RS SYSTEM, SATELLITES & ORBITS

REMOTE SENSING SYSTEM, ORBITING SYSTEM, PLATFORMS AND SATELLITES

REMOTE SENSING SYSTEMS: Ideal and Real Remote Sensing System

Ideal

Real

REMOTE SENSING SYSTEMS : Active and Passive Remote Sensing Passive Remote Sensing System  Sun provides a very convenient source of energy for remote sensing.  Remote sensing system which measures energy that is naturally available are called passive sensors.  Passive sensors can only be used to detect energy when the naturally occurring energy is available.  For all reflected energy, this can only take place during the time when the sun is illuminating the earth.  energy which emitted (such as thermal infrared) can be detected day or night.

REMOTE SENSING SYSTEMS : Active and Passive Remote Sensing Active Remote Sensing System  active sensors, in the other hand, provide their own energy source for illumination.  the sensor emits radiation which is directed to the target of to be investigated.  the radiation reflected from the target is detected and measured by a sensors.  need enough or large amount of energy to adequately illuminate the target.  Advantages – ability to obtain measurements anytime.  examples of active sensors – RADAR, LIDAR

ORBITING SYSTEMS  The path followed by a satellites is referred to as its orbit.  a satellites follows a generally elliptical orbit around the    

earth. time taken to complete one revolution of the orbit – orbital period satellite traces out a path on the earth surface, called its ground track as it moves across the sky. as earth below is rotating, the satellites traces out a different path on the ground in each subsequent cycle.

RS satellite are often launched into special orbits such satellites repeats its path after a fix time interval – repeat cycle of the satellites.

 Satellites orbits is matched to the capability and

objective of the sensors they carry.  Orbits selection can vary in term of altitude, and their orientation and rotation relative to the earth  Different orbits serve different purposes. Each has its own advantages and disadvantages. There are several types of orbits:  Geostationary Orbits

 Synchronous Orbits  Near Polar Orbits

Geostationary Orbits  Geostationary Orbit  Satellites at very high altitudes has

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this geostationary orbit.

Altitudes approximately at 36,000km. these orbits circle the Earth at the same rate as the Earth spins.

This allows satellites to observe and collect information continuously over specific areas.

Geosynchronous orbits allow the satellite to observe almost a full hemisphere of the Earth.

satellites appears stationary with respect to the earth’s surface

Geostationary Orbits  These satellites are used to

study large scale phenomenon such as hurricanes, or cyclones.  These orbits are also used for communication satellites.  The disadvantage of this type of orbit is that since these satellites are very far away, they have poor resolution.  e.g. communication satellites, broadcast satellites.

Near Polar Orbits  Allows sensors and satellites to

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follow the orbits (north-south) and its orbital plane inclined at small angle with respect to earth’s rotation axis. flying at altitude 705km It takes approximately 90-98 minutes for the satellite to complete one orbit.

Polar orbits are often used for earthmapping, earth observation, measuring ozone concentrations in the stratosphere or measuring temperatures in the atmosphere. e.g. Landsat, SPOT, Radarsat

Sun – Synchronous Orbits  Many of the satellites orbits are also sun-synchronous,

which can cover each area of the world at the same local time of day  sun-synchronous orbit is a near polar orbit whose altitude in such that satellite will always pass over the location at a given latitude at a same local solar time. (have the same solar illumination condition, except for seasonal variation)  Application: remote sensing in surface temperature monitoring.  These satellites orbit have an altitude between 700 to 800 km

Ground Swath  As a satellites revolves

around the earth, the sensors “see” a certain portion of the earth.  The area imaged by a sensors referred as swath.  Imagine swaths from space borne sensors generally vary between 10 and 100 km wide.

Ground Swath Satellites

Sensor

Swath Width

NOAA-15

AVHRR

2800 km

Terra

MODIS

2330 km

Landsat

ETM +

185 km

SPOT 5

HRVIR

60 km

IKONOS

OSA

11 km

Satellites Revisit Capability  An orbit repeat cycle will be completed when

satellites retraces its path, passing over the same point on the earth’s surface directly below the satellite (nadir point) for a second time.  A sensor can view an area before and after the orbits passes over a target, thus making the revisit time less than the orbit repeat cycle time.  In Near Polar Orbit, areas at high latitude will be imaged more frequently than the equatorial zone.

