copy Line_11 into Line _13
nice -20 ./4SM.4.08 -Process/nosu -Origin/Tarawa_Kiribati @@
add a -ProfileAB/Z/profile_1/chAB_1_2_3 argument
Now all model parameters seem to be satisfactory for the whole image subset,
- disable the -Extract... and -Calibrate... argument
- check that -Model... argument is enabled
- ensure no mask is used -Model/mask_4
- The two -CP... arguments can be taken out or disabled,
- as this refinement only applies to very limited environment,
- and is certainly not justified over other areas.
- @CP/196.96/157.85/058.64_0.25m @@
- @CP/185.04/130.29/029.71_0.50m @@
- run the script tarawa-subset.sh
- if -Model/Mask_4 is left enabled, only pixels under Mask_4 are processed
- while other pixels are simply duplicated.
- to prevent this, please ensure Mask_4 is disabled into mask_4 with a lowercase m,
- so that 4SM processes the whole image.
- Smoothing: -Smooth_3d/smart+
- -smooth..., smoothing disabled
- -Smooth..., smoothing enabled(for marine pixels only)
- WinRadMax=5 is applied: the circular smoothing window has a radius of 5 pixels
- that is 81 pixels in the smoothing kernel
- d no smoothing of optically deep waters
- D smoothing of pixels masked at mSE=240 (optically deep waters)
- /smart... plain smoothing applies
- /Smart... smart smoothing applies
- + SmoothPlus is enabled
- - SmoothPlus is disabled
- Smart-Smoothing is a complex feature in 4SM.
- Enough of that for the moment!
The two -CP... arguments can be taken out or disabled,
as this refinement only applies to very limited environment,
and is certainly not justified over other areas in this image.
nice -20 ./4SM.4.08 -Process/nosu -Origin/Tarawa_Kiribati @@
- Minimum threshold radiance values are applied in order to control artifacts:
- You need to experiment with those thresholds, see what happens, until satisfied, as -deglint... does not solve all problems.
- Set Lm to 1.0 instead of 4.0, see that
- we seem to have foul waters at some locations inside the lagoon
- the electronic noise suddenly invades the output.
- Set Lm to 255 to disable the use of the NIR band altogether,
- see that this does not affect computed depths over bright sandy bottoms.
- but over very shallow seaweeds or algae, which is not the case here,
- the use of XS3 can make a world of a difference.
- Set Lm to 255 to see the extent of RED coverage.
- set Lm to .../004.p/... to enable progressive Lm
- NIR solution must be enabled: - M0001/00002/00003
- it is controlled through the -Lm[NIR]
- ONE-band-case enabled: note in the - M00001/00002/00003 argument that all three bands are enabled:
- in deeper areas where the Red band is extinct
- depths are computed using XS1 alone (the one-band solution), assuming constant bottom brightness Lbref
- this is obtained by enabling the first band in the -M... argument and choosing an appropriate value for Lbref in -B... argument
- TWO-band-case only
- to disable the one-band case
- change -M00001/00002/00003 into - M@00001/00002/00003 .
- ==> deeper areas are mapped to optically deep waters instead.
- Lbref : is used to compute Z in the ONE-band-case :
- LBref=200 is used for the One-band case for pixels that are assumed to be bright bottoms
- change its value to other values like 170 or 220, see what happens:
- this affects retrieved depth
- choose your prefered value for LBref.
- Lbref : is used to compute Z in the ONE-band-case
- this used for the one-band case for pixels masked at 236:
- typically in areas that are assumed to be dark bottoms, like coral reefs, outer reef slope...
- CoefLM :
- note that the last parameter is set to CoefLM=1.00
- All water column corrected reflectances are multiplied by this CoefLM value.
- Change its value to any other value, like 1.2 or 0.87, see what happens
- see that computed bottom reflectances are affected accordingly
- while computed depths remain unaffected.
- Once/if a new -LsM... argument has been settled and enabled
- make sure you return CoefLM to 1.0
- This argument is comprised of many variables
- which are all provided in the 4sm.def defaults textfile
- try "gedit 4sm.def"
- -Z/MSL0.0/... provides a tide height and datum
- it is only used in the following event:
- seatruth: ?tide height is added to tide-corrected seatruth depth?
- deliverable: tide height is subtracted when writing final deliverable SDB
- ?in order to write a tide-corrected deliverable product
- the 4sm.def defaul text file is written upon the AutoCAL process
- its content may be manually edited as desired
- it is read at the start of reading the command line
- any of its content may be overriden by the command line
- Some blue areas remain, where the average bottom reflectance is saturated to 201
- To avoid that, CoefLM should be set to a value higher than 1.15:
Tarawa atoll is a very complex scene
- It is not possible to account for the many lacks of homogeneity in this scene
- the lagoon water body is open to the ocean westwards
- the lagoon also receives oceanic waters through the hoas
- the reef flat and the reef slope should be modeled with specific calibration for very clear waters
- over 50,000 persons live in the southern part of the atoll
- this must have an impact on the attenuation properties of the waters at a very local scale
- try to extract calibration data for some sub-areas along the southern part of the lagoon, see for yourself
- I have seen the South-West part of the lagoon affected by "milky" waters
- Deeper than 3-5 m, the green band is the only source of information
- the only way to compute a depth is to assume a constant bottom type reflectance:
- LBref=150 in a range of 0-200 is assumed for of supposedlybright bottoms
- LBref= 40 in a range of 0-200 is assumed for areas of supposedly dark bottoms which are (or should be) masked at 236, like the outer reef flat and slope
- Still: a very nice opportunity for training
- existing nautical maps show a maximum depth of ~16 m just north of the main pass at lowest tide
- this shows that our combination of LBref=150 and Kgreen=0.269 seems to "ballpark" the problem quite close!
- A 4-bands multispectral image certainly should be better
- although the attenuation coefficients for Kblue~=0.28 and Kgreen~=0.27 are probably very close to each other for a OIII water type of Jerlov
- this would yield a ratio Kblue/Kgreen very close to 1
- if this would be the case, then the one-band case would be the only way to produce an estimate of water depth deeper than 3-5 m
- it is our experience that the ratio Ki/Kj must be <0.8 for water column correction to be achievable using a multispectral image: Ki<<Kj
see on your screen