plus (ETM+)

•Stressed continuity with
LANDSAT 4 and 5 in that
uses similar orbit and repeat
patterns, as well as a similar
185 km swath width for
imaging

Source: http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter2/chapter2.html

•

Characteristics of ETM+:

Band wavelength spectrums are

slightly different from LANDSAT 5 TM

LANDSAT-7 ETM+ BAND CHARACTERISTICS

Band

Number

Nominal

spectrum

Spectral Range

(µ)

Ground

Resolution

(m)

Data Lines

Per Scan

Data Line

Length (bytes)

Blue

.450 to .515

6,600

green

.525 to .605

6,600

red

.630 to .690

6,600

Near IR

.775 to .900

6,600

mid IR

1.550 to 1.750

6,600

Thermal IR

10.40 to 12.50

3,300

mid IR

2.090 to 2.35

6,600

panchromatic

.520 to .900

13,200

Enhanced Thematic Mapper Plus

LANDSAT TM: applications

Introduction to GIS

Band

Nominal Spectral
location

applications

Blue

Water body penetration, soil-water discrimination,
forest type mapping, cultural feature ID

Green

Green reflectance peak of veg, for veg ID and
assessment of vigor, cultural feature ID

Red

Chlorophyll absorption region, plant species
differentiation, cultural feature ID

Near infra red

Veg types, vigor and biomass content, dilineating water
bodies, soil moisture assessment

mid infra red (1.55-
1.75

Veg moisture, soil moisture, diff of soil from clouds

Thermal infra red

Veg stress analysis, soil moisture, thermal mapping

mid infra red(2.08-
2.35

Discriminating mineral and rock types, veg moisture

LANDSAT

•Its repeat cycle is about 16 days and always crosses
equator at around 10 AM.

•Orbit takes about 99 minutes (14.5 per day)

•Distance between ground tracks of consecutive orbits
is 2752 km at equator because of the earth’s rotation

•By following earth’s rotation with each pass, it can
keep crossing the equator at the same time

Introduction to GIS

LANDSAT

•Swath is 183 km
wide, although that
includes overlap,
since data frame is
170 km

•233 orbits, for each
16-day cycle

Source: http://eosims.cr.usgs.gov:5725/DATASET_DOCS/landsat7_dataset.html

LANDSAT

•Scenes are then indexed by the path and a row

Source: http://eosims.cr.usgs.gov:5725/DATASET_DOCS/landsat7_dataset.html

LANDSAT 7

• LANDSAT 7 has an excellent mission coverage archive

Source: http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter6/chapter6.html

LANDSAT Products

•All data older than 2 years return to "public domain" and
are distributed by the Earth Resource Observation System
(EROS) Data Center of the US Geological Survey

•Available at

http://edcwww.cr.usgs.gov/products/satellite/landsat7.html

•The LANDSAT Reference system catalogues the world
into 57,784 scenes, each 115 miles (183 kilometers) wide
by 106 miles (170 kilometers) long.

LANDSAT Imagery

•

Composite of Red, Green and Blue. Shows manmade features as well as densely

forested areas and agricultural lands.

Materials by Austin

Troy and Weiqi Zhou

except where noted ©

LANDSAT Imagery

•

Composite of NIR, Red and Green. Shows manmade features as well as densely

forested areas and agricultural lands.

LANDSAT Imagery

•

Composite of shortwave infrared, Near-Infrared and Red. Shows manmade

features as well as densely forested areas and agricultural lands

LANDSAT Imagery

Introduction to GIS

Materials by Austin

Troy and Weiqi Zhou

except where noted ©

LANDSAT Imagery

Introduction to GIS

Composite of shortwave infrared, Near-Infrared and Red. Shows manmade features as
well as densely forested areas and agricultural lands

LANDSAT Imagery

Introduction to GIS

Same bands: shows wetlands, urban, open water, forest

LANDSAT Imagery

Introduction to GIS

Same bands: light yellow-green color represents northern hardwood forest. The dark
green patches represent various conifer species

SPOT

•Launched by France

• Stands for Satellite Pour
l'Observation de la Terre

•Operated by the French Space
Agency, Centre National d'Etudes
Spatiales (CNES).

SPOT

•

SPOT 1 launched 1986, decommissioned and the

reactivated in 1997

•

SPOT 2 launched 1990, still going

•

SPOT 3 launched 1993 and stopped functioning 1996

•

SPOT 4 launched in 1998, still going

•

SPOT 5 launched in 2002

SPOT

•

Each SPOT satellite carries two

HRV (high-resolution visible)
sensors, constructed with multilinear
array detectors, or “pushbroom
scanners”

•

These record multispectral image

data along a wide swath

Source: http://www.sci-ctr.edu.sg/ssc/publication/remotesense/spot.htm

SPOT

• The position of each HRV
unit can be changed by ground
control to observe a region of
interest that is at an oblique
angle to the satellite—up to
±27º relative to the vertical.

• Off-nadir viewing allows for
acquisition of stereoscopic
imagery (because of the
parallax created) and provides
a shorter revisit interval of 1 to
3 days.

Source: http://www.sci-ctr.edu.sg/ssc/publication/remotesense/spot.htm

SPOT

•

Oblique viewing capacity

– Greatly improve the viewing frequency (temporal
resolution): allows it to image any area within a 900
kilometer swath; can be used to increase the viewing
frequency for a given point during a given cycle. For a
given location, the interval ranges from a maximum of 4
days to a minimum of 1 day.

– Any point on 95% of the earth may be imaged any day
by one of the three satellites.