Landsat 7 Sensor ( ETM+)

 The Band 6 on Landsat 7 is divided into two bands, high and low gain, Images in two modes

         • Panchromatic Image : operating in visible & near infra red region.(15m Resolution) TM band 1 for 

            Bathymetry ,Solid vegetation, Different forest types identification.

          • Multispectral Images: obtain image data in 7 bands of visible, Near IR & Middle IR region. (30 m

            Resolution)

Two mid IR bands on TM are useful for vegetation and soil moisture status, discriminating soil and rock 

Far IF band for soil mapping, soil moisture and vegetation study.This system currently operated by US Geo survey. As result of this image capturing techniques image cost dropped down. They have seven LANDSAT satellites, the first launched in 1972. Landsat 5 and Landsat7 are in operational. Land sat has multispectral sensors Multi spectral Scanner(MSS) and Thematic Mapper(TM). MSS has 80m and TM has 30m resolution.  

Spectral Resolution (µm)    Band   Spatial Resolution(m)

      Band  1   0.450 – 0.515  

      Band  2   0.525 – 0.605  

      Band 3    0.630 – 0.690 

      Band 4    0.760 – 0.900  

      Band 5    1.550 – 1.750  

      Band 6†  10.40 – 12.5  

      Band 7     2.080 – 2.35  

      Band 8     0.52 – 0.92  

     Blue -Green  30

     Green           30

     Red              30

     Near IR        30

     Mid IR         30

     ThermaL IR  60

     Mid IR         30

     Pan              15

SPOT 2.5m

        This is main earth observation satellites operated by French since 1985. This system has two sensors, Multispectral or panchromatic mode. Multispectral image have 20m and panchromatic mode has 10m resolution. It has three multi spectral bands, Green, Red and Infrared. It aunched in 1998. SPOT is the only satellite system acquire stereo satellite imagery.

ISR

        This is Indian Remote Sensing Satellite has 5 satellites system, Launch in 1995 to 2004. This is main earth observation satellite. Spatial resolution 5.8m to 23.8m

FCC – 3,2,1 PNCC – 2,3,1

QuickBird 0.6m

       Canyon Lands, UT (0.6 m resolution) April 20, 2003.  Launched in 18 OCT,2001, operated by DIGITALGLOBE, 450 km orbit, sun-synchronous, 1-3.5 day revisit period, 0.61 m- 0.72 panchromatic, 2.44 m-2.88M multispectral. Spectral Pan – 1, MS – 4. Radimetric 11bit

Band 1 – Blue 0.45-0.52, Band 2 – Green 0.52-0.6, Band 3 – Red 0.631 – 0.691, Band 4 – NTR 0.76 – 0.9

IKONOS (4 m Multispectral)

       Launched by Space Imaging in 1999, 1 m panchromatic and 4 m multispectral resolution, 681 km orbit, crosses equator between 10 and 11 am daily, revisit 1.5-3 days.

RADAR (Radio Detection and Ranging)

       SLAR (Side looking Airborne Radar) developed by military in 1950’s, and SAR (Synthetic aperture radar), Image is NASA TOPSAR of Pasadena valley, CA.

LIDAR (Light Detection and Ranging) 

      Image: Bainbridge Island, WA courtesy Pudget Sound LIDAR Consortium, 2005

ALOS 

        Advanced Land Observation Satellite system. ALOS launch in 2006. This is an Earth observation satellite. Spatial resolution 10m

Pre-image Procession

       Prior to data analysis, initial processing on the raw data is usually carried out to correct for any distortion due to the characteristics of the imaging system and imaging conditions. Its depend on the user's. These procedures include radiometric correction and field of view of the sensor. 

Eclipses.

Considering two solid opaque objects, Moon and Earth, arranged according to the picture and illuminated by a large source of light Sun. Earth is Eliminated by the rays from Sun which reach it, but owing to the presence of Moon between Sun and Earth, shadows are obtained on parts of Earth. By drawing the extreme rays from Sun it can seen that the region a on Earth receives no light, and this region, known as the umbra, is therefore in total darkness. The region on Earth between a, b, and a, d receives light from only part of Sun, and is hence in partial shadow; such a region is known as a penumbra. Beyond b to c, and beyond d to e, the region is illuminated by rays from the whole of Sun, and is therefore bright. 

