Opacity: Near-Infrared

From May to September 1997, we measured the near-infrared extinction (magnitudes per airmass) in the K_dark band at the South Pole on 43 different days using the GRIM camera. On most days, we made at least two measurements, and on 12 days we made three or more measurements, for a total of 91 separate measurements. The histogram above shows the distribution of extinction for all 91 measurements. The median extinction is 0.11, the 3rd quartile is 0.31, and mean is 0.18. The negative values are not physically meaningful but indicate times of high variability. With a statistically sampled parameter like exinction, negative numbers sometimes arise, an artifact that other researchers have also noted.

*Click image for a larger, readable version.*

This histogram shows the distribution for the average value of K_dark extinction for the 43 days. The median extinction (magnitudes per airmass) is 0.14, the 3rd quartile is 0.2, the mode is 0.083, and the mean is 0.19.

*Click image for a larger, readable version.*

During a 7 day period in July 1997, we measured photometric scatter in the K_dark band by monitoring solitary calibration stars over a 30-minute period, taking an image each minute. In this way, we collected a total of 45 30-minute series. The stars ranged in airmass from 1.1 to 1.7, and during the week the extinction ranged from 0.022 to 0.212 mag/airmass. We then measured the mean and the standard deviation of the instrumental magnitude during the 30-minute series. This histogram shows the distribution of the standard deviation for the 45 measurements. The median scatter is 0.024 mag, the 3rd quartile is 0.04 mag, the mode is 0.016 mag, and the mean is 0.035 mag.

We are preparing a paper summarizing these and other results from 1997. For more information on related work, please see Marks et al. 1999 or Barnaby et al. 1997.

*For more information on site characterization, please see
the site characterization
section.*