Jupiter

Posted on March 7, 2008 by Rashid Faridi

The most massive planet in our solar system, with four planet-sized moons and many smaller moons, Jupiter forms a kind of miniature solar system. Jupiter resembles a star in composition. In fact, if it had been about eighty times more massive, it would have become a star rather than a planet.

On January 7, 1610, using his primitive telescope, astronomer Galileo Galilei saw four small ‘stars’ near Jupiter. He had discovered Jupiter’s four largest moons, now called Io, Europa, Ganymede, and Callisto. Collectively, these four moons are known today as the Galilean satellites.

Galileo would be astonished at what we have learned about Jupiter and its moons in the past 30 years. Io is the most volcanically active body in our solar system. Ganymede is the largest planetary moon and is the only moon in the solar system known to have its own magnetic field. A liquid ocean may lie beneath the frozen crust of Europa. Icy oceans may also lie deep beneath the crusts of Callisto and Ganymede. In 2003 alone, astronomers discovered 23 new moons orbiting the giant planet, giving Jupiter a total moon count of 49 – the most in the solar system. The numerous small outer moons may be asteroids captured by the giant planet’s gravity.

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IRS (Indian Remote Sensing Satellite)

Posted on March 7, 2008 by Rashid Faridi


Following the successful demonstration flights of Bhaskara 1 and Bhaskara 2 launched in 1979 and 1981, respectively, India began development of an indigenous IRS (Indian Remote Sensing Satellite) program to support the national economy in the areas of “agriculture water resources, forestry and ecology, geology, water sheds, marine fisheries and coastal management”. The Indian Remote Sensing satellites are the main-stay of National Natural Resources Management system (NNRMS), for which Department of Space (DOS) is the nodal agency, providing operational remote sensing data services. Data from the IRS satellites is received and disseminated by several countries all over the world. With the advent of high resolution satellites new applications in the areas of urban sprawl, infrastructure planning and other large scale applications for mapping have been initiated.

Remote sensing applications in the country, under the umbrella of NNRMS, now cover diverse fields such as crop acreage and yield estimation, drought warning and assessment, flood control and damage assessment, land use/land cover information, agro-climatic planning, wasteland management, water resources management, under-ground water exploration, prediction of snow-melt run-off, management of water- sheds and command areas, fisheries development, under development, mineral prospecting forest resources survey, Active involvement of the user ministries/ departments has ensured in an effective harnessing of the potential of space-based remote sensing. An important application of IRS data is in the Integrated Mission for Sustainable Development (IMSD) initiated in 1992. IMSD, under which 174 districts have been identified, aims at generating locale-specific action plans for sustainable development.

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 1999. 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: 0.45-0.52 µm 0.52-0.59 µm, 0.62-0.68 µm, and 0.77-0.86 µm. The 38.5-kg LISS-I images a swath of 148 km with a resolution of 72.5 m while the 80.5-kg LISS-IIA and LISS-IIB exhibit a narrower field-of-view (74-km swath) but are aligned to provide a composite 145-km swath with a 3-km overlap and a resolution of 36.25 m.

Each IRS spacecraft is 975 kg at launch with a design life of 2.5-3 years. The 3-axis stabilized spacecraft is essentially rectangular (1.1m by 1.5 m by 1.6 m) with two narrow solar arrays producing less than 1 kW electrical power. The Spacecraft Control Center at Bangalore oversees ail spacecraft operations, but the principal data reception station for the remote sensing payload is located at Shadnagar. Spacecraft data transmissions are effected via X-band and S-band antennas at the base of spacecraft.

IRS-1A and IRS-1B were to be joined in 1993 with IRS-1E, the modified IRS-1A engineering model’ which had been equipped with the LISS-I and a German Monocular Electro-Optical Stereo Scanner. The spacecraft was lost, however, when its PSLV launch vehicle failed to reach Earth orbit. Thirteen months later, in October, 1994, the PSLV functioned correctly, allowing IRS-P2 to assume an 820-km, sun-synchronous orbit. This spacecraft continued in operations until September 1997. With an 870-kg mass (slightly less than IRS-1A and IRS-1B), IRS-P2 carried the LISS-II system with a ground resolution of 32 m across-track and 37m along-track. The total swath width is 131 km, and the CCD array is tuned to four spectral bands between 0.45 and 0.86 am. The spacecraft’s solar arrays provide up to 500 W and are linked to conventional nickel cadmium storage batteries .

