Activity : use LINE_5
Run the Modeler |
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First Modeling - based on the calibration obtained under Mask_4 only:
- please, append a copy of LINE_5 to your script
- then do as directed, step by step
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| After the optical calibration, we are satisfied that - the deglinting scenario seems to be OK
- we understand that LswNIR must be set at ~=5.5
- so that approximately three DNs of sky glint shall be removed from the NIR band
- please note that , unlike sun glint, sky glint is not modulated by waves
- a good fit has been achieved between the BPL pixels and the ratio KI/KJ=0.29
- KNIR~=3.5 m-1 is in good agreement with Kred~=0.634 m-1 and Kgreen~=0.184 m-1
- the Z2 vs Z3 plot is quite good:
- the NIR_solution=Z3 and the Red_solution=Z2 are in good agreement over bright substrates
- therefore, the calibration of the simplified shallow water optical model
- under mask=4 is now complete
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we may now proceed to run the modeling tool |
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About 4SM license - By default, 4SM writes chequered results upon deglinting or modeling, unless
- the image is verified to be licensed
- or it is a tutorial
- Notice -Process/nosu in Line_5 command line:
- this is to preclude any priviledge
- Enable the -LK argument, and run the script
- this wrtites and displays a tarawa-subset.lic text file
- please, review text file tarawa-subset.lic:
- this license key is already included in 4SM code for free tutorials
- Remove or disable the @-LK argument
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Color tables in OpenEV - pctmSE.leg .........is the pseudocolor table to display mask mSE...............in channel bands+1=4
- pctWZ.leg.............is the pseudocolor table to display image_WZ..............in channel bands+2=5
- pctWR.leg.............is the pseudocolor table to display image_WR..............in channel bands+3=6
- pctZ250.leg..........is the pseudocolor table to display image_Z250....... ....in channel_7
- pctB.leg................is the pseudocolor table to display image_B..................in channel_9
- pctZG.leg..............is the pseudocolor table to display image_ZG in cm... ..in channel_28
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- ONLY pixels masked at 4 are processed
- other pixels are just left unchanged
- this is because the mask_4 option is enabled
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| Bottom brightness B - The average water column corrected bottom brightness
- is written to image_B in channel_9
- coded on a scale 0-200
- It is shown below left; see legend for image_B
- this display shows very dark hues where bottom is deepest
- this is unlikely and unacceptable in this environment:
- it can be countered by any of the following tricks:
- increase Lm[red] or Lsw[red]
- increase Lsw for the red band
- increase the threshold Bmin in -B/... argument
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Lm
Syntax_Lm Lm[2] can be increased: try that now - -Lm/0001.0/002.0/255.0
- -Lm/0001.0/004.0/255.0 ...
- increasing this threshold Lm[red] suppresses less acceptable results, and has no efefct on retrieved depth
- this is what we want
-Lm001.00/01.0/255.0
image B in channel_9, low threshold Lm -M@001/00002/00003
-Lm001.00/01.0/255.0
-Model/Mask_4 | -Lm001.00/04.0/255.0
image B in channel_9, high threshold Lm -M@001/00002/00003
-Lm001.00/04.0/255.0
-Model/Mask_4 | |
Lsw and dLsw
Syntax_Lsw
Lsw[2] can be increased: Lsw=Lsw+dLsw try that now - -dLsw001.0/000.2/000.0
- -dLsw001.0/000.6/000.0
- -dLsw001.0/001.6/000.0
- -dLsw001.0/002.6/000.0
- -dLsw001.0/003.6/000.0 ...
- increasing Lsw[red] increases both retrieved depth and bottom brightness accordingly
- do we want that?