PLATFORM, SATELLITES AND SENSORS ď‚— In order for a sensor to collect and record the

energy reflected or emitted from a target or surface, it must reside on a stable platform removed from a target or surface being observed. ď‚— Platform for remote sensing may be situated on

the ground, aircraft or balloons or on space craft or satellites outside the atmosphere.

PLATFORM, SATELLITES AND SENSORS  Ground based sensors are often used to record

detail information of a surface which is compared with information collected by aircraft and satellite sensors.

 Sensors may be placed on a ladder, tall building, crane, etc..

PLATFORM, SATELLITES AND SENSORS  Aerial platform or sensors commonly used - stable

wing aircraft and helicopters.  Aircraft are often used to collect very detailed image and facilitate the collection of data for earth surface at any time.

Remote Sensing from the space – sometimes conducted by space shuttle, or more commonly from satellites.

Satellites – object which revolve around another object (earth).

• man-made satellite include platform launched for R.S according to their purposes.

• satellites permits repetitive coverage of the earth surface.

Sensors and Satellites Resolutions

 Spatial Resolution  Spectral Resolution

 Radiometric Resolution  Temporal Resolution

Spatial Resolution  Spatial Resolution, Pixel Size  Spatial resolution of the sensors refers to the size of

smallest image/object that can be detected.  Most remote sensing images composed from a picture element called pixel.  Image pixel are normally square, and represent certain area of an image.  if a sensors have a spatial resolution 20m, each pixel represents an area of 20m X 20m on the ground.

Spatial Resolution Fine/high resolution: if small object or area can be detected.

Coarse/low resolution: if only large area or image can be detected

Spectral Resolution  Spectral resolution describes the ability of a sensor

to define fine wavelength intervals.  The finer spectral resolution can easily distinguish the character among the features.  Many R.S systems record energy over a spectral wavelength range at various spectral resolution.  This is referred as multispectral sensors.  Very advance multispectral called – hyperspectral sensors.

Radiometric Resolution  Describes actual contents of the image.  Radiometric Resolution refers to the

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smallest change in intensity level that can be detected by the sensing system.

The finer radiometric resolution, the more its ability to detect small different in reflected or emitted energy.

Consider of a “bit” in images. the maximum numbers of level of brightness depend on how many bits of the image. if sensor used 8 bit – max brightness values = 256 ( 0-255) if 4 bit – max brightness values = 16 (0-15).

Many bits are used – much better.

Temporal Resolution  The ability of satellites to revisit the same

area.  The time taken by a satellite to complete 1 circle.  The revisit period of a satellite usually several days.  Time factor in imagine important when:- clouds cover the area – offer limited view - short lived phenomena – flood, oil slick/spill, etc) need to be imaged.

- multi temporal comparisons are required.

- the changing appearance of a feature over time can be used to distinguish it from near similar features. (wheat)

Temporal Resolution Remote Sensor Data Acquisition June 1, 2005

June 17, 2005

16 days

July 3, 2005

16 days

Various Satellites/Sensors

 Weather Satellites/Sensors  Land Observation Satellites/Sensors  Marine Observation Satellite/Sensors  Communication and Broadcasting Satellites

Weather Satellites/Sensors  One of the first civilian satellites in

Remote Sensing application.  Today, several country operates weather or meteorological satellites to monitor weather condition around the globe.  Commonly used coarse/low spatial resolution and provide large image coverage.  Temporal resolution – quite high, providing frequent observations

Weather Satellites/sensors Goes – Geostationary Operational Environmental Satellite  Design by NASA for National Oceanic

and Atmospheric Administration (NASA).  To provide United States National

Weather Service with frequent, small scale imagine of the earth surface and cloud cover.  Have been used over 20 years

 Placed in geostationary orbits, 36,000

km altitude.  2 generation of GOES satellites have

been launched- -1st generation: GOES 1(1975) and GOES 2 (1992).

- 2nd generation: GOES 8(1994).

