More and more digital maps perform an integral role in our daily life.
We often use digital maps to find a necessary city address, map out a route when driving in a car, check out our place of destination before leaving on our trip – either to a civilized place or somewhere wild – or just search different places around the globe.
Most global inhabitants have online access to view a quite detailed map of their city or town. GPS navigators and maps have a permanent place on consumers’ mobile devices.
So, from where do those incredibly detailed and precise maps come—such precisely detailed maps that the great travelers and discoverers of the past could only dream of?
The main sources of the modern maps include:
1) Satellite images of the Earth surface
2) Aerial photography (images taken from aircrafts, various flying crafter with or without a pilot)
3) Images (including panoramic ones) of streets and places taken from cars with specialized equipment;
4) Data (coordinates, images, etc.) submitted by users for specialized map services (like OpenStreetMap).
Data from above-mentioned sources is processed and combined by many companies to present us with different map services like Google Maps, Yahoo Maps, Yandex Maps, and others. We will review each of the map data sources in this and subsequent articles.
Let’s get started with the first point.
Satellite images of the Earth surface.
Satellite maps represent the foundation of our up-to-date cartography
- In 1957, the USSR launched the first artificial satellite.
- 6000+ satellites have since followed.
- Today, about 957 operating satellites revolve around the Earth.
Satellite maps serve many and varied purposes: security, telecommunication, navigation, entertainment, science and, of course, earth surface research.
Satellite imagery is indispensable in many areas such as agriculture, forestry, ecology, geological hydrological searches, education, and reconnaissance. Satellite images are taken of light beams visible to the naked eye and those that are not—the invisible light spectrum (ultra-violet and infra-red range). There are also radar shots that depict terrain maps.
- It is not possible to take one panoramic picture of the whole horizon due to technical limitations (limited mirror area) and circumstances, e.g., cloud cover. The solution for this problem is to combine several shots of the same area made by different satellites or by the same satellite at different times. The problem of limited vision is resolved by shooting in different spectrum diapasons (modern sensors allow this).
- Another issue concerning satellite imagery is the question of privacy, since publically available maps might show secret military or other objects. As a result, map service providers often get requests to “delete”/ “change”/ “hide” restricted areas on their maps.
Until now the main “space cameras” have been satellites belonging to the following countries and organizations:
1. American state organizations: NASA (National Aeronautics and Space Administration) and NOAA (National Oceanic and Atmospheric Administration). Both those organizations sequentially managed the Landsat project, the largest and the greatest long-term program of taking images of the Earth from space.
Started in 1966 as “Earth Resources Observation Satellites”, the program is now known as “Landsat” and continues today.
In the context of this program, eight satellites have been launched in total.
The first one was sent in 1972; the latest one—Landsat 8— was launched on February 11, 2013.
The accuracy of Landsat 8 satellite images is 15 – 60 meters per pixel. The period of data gathering for the whole planet by this satellite is 16 – 18 days.
Initially the Landsat program started as a national one; in 1979, it was handed over to private companies to carry out on a commercial basis. Private companies (Earth Observation Satellite Company [EOSAT], Hughes Aircraft and RCA) were managing operating satellites (Landsat -4, -5), built new satellites (Landsat -6, -7), and possessed exclusive rights of the sale of project data. In return, they partially financed the program.
Landsat satellites have taken billions of images. These images were received by stations in the USA and in other countries represent a unique base for searches in many industries.
During the program lifecycle, there have been various setbacks: Landsat 6 failed to reach orbit, program financing stopped several times or was insufficient.
Finally, the importance of Landsat program was officially recognized by the American government, and in October 1992, “Land Remote Sensing Policy Act (Public Law 102—555)” was adopted. This law made it possible for Landsat 7 to continue its work and guaranteed accessibility of images taken by Landsat at the lowest prices for existing and new users. It is possible to say that adopting this law was a decisive step for contemporary cartography: this law assures public access to the unique data source for many people.
It is also worth noting that all data and images collected by NASA are distributed free of charge.
2. Collaborative projects by European countries:
– European remote sensing satellite (ERS) – What makes this project interesting? This is first project to take Earth images from a polar orbit. When revolving by polar orbit, the satellite passes both poles and also the equator at 90 degrees (i.e. satellite goes along the meridians).
Two satellites were launched (1991 – 2000 and 1995 – 2011 are the life years of each satellite). Each of the crafts exceeded its planned lifetime and brought valuable data of the Earth (land, water, ice, atmosphere) using a variety of the latest measurement methods. Both the satellites were in tandem along the same orbit with a one-day difference.
