Satellites and Sensors

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Satellites and Sensors Satellites and Sensors

Dr. Ragab Khalil

Department of Landscape Architecture Faculty of Environmental Design King AbdulAziz University Room 103

LA502 Special Studies

Remote Sensing

Dr. Ragab Khalil KAAU - FED – LA527: RS 2/49

Overview

• Common platforms

• Types of Remote Sensing

• Key characteristics of Optical Sensors

• Landsat

• SPOT

• Indian Satellites

• Commercial Satellites

• Image coverage and spatial resolution

Common Platforms

1. Ground-Based

2. Airborne

3. Space Shuttle

4. Satellites

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Types of Remote Sensing

Source Sun Object Transmitted by

Remote sensing System Visible -

Reflective infrared Thermal infrared Microwave

Object Reflectance Thermal radiation (temperature, emissivity)

Backscattering coefficient Visible - Reflective infrared Thermal infrared Microwave

0.4 µm 0.7 µm 1 mm

Electro- magnetic

Spectrum 3.0 µm 10 µm

Sensor Optical Sensor System RADAR System

Wavelength Region

Key characteristics of Optical Sensor

example

Spectral characteristics SPOT (HRV/XS)

- Number of spectral bands 3 bands

- wavelength of each band 0.49 - 0.59 µm 0.61 - 0.68 µm 0.79 - 0.89 µm

Spatial characteristics

- Image swath 60 km

- Spatial resolution 20 m

Tow major characteristics of image data acquired by optical sensor system are keys for applications.

Orbits

• The path followed by a satellite is referred to as its orbit.

• We will talk about two types of orbits

Geo-stationary

Near polar

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Geostationary Orbit

Geo-synchronous

• Satellites at very high altitudes approximately 36,000 kilometers

• view the same portion of the Earth's surface at all times

• revolve at speeds which match the rotation of the Earth so they seem stationary, relative to the Earth's surface

• They are used in

telecommunication and weather forecasting.

36000 km

Near-Polar Orbits

Sun-synchronous

• They are continuously orbiting the earth. They are sun-synchronous because they appear with the same time everyday along with the sun.

Swath

• As a satellite revolves around the Earth, the sensor "sees" a certain portion of the Earth's surface. The area imaged on the surface, is referred to as the Swath.

• Imaging swaths for spaceborne sensors

generally vary between tens and

hundreds of kilometers wide.

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Sensing principles

Central Perspective Across-track Along-track

Resolutions

• The characteristics of remote sensing systems can be described by the following types of resolutions:

Spatial resolution,

Spectral resolution

Radiometric resolution, and

Temporal resolution.

• These resolutions control our ability to interpret remote sensing data.

Designing a multi-channel space borne radiometer

• How large are the features of interest? Spatial resolution

• What reflectance characteristics are you trying to measure?Spectral resolution

• How precisely do you have to measure these characteristics?Radiometric resolution

• How frequently and when do you have to measure the features of interest?Temporal resolution

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Spatial Resolutions

• Spatial resolution dictates the amount of discernible details in an image:

The size of the smallest possible feature that can be detected.

• The spatial resolution is mainly controlled by the separation between the sensor and the target. (How high is the satellite)

Spatial Resolutions

• For a homogeneous feature to be detected, its size has to be equal to or larger than the resolution cell.

• If the feature is smaller than this, it may not be detectable as the average brightness of all features in that resolution cell will be recorded.

• However, smaller features may sometimes be detectable if their reflectance dominates within a particular resolution cell allowing sub-pixel or sub-resolution cell detection.

Spatial Resolutions

LANDSAT (30m) LANDSAT (15m) SPOT (10m)

KOMPSAT-1 (6m)

IKONOS (1m)

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Spectral Resolutions

• Spectral resolution describes the ability of a sensor to define fine wavelength intervals.

• Black and white film records wavelengths (0.4µm – 0.7µm).

• Color film is individually sensitive to the reflected energy at the blue (0.4µm–0.5µm),

green (0.5µm–0.6µm), and red (0.6µm–

0.7µm)

wavelengths of the spectrum.

• Color film has higher spectral resolution when compared to black and white film.

Spectral Resolutions

• Multi-Spectral Sensors (MSS) record energy over several separate wavelength ranges at various spectral resolutions.

• Advanced multi-spectral sensors called hyper-spectral sensors, detect hundreds of very narrow spectral bands throughout the visible, near-infrared, and mid- infrared portions of the electromagnetic spectrum.

