trws_deglint

**Deglint and investigate your image**
step 1: update your command line
step 2: write a deglinted image
step 3: the dark pixel assumption step 4: run the Deglinter
step 5: investigate your image Scatter plots for the red polygon Scatter plots for the green polygon Run a profile
step 6: conclusion

step 1: prepare your script for running the Deglinter
Activity : use LINE_2 Run the Calibrator script formated by the AutoCAL process Run the Deglinter Experiment with extraction window -E.shp Experiment about TOA/BOA, Experiment about Smoothing/NoSmoothing Experiment about choosing/drawing glint.shp Experiment about Deglinting/NotDeglinting
First disable Line_1 #LINE_1: build the database, import data, .... #nice -20 ./4SM.8.07 -Process/nosu -Origin/Tarawa_Kiribat................. #exit
LINE 2 Then append #Line_2 it is a copy of the command line formated at line 55 in textfile AutoCAL.txt but, please get it from the reference script
LINE 2: Run the Deglinter Please follow instructions
Order of precedence among 4SM modules RunMakePIX...........highest precedence RunImporter RunScaler RunRecoder RunDN RunDeglinter...............comes before RunCalibrator RunExtractor RunCalibrator RunClassifier RunABProfiler RunZZProfiler RunZZRegressor RunTyper RunModeler......................lowest precedence

step 2: extract a new set of glint regressions

Activity : use LINE_2

If a suitable tarawa-subset_m0_255.gli text file is not available, or if you have deleted it,

maybe you want to modify the glint.shp shapefile, change its shape or its location, try your chance and common sense,
then, upon the next execution of your script:
- 4SM extracts the glint data from the area specified by the glint.shp shapefile
- 4SM writes a glint_regression.sh script which may be launched to display the following plots

Lswnir = 6.5 adopted by the AutoCAL process
Lsw[bands]=6.5 in the commandline
- this value is used to derive all other spactral Lsw values
  - Lswred =14.8
  - Lswgreen=27.4
- therefore -Lsw/027.4/014.8/006.5 are derived from Glint correlation

You may change the 6.5 for any other value that you deem more appropriate
- as 4SM shall derive all other values using the glint correlations

The glint shapefile
over a backdrop of NIR band
The cloud is not included

Cloud/Shadow in the NIR band

Glint shapefile is shown in white

orange=6: this is the darkest cloud shadow
- Lswnir=6.5 is a weighted average of those darkest pixels
yellow=7
green=8

Including the cloud itself inside the glint shapefile

yields virtually the same set of slope/intercept
therefore, the photons backscattered by the cloud
- have virtually the same spectral composition as the glitter at the water surface.
this is not allways the case though

A similar behaviour is observed over a boat's wake.

plot of the glint correlations
without the cloud
-Lsw/27.4/14.8/6.5

plot of the glint correlations
including the cloud
-Lsw/26.9/13.9/6.5

**step 3: FYI, the dark pixel assumption: how it is used**
Activity FYI, nothing to do
Then, on any instance, 4SM uses the adopted deep water radiance Lsw=6.5 in the NIR band, as a seed value, along with the Bias and Slope of these regressions to derive spectral deep water radiance Lsw for all bands a simple geometric calculation which uses the dark pixel assumption.
Get Lsw and Lw from glint correlation Because deglinting is enabled , 4SM uses LswNIR=6.5 as a seed value, along with the glint correlations to derive its own estimates of Lswgreen=27.4 and Lswred=14.8 this is done as part of the pre-processing for any 4SM execution This may be adjusted at will though, by altering manually the value for LswNIR either manually in the command line, or by use of the dLsw argument: LswNIR = LswNIR + dLswNIR Therefore, the practitioner shall later have to settle for an optimized operational seed value for LswNIR upon which the deglinting shall be based.
Lsw, La and Lw based on the seed value for LswNIR provided in the command line for the NIR band, the glint regression text file is used to derive spectral Lsw and Lw values to override those provided for other bands in the command line.

step 4: FYI: deglint the whole image

Activity

4SM goes on to Deglint/Smooth the image

or just part of the image through a -EfirstRow/lastRow/firstLine/lastLine argument

TCC TOA raw	TCC TOA deglinted/smoothed
NIR band, BOA deglinted/smoothed	RED band, BOA deglinted/smoothed
GREEN band, BOA deglinted/smoothed	Zoom Deglinted Green band, channel_22

deep.shp shapefile
Deglinting/Smoothing helps to delineate optically deep waters if you want to prepare a deep.shp shapefile

next to Deglint page 2