Enhanced Line Rate imagery

A new term doing rounds of Remote Sensing circles is Enhanced Line Rate imagery. What actually is Enhanced Line Rate? Pushbroom sensors such as IKONOS acquire data using a line of sensors arranged perpendicular to the flight direction of the spacecraft. It is a large focal plane detector array, capable of generating thousands of line scans per second thus producing digitized ‘continuous’ data. Higher the line rate better is the quality of the images. But this also means heavier data hence more burden on onboard storage. Higher line rates also require longer time-period for acquiring a particular area of interest. In most of today’s high resolution sensors simultaneous imaging in panchromatic and multispectral modes is provided. The pixel size on the detector array of Ikonos is 12 μm for the panchromatic (PAN), and 48 μm for the multispectral (MS) detectors. The panchromatic detector array provides line rate of 6500 lines per second, while multispectral sensor has a line rate of 1625 lines per second.

Similarly GeoEye-1 sensor is capable of acquiring Panchromatic data at line rate of 20000 lines/sec. Multispectral sensor acquires data at 2500 lines per/sec. These lines rates although produce excellent quality of imagery but are found to be slightly redundant for certain kind of products such as Pan Sharpened products. In May, 2011 GeoEye implemented Enhanced Line Rate technology wherein the multispectral pixels are aggregated in along- track direction. After 2:1 aggregation multispectral pixels are resampled to 1:1 squares for pan sharpening using the Panchromatic Band.

 

Advantage of this process is ELR(Enhanced Line Rate) camera slew rate is double that of SLR. This also results in faster collection of large area targets (25% – 30% increase). The quality of resulting ELR image is comparable to the normal SLR image. As can be seen below SLR and ELR images are virtually indistinguishable.

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