5,406 research outputs found
What bandwidth do I need for my image?
Computer representations of real numbers are necessarily discrete, with some
finite resolution, discreteness, quantization, or minimum representable
difference. We perform astrometric and photometric measurements on stars and
co-add multiple observations of faint sources to demonstrate that essentially
all of the scientific information in an optical astronomical image can be
preserved or transmitted when the minimum representable difference is a factor
of two finer than the root-variance of the per-pixel noise. Adopting a
representation this coarse reduces bandwidth for data acquisition,
transmission, or storage, or permits better use of the system dynamic range,
without sacrificing any information for down-stream data analysis, including
information on sources fainter than the minimum representable difference
itself.Comment: submitted to PAS
A Cost-effective Satellite-aircraft-drogue Approach for Studying Estuarine Circulation and Shelf Waste Dispersion
The author has identified the following significant results. Satellites, such as ERTS-1, can be used to obtain a synoptic view of current circulation over large coastal areas. Since in turbid coastal regions suspended sediment acts as a natural tracer, cost is minimized by eliminating the need for expensive injections of large volumes of dye such as Rhodamine-B. One of the principal shortcomings of satellite imaging of coastal currents was its inability to determine current magnitude and to penetrate beyond the upper few meters of the water column. These objections were overcome by complementing satellite observations with drogues tracking currents at various selected depths. By combining the satellite's wide coverage with aircraft or shore stations capable of tracking expendable drogues, a cost effective, integrated system was devised for monitoring currents over large areas, various depths, and under severe environmental conditions
Physical parameters of the Cen X-3 system
Photographic spectra of Cen X-3 show that the primary star has a spectral type near 06.5 with weak, variable emission at wavelength 4640 and 4686. No orbital motion of the emission or absorption lines is detected; for the latter the upper limit is approximately + or - 50 km/s. Analysis of the available data indicates that the primary is a factor of 2-3 less massive than expected from normal evolutionary models while the X-ray source has a solar mass near 1.5
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