The new images made by Endeavour were also formed from two sources, in this case two antennae. The ship made use of the interpherometric system in which two radars emit signals on bands X and C, two electromagnetic waves that rebound off the earth’s ground and return to the space shuttle where they are captured by two groups of antennae, including an external one, fastened by a 60 meter mast. The result is two captured images of literally different positions. By comparing these differences of the reflected signals, an image of the relief is formed. The use of radar for this type of application is more interesting than using optical cameras in planes and satellites because it is possible to operate during day and night, and without the interference of cloud. The optical images can only be done with solar light and a clear sky.
The first piece of work carried out by the researchers at Embrapa’s Monitoring Satellite Unit with the new images came at the request of the Ministry of Defense with the objective of supplying the Brazilian army unit that would go off to Haiti in command of the UNO Peacekeeping Force. “We collected the information from NASA and we mounted maps of the territory in 3-dimensions (3D), making use of SRTM images upon which were superimposed images from various satellites”, Miranda says. Thus, by way of specific software, it is possible to make a journey through the images as if we were in a helicopter flying over a city or region. This same technique was used for demonstrating the relief of the Paraíba Valley, the Greater Sao Paulo Region and part of the coast.
In order to demonstrate the scope of potential of the images, and topographical maps via the SRTM, Embrapa researchers have generated a map of the average temperatures of the State of Sao Paulo, starting from the existing relationships between them and the altitude levels. “This is a new model that looks at altimetry in order to show, through the 90m x 90m resolution, the temperature variation as a function of relief, since when increasing in altitude the temperature decreases.”, Miranda explains. “This type of map is important for zoning within the agricultural industry, because it provides data for a more precise analysis of the appropriateness or not of determined agricultural crops in the various regions of the state.”
The image preparation demanded of the Embrapa Monitoring Satellite Unit a tremendous technical effort during the data processing. “We’d never used such computers. If it hadn’t been for our equipment infrastructure, we would’ve taken a lot longer to prepare the images”, Miranda underlines. “After we had downloaded the data, we began to understand it, in order to organize the projection systems for Brazil.” One of the problems presented by this technology is the non-differentiation of beds of water such as rivers and lakes. “In order to see them, one needs to carry out corrections with the help of other images and maps, principally those of satellites.” For 3-dimensional visualizing, the researchers generated an artificial shadowing of the relief, simulating the sun in the afternoon period, positioned to the north of the area and projecting its rays at an angle of 45 degrees. The image thus obtained is easily projected and the maps are easy to understand.
The first state to have its relief map ready, having come from the SRTM data, was Sergipe, because of its small territorial dimension. The work done during it permitted greater facility in the production of the other Brazilian states. All of the maps and numerical images are compatible on a scale of 1: 250.000, in which every millimeter is equivalent to 250 meters on the ground. The SRTM images and numerical data will be on show at the website of Embrapa’s Monitoring Satellite Unit (www.cnpm.embrapa.br) and in the future on a set of CDs. They will be incorporated into the collection Brazil Seen From Space, launched during 2001 by Embrapa, based on data from the Landsat satellite, and which shows the environmental characteristics of the national territory such as forests, semi-arid areas, agricultural areas without a determination of the relief. Embrapa is going to present the two images (SRTM and Landsat) side by side, on the website and on CDs, on maps sub-divided by the states of the federation.
Maps of Brazil with images captured in space are going to show, in an unprecedented manner, the relief of all of the country. Mountains, erosions, inclines and all types of elevations or slopes of the ground are now more defined, precise and better visualized in the group of images of the Brazilian topography that the Satellite Monitoring Unit of the Brazilian Agricultural Research Corporation (Embrapa) is preparing and going to make available starting from the month of April on the institution’s website. The maps are the result of methodology developed by Embrapa based on the data obtained by the space shuttle Endeavour during a mission carried out in February of 2000. The mission entitled Shuttle Radar Topography Mission (SRTM), generated enormous data (12 terabytes) and covered some 80% of the surface of the planet earth where 95% of the world’s population lives.
