Civil Rights
Movements, leaders, victories and the continuing fight for equality.
q2K BHP
Black History Portal
THE BHP WIRE —
HIDDEN TRUTHS
What's New!
Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
A scatterometer or diffusionmeter is a scientific instrument to measure the return of a beam of light or radar waves scattered by diffusion in a medium such as air. Diffusionmeters using visible light are found in airports or along roads to measure horizontal visibility. Radar scatterometers use radio or microwaves to determine the normalized radar cross section (σ0, "sigma zero" or "sigma naught") of a surface. They are often mounted on weather satellites to find wind speed and direction, and are used in industries to analyze the roughness of surfaces.
Optical diffusionmeters are devices used in meteorology to find the optical range or the horizontal visibility. They consist of a light source, usually a laser, and a receiver. Both are placed at a 35° angle downward, aimed at a common area. Lateral scattering by the air along the light beam is quantified as an attenuation coefficient. Any departure from the clear air extinction coefficient (e.g. in fog) is measured and is inversely proportional to the visibility (the greater the loss, the lower is the visibility).
These devices are found in automatic weather stations for general visibility, along airport runways for runway visual range, or along roads for visual conditions. Their main drawback is that the measurement is done over the very small volume of air between the transmitter and the receiver. The visibility reported is therefore only representative of the general conditions around the instrument in generalized conditions (synoptic fog for instance). This is not always the case (e.g. patchy fog).
 | It has been suggested that this section be split out into another article titled Radar scatterometer. (Discuss) (May 2023) |
A radar scatterometer operates by transmitting a pulse of microwave energy towards the Earth's surface and measuring the reflected energy. A separate measurement of the noise-only power is made and subtracted from the signal+noise measurement to determine the backscatter signal power. Sigma-0 (σ⁰) is computed from the signal power measurement using the distributed target radar equation. Scatterometer instruments are very precisely calibrated in order to make accurate backscatter measurements.
The primary application of spaceborne scatterometry has been measurements of near-surface winds over the ocean.[1] Such instruments are known as wind scatterometers. By combining sigma-0 measurements from different azimuth angles, the near-surface wind vector over the ocean's surface can be determined using a geophysical model function (GMF) which relates wind and backscatter. Over the ocean, the radar backscatter results from scattering from wind-generated capillary-gravity waves, which are generally in equilibrium with the near-surface wind over the ocean. The scattering mechanism is known as Bragg scattering, which occurs from the waves that are in resonance with the microwaves.
The backscattered power depends on the wind speed and direction. Viewed from different azimuth angles, the observed backscatter from these waves varies. These variations can be exploited to estimate the sea surface wind, i.e. its speed and direction. This estimate process is sometimes termed 'wind retrieval' or 'model function inversion'. This is a non-linear inversion procedure based on an accurate knowledge of the GMF (in an empirical or semi-empirical form) that relates the scatterometer backscatter and the vector wind. Retrieval requires an angular diversity scatterometer measurements with the GMF, which is provided by the scatterometer making several backscatter measurements of the same spot on the ocean's surface from different azimuth angles.
Scatterometer wind measurements are used for air-sea interaction, climate studies and are particularly useful for monitoring hurricanes.[2] Scatterometer backscatter data are applied to the study of vegetation, soil moisture, polar ice, tracking Antarctic icebergs[3] and global change.[4] Scatterometer measurements have been used to measure winds over sand and snow dunes from space. Non-terrestrial applications include study of Solar System moons using space probes. This is especially the case with the NASA/ESA Cassini mission to Saturn and its moons.
Several generations of wind scatterometers have been flown in space by NASA, ESA, and NASDA. The first operational wind scatterometer was known as the Seasat Scatterometer (SASS) and was launched in 1978.[5] It was a fan-beam system operating at Ku-band (14 GHz). In 1991 ESA launched the European Remote-Sensing Satellite ERS-1 Advanced Microwave Instrument (AMI) scatterometer,[6] followed by the ERS-2 AMI scatterometer in 1995. Both AMI fan-beam systems operated at C-band (5.6 GHz). In 1996 NASA launched the NASA Scatterometer (NSCAT), on board the NASDA ADEOS I satellite,[1] a Ku-band fan-beam system.[7] NASA launched the first scanning scatterometer, known as SeaWinds, on QuikSCAT in 1999. It operated at Ku-band. A second SeaWinds instrument was flown on the NASDA ADEOS-2 in 2002. The Indian Space Research Organisation launched a Ku-band scatterometer on their Oceansat-2 platform in 2009. ESA and EUMETSAT launched the first C-band ASCAT in 2006 onboard Metop-A.[8] The Cyclone Global Navigation Satellite System (CYGNSS), launched in 2016, is a constellation of eight small satellites utilizing a bistatic approach by analyzing the reflection from the Earth's surface of Global Positioning System (GPS) signals, rather than using an onboard radar transmitter.
