Traverses over the Other Continents - The Caribbean and Central America Part-1 - Remote Sensing Application - Completely Remote Sensing, GPS, and GPS Tutorial
Traverses over the Other Continents - The Caribbean and Central America Part-1

The Caribbean is a broad geographic area that extends south and east of the Gulf of Mexico, and includes islands such as Cuba and Puerto Rico, a string of islands along a plate boundary called the Antilles (the West Indies reached by Columbus), and islands off the northern shores of South America. The Bahamas are generally included in this group. Here they can be seen from space in this NOAA weather satellite image:

Most of the islands of the Bahamas.

The Bahamas lie off the east coast of Florida and are also near Cuba. These coral atolls are evident from the light blue-green waters (caused by reflection of sunlight off suspended sediments of limestone) that surround them, as seen in this astronaut view looking west over the Atlantic Ocean:

The Bahamas from space.

For a moment we will leave the Caribbean and look at another coral island in the Mid-Atlantic. Bermuda is a favorite destination of ocean liner cruises:

This next view from space (mosaic) shows the eastern and southern Caribbean. The map covers the entire Caribbean from Florida to Venezuela:

Composite image of much of the Caribbean.
Map of the Caribbean.

The largest of the Caribbean islands is the nation of Cuba, seen in this MODIS image:

MODIS image of Cuba.

The capital of Cuba, Havana, appears in this Landsat subscene

Havana, Cuba.

More details of this city, once a popular tourist destination for Americans in pre-Castro years, appear in this SPOT image:

SPOT image of Havana, Cuba

At the bottom of the first Cuban image is Jamaica. Here is a closer look contained in an astronaut photo:

Jamaica, as seen by astronauts aboard the International Space Station.

Typical of the northern islands are Puerto Rico and the Virgin Islands. The first image is an STS astronaut-taken photo of Puerto Rico, which by treaty is allied to the United States as a Territory:

Puerto Rico, as seen from the Space Shuttle.

It is not obvious from this photo that the interior of Puerto Rico is mountainous. A DEM topographic image reveals the extent of these mountains:

Topographic color image of Puerto Rico constructed from Digital Elevation Map (DEM) data; lowlands appear in blue.

Puerto Rico contains the only true tropical rain forest in territories tied to the U.S. This view is from the El Yunque National Park:

The mountainous 'jungle' of eastern Puerto Rico.

San Juan is one of the oldest cities in the western hemisphere (Columbus discovered Puerto Rico in 1493). Here is a view of the old city in the foreground, the new city further back, and the western mountains in the distance.

Aerial view of San Juan.

One of San Juan's landmarks is the El Morro fortress:

The El Morro fortress and park; enlarged IKONOs image.

A short distance to the east of Puerto Rico are the Virgin Islands, seen in this astronaut photo:

The Virgin Islands.

The left (west) two islands are U.S. territories, being the islands of St. Thomas and St. John (to its east). The large island in the middle is the British Virgin Island of Tortola.

The Lesser Antilles is a long chain of island that run from the Virgin Islands south to Grenada, then east through Trinidad to the Dutch islands of Curacao and Aruba. The Outer Antilles face the Atlantic Ocean, as seen here in this MODIS view:

The Antilles Islands (from the top) of Antigua, Montserrat, Dominica, Martinique, Santa Lucia, St. Vincent, and Grenada.

Typical of this eastern group, popular in winter with tourists looking for warm climes and dreamy beaches, in the Windward Islands is the volcanic island of Martinique; note the wind shadows:

Astronaut photo of Martinique.

The small island of Aruba, off the Venezuelan coast marks the end of the Antilles. This island, a semi-desert, has been photographed by the Shuttle astronauts:

Astronaut photo of Aruba, part of the Dutch Antilles.

We now head westward across the Gulf of Mexico and move south of the U.S. border into northeast Mexico, in the States of Nuevo Laredo and San Luis Potosi (left two-thirds of the image below) and Tamaulipas (right). The strongly folded sedimentary rocks of the Sierra Madre Orientale run through the center of the scene. Coastal plains make up the area to the east and semi-desert at high elevations occupies the land to the west. The reds denote regions that can experience 30 inches (75 cm) of rainfall each year owing to moisture moving inland from the Gulf of Mexico. This is a monsoonal climate, with wet, hot summers and dry cold winters. The plains supports typical subtropical savannah vegetation and the mountains are havens of both broadleaf and coniferous trees. The arid interior to the west is host to brushy plants and cactus.

 Part of the Sierra Madre Orientale of northern Mexico, with rain forests to the east and a barren desert landscape in the lowlands to the west.

