2MASS "Hot-Pixel" Analysis: Calibration vs. Science Scans

This is a comparison between hot pixels for
68 970424n calibration scans and 28 970424n science scans, and also for
35 970622n calibration scans and 28 970622n science scans.

Figure 1--- Comparison of Cal vs. Sci Scan FREX Distributions

Date Scan Type
(# Scans) #OR Hot Pixels Sum of FREX Images #Scans with FREX>=4 Histogram CDF
970424n Cal
(68) 20
Tabular Data
OR mask in Fowler's Format
FITS Image
k.scan_cnt.tbl
Sci
(28) 40
Tabular Data
OR mask in Fowler's Format
FITS Image
k.scan_cnt.tbl
970622n Cal
(35) 27
Tabular Data
OR mask in Fowler's Format
FITS Image
k.scan_cnt.tbl
Sci
(28) 52
Tabular Data
OR mask in Fowler's Format
FITS Image
k.scan_cnt.tbl

Total Hot Pixel Counts (OR mask) in Calbration vs. Science Scans

For an equal number of cal scans and sci scans, if hot pixels events are random in time, we would expect (exp_time_sci/exp_time_cal) = 6 times more hot pixels in sci scans than in cal scans. On 970424n we have (28/68)=0.4 as many sci scans as cal scans, so we expect 6*0.8 = 2.4 times as many hot pixels in the science scans; we observe (40/20)=2.0 times as many. Similar logic applied to the 970622n data means we expect 6*(28/35) = 4.8 times as many hot pixels in the science scans; we observed (52/27)= 1.9 times as many.

Conclusion: The chance a hot pixel event will occur is not random in time.

Persistent Hot Pixels (AND mask) in Calbration vs. Science Scans

On 970424n there is no hot pixel persitent across all K-array 68 calibration scans; likewise for the 28 science scans.

On 970622n, there is no hot pixel persitent across all K-array 68 calibration scans on 970424n; however among the 28 science scans there is 1 persistently hot pixel: (53,251). Note also that pixel (53,251) does trigger as "hot" in 32 out of the 35 calibration scans on this night.

Commonality Between Hot Pixels in Sci. Scans and Cal. Scans

970424n:

15 of the 20 hot pixels (75%) in the cal scans are also hot in the sci scans. These 5 remaining hot pixels in the cal scan (OR mask) do not occur in the sci scans:

Running     X      Y         Sum of FREX
Pixel #
--------  ----    ---        -----------
      6     98    180           4
      9    156     59           4
     10    157    226           4
     11    158     88           8
     12    158    223           4

Generally, individual pixels that consistently fire hot in the largest number of cal scans (high sum of FREX values) also appear hot in the sci scans, with few exceptions.

Running     X      Y         Sum of FREX
Pixel #                       Sci & Cal
--------  ----    ---        -----------
      1      4    233           4
      2     13    109          56
      3     14    240           4 &  16
      4     32     69          18 &  17
      5     34    207           4
      6     56    236          58 &  13
      7     58    231           4
      8     62    181           4
      9     69     75           4
     10     86    159           4
     11     87    202           4
     12     88    231           4
     13     89    189           4
     14     92    155          17 &  11
     15     95    223         183 &  22
     16    113     25         108 &  53
     17    119    232           4
     18    133     92           4
     19    134    176           4
     20    139    213           8 &   5
     21    141     12          10
     22    143    246          43
     23    148    149           4
     24    154    253           9
     25    157    249           4
     26    159     65          55 &  26
     27    166    179         103
     28    168    232         368 &  37
     29    170     25           4
     30    174    177          74 &  14
     31    190    232          44 &  31
     32    193    213         102 &  22
     33    200    115          25 &  10
     34    204     72         166 &  41
     35    214     28           4
     36    218    238           4
     37    219    220          16 &   7
     38    222    184          10
     39    231     87           4
     40    238    147           6

Generally, pixels that have a very large number of frame extractions in any individual cal scan (high FREX value) also appear hot in the sci scans.
Conclusion: Examination of the cal scans detects the same hottest pixels that appear in the sci scans, but it does miss some.

970622n:

17 of the 27 hot pixels (63%) in the cal scans are also hot in the sci scans. These 10 remaining hot pixels in the cal scan (OR mask) do not occur in the sci scans:

Running     X      Y         Sum of FREX
Pixel #
--------  ----    ---        -----------
      3     14     56           4
      4     20    221           4
      5     22     97           4
      6     26     55           4
      7     28    200          26
      9     50    235          23
     12     78    222           9
     18    167    223           4
     22    204     72          20
     23    206     95          17

Generally, individual pixels that consistently fire hot in the largest number of cal scans (high sum of FREX values) also appear hot in the sci scans, with few exceptions.

Running     X      Y         Sum of FREX
Pixel #                       Sci & Cal
--------  ----    ---        -----------
      1      3    168         194 &  60
      2      8    248          30
      3     12    202           9
      4     13    156         327 &  55
      5     13    210          13
      6     17     39           4
      7     20    219           6
      8     26    244           4
      9     28    239          25
     10     34    111          47
     11     34    169           9 &   7
     12     36    222           4
     13     50    186          15
     14     53    251         661 & 114
     15     56    236         368 &  10
     16     59    199          12
     17     62     65           8
     18     65    212           9
     19     70    158          67
     20     72    153           4
     21     78    225          60 &  12
     22     79    229           4
     23     96    127           4
     24     99    176          37
     25    107     21           4 &  21
     26    115    167           4
     27    118    227          61
     28    131    231           5
     29    149    205           9
     30    156    171           8
     31    158    147           4
     32    164    140          52 &  37
     33    166    179          73 &   4
     34    167     81          39 &   5
     35    179    202           4
     36    188    110          61 &   8
     37    190    232         479 &  37
     38    191    237         308 &  51
     39    197    121          48
     40    199    219           9
     41    199    255           4
     42    209    216          89 &   5
     43    210    185          27
     44    211    255          14
     45    219    220          84 &  10
     46    227    247           4
     47    229    151           4
     48    230    114           8
     49    237    220         105 &  15
     50    242    191         222 &  28
     51    243    219           4
     52    245    235           4

Conclusion: consistent with above.

Last update: 26-Aug-97, Joe Mazzarella (mazz@ipac.caltech.edu )

Date	Scan Type (# Scans)	#OR Hot Pixels	Sum of FREX Images	#Scans with FREX>=4	Histogram	CDF
970424n	Cal (68)	20	Tabular Data OR mask in Fowler's Format FITS Image	k.scan_cnt.tbl
	Sci (28)	40	Tabular Data OR mask in Fowler's Format FITS Image	k.scan_cnt.tbl
970622n	Cal (35)	27	Tabular Data OR mask in Fowler's Format FITS Image	k.scan_cnt.tbl
	Sci (28)	52	Tabular Data OR mask in Fowler's Format FITS Image	k.scan_cnt.tbl