• Such sensors facilitate fine discrimination between different targets based on their spectral response in each of the narrow bands.

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Radiometric Resolution

• Radiometric resolution of an imaging system describes its ability to discriminate very slight differences in the recorded energy.

• The finer the radiometric resolution of a sensor, the more sensitive it is to detecting small differences in reflected or emitted energy.

• For digital imagery, the radiometric resolution is defined by the number of bits used for coding the recorded grey values.

By comparing a 2-bit image with an 8-bit image, one can see that there is a large difference in the level of discernible details.

Radiometric Resolutions

8 bits per pixel 2 bits per pixel

Temporal Resolutions

• Temporal resolution of a remote sensing system refers to the frequency with which it images the same area.

• Frequent imaging is important for:

Disaster & environmental management.

For example, floods, oil slicks, spread of forest disease from one year to the next.

Change detection applications.

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Multi-Temporal Imagery

Calgary 56 Calgary 72

Multi-Temporal Imagery

Calgary 99 Calgary 2002

Satellites

• Landsat

• SPOT

• IRS

• Others

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The Landsat Satellites

Landsat program

4/15/99

Landsat Sensors

• Return Beam Vidicon (RBV)

• Multispectral Scanner (MSS)

• Thematic Mapper (TM)

• Enhanced Thematic Mapper Plus

(ETM+)

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MSS Bands

Channel Wavelength Range

(µm) Landsat 1,2,3 Landsat 4,5

MSS 4 MSS 1 0.5 - 0.6 (green)

MSS 5 MSS 2 0.6 - 0.7 (red)

MSS 6 MSS 3 0.7 - 0.8 (near infrared)

MSS 7 MSS 4 0.8 - 1.1 (near infrared)

Spatial Resolution: 79 meters

Swath width =183 km

Typical colors on images

• If you take these three bands and display band 4 in red, band 2 in green and band 1 in blue. The colors on image will be:

black lava and asphalt

white snow and clouds

bluish gray cities

white or yellow sand

yellowor green red soils and rocks

pinkish red grassland

brownish red coniferous

dark red deciduous

lightto dark blue silty water

black clear water

Image color Land cover

TM Bands

Spatial Resolution: 30 meters (120 meters for band 6)

Wavelength Range (µm) TM 1 0.45 - 0.52 (blue) TM 2 0.52 - 0.60 (green) TM 3 0.63 - 0.69 (red)

Wavelength Range (mm) TM 4TM 4 0.76 0.76 --0.90 (near IR)0.90 (near IR) TM 5

TM 5 1.55 1.55 --1.75 (short IR)1.75 (short IR) TM 6TM 6 10.4 10.4 --12.5 (thermal IR)12.5 (thermal IR) TM 7TM 7 2.08 2.08 --2.35 (short IR)2.35 (short IR)

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TM Bands

TM1 TM2

TM3 TM4

TM5 TM7

TM Bands

Spatial Resolution: 30 meters (120 meters for band 6) Application

TM 1 water penetration studies, differentiating soil and rock surfaces from vegetation and for detecting cultural features.

TM 2 water turbidity differences, discriminating broad classes of vegetation (measures reflectance peak); cultural/urban feature identification

TM 3 discriminating vegetation and soil (plant chlorophyll absorption);

discriminating urban and rural areas

TM 4 distinguishing vegetation varieties and conditions; locating and delineating water bodies; distinguishing between dry and moist soils TM 5 plant vigor or species type, sensitive to moisture in soil and vegetation;

discriminating snow and cloud-covered areas

TM 6 estimates of soil moisture, identifying different types of rocks; and detecting thermal pollution in water bodies

TM 7 detecting clay alteration zones associated with mineral deposits;

sensitive to vegetation moisture content

Landsat Image Cape Canaveral

RBV Image ETM+ Image

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Système Pour l’Observation de la Terre

SPOT

• SPOT 1,2,3,4 launched in 1986, 90,93, 98 and SPOT 5 in 2002

• Altitude of 832 km, inclination 98 deg. (i.e near-polar orbit) (circular)

• All satellites are sun-synchronous with orbit repetition every 26 days.

• First satellite to use along-track, or pushbroom scanning technology.

