Earth s Gravitational Pull

Transcription

1 Satellite & Sensors

2 Space Countries

3 Earth s Gravitational Pull The Earth's gravity pulls everything toward the Earth. In order to orbit the Earth, the velocity of a body must be great enough to overcome the downward force of gravity One important fact to remember is that orbits within the Earth's atmosphere do not really exist. Atmospheric friction caused by the molecules of air (causing a frictional heating effect) will slow any object that could try to attain orbital velocity within the atmosphere. In space, with virtually no atmosphere to cause friction satellites can travel at velocities strong enough to counteract the downward pull of Earth's gravity The satellite is said to orbit around the Earth

4 Satellites Orbit

5 Geosyncronous Satellites GEO are circular orbits around the Earth having a period of 24 hours. A geosynchronous orbit with an inclination of zero degrees is called a geostationary orbit. A spacecraft in a geostationary orbit appears to hang motionless above one position on the Earth's equator. For this reason, they are ideal for some types of communication and meteorological satellites. A spacecraft in an inclined geosynchronous orbit will appear to follow a regular figure-8 pattern in the sky once every orbit. To attain geosynchronous orbit, a spacecraft is first launched into an elliptical orbit with an apogee of 35,786 km (22,236 miles) called a geosynchronous transfer orbit (GTO). The orbit is then circularized by firing the spacecraft's engine at apogee.

6 Typical Geostationary Coverage

7 Metereological Satellites

8 Polar Orbits PO are orbits with an inclination of 90 degrees. Polar orbits are useful for satellites that carry out mapping and/or surveillance operations because as the planet rotates the spacecraft has access to virtually every point on the planet's surface Most PO are circular to slightly elliptical at distances ranging from 700 to 1700 km ( mi) from the geoid. At different altitudes they travel at different speeds.

9 Low-Spatial-resolution Sensors GOES Geostationary Operational Environment Satellite AVHRR Advanced Very High Resolution Radiometer MODIS Moderate Resolution Imaging Spectroradiometer SeaWiFS Sea-Viewing Wide Field-of-view Sensor

10 Satellites q Early satellites ARYABHATTA ( 360 kg ) ROHINI ( 40 kg ) Stretched ROHINI Series ( 150 kg ) BHASKARA I & II ( Remote Sensing ) APPLE ( Communication ) q Indian Remote Sensing Satellites ( IRS; Polar) q Indian National Satellites (INSAT; Geosynchronous )

11 GOES Geostationary Operational Environment Satellite The GOES I-M Imager is a five channel (one visible, four infrared) imaging radiometer designed to sense radiant and solar reflected energy from sampled areas of the earth.

12 GOES Geostationary Operational Environment Satellite

13 AVHRR Advanced Very High Resolution Radiometer Measuring the same view, this array of diverse wavelengths, after processing, permits multi spectral analysis for more precisely defining hydrologic, oceanographic, and meteorological parameters. Comparison of data from two channels is often used to observe features or measure various environmental parameters. The three channels operating entirely within the infrared band are used to detect the heat radiation from and hence, the temperature of land, water, sea surfaces, and the clouds above them.

14 AVHRR Advanced Very High Resolution Radiometer

15 MODIS Moderate Resolution Imaging Spectroradiometer is a payload scientific instrument launched into Earth orbit by NASA in 1999 on board the Terra (EOS AM) Satellite, and in 2002 on board the Aqua (EOS PM) satellite. The instruments capture data in 36 spectral bands ranging in wavelength from 0.4 µm to 14.4 µm and at varying spatial resolutions (2 bands at 250 m, 5 bands at 500 m and 29 bands at 1 km). Together the instruments image the entire Earth every 1 to 2 days. They are designed to provide measurements in large-scale global dynamics including changes in Earth's cloud cover, radiation budget and processes occurring in the oceans, on land, and in the lower atmosphere.

16 MODIS Moderate Resolution Imaging Spectroradiometer

17 SeaWiFS Sea-Viewing Wide Field-of-view Sensor The purpose of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project is to provide useful data on ocean color to the Earth science community. Subtle changes in ocean color indicate various types and numbers of marine phytoplankton (microscopic marine plants), knowing this information can have both scientific and practical uses. The SeaWiFS Project will develop and operate a research tool that will process, calibrate, validate, archive and distribute data received from the Earthorbiting ocean color sensor.

18 SeaWiFS Sea-Viewing Wide Field-of-view Sensor

19 Other Players ATRS - The ATSR channels are at wavelengths of 1.6um (visible) and three thermal bands at 3.7um, 11um, and 12um. AATSR - data have a resolution of 1 km at nadir, and are derived from measurements of reflected and emitted radiation taken at the following wavelengths: 0.55 µm, 0.66 µm, 0.87 µm, 1.6 µm, 3.7 µm, 11 µm and 12 µm.

