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MMA Memo #223

Yet Another Look at Anomalous Refraction

M.A. Holdaway [1], David Woody [2]

July 22, 1998

Keywords: anomalous refraction, atmospheric phase, pointing errors, Chajnantor

The previous treatments of anomalous refraction by Holdaway (MMA Memo 186) and by Butler (MMA Memo 188) were in error in two ways. First, they only accounted for one dimension of anomalous refractive pointing. For the zenith case, this increases the pointing error by root(2). Second, the assumed elevation dependence of the phase structure function was incorrect. Working from Holdaway and Ishiguro (MMA Memo 127), both Holdaway and Butler assumed that the phase structure function, calculated with the physical baseline, varies directly with airmass. Reevaluating the situation indicates that the phase structure function must be calculated with the projected baseline. The result is a less pronounced increase of anomalous refractive pointing jitter with airmass. Finally, because the phase structure function must be calculated with the projected baseline, we have incorrectly transferred the phase structure function from the phase monitor system to the zenith (and to all other elevations as well). The net effect of these three errors is an increase in the anomalous refractive pointing jitter of about 25-50% for most observations over the values reported by Holdaway and by Butler. We still find a weak dependence of anomalous refractive pointing on the dish diameter. Further, we indicate how the anomalous refraction might be considered in antenna design.

[1] NRAO
[2] OVRO


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Last modified: 09 December, 1999

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