satellite vs aerial photo

7/30/2019 satellite vs aerial photo

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COMPARISON BETWEEN SATELLITE IMAGERY AND AERIAL

PHOTOGRAPH

Advantages of satellite imagery Characteristics of aerial photographsGreater Areal Extent Higher Resolution

Digital data Analogue photos

Repetitive Coverage Lower cost of 'launch'

Regular (predictable) Distortion 3D Stereo Effect

Greater Wavelength Range Higher understanding

Analysis / GIS Easier interpretation

According to Chris Pershing, the inventor of the patent-pending EagleViewsoftware, it is as simple as the resolution or the closeness of the image, Somesatellites are able to produce higher resolution images.

However, the U.S. and many other foreign governments restrict the resolution ofcommercially available satellite images. In the United States for example,commercial satellite images are limited to 0.5 meters / pixel (18 inches / perpixel).

In contrast, aerial images are not subject to the resolution limits imposed on

satellites, continued Pershing. Aerial images are available at resolutions down to4 to 6 inches per pixel for most of the populated areas in the US. Moving out tolesser populated areas, aerial images are also now widely available at 12 inchesper pixel, still significantly better then satellite.

To clarify how pixels relate to distance, according to Wikipedia, The resolutionnumber represents the distance covered by one pixel in the image. Therefore, a 1meter image is an image where 1 pixel is equal to 1 meter. A 1000 x 1000 pixelimage at 1 meter resolution would cover an area 1000 meters by 1000 meters, orone square kilometer.

HOW DOES SATELLITE IMAGERY COMPARE WITH AERIALPHOTOGRAPHY?

Created on Sunday, 04 April 2010 00:00Written by Jeff Thurston

A comparison of satellite imagery with aerial photogrammetry today must take intoaccount advances in both approaches to the production of useful landscape andearth observation data today. Whereas most debate previously surrounded issuesrelated to resolution and accuracy, the costs of purchasing satellite imagery havedropped substantially and satellites revisit the same location weekly or daily in

some cases. Inability to revisit sites regularly at short intervals has traditionally
http://www.sensysmag.com/dialog/perspectives/12317-how-does-satellite-imagery-compare-with-aerial-photography.htmlhttp://www.sensysmag.com/dialog/perspectives/12317-how-does-satellite-imagery-compare-with-aerial-photography.htmlhttp://www.sensysmag.com/dialog/perspectives/12317-how-does-satellite-imagery-compare-with-aerial-photography.htmlhttp://www.sensysmag.com/dialog/perspectives/12317-how-does-satellite-imagery-compare-with-aerial-photography.html


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been an issue where applications involving up-to-date and shorter visitation timeswere needed.

Aerial photography, gathered through the use of airplanes flying over thelandscape remains an important method for gathering remotely sensed imagery

about the planet. Satellites cannot be in two places at the same time, butairplanes equipped with cameras can. Airplanes can wait for improved cloud cover- satellites can't (they pass over locations and must cycle). And, we are probablynearing the day when aerial cameras will be combined with LiDAR into the samedevice to provide both kinds of data at the same time, something satellite imageryis likely not about to provide for some time to come.

Vexcel, for example, can provide aerial photography down to 6.50cm resolutiontoday. But satellite imagery is not far off withGeoEye-1, for example, providingpanchromatic imagery down to 0.41m resolution - although military customersmay only be allowed to use this high-end product with consumers gaining access

to 0.50m products. DigitalGlobe is also providing 0.50m resolution imagerythrough it's WorldView-1 satellite. Bing Maps is continually releasing new andupdated imagery for different locations around the world.

Resolution is only part of the value today. Advances in automated imageextraction, GIS and even CAD connected to imagery workflows are shiftingaerial photogrammetry from what was primarily oriented around hardware andstereoscopic interpretation toward advanced work flows that result in thedevelopment of 3D models, spatial databases with extended attribution and nearreal-time virtual reality.

When we used to compatr satellite images to aerial photogrammetry, our frame ofreference seemed oriented toward 'the map' but today the very concept of a mapis changing. Cloud services are providing new opportunities for services to bedelivered to buyers who have both advanced professional capabilities and useneeds while also meeting volunteer organisations and individuals who benefit fromthe information they provide, but who could care less how it is actually done.

