Figure 4 shows more details in the roof in the original 11bit image than in its 8bit counterpart. Only in some crucial areas do differences appear between the original 11bit and the derived 8bit grey values. However, the grey values within one scene will not cover the whole range and a qualified change from 11bit to 8bit grey values does not lead to significant loss of information. OrbView-3, Ikonos and QuickBird have a radiometric resolution of 11bit, with which 2,048 grey valu-es can be represented. The effective GSD as determined by point-spread analysis of sharp edges does not show loss of resolution against the nominal GSD, but it can be manipulated by contrast enhancement. The resulting slowdown factor is 1.4 (Figure 3). OrbView-3 takes 2,500 double lines per second, but the satellite footprint speed is 7.1km/sec, which requires permanent change of view direction to slow down angular speed.
The effective GSD of 1m resulting from such over-sampled pixels differs from nominal GSD of 1m. OrbView-3 uses staggered CCD-lines two CCD-lines are shifted by 0.5 pixels against each other so that the pixel size projected on the ground for nadir view is 2m and adjacent pixels overlap 50% in both directions (Figure 2). Many of these differences result from sensor configuration, radiometric resolution, recording conditions and terrain characteristics. Buildings are still visible but they cannot be mapped in detail, and sometimes back-gardens will be identified as streets. On the other hand, the 5m GSD of Spot 5 limits the use of these images to the creation of maps of smaller scale. The GSD of 0.62m offered by QuickBird enables identification of more detail. OrbView-3 and Ikonos have approximately the same resolution, but comparison shows that edges are sharper in the Ikonos image and that whilst OrbView-3 shows cars only as blobs, structural elements are visible in Ikonos. As a rule of thumb, the GSD should be at least 0.1mm of the map scale, corresponding to scale 1:10,000 for 1m GSD.Įxamination of information content has to be done by visual inspection (Figure 1). In mapping terms both geometric accur-acy and information content are important, but the required geometric accuracy can be reached without difficulty provided that images are not degraded by at-mosphere and sun-elevation effects. In operation since 2004, OrbView-3 is one of the recent very high-resolution space sensors, offering images of 1m panchromatic and 4m multispectral Ground Sampling Distance (GSD). However, they are not suited for 1:5,000 mapping, for which scale Ikonos images also show limitations. Although OrbView-3 images are qualitatively slightly inferior to Ikonos panchromatic scenes, they can be used for the generation of topographic maps at scale 1:10,000. The information content of OrbView-3 and Ikonos imagery is compared, using the Zonguldak area in Turkey as test area.
Information Content of High-resolution Satellite Image Posted in GIS Maps, GIS Raster Data | Tagged Pakistan, Pakistan GIS, Pakistan GIS Data, Pakistan GIS Raster Data, Pakistan Population Map, Population Data Pakistan, Population Density Pakistan | Leave a reply Pakistan Soil Data based on Shear wave Velocity of 30 metersĪn analysis of mapping potential from OrbView 3 Images is given below (extracted from GIM International) Versions: (i) Adjusted to match UN national estimates and (ii) Unadjustedįormat: Geotiff (zipped using 7-zip (open access tool) Spatial Resolution: 0.000833 degrees (~100m at the equator) This appears to be the highest resolution data on the subject available in open source as of today. The AsiaPop project was initiated in July 2011 with an aim of producing detailed and freely-available population distribution maps for the whole of Asia. High resolution, contemporary data on human population distributions are a prerequisite for the accurate measurement of the impacts of population growth, for monitoring changes and for planning interventions.
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