4SM WV2 Perth Mosaic Panchromatic

Is the PAN band trustworthy
for water column correction?
The problem
Noise and penetration
Optical calibration
Using the PAN band

The problem

In 4SM, Yellow band may be used down to ~12 m in clear waters over bright bottoms, much less over dark bottoms:
- Yellow against Green, Blue and Purple
In 4SM, where Yellow band is extinct, we are left with
- Green against Blue and Purple
In 4SM, where Yellow band is extinct, the combination Green against Blue and Purple cannot resolve variations in bottom greenness:
- green bottoms yield underestimated depths
- brown bottoms yield overestimated depths

The solution: use the Panchro band

The WV2 panchromatic band covers most of the multispectral bands at 0.5 m ground resolution
Once 4x4 sum-aggregated to 2 m ground resolution, the PAN pixel becomes 16 times stronger, and is co-registered with the MULTI pixel
Its effective wavelength is very high at shallow bottom depths and decreases gradually as the bottom depth increases
Therefore the PAN band may not be calibrated into a constant diffuse attenuation coefficient
- as K_pan decreases gradually as the bottom depth increases

Noise and penetration

Yellow band

it is much less noisy than the PAN band
it exhibits penetration down to at most ~12 m in very clear waters over very bright bottoms

Panchromatic band

it is still quite noisy:
- striping is bad; this warrants high threshold
it exhibits penetration up to 20 m here over very bright bottoms
this is distinctly deeper than Yellow band
but still much less than Green band

Green band

it is much less noisy than the PAN band
it exhibits penetration down to at most ~40 m in very clear waters over very bright bottoms

Calibrating the PAN band

Calibration diagram for bands Blue, PAN, Yellow and Red bands BiDim histogram only shows shallow pixels	Calibration diagram for bands Purple, PAN, Yellow and Red bands BiDim histogram only shows shallow pixels
This assumes the Brightest pixels are over brightest bottoms	This assumes the Brightest pixels are over brightest bottoms
Collecting BPL pixels for optical calibration requires quite a lot of masking of alien pixels in this image	Collecting BPL pixels for optical calibration requires quite a lot of masking of alien pixels in this image

Using the PAN band for modeling: most promising

Z4 vs Z5 along Profile_Black This plot compares depth results obtained as follows: Z4: GREEN uses PAN against Green_Blue_Purple Z5: RED uses Yellow against Pan_Green_Blue_Purple The correlation is quite good: R²=0.87 Therefore, where the Yellow band is extinct, the Pan band can take over efficiently It also displays the BOA watercolumn corrected reflectance for the Purple, Blue and Green bands obtained while modeling Z5: over the 0-6 m depth range, and from very dark to fairly bright bottoms, the range of bottom types is quite large, as illustrated by these plots	Location of profile black Altogether, this result is excellent It gives a strong indication that, YES, the Panchromatic band is trustworthy for watercolumn correction work, at least over the 0-6 m depth range here Essentially, it depicts an evenly sloping platform with very strong variations in bottom brightness covered in green vegetation over the bright areas: see section B from 0.4 to 1.2 km covered in brown vegetation over dark areas: see section D from 1.0 to 2.3 km Note that depths are consistant over very dark shoals with isolated very bright spots
PAN depth range beats Yellow depth range by large It remains to be seen how Pan against Purple, Blue and Green behave over deeper bottoms This can only be investigated using suitable seatruth	Potential for bottom typing Watercolumn-corrected BOA reflectances are shown in these plots for the Purple, Blue and Green bands Note that the potential for bottom typing is excellent mainly dark brown spectral signatures in section D from 1.0 to 2.5 km, with a few local green signatures mainly bright green spectral signatures in section B from 0.4 to 1.2 km shoals are clearly very dark brown bottoms

perth-mosaic-data
perth-mosaic-pan
perth-mosaic-calibration
perth-mosaic-results

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