We saw another part of the Sierra Madre Orientale on page 2-6. Here is a different Landsat image which shows both the mountains and the city of Monterey:

Monterey midst the Sierra Madre Orientale.

The Sierra Madre Oriental provide a spectacular backdrop for Monterey, as is evident in this photo (the architectural feature is the Puente de la Unidad, a suspension bridge):

Monterey, Mexico.

On to central Mexico and a peak at the oldest city in the Western hemisphere, the present day Mexico City, built on a site where in the 12th century stood Tenochitlan, inhabited continuously since then. Mexico City now is seen as a blue area in the upper left part of the image. In 1973, M.C. had just over 7 million but has grown so rapidly that it will approach 30 million early in the 21st Century. Parts of the city stand on swampy ground and lake beds, particularly susceptible to failure and building collapse during the strong earthquakes that frequent the region. To its east are a line of active to dormant volcanoes, marking the surface expression of subduction of the Pacific plate under the North American plate.The two biggest volcanoes are Istaccihuatl and Popocatepetl, both snow-capped in this May scene, that lie to the southeast of M.C. Their slopes, and highlands elsewhere, are forested (reds) but most of the land is arid and sparsely vegetated. Most of the region shown is elevated - at 2800 m (7500 ft) at M.C. and higher.

 Mexico City (blue area upper left), volcanic mountains, and desert lands in central Mexico.

The sprawl of Mexico City is evident in this satellite image:

Mexico City.

Mexico City is now the largest city in the western hemisphere. It has grown from less than 10 million in the 1970s to more than 21 million in 2010. It also a very old city, having been started by the Aztecs in the 1300s. These two Landsat images show the spreading of the city in the last 40 years.

Growth of Mexico City between 1973 and 2009.

Combining Landsat and DEM data yields this perspective view of Mexico City. The two volcanoes appear to its south-southeast. The ring of hills around much of Mexico City indicates why it is often a smog-drenched city since winds may be too blocked to drive the gases away.

Perspective view of Mexico City, made by combining Landsat and DEM data.

Here are two ground views of part of Mexico City. The first shows the central high rise area in the background with the church of Our Lady of Guadalupe in the foreground. The second shows part of the famed Avenue de la Reforma:

Part of Mexico City.
Avenue de la Reforma.

This aerial view shows the city park and the Chapultepec palace, with part of the central city.

Another view of Mexico City, with

Mexico City is situated at the edge of a volcanic belt. Here are the volcanic peaks of Iztaccihuatl and Popocatepetl in the background, with the southeastern edge of the city in the foreground.:

Part of Mexico City, with two stratocones in the background,.

Popocatepetl is one of several dormant volcanoes in this part of Mexico. Here it is as seen by SPOT:

Popocatepetl, SPOT image.

Popocatepetl is not the most active volcano in Mexico. That 'honor' belongs to Colima, seen in this ASTER image:

ASTER image of the volcano Colima.
The Colima volcano erupting.

There is a fair number of volcanoes, many dormant and some extinct in Mexico. Consider this map:

Volcanoes in Mexico.

The map reveals two different lines of volcanoes. The major one crosses the country in a trend that does not quite follow the present day subduction zone where the Cocos plate is diving below the North American plate. One model postulates a hot spot that has led to volcanoes of progressively younger age to the southeast as the North American and Pacific plates interact. The second, to the south, is along an active zone.

Mexico's second city is Guadalajara. Here is a satellite perspective of that city made from Landsat imagery:

Perspective view of Guadalajara.

A must-see when visiting Mexico are the ruins at Teotihuacan, northeast of Mexico City. This ancient metropolis was built by progenitors of the Aztecs, perhaps the Tototacs, about 100 BCE. Included were temples for worship of their gods. Several of these were pyramids, including the Pyramid of the Sun - third largest in the world. Here is an IKONOS image of that Pyramid, and a ground scene:

The Pyramid of the Sun, seen from space
Part of the Avenue of the Dead at Teotihuacan.

Mexico has become a popular destination for tourists, especially in the winter. Among ocean resorts are Acapulco on the west coast and Cancun and Cozumel on the Caribbean (in the Yucatan). This Landsat image of Cozumel reveals that it is an island and the main town is on the sheltered west side:

Cozumel, Mexico.

Cancun also is an island, as seen in this Landsat image:

Cancun, Mexico

We move south into Central America through Guatemala into Nicaragua. The countries of Central America are shown in this map:

Map of Central America.

Why is Central America where it is and is there in the first place? The answer is suggested by this geologic diagram:

The Plate Tectonics of Central America.