20 Other Players MERIS

21 Other Players IRS-P4

22 Medium-Spatial-Resolution-Sensors Landsat Earth Resources Technology Satellite (ERTS-1) Spot Systeme Pour l Observation de la Terre IRS Indian Remote Sensing Satellite IRS-P6 - Indian ResourseSat Aster Advanced Spacebourne Thermal Emission and Reflection Radiometer

23 Landsat Landsat 1,2,3 4,5 (TM)6,7 (ETM+) Match the band combinations with their respective images 5 Thematic Mapper spectral band definitions: Band 1: micrometers (blue-green) Band 2: micrometers (green) Band 3: micrometers (red) Band 4: micrometers (near infrared) Band 5: micrometers (near infrared) Band 6: micrometers (thermal infrared) Band 7: micrometers (shortwave infrared)

24 3, 2, 1 Landsat Landsat 1,2,3 4,5 (TM)6,7 (ETM+) 3,4,5 3,2,1 4,3,2 5,4,3 5 Thematic Mapper spectral band definitions: Band 1: micrometers (blue-green) Band 2: micrometers (green) Band 3: micrometers (red) Band 4: micrometers (near infrared) Band 5: micrometers (near infrared) Band 6: micrometers (thermal infrared) Band 7: micrometers (shortwave infrared)

25 Landsat What does NIR tell us? Since NIR has longer wavelengths than visible light, it exhibits peculiar properties that can be exploited for remote sensing applications. Some of the information that can be obtained from NIR is crop stress (water and nutrient stress being the most common) and weed/pest infestations. Chlorophyll pigment absorbs most energy at about 650 nm (red) and around 450 nm (blue). Other pigments absorb more visible wavelengths, but the most absorption occurs in the red and blue portions of the spectrum. This absorption removes these colors from the amount of light that is transmitted and reflected, causing the predominant visible color that reaches our eyes as green. This is the reason healthy vegetation appears as a dark green. Unhealthy vegetation, on the other hand, will have less chlorophyll and thus will appear brighter (visibly) since less is absorbed and more is reflected to our eyes. This increase in red reflectance along with the green is what causes a general yellow appearance of unhealthy plants.

26 Landsat and Infrared Another feature of vegetation is the strong reflectance within the NIR. Since NIR is not absorbed by any pigments within a plant, it travels through most of the leaf and interacts with the spongy mesophyll cells. This interaction causes about half of the energy to be reflected and the other half to be transmitted through the leaf. In plants with turged and healthy mesophyll cell walls and in dense canopies, more NIR energy will be reflected and less transmitted. This cell wall/air space interaction within these cells causes healthy vegetation to look very bright in the NIR. In fact, much more NIR is reflected than visible.

27 Landsat and Infrared By monitoring the amount of NIR and visible energy reflected from a plant, it is possible to determine the health of that plant. High NIR reflectance / Low visible reflectance = Healthy Low NIR reflectance / High visible reflectance = Unhealthy

28 Landsat and Infrared First, we need to know that a spacecraft (Landsat, SPOT, or the SIR-C radar) does not "see" in color. Every image is obtained in black and white at a precise wavelength (usually between 0.4 to 12.0 microns). These electronic cameras only collect information in black and white, but they can obtain many images at the same time in different parts of the spectrum. If we look at the diagram below of the spectrum, we see several broad regions that include the ultraviolet (wavelengths between microns), visible (0.4 to 0.7 microns), near-infrared (0.7 to 1.2 microns), the solar reflected infrared (1.2 to 3.2 microns), the mid-infrared (3.2 to 15 microns) and the far infrared (longer than 15.0 microns).

29 Landsat and Infrared

30 Landsat and Infrared The value in obtaining multiple images at different wavelengths can be seen in the above figure. Here we show the individual images that were obtained by Band 2 ( microns), Band 7 ( microns) and Band 11 ( microns). Careful inspection of these three images shows that the different parts of Honolulu have different brightnesses at different wavelengths. For example, at points "a" in Band 2, we can see through the shallow water along the coastline to see the coral reef along Waikiki. At point "b" in Band 2, the rain forest on the Koolau Range is quite dark, but at the same place in Band 7, the vegetation appears quite bright. This is due to the reflective nature of chlorophyll in the leaves at this wavelength.

31 Landsat and Infrared Indeed, the relative brightness between the rain forest and the city is flipped as we look at the two images. This change in contrast is also seen between Bands 7 and 11. If we look at area "c" in Band 11, we see some dark patches. These are clouds, which in the thermal infrared are cold, but at shorter wavelengths (Bands 2 and 7) are highly reflective due to the water droplets and so are bright. Band 11 is very sensitive to temperature, and we can also find things that are warm (i.e., bright) in this image that are dark in other bands. Areas "d", which include parts of the airport runways and the sides of Diamond Head facing the sun, are both warmer than the average scene and so are bright. It is interesting to try to compare these areas in Band 2 or 7, since they are obviously quite different.

