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UAE Space Reconnaissance Center
High resolution imaging is a considerably wide term and not only refers to remote sensing imaging, but also a number of other allied imaging processes and applications. The range of applications depends on a variety of factors, one of the most significant being – resolution. Resolution starts right from the ultra-high resolution microscopic imaging with angstrom levels of spatial resolution to hand held analogue and/or digital cameras and multispectral scanners of very high resolution with mm or few cm levels of spatial resolution.
This paper mainly concentrates on satellite and airborne imaging of earth surface in general and its use in the Middle East in specific.
Imaging Sensors and Platforms
Imaging sensors involve both analogue and digital imaging, multispectral scanning, and laser/LIDAR technology. Photographic imaging utilizes a combination of camera lenses and photographic films which can be black/white (B/W), color, IR or color IR. Thermal imaging sensors can be used separately. The microwave imaging SAR systems are used on board aerial and satellite platforms, and mainly employ microwave bands of ~3 – 25 cm, whereas the LiDAR systems utilize sharp laser beams to determine point elevations above ground. The later is mainly restricted to airborne platforms. The platform can be a tiny device or camera dedicated for medical imaging, or fixed on a normal or electronic microscope, or it can be a hand held camera in the field, or on top of a tower. Above the ground, there are various kinds of airborne, satellites and spaceborne platforms. Satellite platforms have exceeded 7000 and these vary in size, payload, altitude and applications.
Emirates Palace, Abu Dhabi, IKONOS 1m image, 2005 (SRC Archives)
Types of Resolution
Resolution is the most important factor which determines the quality of images and size and kind of features that can be discriminated by an imaging system. Four resolution types are involved: spatial, spectral, radiometric and temporal. Spatial resolution is referred to the size of the minimum area that can be discriminated by an imaging system – smaller the number, better the resolution. The spectral resolution of imaging systems is related to the number and width of imaging bands. It can be coarse as in the case of panchromatic sensors (e.g. 0.5-0.9 microns) or medium resolution in case of multi-spectral systems, when few to 10 or 20 narrow bands (100’s of nanometers wide) are employed. Radiometric resolution is referred to the number of discrete radiance levels radiance discriminated by the sensor, the more is the number the better is the resolution. Temporal resolution reflects how frequent an imaging system can acquire images of an area, usually expressed in days.
Resolution and Accuracy
Remote sensing imaging systems are designed to collect reflected or emitted radiation from objects on earth or other planets, by utilization of sensors which record radiation of wavelengths varying from visible to near-IR, middle and thermal IR to Microwaves (~0.4 microns – ~25cm) .
The term high resolution “spatial” imaging systems can involve those systems which can support large scale mapping, through their high spatial resolution (~1-2m) and reasonable system position accuracy. However, this can be greatly improved by using accurate GCPs.
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