GOES Bands

Weather Satellites/sensors

NOAA AVHRR – Advanced Very High Resolution Radiometer  Useful for meteorological as well as other application.  near polar orbits (830-870 km).  Two satellites – each providing global coverage work together to ensure that the data not more than 6 hours old.  Sensors detect energy in visible, NIR and MIR and Thermal IR at spectrum portion  Have a swath width – 3000 km.

NOAA AVHRR Bands

Marine Observation Satellite/Sensors  The earth’s ocean cover more than two third of the

earth’s surface and play an important role in the global climate system.  They also contain an abundance of living organism and natural resource which are susceptible to pollution and other man induced hazard.  There are satellites that which have been design specifically for ocean and marine observation and monitoring purposes

Marine Observation Satellite/Sensors  Nimbus 7 Satellite – launched in 1978 – carried 1st sensor –

Coastal Zone Colour Scanner (CZCS) specifically intended for monitoring earth ocean and water bodies.  MOS – 1st Marine Observation Satellites (MOS-1)– launched by Japan on February 1987. 2nd Marine Observation Satellite (MOS-1b) launched on February 1990.  SeaWIFS (Sea-Viewing Wide-Field of View Sensor) – specifically design for various ocean monitoring – ocean primary production and phytoplankton processes, ocean influences or climate processes

Marine Observation Satellite/Sensors These ocean-observing satellites systems are important for global and regional scale monitoring of ocean pollution and health, and assist scientist in understanding the influences and impact of the ocean on the global climate system.

Land Observation Satellites/Sensors

 Landsat Series

 Spot  Commercial High Spatial Resolution

Satellites  Radar

Landsat Series This US (NASA) satellite remotesensing programme was the first civil Earth-observing satellite programme. It started with the first Landsat satellite’s launched in 1972.

The first LANDSAT series The first three satellites were identical and their payloads consisted of two optical instruments, a multispectral sensor (MultiSpectral Scanner or MSS)and a series of video cameras (Return Beam Vidicons or RBVs).

LANDSAT Series The first LANDSAT series altitude: 907-915 km orbit: sun-synchronous polar period of revolution: 103 minutes repeat cycle: 18 day satellites :

LANDSAT 1

(23/07/1972 06/01/1978)

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LANDSAT 2

(22/01/1975 05/02/1982)

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LANDSAT 3

(05/03/1978 31/03/1983)

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LANDSAT Series The second LANDSAT series The next two satellites (LANDSAT 4 and 5) were equipped with two mutispectral sensors, i.e., a multispectral scanner (MSS) and a Thematic Mapper (TM). altitude: 705 km inclination: 98.2 degrees orbit: sun-synchronous polar period of revolution: 98.9 minutes repeat cycle: 16 days satellites :

LANDSAT 4

(16/07/1982– 07/1987)

LANDSAT 5

(01/03/1985)

LANDSAT Series The third LANDSAT series The last generation of Landsat satellites started with a failure, for Landsat 6 was lost just after its launched on 3 October 1993. Landsat 7 was launched in 1999 and is equipped with a mutispectral sensor known as the Enhanced Thematic Mapper Plus or ETM+.  altitude: 705 km inclination: 98.2 degrees orbit: sun-synchronous polar period of revolution: 98.9 minutes repeat cycle: 16 days  satellites :LANDSAT 6(03/10/1993 –03/10/1993)  LANDSAT 7(15/04/1999 )

SPOT SERIES  The SPOT (Satellites Pour l’Observation de la Terre or

Earth-observing Satellites) remote-sensing programme was set up by France in partnership with Belgium and Sweden.  SPOT 1, 2 & 3

The first three satellites were identical and their payloads consisted of two identical HRV (Visible High-Resolution) optical instruments, data recorders (on magnetic tapes), and a system for transmitting the images to the groundbased receiving stations (downlink).