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Bmin
Syntax_B - BminN is used to exclude image brightness less than Bmin=N to appear in the results:
- For example, if a pixel is modeled by the Red solution and yields B<Bmin, then
- it is processed by the next solution (Green solution) if possible
- or it is mapped as deep water
- By doing this, the practitioner assumes that a brightness less than 10 does not exist in this scene, and therefore may not be accepted
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Below are some explanations
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-M@0001/0002/0003 controls the solutions
Syntax_M - -M@0001/0002/0003...............prevents the One-band solution
- -M00001/0002/0003...............enables the One-band solution
- -M@0001/0002/0003..............enables the Red solution
- -M@0001/0002/0003..............enables the NIR solution
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Lm -Lm/0001.0/001.0/255.0
Syntax_Lm
threshold value for bottom contrast Ls-Lsw - Lm thresholds are scaled on a range of normalized radiance 0-200
- if no -Lm... argument is provided, defaults are -Lm/001/001/255
- for the tarawa-subset tutorial
- Lmnir=255: the NIR solution is prevented here
- Lmred=1: see for yourself that Lmred=1 gives a chance to noisy/foul low radiances in the red band
- to produce conspicuous dark artifacts in bottom reflectance
- find your own prefered -Lm... values :
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-LL... argument
Syntax_LL
Line_message on screen upon modeling - -LL10 causes a message on your session screen for one in ten lines processed
- -LL100 causes a message on your session screen for one in a hundred lines processed
- -LL1 causes a message on your session screen for each and every line processed
- etc
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- -Model/mask_4
- mask_4 is disabled: therefore all shallow pixels shall be processed
- -Model/Mask_4
- Mask_4 is enabled: therefore only shallow pixels which exhibit mSE=4 shall be processed
- other pixels are left unchanged
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Smooth or NoSmooth - try your own -Smooth... argument
- review radius of circular smoothing kernel in image WR (in channel_6)
| Deglinting/NoSmoothing/Modeling
is done in 0.033 minutes on my machine
-LL100 | 
Deglinting/Smart_Smoothing/Modeling
is done in 0.050 minutes on my machine
-LL100 | |
One-band case -M@00001/00002/00003
Syntax_M optically deep? - see that no modeling is performed if Lsred<Lmred: such pixels are treated as optically deep
- then most of the lagoon waters are considered optically deep, whereas there is valuable information in the green band
- we can decrease Lmred to 0.5, or even to 0.2
- beware that this opens the door to the fox: system noise shall put out a nice show
- NOT a good solution!
| | image_B in channel_9: average bottom brightness
we want to assume that the lagoon bottom is made of bright/clean coral sand/mud
Please change -B/tclNe/Bmin0/cLM1.0
into -B/tclNe5.00/LBref200_100/Bmin0/cLM1 - if this is right, then we may apply the one-band case using the green band only
- but a "brightness" must be assigned to those deeper lagoon bottoms
- LBref[1]=200 on a scale from 0 to 200 in normalized BOA radiance
- we shall use a value of LBref[1]=170
| | to enable the "one-band case", - you must change from -M@000001/00002/00003
| | one-band case depths are computed as Z=(log(LBref[1]-Lwgreen) - log(Lgreen-Lwgreen)) / Kgreen try your own prefered value for LBref[1] |
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| -Model/Mask_3
-M@000001/00002/00003
-Lm001.00/001.0/005.0 | -Model/Mask_3
-M@000001/00002/00003
-Lm001.00/004.p/005.0 | | -Model/mask_3
-M@000001/00002/00003
-Lm001.00/004.p/005.0 | | -Model/mask_3
-M0000001/00002/00003
-Lm001.00/004.p/005.0 | - See how -Lm001.00/04.00/005.0 helped a lot to prevent lousy/unexpected dark bottoms
- try -Lm001.00/02.50/005.0, might be sufficient to counter some turbidity that seems to affect the water at depth in the red band
- Progressive Lm
- see that -Lm001.00/04.0p/005.0 does a better job
- try other values; make up your own mind: it's all there for you to decide by yourself
- -Model/Mask_3
- causes modeling/updating only of shallow pixels which read 3 in mask mSE
- for other pixels, 4SM does not change anything
- this allows the practionner to apply specific modeling conditions to areas that deserve them
- -M0000001/00002/00003
- see that the one-band case has been applied
- finally, disable the mask option: -Model/mask_3
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| Saturation Also note that some very shallow areas under Mask=3
are saturated to B=201 and colored in deep blue. Why is that? Something weird happens there. We need to know! |
The above modeling applies to the calibration
obtained inside the lagoon under mask=4.
We need to know whether these conditions apply to the whole image subset.
We are in for a big surprise!
Modeling over the reef rim or the outer reef slope
would require specific parameters,
as the water there is cristal clear!
Tarawa atoll is the home to a population of 56,000 persons,
so the lagoon waters are under high anthropogenic pressure.
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Next to Calibration under mask_3
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