Impact of New Seeing Shape Scoring Limits

I. Mean Scan Seeing Shape

One of the new scan QA scoring factors being considered is to the set scan quality score to 0 for all scans with mean seeing shape values >1.25 in one or more bands. This limit is consistent with the seeing limit used as a cutoff for inclusion in Catalog Generation.

To examine the statistical impact of this new threshold on rescan requirements, we have reviewed the seeing shapes measured in 50,349 survey scans with existing net quality scores >0 (24,946 northern and 25,403 southern) observed between the start of operations and 991111n and 991109s. The table below lists the number of scans having a mean seeing shape value >1.25 in at least one band and an existing quality score greater or equal to the specified value in each hemisphere, and total.

Q> North - N(sh>1.25) South - N(sh>1.25) Total - N(sh>1.25)

10 63 28 91

9 75 29 104

8 112 42 154

7 116 48 164

6 126 50 176

5 145 50 195

4 153 52 205

3 198 58 256

2 262 71 333

1 603 95 698

These statistics do not take into account scans that may be downgraded for any of the other new scan quality scoring factors. Rejecting all scans with existing scores of Q>0 and mean shape values >1.25 would result in at most 698 scans needing reobservation. This represents 1.4% of all Q>0 scans, 2.4% of northern Q>0 scans, and 0.4% of southern Q>0 scans.

II. Maximum Seeing Shape in a Scan

Maximum seeing shape data have also been accumulated for the same 50,349 scans used in the analysis above. A Maximum Seeing Shape quality factor was evaluated for these scans, using the proposed algorithm:

quality factor = max { 0, min[ 1 , 4.0 * (1.5 - maxJsh) ] }

The final quality for each scan was then evaluated using the combination of the mean seeing threshold and the maximum seeing shape algorithm. Each cell of the matrix below lists the number of scans that have an existing quality score shown on the y-axis (Qold and a new quality score (Qnew shown on the x-axis. The first column after the old quality score contains the number of scans currently having that quality score. For example, 2542 scans currently have Q=9. Applying the new shape scoring factors to the current Q=9 scans would leave 2358 scans with Q=9, 41 with Q=8, 29 with Q=7, etc.

Qnew

Qold Nold 0 1 2 3 4 5 6 7 8 9 10

10 37857 89 16 16 19 37 43 67 103 127 169 37171

9 2542 19 5 6 12 16 29 27 29 41 2358 0

8 2208 65 7 14 18 21 32 40 50 1960 0 0

7 1961 13 3 3 13 19 20 26 1864 0 0 0

6 634 16 4 12 13 14 21 554 0 0 0 0

5 723 29 19 17 25 38 595 0 0 0 0 0

4 290 13 18 9 20 230 0 0 0 0 0 0

3 992 62 31 75 824 0 0 0 0 0 0 0

2 826 171 179 476 0 0 0 0 0 0 0 0

1 2316 708 1608 0 0 0 0 0 0 0 0 0

Simple integrals over regions of this table provide a measure of the impact of the proposed shape scoring algorithms. For example, applying the new shape scoring thresholds to the 45,925 scans that currently have Q>5 would lower the score of 619 of those scans (1.3%) below 5.

R. Cutri and R. Beck - IPAC
Last Update - 6 December 1999

Q>	North - N(sh>1.25)	South - N(sh>1.25)	Total - N(sh>1.25)
10	63	28	91
9	75	29	104
8	112	42	154
7	116	48	164
6	126	50	176
5	145	50	195
4	153	52	205
3	198	58	256
2	262	71	333
1	603	95	698

		Qnew
Qold	Nold	0	1	2	3	4	5	6	7	8	9	10
10	37857	89	16	16	19	37	43	67	103	127	169	37171
9	2542	19	5	6	12	16	29	27	29	41	2358	0
8	2208	65	7	14	18	21	32	40	50	1960	0	0
7	1961	13	3	3	13	19	20	26	1864	0	0	0
6	634	16	4	12	13	14	21	554	0	0	0	0
5	723	29	19	17	25	38	595	0	0	0	0	0
4	290	13	18	9	20	230	0	0	0	0	0	0
3	992	62	31	75	824	0	0	0	0	0	0	0
2	826	171	179	476	0	0	0	0	0	0	0	0
1	2316	708	1608	0	0	0	0	0	0	0	0	0