32 Landsat and Infrared Having seen that different bands (or wavelengths) have a different contrast, we can now study how the computer can produce a color image from a remote sensing data set. To do this, we take three images, which are the black and white images corresponding to Bands 2, 8 and 10.

33 SPOT Wednesday 15 August at 23 hours 40 minutes and 57 seconds UTC, an earthquake of magnitude 8 on the Richter scale shook Peru s coastline and the capital city Lima. The quake flattened 70% of the city of Pisco, spreading panic among its 130,000 inhabitants. A com parison of a SPOT 5 satellite image acquired 21 August and an archive image of 10 January 2006 highlights the trail of destruction. The streets crisscrossing the city are lying under rubble and collapsed buildings show up in the different texture of the post-quake image. Such texture differences make it possible to measure the exact extent of quake damage.

34 SPOT

35 SPOT of Mount Saint Michel

36 IRS Indian Remote Sensing Satellite The first two IRS spacecraft, IRS-1A (March' 1988) and IRS-1B (August, 1991) were launched by Russian Vostok boosters from the Baikonur Cosmodrome. IRS-1A failed in 1992, while IRS-1B continued to operate through From their 22-day repeating orbits of 905 km mean altitude and 99 degrees inclination, the two identical IRS spacecraft hosted a trio of Linear Imaging Self-Scanning (LISS) remote sensing COD instruments working in four spectral bands: µm µm, µm, and µm. The 38.5-kg LISS-I images a swath of 148 km with a resolution of 72.5 m while the kg LISS-IIA and LISS-IIB exhibit a narrower fieldof-view (74-km swath) but are aligned to provide a composite 145-km swath with a 3- km overlap and a resolution of m.

37 IRS-P6 (ResourceSat-1) IRS-P6 (RESOURCESAT-1) will be a state-of-art satellite mainly for agriculture applications and will have a 3-band multispectral LISS-IV camera with a spatial resolution better than 6 m and a swath of around 25 km with across track steerability for selected area monitoring. An improved version of LISS-III with four bands (red, green, near IR and SWIR), all at 23 m resolution and 140 km swath will provide the essential continuity to LISS-III. These sensors will provide data which will be useful for vegetation related applications and will allow multiple crop discrimination and species level discrimination. Together with an advanced Wide Field Sensor (WiFS) with 80 m resolution and 1400 km swath, the payloads will greatly aid crop/vegetation and integrated land and water resources related applications. The IRS-P6 is slated for launch by PSLV by end of 2000.

38 ALOS Advanced Land Observation Satellite (Japan) This image shows the areas of Tokyo Bay. Read spots in the bay likely indicate a plague of phytoplankton. 2006/06/01 Daichi

39 ASTER The ASTER instrument consists of three separate instrument subsystems. Each subsystem operates in a different spectral region, has its own telescope(s), and was built by a different Japanese company. ASTER's three subsystems are: the Visible and Near Infrared (VNIR), the Shortwave Infrared (SWIR), and the Thermal Infrared (TIR).

40 High-Spatial-Resolution-Sensors IKONOS Space Imaging (formerly EOSAT) forming GeoEye Quickbird - Digitalglobe OrbView - GeoEye-1, formerly known as OrbView-5, is the next-generation high-resolution imaging mission of GeoEye, Dulles, VA, USA. In January 2006, the commercial imaging company GeoEye was formed, made up of former Orbimage of Dulles VA, and of former Space Imaging of Thornton, CO (Orbimage acquired Space Imaging in 2005 and gave the merged company the new name of GeoEye). The newly formed GeoEye company is the world's largest commercial satellite imagery provider.

41 The IKONOS Satellite is a high-resolution satellite operated by GeoEye. Its capabilities include capturing a 3.2m multispectral, Near-Infrared (NIR)/0.82m panchromatic resolution at nadir. Its applications include both urban and rural mapping of natural resources and of natural disasters, tax mapping, agriculture and forestry analysis, mining, engineering, construction, and change detection. It can yield relevant data for nearly all aspects of environmental study. IKONOS images have also been procured by SIC for use in the media and motion picture industries, providing aerial views and satellite photos for many areas around the world. Its high resolution data makes an integral contribution to homeland security, coastal monitoring and facilitates 3D Terrain analysis. IKONOS

42 Quickbird

43 OrbView NGA announced on September 30, 2004 that it has selected ORBIMAGE as its NextView second vendor after a competitive selection process conducted over the last six months. The contract, awarded September 30, 2004, runs through September 30, 2008 and will provide ORBIMAGE with both long-term revenue commitments as well as capital for the development of OrbView-5, ORBIMAGE's next-generation high-resolution imaging satellite. The contract, known as NextView ORBIMAGE, also assures NGA of greater access and priority to high-resolution commercial satellite imagery.