The SPOT payload

• Each HRV is capable of sensing either in

a high spatial resolution (10 meter) single-channel panchromatic (PLA) mode, or

a coarser spatial resolution (20 meter) three-channel multispectral (MLA) mode.

• Each HRV offers an oblique viewing capability, the viewing angle being adjustable through +/- 27deg.

relative to the vertical

• The unique characteristics of SPOT imagery is the ability to obtain Stereoscopic View which is important in 3D applications

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SPOT

HRV Mode Spectral Ranges

• Mode/Band Wavelength Range

(µm)

• Panchromatic (PLA) 0.51 - 0.73 (blue-green-red)

• Multispectral (MLA)

• Band 1 0.50 - 0.59 (green)

• Band 2 0.61 - 0.68 (red)

• Band 3 0.79 - 0.89 (near infrared)

Altitude= 832 km Swath width =60 - 80 km / 26 day

IRS

• The Indian Remote Sensing (IRS) satellite series, combines features from both the Landsat MSS/TM sensors and the SPOT HRV sensor.

• The third satellite in the series, IRS-1C, launched in December, 1995 has three sensors:

a single-channel panchromatic (PAN) high resolution camera,

a medium resolution four-channel Linear Imaging Self scanning Sensor (LISS-III),

and a coarse resolution two-channel Wide Field Sensor (WiFS).

IRS Sensors

Sensor Wavelength Spatial Resolution Swath Width Revisit Period

PAN 0.5 - 0.75 5.8 m 70 km 24 days

LISS-II

Green 0.52 - 0.59 23 m 142 km 24 days

Red 0.62 - 0.68 23 m 142 km 24 days

Near IR 0.77 - 0.86 23 m 142 km 24 days Shortwave IR 1.55 - 1.70 70 m 148 km 24 days WiFS

Red 0.62 - 0.68 188 m 774 km 5 days

Near IR 0.77 - 0.86 188 m 774 km 5 days

Altitude = 817 km

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Weather Satellites and Sensors

Examples:

(1) GOES (Geostationary Operational Environmental Satellite)

(2) NOAA AVHRR ( National Oceanic and Atmospheric Administration) (Advanced Very High Resolution Radiometer)

(3) DMSP (Defense Meteorological Satellite Program) (4) Meteosat

NOAA AVHRR Bands

Wavelength Spatial Resolution Application 1 0.58 - 0.68 (red) 1.1 km cloud, snow, and ice

monitoring

2 0.725 - 1.1 (near IR) 1.1 km water, vegetation, and agriculture surveys 3 3.55 -3.93 (mid IR) 1.1 km sea surface temperature,

volcanoes, and forest fire activity

4 10.3 - 11.3 (th IR) 1.1 km sea surface temperature, soil moisture

5 11.5 - 12.5 (th IR) 1.1 km sea surface temperature, soil moisture

Altitude= 833 km Swath width = 2400 km

AVHRR Global Composite

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AVHRR Sea Surface Temperature

Marine Satellites and Sensors

• Coastal Zone Color Scanner (CZCS)

• Marine Observation Satellite (MOS)

• SeaWifs

Commercial Satellites

• Space Imaging IKONOS

• Orbimage OrbView 3, 4

• Earthwatch Quickbird

• Resource-21

• SPIN

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IKONOS

GeoEye-1

GeoEye-1 Specifications

• Imaging Mode Panchromatic Multispectral

• Spatial Resolution .41 meter 1.65 meters

• Spectral Range 450-900 nm 450-520 nm (blue) 520-600 nm (green) 625-695 nm (red) 760-900 nm (near IR)

• Swath Width 15.2 km

• Off-Nadir Imaging Up to 60 degrees

• Dynamic Range 11 bit per pixel

• Mission Life Expectation > 10 years

• Revisit Time Less than 3 day

• Orbital Altitude 681 km

• Nodal Crossing 10:30 am

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Dr. Ragab Khalil KAAU - FED – LA527: RS 49/49 LANDSAT (MSS/TM)

185 x 185 km

SPOT (HRV) 60 x 60 km

IRS-1C(PAN) 70 x 70 km

Image coverage and spatial resolution

IRS-1C(PAN) 5.8 m LANDSAT TM (Band 6)

120 m

LANDSAT MSS 80 m

LANDSAT TM (Band 1-5 & 7) 30 m

SPOT (HRV/XS) 20 m

SPOT (HRV/PAN) 10 m IKONOS

11 x 11 km IKONOS (PAN)

1m