Only recently geologically, in the last 4 million years, has Central America existed as a land bridge. After the North and South American plates split from Pangaea, they traveled westward separately as they moved against the Pacific plate. Nestled between them are smaller plates. The Cocos tectonic plate is being squeezed by the Pacific plate on the west and the Caribbean plate that is caught between the North and South American plates to the east. As a result volcanoes have developed in the sedimentary rock units shoved up above a subduction zone - this has resulted in the land bridge that joins North and South America, namely Central America.

Central American volcano map.

The Volcano Arenal, in Costa Rica, is typical of the stratocones that extend along most of Central America:

Volcano Arenal.

From a space perspective, we look first at Guatemala, shown in a MODIS natural color image. The west coast is relatively arid; note the line of volcanoes indicated by snow capping. The interior is a tectonic belt and is higher, accounting for the vegetative cover that denotes a jungle.

Guatemala.

Nicaragua's western region, against the Pacific Ocean, appears below. The larger body of water inland is Lake Nicaragua, with several volcanoes on islands within. In the upper left is Lake Managua, with the capital city, Managua, along its south shore. Circular lakes are fillings of central vents or calderas. The lower elevations consist of semi-arid vegetation, with some farmlands. Areas of red represent uplands with forest cover, with more mountainous highlands at the upper right corner.

Western Nicaragua, in Central America. This scene shows the large Lake Managua and several volcanoes built on the strong folded rocks of the region.

This part of Central America, which includes Guatemala, Honduras, and El Salvador, is especially mountaineous, with its ranges marking the upthrown crustal blocks at a plate boundary. The relief map made from SRTM (radar) data bring out the rugged topography (note the fault lines that are etched out from the terrain):

SRTM relief map of part of Central America.

Costa Rica has, in recent years, become popular as a tourist attraction and for some Americans a splendid retirement place. It is largely forested as is evident in this satellite view:

Costa Rica as seen from space.

It is also mountainous, as evident in this ground scene

The central mountain range of Costa Rica.

The capital of Costa Rica is San Jose, shown next in a satellite image looking straight down and then in a perspective view made by combining SRTM topographic data with a Landsat image:

San Jose satellite view.
Perspective view of the valley hosting San Jose (near center).

As we approach the South American continent, we move from Costa Rica into Panama, shown first in another relief map created from SRTM data and then using a SAR radar image made by the Japanese Fuyo-1 satellite:

Relief map of southern Central America, made from Shuttle Radar Topography Mission data; the Panama Canal is not shown in this version.
Fuyo-1 image of Panama.

In the scene below, a Landsat-DEM perspective image we see a perspective view of the "Big Ditch" that was one of President Teddy Roosevelt's greatest accomplishments - the Panama Canal, which rivals the Suez Canal (see page 6-13) as the greatest aid in oceanic navigation. A French company, which had dug the Suez Canal, made an attempt in the 1880s to excavate a Panama Canal, but had to desist because of insufficient funding. The present canal was started in 1903 and finished in 1914. Approximately 83 km (52 miles) of canal was actually dug, but much of the passageway consists of natural lakes.

Scene showing the Panama Canal under construction.

Just as the Suez Canal obviates the need to sail around Africa for Europeans to get to Asia, so does the Panama Canal allow ships from the east to get to Asia without having to sail around South America. The canal is shown in this perspective, made from Landsat and SRTM inputs.

Perspective Landsat image of the Panama Canal.

In this next image, Landsat data are displayed in colors that represent the calculated NDVI (a measure of vegetation density, see Section 3) for the area that include the Canal and Lake Gatun. Most of the land on either side has a strong NDVI rating, expected since this is heavily forested tropical "Jungle".

The Panama Canal in a version made as an NDVI image using Landsat data.

Here is a map showing the main landmarks along the Panama Canal.

Unlike the earlier Suez Canal, the Panama Canal requires a series of locks to acommodate the difference in sea level heights between the Atlantic (Gulf of Mexico) Ocean and the Pacific Ocean (the Pacific is about 5 meters higher). If going westward, a boat enters a lock, behind it another lock gate swings shut, and water is pumped in to raise the boat level to that of the next lock entered. Here are two diagrams of this lock system:

Cross-section through the Panama Canal, looking south, showing the individual locks in the water rising-lowering system.
How individual locks help to raise or lower a ship passing through the Panama Canal.

Here is an aerial view of the Gatun locks:

The Gatun locks.

Most of the canal is without obvious artificial sides; the canal where dug appears almost like a stream bank:

A ship passing through the Panama Canal.

Source: http://rst.gsfc.nasa.gov/