Scatterometers helped to prove the hypothesis, dating from mid-19th century, of the anisotropic (direction dependent) long distance dispersion by wind to explain the strong floristic affinities between landmasses.
A work, published by the journal Science in May 2004 with the title "Wind as a Long-Distance Dispersal Vehicle in the Southern Hemisphere", used daily measurements of wind azimuth and speed taken by the SeaWinds scatterometer from 1999 to 2003. They found a stronger correlation of floristic similarities with wind connectivity than with geographic proximities, which supports the idea that wind is a dispersal vehicle for many organisms in the Southern Hemisphere.
Scatterometers are widely used in metrology for roughness of polished and lapped surfaces in optical (i.e. total integrated scatterometry developed by Dr. Jean M. Bennett and colleagues[9][10][11][12]), semiconductor and precision machining industries.[13] They provide a fast and non-contact alternative to traditional stylus methods for topography assessment.[14][15] Scatterometers are compatible with vacuum environments, are not sensitive to vibration, and can be readily integrated with surface processing and other metrology tools.[16]
Examples of use on Earth observation satellites or installed instruments, and dates of operation:[17]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
A scatterometer or diffusionmeter is a scientific instrument to measure the return of a beam of light or radar waves scattered by diffusion in a medium such as air. Diffusionmeters using visible light are found in airports or along roads to measure horizontal visibility. Radar scatterometers use radio or microwaves to determine the normalized radar cross section (σ0, "sigma zero" or "sigma naught") of a surface. They are often mounted on weather satellites to find wind speed and direction, and are used in industries to analyze the roughness of surfaces.
Tehuantepecer, or Tehuano wind, is a violent mountain-gap wind that travels through the Chivela Pass in southern Mexico, across the Isthmus of Tehuantepec. It is most common between October and February, with a summer minimum in July. It originates from eastern Mexico and the Bay of Campeche as a post-frontal northerly wind, accelerated southward by cold air damming, that crosses the isthmus and blows through the gap between the Mexican and Guatemalan mountains. The term dates back to at least 1929. This wind can reach gale, storm, even hurricane force. The leading edge of its outflow (or cold front) may form rope cloud over the Gulf of Tehuantepec. These winds can be observed on satellite pictures such as scatterometer wind measurements, they influence waves which then propagate as swell and are sometimes observed 1,600 km (1,000 mi) away (such as in the Galapagos Islands). These strong winds bring cooler sub-surface waters to the surface of the tropical eastern Pacific Ocean and may last from a few hours to 6 days.
The NASA QuikSCAT (Quick Scatterometer) was an Earth observation satellite carrying the SeaWinds scatterometer. Its primary mission was to measure the surface wind speed and direction over the ice-free global oceans via its effect on water waves. Observations from QuikSCAT had a wide array of applications, and contributed to climatological studies, weather forecasting, meteorology, oceanographic research, marine safety, commercial fishing, tracking large icebergs, and studies of land and sea ice, among others. This SeaWinds scatterometer is referred to as the QuikSCAT scatterometer to distinguish it from the nearly identical SeaWinds scatterometer flown on the ADEOS-2 satellite.
In aerospace, Assembly, Test, and Launch Operations (ATLO), also known as Mission System Integration and Test (MSIT) is the phase of a spacecraft project that comprises building the spacecraft, testing it, and getting it launched. Pictured to the right is John Wirth (left) and Kieran McKay (right) at Kennedy Space Center with ISS-RapidScat, the radar scatterometer which was built at JPL. Specifically, they were testing the rotating radar's capabilities at the Space Station Processing Facility.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.