WAC1 Problems, Advantages of Swapping out with WAC2

June 4, 2008

Visible Flat Field - WAC1

Median merge of flat mosaic acquired on August 16 with Xenon source and integrating sphere, areas of saturation are zeroed out (top to bottom 415, 560, 600, 650, 690 nm).Mirrored left to right to match images after processing.

Out-of-band leak in in 560 nm filter - degrades spectral and spatial resolutionTears in 640 and 680 nm filters degrade spatial resolution

415 nm

560 nm

600 nm

650 nm

690 nm

3

WAC Performance Concerns• Some areas of concern were noted during WAC

Calibration efforts:– Dark current stability, pattern noise and time variable offset

thought to be due to thermal effects - will verify in thermal vac– Filter response vs. position

• Blemishes (560 nm, 640 nm, UV)• Out of band leak 560 nm

– Scattered light glint• Affects first ~40 columns in all VIS bands• Most likely due to glint off light shield• Mitigate by zeroing affected columns, effectively reduces

FOV by 4%, 8% for polar movies• Does not affect color data

Confidential and Proprietary - MSSS 3

Artifacts in Filter Assembly• Tear in filter during removal of

mask– Worst tear cases in 650 and 690

filters

• Also uneven deposition of some layer(s) in 560 nm (swirls)

• 415 and 600 nm filters relatively clean

• UV filters– Manufacture defects– Integration contamination

• Flats acquired with Xenon lamp (flat in VIS)

Blowup of Central Portion of VIS Region

415 nm

560 nm

600 nm

650 nm

690 nm

Mask Removal Tears

During interlayer mask removal some regions of existing layers were torn off or damaged.

The most serious tear is found in the middle of the 650 nm filter (A). Note that damage was extensive enough in areas A through D such that saturation occurs in much of the damaged area during nominal exposures. Regions that were saturated in the mosaic data were set to zero in the composite flat field.

Note: the left side of the array is contaminated with scattered light (extremes set to zero). We do not understand the source.

Out-of-Band 560 nm

• Red data for nominal portion of filter

• Blue data centered on blemish (swirl)

• Note leak in the 585 to 680 region

560 nm Row Profiles

• Blue, line 44 through the swirls

• Red, line 33 through clean region

• Note that leak is 2x nominal in extreme cases

560 nm Row Ratios

• Red line is ratio of line one over line 12

• Blue line is ratio of line one over line 13

• Will need to mask rows 12 and 13 and probably portions of 11 and 10

• Plus and minus 2% represents normal flat variation - most trouble in columns 160 to 380 (0 to 200 in color mode)

Note: only showing color columns

560 nm, Good Rows Ratio

• Median 1.03• Stdev 0.013

Color Chart and Slabs

Above: Lab setup photo

RGB Composite 650, 560, 415• Note that image has been

mirrored left to right, thus worse 560 swirls now on right side of image

• Since 560 nm swirls are due to 585 to 680 nm leaks redder squares should have greater artifacts. Pure green materials should have no artifacts.

• Artifacts in box “A” are 30% lower than nominal area in box

• Red = 650 nm, Green = 560 nm, Blue=415 nm

• Arrow indicates leak in 650 associated with central tear

White speckles in ratio in lower left box (white square) represent saturated data

A

VIS Flat Remediation Strategy

Median merge of flat mosaic acquired on August 16, areas of saturation are zeroed out(top to bottom 415, 560, 600, 650, 690 nm).

http://lroc.sese.asu.edu/WORK/CALB/WAC1/FLAT/index.html

From above with thresholding, editing, and best zones indicated with horizontal lines.

560 nm, 14 lines, no overlap

Repeat mosaic of flat to show remaining artifacts

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560 nm, 14 lines, 1 overlap

The remaining bright swirls are out of band leaks

560 nm band may be a complete loss?

UV Filters

Stretched and annotated UV flat field (073007). Note the edge band at the bottom of the 315 nm filter. Sizes of the marked blemishes are listed below.The center of these blemishes are typically at 25% of the background. The curved strand of foreign material in the middle of the 360 nm band was introduced during integration of the filter assembly to the CCD. Nature of the circular blemishes (yellow arrow shows example) is not understood, do not know if such will flat filed out or not.

Blemish sizes in pixels: A x=5 y=5, B x=7 y=8, C x=5 y=5, D x=7 y=8,E x=6 y=7, F x=5 y=7, G x=5 y=4

Summed 4x

Glint - Contamination 40 Columns

Frame 2OFS7.DDD showing artifact when fat point was outside field at (az=342, el=43.3). Exposure time was ~600x that of normal exposure. Note: as fat point source moved vertically glint also moves.

Enlargement of frames 2OFS53 and 2OFS24 showing sharp edge of glint. Both images were stretched 75 and 400 to 0 to 255.In normally exposed images ~40 columns in all VIS bands are seriously degraded.