Illustrates the eclipse of the sun

At some stage in their movement round the sun, S, the moon M comes between it and the earth E. A total eclipse is observed at the region a on the earth, and a partial eclipse is observed at the regions b and d. Observers at c and e on the earth receive rays from the whole of the sun, so that no eclipse is seen. The sun’s appearance at different points on the earth is illustrated by small circles below the main figure.

                The moon is not a Iuminous object; it merely reflects light from the sun. An eclipse of the moon happens when the earth comes between it and the sun, since the moon is then in the shadow of the earth and is no longer illuminated by the sun.

Summary:

Eclipses of the sun are due to the shadow formed when the moon passes between the sun and earth. An umbra is a region of total shadow; a penumbra is a region of partial shadow.    

REFERENCE
M. Nelkon M.Sc.(Lond.), A.K.C

GPS Signal Errors

Measurement Errors

            Range uncertainty (Due to clock/Atmospheric error)

Errors in position

            Intersection area with error

Errors in GPS Signal

            Orbit error

            Ionospheric error 

            Topospheric error

            Receiver noise

            Multipath

            Jamming

System and Receiver errors

Clock error

Transmission delay

Imprecision in algorithm for range decoding

Multi path errors

Causes of Range Uncertainty

Ionospheric effects                          3 meter

Atmospheric effects                        0.5 meter

Satellite/system errors                      2 meters

Receiver errors                               0.5 meter

Multipath                                         depends

Total Range Error                           6 meters

TOTAL Positional Error                 10 meters

GPS accuracy of GPS depend on

            Dependent errors

                        Noise

                        Multipath

                        Receiver hardware limitation

            Independent errors

                        Satellite clock errors

                        Error in broadcast ephemeris data

                        Signal propagation delay due to Ionosphere and Troposphere

Differential GPS

The differential correction techniques used to enhance the quality of location data gathered GPS receivers.

Differential correction can be applied in

Real-time directly from the field

When postprocessing data in the office

Combining both methods provides flexibility during data collection and improves data integrity

L2 Carrier

This is a carrier frequency

The L1 carrier is modulated by both the C/A and P codes

L1 carrier cycles have a wavelength of 19 cm.

Transmit timing information by the GPS satellites

L2 Carrier

This is a carrier frequency

L2 carrier is only modulated by the P code

L1 carrier cycles have a wavelength of 24.4 cm

Transmit timing information by the GPS satellites

GPS Satellite signal to Positioning

When a GPS Satellite is rotating around the earth it will transmit continuously satellite signal to the earth.

Measure arrival time of GPS signals from several satellites simultaneously

To determine a position on earth, the receiver has to calculate its range (distance) to several satellites.

Decode the GPS signal and figure out the signal propagation

Decode the navigation message and convert it into satellite positions.

Use at least 4 pseudoranges acquired at the same time from 4 different satellites to compute a position

GPS Satellite distance or range

There are two types to calculate distance or range to satellites:

             Code Ranging by Code Matching

             Carrier Phase Ranging by Shift measurements

Code Ranging by Code Matching

Code rang or pseudo range is the distance between satellite and the receiver.

Code range calculated by (D_i) = C_L X ∆_t (C_L=Speed of the light, ∆_t=Signal travel time)

Synchronized the satellite and receiver to generate same frequency (Code) same time.

P code is more accurate than the C/A code

Carrier Phase Ranging by Shift measurements

Measure the wavelengths from satellite to receiver to calculate range or distance.

The wavelengths of the carrier waves are very short, L1 - 19cm and L2 -24cm.

More accurate than P code distance calculation. 

Carrier phase can be measured to millimeters.

L1 and L2 Atomic clock The atomic clocks are synchronized to Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time Atomic standards clocks are using in monitoring stations.  Stability of at least 10-13 sec

GPS Signal

          The signal leaves from GPS satellite antenna with a combination of the three components:

                - Carrier wave

                - Ranging codes

                - Navigation Message

       GPS Satellites transmit frequencies L1=1575.42 MHz and L2=1227.6 MHz modulated with two types of code, P-code and C/A code and with navigation message. Fundamental frequency is 10.23 MHz and can be modify to different frequency. This P-Code and C/A code come with two carrier frequency L1 and L2.

Modernization of GPS Signal 

GPS codes and carrier phase

P(Precise) Code

P-code PRN code is 6.1871 × 1012 bits long

The C/A code is a repeating 1 MHz Pseudo Random Noise (PRN) Code

Each satellite repeats its portion of the P code every 7 days

P code is unique for each satellite

P-code was modulated with the W-code to generate the Y-code

Users can’t access the P Code and Y code on both L1 and L2 without an encryption key. 