The space mission was an operation projected and financed the North American Space Agency (NASA), the National Geospatial-Intelligence Agency (NGA), in collaboration with the Italian Space Agency (ASI) and the German Aerospace Center (DLR). With the raw and free data in hand, the Embrapa team from the city of Campinas, coordinated by Evaristo Eduardo de Miranda, started working in 2002, when NASA released the files of South America still in the form of numbers or images that would not have reminded one of colored and easy to understand maps. Finalized, the images went through a series of useful applications, principally in the area of territorial planning and of environmental mounting. “Within the applications are the sustainable development of agriculture; programs for the management of river basins; the preservation of forestry resources; ecological and economic zoning; studies on conservation of soils in order to identify and avoid erosion and even the implanting of rural electrification and highways”, Miranda says. “By analyzing the maps, we can verify, depending on the direction, the declines and inclines of a highway, as well as its altitude, which could facilitate the planning of journeys and the transport of heavy cargoes, for example.” The SRTM maps could also contribute to the improvement of the existing altimetry cartography, principally in the isolated areas of the Amazon.
The altitude data is also going to benefit telecommunications. With the maps in hand, the companies will have greater facility in identifying the best geographical locations for cellular phone transmission towers, for example “I believe that the recently established program Public-Private Partnerships (PPPs) for the execution of infrastructure works could also benefit from the SRTM images when dealing with a highway network, showing that it can be expanded with minimal negative interference to the environment.”, says Miranda. The images prepared by Embrapa show the altitude and relief at intervals of 90 meters by 90 meters (squares of 8,000 m2). In the maps generated by Embrapa for the municipality of Sao Paulo, for example, the Paulista spine (the elevated land where Paulista Avenue is located) is perfectly visible, as well as the beds and the and confluences of the rivers Tamanduateí, Tietê and Pinheiros, as well as the Colônia crater, in the district of Parelheiros, probably formed by a meteorite.
“We hope the American government releases the original resolution captured by Endeavour, of 30 meters by 30 meters”, Miranda says. The White House decided to restrict the resolution of the images after the attacks of September 11th of 2001. “We believe that, shortly, they are going to liberate the 30 x 30 meters images, as they are already doing so for some research programs.” Even with these restrictions, the SRTM images still produce a sophisticated product that brings advances in obtaining topographic data and also in the use of radar for this type of work. “Only to get an idea of the dimension of sophistication of the SRTM we can compare it with the Radam (Radar for Amazonia) Project that produced images (and not topography) by way of the radar in aircraft, principally in the Amazonian region in the decade of the 70’s. If we were to group together all of the flying hours, they spent almost three years of make the images of all of Brazil with various space discontinuities, whilst the Endeavour carried out in eleven days the homogenous measurement of almost all of the planet.”
A shuttle for many journeys
In order to form the complete and precise topographical map of the earth, the space shuttle Endeavour flew with a 60-meter length mast that was extended in outer space, at an altitude of 233 kilometers. At the tip of the mast there had been installed one of the antennae that received the radar waves on bands X and C, used in the formation of the image. Another mast was in the space shuttle’s cargo hold. In order to complete the eleven day mission, between the 11th and the 22nd of February 2000, Endeavour orbited the earth sixteen (16) times per day, completing 176 orbits, at a velocity of 7.5 kilometers per second (7.5 km/s). With a crew of six on board, this was the ninety-seventh mission of space shuttles and the fourteenth for Endeavour. This shuttle, which was launched from and landed at the John F. Kennedy Space Center, in Florida, is the fifth space shuttle of the series. Its sister ship is being prepared to take off this coming May to take equipment to the International Space Station, thus restarting the space shuttle flights that were interrupted with the loss of Columbia and its crew on the 1st of February 2003, when the spaceship disintegrated during re-entry into the earth’s atmosphere. In July it should he the turn of the third space shuttle, Atlantis, to blast into space.