Artifact RemediationStrategies

• Zero out 40 columns of glint (BW mode)• 14 line readout to minimize contaminated zones• Zero out remaining bad zones• Process to 100 m/pixel maintaining bad zones as nulls (appear as black

holes in data)• 560 nm band may be a complete loss?

• Strategy 1: Create lower resolution continuous products for global color assesment (still use full resolution in conjunction)– Rxample: If largest bad area is 4 lines “tall” resample at 6 line resolution - need

good data above and below to interpolate. 100 meter data resampled to 500 meter map product

• Strategy 2: merge data taken at different times– Photometric challenges– Sub-pixel registration challenges– Produc delivery schedule degradation

Law of Unintended Consequences

• Strategy to readout 14 lines mitigates much of the bad areas

• Requires speed up electronics

• Results in degradation of 415 nm band through increased noise

• Might be fixable through firmware upgrade

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Line 0 and 2 have anomalously high dns, ~10% of dynamic range with worst pixels 40% of dynamic range (8-bit companded data)

MEDIAN - LINE 2

STD AT EACH PIXEL – LINE 2

ALL VIS BANDS

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Line 0, 415 nm

Max value is ~600 DN out of 1800, average scene at 900 DN (de-companded 11-bit data)

21

Line 1, 415 nm

Unusually low, something is wrong

22

Line 2, 415 nm

Similar to line 0

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Line 3, 415 nm

Background back to normal, note column noise

24

Line 4, 415 nm

Background back to normal, note column noise

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Consequences• Either accept saturation in lines 0 and 2 and have acceptable SNR across

array, result in loss of 3 lines of data out of 14 in 415 filter, effectively degrade resolution to something like 400 m/pixel

• Or, cut down integration by 2x and keep all 14 rows, however lower SNR by 2x across all bands and line 1 is probably unusable

• Either option significantly degrades color data

• Increased noise in 415 nm does not effect BW mode– Global basemap– Polar multi-temporal imaging

• Possible firmware fix? Being worked by MSSS– EEPROM patch after integration to LRO

Science DegradationOverview

• Degradation of 560 nm (out-of-band leak) and 415 nm (increased noise) degrades characterization of broad opaque minimum

• Tears in 650 and 690 result in localized loss of data and/or overall degradation of mosaic resolution

• Glint off light shield results in narrowing of BW FOV by 4% thus degrading polar temporal observations coverage (by 8%)

Global Multispectral Mapping

• WAC UV / Visible– 315, 360, 415, 560, 600, 640, 680

nm bandpasses– Acquire global dataset at 100

m/pixel VIS, 400 m/pixel UV– Map TiO2 soils (hold H, He)– Pyroclastic glasses (volatiles)– Olivine (magmatic processes)

• Meshes with Clementine– 100-200 m/pixel– 415, 750, 900, 950, 1000 nm

bandpasses

• 415 and 560 nm bands critical to assessing UV slope and opaque minima LROC WAC bandpasses and key lunar

mineral spectra (12063R Rock, 12070S Soil)

Ilmenite Basalt

Tie to Apollo Sample Sites• Spectral interpretations depend on tie to soil

chemistry from Apollo stations• Loss of resolution and local “holes” in data

degrade parameter calibration

Clementine (A) and HST (B) images of AP17 showing sample stations at 100 m/pixel, WAC will obtain 75 m/pixel

New WAC Filter Assemblies

• Inspected by Mark Robinson (ASU) and Joe Calabrese (GSFC) May 22, 2008

• Eight VIS+UV filter assemblies• Assemblies one and two show significant

improvement over that installed in WAC1, though assemblies have numerous blemishes

• Best four assemblies delivered to MSSS on May 24• MSSS inspection completed• Assemblies 1 and 2 successfully attached to CCDs

on June 3

WAC2 - Assembly #1

Visible band portion of Barr WAC Filter Assembly 1 (WAC2_001), the shortest wavelength is at the bottom while the longest is at the top. The black vertical wedge on the left is a gore in the mosaic, the gray shaded areas on the left and right indicate approximate regions outside the color readout zone. The gray shaded areas on the left and right indicate approximate regions outside the color readout zone. The 600, 640, and 680 nm filters are the best candidates for BW full frame imaging.

UV2 - Assembly #1

WAC Filter Assembly 1 UV2 (top, nearest VIS filters). The black box shows the size of the 512 x 16 area that will be read out, not necessarily from that particular location. We will want to readout as near to the bottom of this filter as possible.

UV1 - Assembly #1

WAC Filter Assembly 1 UV1 (bottom). The black box shows the size of the 512 x 16 area that will be read out, not necessarily from that particular location. We will want to readout as near to the top of this filter as possible.