In the context of remote sensing, algorithms generally specify how to determine higher-level data products from lower-level source data. For example, algorithms prescribe how atmospheric temperature and moisture profiles are determined from a set of radiation observations originally sensed by satellite sounding instruments.
2. The angular distance of an Earth satellite (or planet) from its perigee (or perihelion) as seen from the center of the Earth (sun). See Keplerian elements for examples of use.
Important antenna considerations include the following:
1) The physical size of antenna components is determined by the frequency of the transmissions it will receive--the higher the frequency the shorter the elements. At high frequencies, use of a satellite dish will compensate for the reduced amount of energy intercepted by shortened components.
2) The antenna design should fit the type of radio frequency (RF) signal polarization it will receive. The orientation of radio waves in space is a function of the orientation of the elements of the transmitting antenna. A circularly polarized wave rotates as it propagates through space. Antennas can be designed for either right or left-handed circular polarization. Earth-based communication antennas are either vertical or horizontal in polarization, and not suited for space communication. Police and cellular phone transmissions use vertical polarization because a simple vertical whip antenna is the easiest sort of omnidirectional antenna to mount on a vehicle.
3) The antenna needs to produce sufficient signal gain to produce noise-free reception.
4) The antenna should be clear of conductive objects such as power lines, phone wires, etc., so height above the ground becomes important.
Basic antenna components are:
1) Driven element--the parts connected to and receiving power from the receiver/transmitter;
2) Parasitic elements--the parts dependent upon resonance rather than connection to a power source;
- A director or parasitic element that rein forces radiation on a line pointing to it from the driven element;
- A reflector or parasitic element that rein forces radiation on a line pointing from it to the driven element.
A fundamental form of antenna is a single wire whose length approximately equals half the transmitting wavelength. Known as a dipole antenna, it is the unit from which many more complex forms of antennas are constructed.
One of the most common forms of VHF antenna is the Yagi/beam, named for the Japanese scientist who first described the principles of combining a basic dipole (driven element) and parasitic elements. A common TV antenna is an example of this type. A Yagi/beam antenna is directional and therefore includes a rotator to aim (direct) the antenna. See yagi.
An omnidirectional antenna has a wide beamwidth and consequently does not require "tracking" (aiming the antenna toward the signal source). An example of an omnidirectional antenna is the turnstile antenna, a variation of the standard dipole antenna well suited for space communications. The quadrifilar helix antenna is omnidirectional and an inherently excellent antenna for ground station use. Quadrifilars are also used on NOAA's polar-orbiting environmental satellites.
The parabolic reflector or satellite dish antenna collects RF signals on a passive dish-shaped surface. A feedhorn antenna--a simple dipole antenna mounted in a resonant tube structure (cylinder with one open end)--transfers the RF energy to a transmission line. The bigger the dish, the greater the amount of RF energy intercepted, and therefore the greater the gain from the signal.
At the exosphere, beginning at 500 to 1,000 km above the Earth's surface, the atmosphere blends into space. The few particles of gas here can reach 4,500oF (2,500o C) during the day.
29.92 inches or 760 mm of mercury
1013.25 millibars(mb) or 101,325 pascals (Pa)
APT images are transmitted by polar-orbiting satellites such as the TIROS-N/NOAA satellites and Russia's METEOR, which orbit 500-900 miles above the Earth, and offer both visible and infrared images. An APT image has thousands of squares called picture elements or pixels. Each pixel represents a four-km square.
2. In radiometry, a relatively narrow region of the electromagnetic spectrum to which a remote sensor responds; a multispectral sensor makes measurements in a number of spectral bands.
3. In spectroscopy spectral regions where atmospheric gases absorb (and emit) radiation, e.g., the 15 µm carbon dioxide absorption band, the 6.3 µm water vapor absorption band, and the 9.6 µm ozone absorption band.
To convert centigrade to Fahrenheit; multiply the centigrade temperature by 1.8 and add 32o. F = 9/5C + 32.
To convert Fahrenheit to centigrade: subtract 32o from the Fahrenheit temperature and divide the quantity by 1.8. C = (F -32) / 1.8.
False color can be applied to the image by assigning a graduated color palette to represent the gray shades. The color is "false" because it represents an assigned, not actual, color.
to study global climate change. MTPE will use space-, aircraft-, and ground-based measurements to study our environment as an integrated system. Designing and implementing the MTPE is, of necessity, an international effort. The MTPE program involves the cooperation of the U.S., the European Space Agency (ESA), and the Japanese National Space Development Agency (NASDA). The MTPE program is part of the U.S. interagency effort, the Global Change Research Program.
Earth Observing System Data & Information System (EOSDIS) The system that will manage a dataset of Earth science observations to be collected over a 15-year period. Existing data indicates that the Earth is changing, and that human activity increasingly contributes to this change. To monitor these changes, a baseline of "normal" performance characteristics must be obtained. For the Earth, these baseline characteristics must cover a global scale and a long enough period that the variation caused by seasonal changes and other cyclical or periodic events (e.g., El Nino and the solar cycle) may be included in the analyses. The baseline characteristics also must enable scientists to quantify processes that govern the Earth's system. Functionally EOSDIS will provide computing and networking facilities supporting EOS research activities, including data interpretation and modeling; processing, distribution, and archiving of EDS data; and command and control of EGS observatories.
2) The distance, measured from the center of the surface of a parabolic or spherical reflector (e.g., satellite dish) where RF energy is brought to essential point focus.
A cold front occurs when a cold air mass
moves into an area occupied by a warmer air
mass. Moving at an average speed of about
20 mph, the heavier cold air moves in a
wedge shape along the ground. Cold fronts bring lower temperatures and can create narrow bands of violent thunderstorms. In North America, cold fronts form on the eastern edges of high pressure systems.
A warm front occurs when a warm air mass moves into an area occupied by a colder air mass. The warm air is lighter; 50 it flows up the slope of the cold air below it. Warm fronts usually form on the eastern sides of low pressure systems, create wide areas of clouds and rain, and move at an average speed of 15 mph.
When a cold front follows and then overtakes a warm front (warm fronts move more slowly than cold fronts) lifting the warm air off the ground, an occluded front forms.
GOES observes the U.S. and adjacent ocean areas from vantage points 35,790 km (22,240 miles) above the equator at 75o west and 35o west. GOES satellites have an equatorial, Earth-synchronous orbit with
a 24-hour period, a resolution of 8 km, an IR resolution of 4 km, and a scan rate of 1864 statute miles in about three minutes. See geostadonary The transmission of processed
weather data (both visible and infrared) by GOES is called weather facsimile (WEFAX). GOES WEFAX transmits at 1691 + MHz and is accessible via a ground station with a satellite dish antenna.
GOES carries the following five major sensor systems:
1) The imager is a multispectral instrument capable of sweeping simultaneously one visible and four infrared channels in a north-to-south swath across an east-to-west path, providing full disk imagery once every thirty minutes.
2) The sounder has more spectral bands than the imager for producing high-quality atmospheric profiles of temperature and moisture. It is capable of stepping one visible and eighteen infrared channels in a north-to-south swath across an east-to-west path.
3) The Space Environment Monitor (SEM) measures the condition of the Earth's magnetic field, the solar activity and radiation around the spacecraft, and transmits these data to a central processing facility.
4) The Data Collection System (DCS) receives transmitted meteorological data from remotelylocated platforms and relays the data to the end users.
5) The Search and Rescue Transponder can relay distress signals at all times, but cannot locate them. While only the polar-orbiting satellite can locate distress signals, the two types of satellites work together to create a comprehensive search and rescue system.