Earlier I reported onBlomURBEX, a European based company that is offering acombination of integrated services online whose aerial imagery provides the basisfor their development. Infoterra SKAPE is another product that I have worked

with which integrates high-resolution satellite imagery with advanced markupcapabilities right on the image using Cloud based services. The benefits of theconnection of Vexcel images to Microsoft's pipeline ofMicrosoft SQL Server forSpatial Dataseems obvious.

While the GIS community has grasped the significance of imagery for Cloudservices oriented toward advanced geoprocessing, the connection of aerialimagery to building design and architectural designs in CAD environments,through Cloud services, is not as yet obvious. Imagine designing a building withinan imagery environment, crazy idea?

New innovations in computer technology, visualisation and Internet deliveredservices are stretching the benefits of satellite and aerial imagery away from
http://download.microsoft.com/download/D/5/A/D5A4BAA2-1344-4094-9CA0-75B1AC36F5DA/Radiometric_Performance.pdfhttp://download.microsoft.com/download/D/5/A/D5A4BAA2-1344-4094-9CA0-75B1AC36F5DA/Radiometric_Performance.pdfhttp://launch.geoeye.com/LaunchSite/about/fact_sheet.aspxhttp://launch.geoeye.com/LaunchSite/about/fact_sheet.aspxhttp://launch.geoeye.com/LaunchSite/about/fact_sheet.aspxhttp://www.digitalglobe.com/index.php/86/WorldView-1http://www.digitalglobe.com/index.php/86/WorldView-1http://www.bing.com/toolbox/blogs/maps/archive/2010/03/05/bing-maps-imagery-release-february-2010-part-2.aspxhttp://www.bing.com/toolbox/blogs/maps/archive/2010/03/05/bing-maps-imagery-release-february-2010-part-2.aspxhttp://www.bing.com/toolbox/blogs/maps/archive/2010/03/05/bing-maps-imagery-release-february-2010-part-2.aspxhttp://www.ecognition.com/products/whats-new-ecognition-8http://www.ecognition.com/products/whats-new-ecognition-8http://www.ecognition.com/products/whats-new-ecognition-8http://www.esri.com/news/arcuser/0499/imagedata.htmlhttp://www.esri.com/news/arcuser/0499/imagedata.htmlhttp://gisandscience.com/2010/03/17/augmented-reality-and-photogrammetry-a-synergy-to-visualize-physical-and-virtual-city-environments/http://gisandscience.com/2010/03/17/augmented-reality-and-photogrammetry-a-synergy-to-visualize-physical-and-virtual-city-environments/http://www.blomasa.com/blom-information-services/products--services/blomurbex_reg_.htmlhttp://www.blomasa.com/blom-information-services/products--services/blomurbex_reg_.htmlhttp://www.blomasa.com/blom-information-services/products--services/blomurbex_reg_.htmlhttp://www.sensysmag.com/vectorone/?p=4832http://www.sensysmag.com/vectorone/?p=4832http://www.microsoft.com/sqlserver/2008/en/us/spatial-data.aspxhttp://www.microsoft.com/sqlserver/2008/en/us/spatial-data.aspxhttp://www.microsoft.com/sqlserver/2008/en/us/spatial-data.aspxhttp://www.microsoft.com/sqlserver/2008/en/us/spatial-data.aspxhttp://www.microsoft.com/sqlserver/2008/en/us/spatial-data.aspxhttp://www.microsoft.com/sqlserver/2008/en/us/spatial-data.aspxhttp://www.microsoft.com/sqlserver/2008/en/us/spatial-data.aspxhttp://www.sensysmag.com/vectorone/?p=4832http://www.blomasa.com/blom-information-services/products--services/blomurbex_reg_.htmlhttp://gisandscience.com/2010/03/17/augmented-reality-and-photogrammetry-a-synergy-to-visualize-physical-and-virtual-city-environments/http://www.esri.com/news/arcuser/0499/imagedata.htmlhttp://www.ecognition.com/products/whats-new-ecognition-8http://www.ecognition.com/products/whats-new-ecognition-8http://www.bing.com/toolbox/blogs/maps/archive/2010/03/05/bing-maps-imagery-release-february-2010-part-2.aspxhttp://www.digitalglobe.com/index.php/86/WorldView-1http://launch.geoeye.com/LaunchSite/about/fact_sheet.aspxhttp://download.microsoft.com/download/D/5/A/D5A4BAA2-1344-4094-9CA0-75B1AC36F5DA/Radiometric_Performance.pdf


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resolution alone to include processing and delivery of information and ultimatelynew knowledge that businesses can differentiate upon. If I asked you today, "doyou want 1 meter imagery without services or 5 meter imagery with services"which would you choose?

