Doppler radar uses the Doppler effect to measure the speed (radial velocity) of targets. Radial velocity is how fast the target is coming towards, or going away from, the radar. The Doppler effect will shift the received frequency up or down, based on the radial velocity of a target in the beam. This gives a direct and highly accurate measurement of target velocity, but only the radial velocity. Doppler radar by itself doesn't measure the azimuthal velocity (how fast it is going in other directions).
Doppler radars may be Coherent Pulsed, Continuous Wave, or Frequency Modulated.
Horseshoe crab
The horseshoe crab or king crab is a benthic or bottom-dwelling creature. It is not a crab at all, but a relative of the arachnids. Its main habitats are coastal areas and river estuaries.
"Limulus polyphemus" is the best-known of the four species.
On its dome-shaped carapace, the horseshoe crab has four small eyes. It has two compound eyes at the sides of the carapace, and two simple eyes on the front.
A horseshoe crab has twelve legs: five pairs of walking legs and a set of tiny pincers. The long, spiky tail is not used as a weapon or for defense; instead, it is just used for steering and flipping the body over if it gets turned upside down.
Atlantic horseshoe crabs, "Limulus polyphemus", can be found all over the eastern coast of North America and Mexico. Buried under mud or sand, they eat small clams, crustaceans, and worms. All over the coast, you will find their shells washed up on shore. Some of these shells are quite big, as the horseshoe crab can grow up to two feet long and a foot wide. Horseshoe crabs go through moults to reach that size.
The horseshoe crab population ranges from the Yucatán Peninsula to northern Maine, but they are most commonly found in the mid-Atlantic region between Virginia and New Jersey. Each major estuary along the coast has its own horseshoe crab population, distinguished from one another by size, colour and eye pigment. The females lay about 100,000 eggs.
The other three species are also called horseshoe crabs. The Japanese horseshoe crab ("Tachypleus tridentatus") is found in the Seto Inland Sea, and is considered an endangered species because of loss of habitat. Two other species occur along the east coast of India: "Tachypleus gigas" and "Carcinoscorpius rotundicauda". All four are quite similar in form and behavior.
Horseshoe crabs may be threatened by Asian overconsumption.
The horseshoe crab has an effective immune system. Its brackish maritime environment is a perfect home for bacteria.
The blood of horseshoe crabs contains an enzyme that causes very rapid clotting in response to the presence of infectious bacteria. This response is used by medical and pharmaceutical companies to detect those kinds of bacteria in products, before the products are sold.
Horseshoe crabs are relatives of the Eurypterids (sea scorpions), whose first fossils appeared at the same time. They are quite ancient. They were definitely present in the early Ordovician, 450 million years ago, in a Burgess Shale-type environment. Their body shape has not changed much since then, though fossils in this group are scarce. The Atlantic horseshoe crab itself has no fossil record at all, and the genus "Limulus" goes back only some 20 million years, not 200 million.
The order they belong to, the Xiphosura, are basal to a clade of the Eurypterida and the Arachnida. It is estimated that the Xiphosura diverged from the Arachnida 480 million years ago.
Because they are famous as so-called "living fossils", the evolutionary record and the genetics of the horsehoe crabs have been studied with interest.
Atlantic hurricane
An Atlantic hurricane is a tropical cyclone that forms in the Atlantic Ocean, usually in the Northern Hemisphere during the summer or autumn, with one-minute maximum sustained winds of at least 74 mph (64 knots, 33 m/s, 119 km/h). When applied to hurricanes, "Atlantic" generally refers to the entire "Atlantic basin", which includes the North Atlantic Ocean, Caribbean Sea and the Gulf of Mexico.
Most Atlantic tropical storms and hurricanes form between June 1 and November 30. The United States National Hurricane Center monitors the basin and gives out reports, watches and warnings about tropical weather systems for the Atlantic Basin as one of the Regional Specialized Meteorological Centers for tropical cyclones as defined by the World Meteorological Organization.
Tropical disturbances that reach tropical storm intensity are named from a pre-determined list. On average, 10.1 named storms form each season, with an average of 5.9 becoming hurricanes and 2.5 becoming major hurricanes (Category 3 or greater). The climatological peak of activity is around September 10 every season. Hurricane Wilma of 2005 was the most powerful hurricane ever recorded in history.
Buras-Triumph, Louisiana
Buras-Triumph is an unincorporated community in Plaquemines Parish, Louisiana, United States.
The population was 3,358 at the 2000 census. On the peninsula, Buras is higher, with Triumph southeast of Buras.
Buras-Triumph has become famous as the location where, on August 29, 2005, at 6:10 AM CDT, the eye of Hurricane Katrina made its strongest landfall. However, the storm surge and high winds began on the previous day, August 28, 2005. During those 2 days, the area was destroyed as a result.
Dry Tortugas
The Dry Tortugas are a small group of islands. They are at the end of the Florida Keys, United States. They are about west of Key West, and west of the Marquesas Keys, at , the closest islands. Still farther west is the Tortugas Bank, which is now underwater. The islands were discovered in 1513 by Spanish explorer Juan Ponce de León. They are an unincorporated area of Monroe County, Florida and belong to the Lower Keys Census County Division. With their surrounding waters they make up the Dry Tortugas National Park.
Aventura, Florida
Aventura is a city found in the northeastern part of Miami-Dade County, Florida. The city name is from the Spanish word for "adventure," and was named "Aventura" because that was the name of the original group of condominium developments in the area. The name predates the well known mall (Aventura Mall) built near the condominium developments. According to the U.S Census estimates of 2006, the city had a population of 30,027.
Florida Keys
The Florida Keys is an archipelago of about 1700 islands in the southeast United States. They begin at the southeastern tip of the Florida peninsula, about 15 miles south of Miami, and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry Tortugas. The islands lie along the Florida Straits, dividing the Atlantic Ocean to the east from the Gulf of Mexico to the west, and defining one edge of Florida Bay. At the nearest point, the southern tip of Key West is just 98 miles (157 km) from Cuba. The Florida Keys are between about 23.5 and 25.5 degrees North latitude, in the subtropics. The climate of the Keys however, is defined as tropical according to Köppen climate classification. More than 95 percent of the land area is in Monroe County, but a small portion extends northeast into Miami-Dade County, primarily in the city of Islandia, Florida. The total land area is 355.6 km² (137.3 sq mi). As of the 2000 census the population was 79,535, with an average density of 223.66/km² (579.27/sq mi), although much of the population is concentrated in a few areas of much higher density, such as the city of Key West, which has 32% of the entire population of the Keys.
The city of Key West is the county seat of Monroe County, which consists of a section on the mainland which is almost entirely in Everglades National Park, and the Keys islands from Key Largo to the Dry Tortugas.
Upper keys
Middle keys
Lower keys
Climatology