SPOT SERIES SPOT 1, 2 & 3 altitude: 822 km orbit: sun-synchronous polar period of revolution: 101 minutes repeat cycle: 26 day  satellites :  SPOT 1(21/02/1986 - still

operational)  SPOT 2(21/01/1990 - still operational)  SPOT 3(25/09/1993 - 14/11/1996)

SPOT SERIES SPOT 4  The second most recent addition to the

SPOT family is an enhancement of the earlier versions. Its payload consists of several sensors (two identical HRVIR (Visible & Infrared High-Resolution) optical sensors and the VEGETATION sensor), data recorders (on magnetic tapes), and a system for transmitting the images to the ground-based receiving stations.  altitude: 830 km inclination: 98 degrees orbit: sun-synchronous polar period of revolution: 101 minutes repeat cycle: 26 days satellite: SPOT 4 (24/03/1998 – still operational)

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SPOT 5 The main payload consists of high resolution imaging instruments delivering the following product improvements compared to Spot 4 Higher ground resolution: 5 metres and 2.5 metres (instead of 10 m) in panchromatic mode higher resolution in multispectral mode: 10 m (instead of 20 m) in all 3 spectral bands in the visible and near infrared ranges.

The field width of each instrument: 60 km, same as Spot 1, 2, 3 and 4.

SPOT SERIES SPOT 5 altitude: 832 km orbit: sun-synchronous polar period of revolution: 101 minutes repeat cycle: 26 days satellite: SPOT 5 (04/05/2002 – still operational)

High Resolution System IKONOS

 Next generation of high spatial

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imaging sensors.

First successful launch of commercially developed high spatial resolution earth observation satellites occurred on September 24, 1999.

IKONOS occupies a 682km sun-synchronous orbit.

The revisit time every 11 days.

Swath width 11 km.

Spatial resolution – 1m

QuickBird  highest resolution satellite imagery currently available to the public.  launched on October 18, 2001.  Sun-synchronous orbit, low orbit-450 km.  average revisit time – 1 to 3.5 days.  0.61 spatial resolution.  swath width – 16.5 km

QuickBird Image

High Spatial Resolution Satellite Imagery GeoEye-1 ď‚— A second-generation high-resolution imagery satellite with 0.41-meter panchromatic and 1.65-meter multispectral resolution WorldView-1 ď‚— A second-generation high-resolution satellite with 0.50meter panchromatic resolution WorldView-2 ď‚— A second-generation satellite with 0.46-meter panchromatic and 1.84-meter eight-band multispectral resolution. WorldView-2 is scheduled to launch in mid2009

WorldView-1 ď‚— WorldView-1, launched

September of 2007, is the most agile satellite ever flown commercially. The high-capacity, panchromatic imaging system features half-meter resolution imagery. ď‚— Operating at an altitude of 496 kilometers, WorldView-1 has an average revisit time of 1.7 days and is capable of collecting up to 750,000 square kilometers (290,000 square miles) per day of half-meter imagery.

Land Observation Satellites LIDAR - Light Detection and Ranging.

- Optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target.

- Use laser pulses - the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal.

- LIDAR technology has application in archaeology, geography, geology, geomorphology, etc...

LIDAR technology offers the opportunity to collect terrain data of steep slopes and shadowed areas (such as, the Grand Canyon), and inaccessible areas (such as, large mud flats and ocean jetties).

These LIDAR applications are well suited for making digital elevation models(DEM), topographic mapping, and automatic feature extraction. Applications are being established for forestry assessment of canopy attributes, and research continues for evaluation canopy closure, and forest biometrics.

Radar  Radio Detecting and Ranging  Active sensors which provide their own source of 

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electromagnetic energy.

Emit microwave radiation in a series of pulse from an antenna, looking obliquely at the surface, perpendicular to the direction of motion.

When energy reaches the target, some of the energy is reflected back towards the sensors.

This backscattered microwave radiation is detected, measured and timed.

The time required for the energy to travel to the targets and return back to the sensor determines the distance or range to the target.

 Image can be acquired during day

and night.  Microwave energy also able to penetrates clouds, haze, snow, smoke and most rains, making it all weather sensor.  Airborne System – SAR (AIRSAR), SLAR  Spaceborne System – ERS1, ERS2, SEASAT1, JERS1, SRTM, Radarsat,

SRTM – Kedah, Malaysia

RADARSAT – Hinchinbrook Island