But the differences in revisitation are critically important. And these decisions arehighly oriented to the application at hand. It is now hard to imagine agriculturalproducers accepting imagery of any kind only once a growing season. Whenearthquakes happen now, As both Chile and Haiti have recently proven, theexpectation and demand is for immediate pictures to assess the situation.

A shift toward earth processes is underway that is related to high-resolution andtimely imagery. Water movement, carbon dynamics, atmospheric aerosols,security applications and others are all resulting in applications that are'deepening' as they seek to understand and monitor the processes that give riseto the spectral responses within imagery sources themselves. Do we have enough

people to understand these processes, let alone how they are interpreted andexpressed through imagery?

The comparison of satellite imagery to aerial photogrammetry today is not assimple as it once was. Advances on many fronts including computation, services,knowledge, hardware and software not to mention cost are all considerations.Perhaps the best comparison lies in the alignment of convergence for each ofthese toward usefulness. If your imagery is not pointing toward increasedusefulness today, and in a speedy way, then it probably is not measuring up.

AERIAL PHOTOGRAPHY VERSUS SATELLITE IMAGERY - HAS SATELLITEIMAGERY REPLACED AERIAL PHOTOGRAPHY?

In the last ten years we have seen spectacular developments in the clarity andavailability of satellite imagery. Microsoft and Google are examples of companiesthat now offer the public satellite images, also known as remote sensing images.While these images are fascinating and in many cases potentially useful, somepeople question whether these developments mean the end of traditional aerialphotography. The resounding answer is "No, aerial photography is alive and well."

One reason aerial photography remains a valuable tool is because of its superiorresolution. Particularly with the advent of commercial digital equipment, an aerialplatform provides very high resolution images, whereas satellite resolutionremains limited by both technology and by Federal law. In 1999, commercialsatellites could capture a resolution of one-meter in black and white, andsomewhat less detail in color. That is to say that the smallest detail that could becaptured and clearly delineated was at least one meter in size. There exists apopular rumor that military satellites can read an automobile's license plate fromspace, and that is probably an exaggeration, but it does not matter even if it istrue. You, as a private citizen, cannot buy or use those images anyway. Currentlaw limits the resolution of commercially available satellite images to 0.5 meters.

That means that the smallest detail that can be clearly delineated is at least 0.5meters, or 19.5 inches across. An aerial photograph in highest digital resolution


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taken from 1000 feet above the ground is approximately five times betterresolution than the best commercially available satellite imagery.

Another difference between aerial photographic images and satellite images is thetimeliness and availability of the images. Commercial satellites orbit the earth from

about 400 miles above mean sea level. They orbit in a pattern and a speed thatallows them to pass over the same point on the earth about once every threedays. This is just fine for surveying and mapping. It does not generally allow forcapturing events. Generally speaking, the earth is clouded over about 60 per centof its surface at any particular time. The three-day cycle for a satellite to fly overone point can mean that it may take from a few to several dozen cycles before aclear shot is available. Aerial flight is also subject to weather, but airplanes can flyunder cloud cover and are available for a photographic launch anytime betweensunrise and sunset. A limitation on aerial photography because of weather isgenerally a matter of a few days, not usually weeks or months.

One advantage aerial photography has over satellite imagery is the creativeaspect of composition. Satellite images are generally taken from directlyoverhead. Satellite images can be taken from an oblique angle but this introducesadditional distance from the target and requires repositioning the satellite cameraangle. Aerial photos, in contrast, are generally taken from an oblique angle. Thisallows one to photograph from all sides and at different heights, introducing variedcomposition and enhanced utility. There is also the factor of light in thecomposition of the photograph. A satellite uses whatever light is available at thetime it passes over its target. In an aerial photography session the photographerchooses light that best suits the composition of the target images. The amount ofsunlight, the angle of the light, the shadows the light produce and the time of dayall contribute to a photograph that is both useful in conveying information andaesthetically pleasing.

Satellite imagery will no doubt evolve in its ability to document, map and survey ina variety of light spectra. It is an increasingly fascination mode of imagery.However, aerial photography remains a superior mode of capturing images fromthe air where direction, angle, composition and timeliness of availability are keyrequirements in capturing the target image.

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satellite vs aerial photo