Satellite imagery and aerial photography have been compared against each other often – since the launch of the world’s first satellites useful for geographic information systems (GIS) and advanced image processing techniques. Previous comparisons focused primarily on issues related to resolution and accuracy. Today we are as likely to see those comparisons continue, but timing, spectral response, cost and extended image – data services enter into the debate now. How Does Satellite Imagery Compare with Aerial Photography?
A comparison of satellite imagery with aerial photogrammetry today must take into account advances in both approaches to the production of useful landscape and earth observation data today. Whereas most debate previously surrounded issues related to resolution and accuracy, the costs of purchasing satellite imagery have dropped substantially and satellites revisit the same location weekly or daily in some cases. Inability to revisit sites regularly at short intervals has traditionally been an issue where applications involving up-to-date and shorter visitation times were needed.
Aerial photography, gathered through the use of airplanes flying over the landscape remains an important method for gathering remotely sensed imagery about the planet. Satellites cannot be in two places at the same time, but airplanes equipped with cameras can. Airplanes can wait for improved cloud cover – satellites can’t (they pass over locations and must cycle). And, we are probably nearing the day when aerial cameras will be combined with LiDAR into the same device to provide both kinds of data at the same time, something satellite imagery is likely not about to provide for some time to come.
Vexcel, for example, can provide aerial photography down to 6.50cm resolution today. But satellite imagery is not far off with GeoEye-1, for example, providing panchromatic imagery down to 0.41m resolution – although military customers may only be allowed to use this high-end product with consumers gaining access to 0.50m products. DigitalGlobe is also providing 0.50m resolution imagery through it’s WorldView-1 satellite. Bing Maps is continually releasing new and updated imagery for different locations around the world.
Resolution is only part of the value today. Advances in automated image extraction, GIS and even CAD connected to imagery workflows are shifting aerial photogrammetry from what was primarily oriented around hardware and stereoscopic interpretation toward advanced work flows that result in the development of 3D models, spatial databases with extended attribution and near real-time virtual reality.
When we used to compatr satellite images to aerial photogrammetry, our frame of reference seemed oriented toward ‘the map’ but today the very concept of a map is changing. Cloud services are providing new opportunities for services to be delivered to buyers who have both advanced professional capabilities and use needs while also meeting volunteer organisations and individuals who benefit from the information they provide, but who could care less how it is actually done.
Earlier I reported on BlomURBEX, a European based company that is offering a combination of integrated services online whose aerial imagery provides the basis for their development. Infoterra SKAPE is another product that I have worked with which integrates high-resolution satellite imagery with advanced markup capabilities right on the image using Cloud based services. The benefits of the connection of Vexcel images to Microsoft’s pipeline of Microsoft SQL Server for Spatial Data seems obvious.
While the GIS community has grasped the significance of imagery for Cloud services oriented toward advanced geoprocessing, the connection of aerial imagery to building design and architectural designs in CAD environments, through Cloud services, is not as yet obvious. Imagine designing a building within an imagery environment, crazy idea?
New innovations in computer technology, visualisation and Internet delivered services are stretching the benefits of satellite and aerial imagery away from resolution alone to include processing and delivery of information and ultimately new knowledge that businesses can differentiate upon. If I asked you today, “do you 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 are highly oriented to the application at hand. It is now hard to imagine agricultural producers accepting imagery of any kind only once a growing season. When earthquakes happen now, As both Chile and Haiti have recently proven, the expectation and demand is for immediate pictures to assess the situation.
A shift toward earth processes is underway that is related to high-resolution and timely 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 rise to the spectral responses within imagery sources themselves. Do we have enough people to understand these processes, let alone how they are interpreted and expressed through imagery?
The comparison of satellite imagery to aerial photogrammetry today is not as simple 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 of these toward usefulness. If your imagery is not pointing toward increased usefulness today, and in a speedy way, then it probably is not measuring up.
Additional Information:
Photogrammetry Versus LiDAR: Clearing the Air
ISFEREA – Geo-Spatial Information Analysis for Global Security and Stability
Object-Oriented Classification of High Resolution Satellite Image for Better Accuracy
LiDAR and High Resolution Stereo Satellite images for – Map India 2010
Report EuroSDR – State-of-the-art of automated generalisation in commercial software
Towards Integration of Laser Scanning and Photogrammetry
NASA Mission Bridges Satellite Gap; NSIDC Bridges Data Access