As of late 1999 five IRS satellites were operating, and more were scheduled for launch by the year 2000. IRS-1C, successfully launched on December 28, 1995 on board a Molniya rocket of Russia, was the last Russian launch of the program (Molniya rather than Vostok, while IRS-1D was orbited by India’s PSLV. IRS-P3 was launched by PSLV in 1996 with a German modular electro-optical scanner and an Indian visible-lR scanner.

The Indian Space Research Organization (ISRO) and its commercial marketing arm, ANTRIX Corp. Ltd., successfully launched the IRS-1D Earth imaging satellite on 29 September 1997 from Sriharikota, India. The satellite is an identical twin to the IRS-1C, launched in December 1995. The dual use of these satellites provides 5.8-meter resolution images to customers twice as often as was possible with just the IRS-1C.

IRS-1C and IRS-ID introduced a heavier (1,350 kg), more capable Earth observation platform. The spacecraft bus will be similar to those of IRS-1A and IRS-IB, but a slightly larger solar array generates more than 800 W. Both IRS-1C and 1D produce 5.8-meter panchromatic (0.50.75 µm – black and white) imagery, which is resampled to five-meter pixel detail. This resolution, which as of early 1998 was the best of any civilian remote sensing satellites in the world, is superior to the 8-meter resolution initially reported for the panchromatic imager. These satellites are also equipped with two-band Wide Field Sensors (WiFS) that cover a 774-square-kilometer (481-square-mile) area in a single image, as well as LISS-3 4-band (0.52-0.59, 0.62-0.68, 0.77-0.86, and 1.55-1.70 µm) multispectral sensors that provide 23.5-meter resolution multispectral coverage. The 23.5-meter resolution imagery is resampled to produce 20-meter pixel detail. The spacecraft also carry a 2-channel (0.62-0.68 and 0.77-0.86 µm) wide-field sensor (190 m resolution) .

The IRS C,D Pan sensor sacrifices swath width for its higher resolution. However, it can be pointed off the orbit path which allows 2 to 4 day revisits to specific sites. IRS-1C and IRC-1D data can be received and procured from EOSAT (USA) or in India at the NRSA, Hyderabad.

Upcoming launches include IRS-P5 in 1998, IRS-2A in 2000, and IRS-2B in 2004, all with the new LISS-4 sensor suite.

IRS-P4 (OCEANSAT-1) will have payloads, specifically tailored for the measurements of physical and biological oceanography parameters. An Ocean Color Monitor (OCM) with eight spectral bands, Multi-frequency Scanning Microwave Radiometer (MSMR) operating in four frequencies will provide valuable Ocean-Surface related observation capability. The OCEANSAT-1 was slated for launch by PSLV in early 1998.

IRS-P5 (CARTOSAT-1) has an improved sensor system that provides 2.5 m resolution with fore-aft stereo capability. This mission caters to the needs of cartographers and terrain modelling applications. The satellite will provide cadastral level information up to 1:5000 scale and will be useful for making 2-5 m contour maps.

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.

The IRS-2 series (OCEANSAT-2/CLIMATSAT-1/ATMOS-1) will be an integrated mission that will cater to global observations of climate, ocean and atmosphere. Microwave instruments to cater for oceanographic applications will be mainly a Ku band Altimeter, Ku band Scatterometer, Microwave Radiometer and Thermal Infrared Radiometer for observing oceanographic parameters like winds, sea surface temperature, waves, bathometry and internal waves. Instruments for atmospheric chemistry applications include spectrometers, sounders and radiometers for studying the atmospheric constituents, pollution and for monitoring ozone and greenhouse effect. Instruments to observe climate and meteorological parameters will include microwave sounders, radiometers and rain radars.

IRS-3, beyond 2002, will have all weather capabilities with multi-frequency and multi polarisation microwave payloads and other passive instruments.

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Natural Disasters: Cyclones

Posted on March 6, 2008 by Rashid Faridi


 

Cyclonic-force winds may be encountered all over the
globe, but it is only above the warm seas of the tropics that
a ripple of instability in the air can become a genuine
cyclone, the deepest of all low-pressure weather systems.

Cyclones are huge revolving storms caused by winds blowing around a central area of low atmospheric pressure. In the northern hemisphere, cyclones are called hurricanes or typhoons and their winds blow in an anti-clockwise circle. In the southern hemisphere, these tropical storms are known as cyclones, whose winds blow in a clockwise circle.

What is a Cyclone?

How do Cyclones occur?

Cyclones develop over warm seas near the Equator. Air heated by the sun rises very swiftly, which creates areas of very low pressure. As the warm air rises, it becomes loaded with moisture which condenses into massive thunderclouds. Cool air rushes in to fill the void that is left, but because of the constant turning of the Earth on its axis, the air is bent inwards and then spirals upwards with great force. The swirling winds rotate faster and faster, forming a huge circle which can be up to 2,000 km across. At the centre of the storm is a calm, cloudless area called the eye, where there is no rain, and the winds are fairly light.

