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SO234 remote sensing lab
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Topex: The three-frequency TOPEX Microwave Radiometer(TMR)measures the sea surface microwave emissivity(brightness temperatures)at three frequencies (18, 21 and 37 GHz)to
provide the total vapor content in the
troposphere along the altimeter beam. The 21 GHz channel is the primary channel for water vapor measurement. The 18 and 37 GHz channels are respectively used to remove the effects of wind speed and cloud cover on the
water vapor measurement. Measurements are combined to obtain the error in the satellite range measurements caused by pulse delay due to water vapor and to obtain the sigma naught correction for liquid water absorption.
GOES: The objective of the geostationary
operational environmental satellite(GOES)system is to maintain a continuous data stream from a two-GOES system, primarily to support the National Weather Service requirements. The program objective is to meet requirements by procuring, through the GOES Acquisition Manager (NOAA/SAO) and NASA/GSFC, spacecraft, instruments, launch services, and ground equipment. The GOES program also invests in new product development and assists with implementing the approved products into
operations.
AVIRIS: The AVIRIS instrument contains 224 different detectors, each with a wavelength sensitive range (also known as spectral bandwidth) of approximately 10 nanometers(nm), allowing it to cover the entire range between 380 nm and 2500 nm. When the data from each detector is plotted on a graph, it yields a spectrum. Comparing the resulting spectrum with those of known substances reveals information about the composition of the area being viewed by the instrument. AVIRIS uses a scanning mirror to sweep back and forth ("whisk broom" fashion), producing 614 pixels for the 224 detectors each scan. Each pixel produced by the instrument covers an approximately 20 meter square area on the ground (with some overlap between pixels), thus yielding a ground swath about 11 kilometers wide. The ground data is recorded on board the
instrument along with navigation and
engineering data and the readings from the AVIRIS on-board calibrator. When all of this data is processed and stored on the ground, it yields approximately 140 Megabytes (MB) for
every 512 scans (or lines) of data. Each 512 line set of data is called a "scene", and corresponds to an area about 10km long on the ground. Every time AVIRIS flies, the instrument takes
several "runs" of data (also known as "flight lines"). AVIRIS tapes have had anywhere from one to fifteen runs on them, with each run having anywhere from one to almost forty scenes. A full AVIRIS tape can yield about 16 Gigabytes (GB) of data per day.
ERS-1: On 17 July 1991, the European
Remote-Sensing Satellite, ERS-1, the first European satellite to carry a radar altimeter, was launched into an 800 kilometer altitude and 98.5 deg inclination orbit. During the first few
months, the Commissioning Phase, all
instruments were calibrated and validated. Since then ERS-1 has been flying two Ice Phases (in which the repeat period was 3 days), a Multi-Disciplinary Phase (a 35-day repeat orbit lasting from April 1992 till December 1994), and the Geodetic Phase, which started in April 1994 and has a repeat period of 168-days. Since launch the satellite has monitored the sea
surface almost continuously. The accuracy of its altimeter range measurements has been estimated to be a little under 5 cm.
G.P.S.: GPS is one of history's most exciting and revolutionary developments, and new uses for it are constantly being discovered. But before we learn more about GPS, it's important
to understand a bit more about navigation. GPS, which stands for Global Positioning System, is the only system today able to show you your exact position on the Earth anytime, in
any weather, anywhere. GPS satellites, 24 in all, orbit at 11,000 nautical miles above the Earth. They are continuously monitored by ground stations located worldwide. The satellites transmit signals that can be detected by anyone with a GPS receiver. Using the receiver, you can determine your location with great precision.
SEAWIFS:
HRPT satellites give 1.1km resolution in 5 spectral bands. Two are visible, and 3 infrared. There are about 12 good images a day and this system will provide the
very highest resolution possible from weather satellites. Because there are 5 sensors they can be mixed together to provide stunning colour images showing an
incredible amount of detail. Remember that APT gives a pixel size of 4km and therefore an area of 16 square km per pixel. HRPT gives a pixel size of 1.1km and
therefore an area of 1.21 square km per pixel, an amazing increase of 13 times resolution. But there is more, remember that there are 5 bands and that this is also a
digital system that gives 10 bit data, 1024 grey or colour levels per band, giving a total of 50 bit data. The system is, though, both complex and expensive and is very
definitely not for the beginner. A 90cm (3 foot) dish has to be tracked across the sky as the satellite orbits. This is all taken care of automatically and works really
well in practice. There are only a few HRPT system manufacturers in the world, no commercially available receiver is capable of receiving HRPT and so, unless you
are good at receiver design and home construction, you need to purchase a complete system from us.
AVHRR: Advanced Very High Resolution Radiometer, same satellite type as SEAWIFS. HRPT satellites give 1.1km resolution in 5 spectral bands. Two are visible, and 3 infrared. There are about 12 good images a day and this system will provide the
very highest resolution possible from weather satellites. Because there are 5 sensors they can be mixed together to provide stunning colour images showing an
incredible amount of detail. Remember that APT gives a pixel size of 4km and therefore an area of 16 square km per pixel. HRPT gives a pixel size of 1.1km and
therefore an area of 1.21 square km per pixel, an amazing increase of 13 times resolution. But there is more, remember that there are 5 bands and that this is also a
digital system that gives 10 bit data, 1024 grey or colour levels per band, giving a total of 50 bit data. The system is, though, both complex and expensive and is very
definitely not for the beginner. A 90cm (3 foot) dish has to be tracked across the sky as the satellite orbits. This is all taken care of automatically and works really
well in practice. There are only a few HRPT system manufacturers in the world, no commercially available receiver is capable of receiving HRPT and so, unless you
are good at receiver design and home construction, you need to purchase a complete system from us.
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Questions
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Q: How far into the ocean water column do satellites penetrate? Why?
A: Because satellites use radar, lasers, and color and infrared scanners, they are only able to moniter the top few meters of the water column, due to these instruments inability to penetrate deeper.
Q: What is the use of remote sensing in
Oceanography?
A: Satellites help oceanagraphers obtain sea surface temperatures and other important information hourly, that would take a ship weeks to obtain. They can also use them to observe weather, greenhouse effects, El Nino, and other natural phenomena that occur in the ocean.
Q: What is the difference between active and passive satellites?
A: Active satellites send out and receive their own signals. Passive satellites receive thermal radiation from the Earth when it is radiated by
solar energy. Examples of active satellites are G.P.S. and Topex, and examples of passive satellites are GOES and AVIRIS.
Q: What does it mean to filter a satellite?
A: Filtering is the ability to selectively pass desired frequencies and remove undesired ones.
Q: Why is band width important to satellite oceanography? State an advantage and disadvantage to having a narrow band width satellite receiver.
A: Band width is important to satellite
oceanography for global and regional scale monitering of ocean pollution and health, and assist scientists in understnding the influence and impact of the oceans on the global climate system. An advantage in having a narrow band width satellite receiver is the clear frequency required to pass a specific modulated signal without distortion or loss of data. A disadvantage would be a result in loss of data during modulation peaks.
Q: Why don't satellites have infinite bandwidth capabilities? What would be an advantage?
A: Infinite bandwidth require a lot of energy and pass excessive noise along with the signal. An advantage would be the ability to survey a very large area.
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