P-Code modulates both the L1 and L2 carrier phases

C/A Code

The C/A Code (Coarse Acquisition) modulates the L1 carrier phase.

The C/A code repeats every 1023 bits (one millisecond)

Navigation Message

Navigation Message modulates the L1-C/A code signal

The Navigation Message is a 50 Hz signal consisting of data bits that describe the GPS satellite orbits.

The Navigation Message corrects Clock corrections, and other system parameters.

Satellites in the Orbit

Global Positioning System is used for

Positioning and Navigation

To take very accurate time

Ranging or Distant measurement

GPS Segments;

        GPS need three factors to work 

Space Segment

The space segment consists of the satellites themselves

Altitude of 20,000km

32 operational satellites

Four to twelve GPS satellites visible from any point on the earth

There are six orbital planes with at least four satellites in each plane

Period of the satellite 11hrs and 56mins to orbit the earth

Generate and Transmit code, carrier phases and navigation message

Control Segment

There are five major monitoring/tracking stations spaced around the globe and one Master Control Station located in Colorado Springs, Colorado

Each station sends information to the Control Station which facilitate control station to control them and predict their orbits

Monitor the clock errors

Each stations monitor and check up the satellites twice a day

The monitoring stations transmitted all the tracking data to the master control station

User Segment

The user requires a GPS receiver in order to receive the transmissions data from the satellites.

GPS receiver calculates the location (Longitude and latitude) based on signals from the satellites.

The users consist of military and civilians.

Users will get the accurate time

Number of applications to use (GIS, Traffic and transport, Security service, Disaster managements)

Satellites & Real time Satellites Tracker

What is satellite        

A satellite normally go around the earth and do very impotent jobs for earth. There are two kind of satellite available in orbit. They are natural and man made. Natural satellites like moon and stars, man made satellites are other artificial machines in the orbit.   

Orbit

When a satellite is launched to the space, it is placed in orbit around the earth. The earth's enormity holds the satellite in a certain path as it goes around the earth, and that path is called an "Orbit". There are three kind of orbits;


LEO (Low Earth Orbit)

• Satellites circling 100 to 300 miles above the earth's surface.

• it is close to the earth it travel very fast to avoid being pulled out of orbit by gravity and crashing into the earth.

• It travel in low earth orbit about 17,500 miles per hour. 

• These satellites can circle the whole earth in about an hour and a half.

MEO (Medium Earth Orbit )

• Satellites circling 6,000 to 12,000 miles above the earth’s surface.

• Satellites circling mediumaltitude of the earth.

• It takes 4 to 8 hours to go around the earth.

GEO, or Geostationary Earth Orbit

• A satellite in geosynchronous orbit circles the earth in 24 hours

• They appear "fixed" with respect to a given spot on earth

• Satellites circling 22,282miles above the earth’s surface. 

• Satellites circling high orbit of the earth.

• GEO satellites can cover a large part of the planet.

• Three GEO satellites can cover the globe, except for the parts at the North and South poles.

Due to satellite configuration four to twelve (4-12) satellites are visible to any place on the earth at any time.

GPS Segment

Space Segment

Minimum of 32 operational satellites in six circular orbits.

User Segment

Consists of the receivers, processors, and antennas that allow land, sea, or airborne operators to receive the GPS satellite broadcasts and compute their precise position, velocity and time.

Control Segment

Consists of a master control station in Colorado Springs, with five monitor stations and three ground antennas located throughout the world

GPS Constellation Status

      The current GPS constellation consists of 32 Block II/IIA/IIR/IIR-M satellites. GPS constellation and individual satellite status is updated every working day. You can visit following link to update today working satellitesstatus.

http://www.navcen.uscg.gov/?Do=constellationStatus


Following application show the Real time satellites path and it included flowing satellites;



ISS(ZARYA), CELESTISII/FALCON 9 R/B, GOES 12, GOES 15, PRISM(HITOMI), BONU MI, NAVSTAR 37 (USA 117),  NAVSTAR 66 (USA 232), OTV2 (USA 226), VENESAT-1, NAVSAR 63 (USA 203), NAVSAR 55 (USA 178), NAVSAR 62 (USA 201),  NAVSAR 29 (USA 87),  NAVSAR 34 (USA 94),  NAVSAR 51 (USA 166),  NAVSAR 36 (USA 100), NAVSAR 43 (USA 132),  NAVSAR 46 (USA 145), YAOGAN 15