As the cyclone builds up it begins to move. It is sustained by a steady flow of warm, moist air. The strongest winds and heaviest rains are found in the towering clouds which merge into a wall about 20-30 km from the storm’s centre. Winds around the eye can reach speeds of up to 200 km/h, and a fully developed cyclone pumps out about two million tonnes of air per second. This results in more rain being released in a day than falls in a year in a city like London.

When and where do Cyclones occur?

Cyclones begin in tropical regions, such as northern Australia, South-East Asia and many Pacific islands. They sometimes drift into the temperate coastal areas, threatening more heavily populated regions to the South. Northern Australia has about four or five tropical cyclones every year during the summertime wet season. For a cyclone to develop, the sea surface must have a temperature of at least 26ºC.

Why do Cyclones occur?

When warm air rises from the seas and condenses into clouds, massive amounts of heat are released. The result of this mixture of heat and moisture is often a collection of thunderstorms, from which a tropical storm can develop.

The trigger for most Atlantic hurricanes is an easterly wave, a band of low pressure moving westwards, which may have begun as an African thunderstorm. Vigorous thunderstorms and high winds combine to create a cluster of thunderstorms which can become the seedling for a tropical storm.

Typhoons in the Far East and Cyclones in the Indian Ocean often develop from a thunderstorm in the equatorial trough. During the hurricane season, the Coriolis effect of the Earth’s rotation starts the winds in the thunderstorm spinning in a circular motion.

Cyclone Danger

Cyclones create several dangers for people living around tropical areas. The most destructive force of a cyclone comes from the fierce winds. These winds are strong enough to easily topple fences, sheds, trees, power poles and caravans, while hurling helpless people through the air. Many people are killed when the cyclone’s winds cause buildings to collapse and houses to completely blow away.

A cyclone typically churns up the sea, causing giant waves and surges of water known as storm surges. The water of a storm surge rushes inland with deadly power, flooding low-lying coastal areas. The rains from cyclones are also heavy enough to cause serious flooding, especially along river areas.

Long after a cyclone has passed, road and rail transport can still be blocked by floodwaters. Safe lighting of homes and proper refrigeration of food may be impossible because of failing power supplies. Water often becomes contaminated from dead animals or rotting food, and people are threatened with diseases like gastroenteritis.

Major Cyclones, Hurricanes and Typhoons

Year

Area of Cyclone

Death toll (est.)

1900

Galveston, Texas, USA

10 000 – 12 000

1906

Society and Cook Islands

10 000

1963

Bangladesh

15 000

1964 (May)

Bangladesh

35 000

1965 (Jun)

Bangladesh

15 000

1970

Caribbean coast

1 000 000

1977

Honduras

100 000

1985

South-eastern India

15 000 – 100 000

1991

Bangladesh

139 000

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Cyclones and Anticyclones

Posted on March 6, 2008 by Rashid Faridi

Cyclones and Anticyclones

Cyclones are areas of low pressure. Cyclones usually exhibit nearly circular isobars. If isobars are oblong or elongate with the lowest pressure near the center we call them troughs. As air enters an area of low pressure from all directions, the Coriolis effect bends the direction of the wind to the right of its path. This creates a counterclockwise rotation around the low and  convergence near the center of the system. As the air collides near the center it is forced aloft where   divergence takes air away from the center of the system. The upper-level divergence is necessary for the system to be maintained as an area of low pressure. Without the divergence, the system would fill with air and the horizontal pressure differences would be equalized causing the system to dissipate. Anticyclones are areas of high pressure that exhibit nearly circular isobars. If isobars are oblong or elongate with the highest pressure near the center we call them ridges. For high pressure areas, air descends toward the surface due to convergence aloft. As the air nears  the surface it is forced outward (divergence) from the center. The Coriolis effect bends the air to the right of its path creating a clockwise rotation around the high.

Figure PC.6 Circulation within alow pressure system in the Northern Hemisphere

anticyclone

Figure PC.7 Circulation within a high pressure system in the Northern Hemisphere

cycloneFigure PC.8 Cyclone in the Southern Hemisphere 
(Click image to enlarge)

Because the Coriolis effect works in the opposite direction in the Southern Hemisphere, circulation around lows are clockwise and inward toward the center at the surface and highs exhibit a diverging, counterclockwise rotation. You can see this effect in the cloud pattern created by a cyclone in the Southern Hemisphere.

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