– Envisat (“Environmental Satellite”) project – this project is over since contact with the revolving satellite was lost. The satellite was launched on March 1, 2002; it stopped responding on April 8, 2012. Why is this interesting? This satellite was going by the polar sun synchronous orbit that assumes passing the equator at the same local time on every pass and thus taking images with the same shadow on every pass.
Until now, Envisat has been the largest civil satellite launched from Earth. It is still revolving around our planet on a 101-minute cycle, and presents a real collision threat to other aircrafts.
Data collected by this satellite’s sensors during its work time is used in many scientific disciplines like biological oceanography, hydrology, cartography and others.
– Pleiades Project is part of the European satellite system of remote sensing of Earth programs and has been managed by CNES, a French space agency, since 2001. The Pleiades Project includes two identical satellites (Pleiades-1A and Pleiades-1B) representing the latest achievement in the spatial resolution area. These space crafts move along the same orbit ensuring daily shots of the same objects. Besides other tasks, the Pleiades satellite group helps monitor emergencies and eliminates consequences of natural disasters.
3) Russia used the “Don”– series satellites to collect images of the terrestrial surface in context of photoreconnaissance. Image resolutions provided by Don Satellites is 0.95 meter per pixel. This program was carried out between 1989 and 2006.
4) Satellites of commercial companies
– DigitalGlobe is currently the largest commercial operator of civil satellites for remote Earth sensing. Its satellites are equipped with sensors and equipment producing photographs of the highest resolution. This company provides the most substantial part of high resolution data found at Google Maps/Earth and Virtual Earth services.
DigitalGlobe operates with the following range of satellites:
- WorldView-1 (resolution is 0.5 m per pixel)
- WorldView-2 (resolution is 0.46 m per pixel),
- QuickBird (resolution is 0.61 m per pixel),
- GeoEye-1 (resolution is 0.41 m per pixel)
- IKONOS (resolution is 1 m per pixel).
- WorldView-3 (resolution is 0.31 m per pixel) – this satellite was launched on August 13, 2014.
In September 2016, the company plans to send a satellite—called the WorldView-4 с—that will provide images with resolution of 0.25-0.34 meter per pixel.
The total daily photo coverage of DigitalGlobe satellites is more than 3.5-million square kilometers of the Earth’s surface.
DigitalGlobe satellites provide shots with the highest spatial resolution and extended spectral range (in about 17 spectral channels) that are indispensable for cartography, monitoring surface changes, agricultural research, etc. These satellites employ the latest Short Wave Infrared (aka Short Wavelength Infrared [SWIR]) of shooting that allows building complex maps and models of rocks, grounds and soils. Maps and models received by this method are very helpful for ecological research, minerals searches, monitoring of objects in areas with low visibility, like fires.
The main competitor of DigitalGlobe is Airbus Defence & Space and its subdivision, Spot Image.
Currently Airbus Defence & Space provides a range of six Earth observation satellites that can be individually customized to specific requirements: either to get weather-independent data or to get very-high-resolution imagery, etc.
Based on the brief review of the up-to-date satellite imagery, it is possible to make the following summary:
Right now we are lucky to have access to the results of scientific-technical progress in the area of satellite imagery of our planet—mainly free of charge or for a small fee depending on the policy of the mapping service provider.
Thanks to the efforts of several generations of scientists and constructors, we can observe our cities and towns, individual buildings, to distant quarters of our Earth. And that is all thanks to the detailed and precise maps accumulated for 40 – 50 years of satellite flights and to the digital services for images decryption and processing.
The technical tendency of the satellite imagery development lies in increasing precision of the imagery, growing image specification and also usage of different highly sensitive gear to compose the full picture surmounting visual objectives for shooting.
Besides the technical progress, our happy possibility to use satellite maps is also assured by the legislative regulation of the map data in many countries that opens this data to the public and limits data speculation preventing monopoly in this area.
The tendency of satellite map evolution is increasing the weight of commercial projects comparably with state programs in the total sum of the Earth surface research flights. However, production and launching of satellites still remain a quite expensive and long-term project that only large companies can afford; consequently, those companies are currently the greater players on this field.
It is great to see that earth surface remote sensing projects focus more on scientific-research than military projects. Another advantage of similar projects is that often efforts of several countries should be united to handle the project scope, and this also serves uniting our planet.
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