The table below shows, for all UKIRT standards nights from 2001 through 2002, estimates of the atmospheric water vapour (as measured by CSO optical depth at 225 GHz) and the photometric quality of the night (yes or no). The left hand set is sorted into photometric and nonphotometric nights, the righthand set is sorted by tau (split at 0.1 to give a roughly equal number of points).

Our thanks to the CSO for their archive of tau measurements. For a more detailed description of tau statistics, click here.

Date	Photometric	tau	BLOCK AVERAGE		Date	Photometric	tau	BLOCK PHOTOMETRIC PERCENTAGE
20020806	n	0.2	0.28		20020216	y	0.06	67%
20020717	n	0.1		20010218	n	0.06
20020514	n	0.3		20010217	y	0.06
20020513	n	0.3		20010521	y	0.09
20011213	n	1		20020717	n	0.1
20011212	n	1		20010813	y	0.1
20010826	n	0.15		20010618	n	0.1
20010711	n	0.15		20010529	y	0.1
20010710	n	0.35		20010423	y	0.1
20010618	n	0.1		20010617	n	0.12	14%
20010617	n	0.12		20010429	n	0.12
20010616	n	0.13		20010616	n	0.13
20010430	n	0.14		20010430	n	0.14
20010429	n	0.12		20010826	n	0.15
20010218	n	0.06		20010828	y	0.15
20020216	y	0.06	0.11		20010711	n	0.15
20010828	y	0.15		20020806	n	0.2
20010813	y	0.1		20010804	y	0.2
20010804	y	0.2		20020514	n	0.3
20010529	y	0.1		20020513	n	0.3
20010521	y	0.09		20010710	n	0.35
20010423	y	0.1		20011213	n	3
20010217	y	0.06		20011212	n	3

By A. Adamson
Email: a.adamson@jach.hawaii.edu