| MASK??
"I would like to explore working with unmasked data if possible for future projects." - ==> I'm not working with any mask, other than a segmentation of either lands or marine pixelwise which is stored in channel 5
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| "Why was one masked more (at around 8m in places) than the other?
Can unmasked data always be produced?" - Where the bottom brightness is interpreted to be very dark, then the bottom-contrast becomes negligeable at even much shallower depths, and therefore no depth estimate may be produced.
- Gain this is controlled through the -Lm... argument: see 4sm_help_Lm
- I know! that is FRUSTRATING. But there is nothing that can be done about it.
- But the following improve the potential dramatically:
- brighter sea bottom (of course!!)
- more sun light,
- more wavebands,
- clearer waters,
- deep-cooled sensor,
- and last but not least 16 bits data
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| Reduce the detail?
"For the 2003-01-10 results, if you compare the de-glinted channels (ch24, 25, 26) with the original data, I am sure there must be some additional smoothing filter applied. It looks more than just the de-glinting and seems to reduce the detail on some features and starts to remove some deep narrow ridges or points.
Can you advise please. " -
Smart smoothing does not mix marine and non-marine pixels: see 4sm_help_Smooth -
Your concern is about deep features which return a bottom-reflected signal which is just above the noise: -
Sure even a very smart smoothing is likely to wipe out very faint but real features. -
More so if the sets the -Lm... threshold argument values in order to prevent odd "results" from populating the otherwise deep waters: see 4sm_help_Lm: this is probably where you seem to think that I have been applying "masks" -
Then you have to realize that modeling needs sufficient bottom contrast (Ls-Lsw) in at least two bands: this means that as the green band looses bottom contact, the blue band still returns fairly strong bottom-reflected signal. So if you still want a depth estimate for those pixels with significant bottom contrast in the sole blue band, then I must use the "one-band case". see optical_modeling/sld054 -
Operating the "one-band case" for pixels which have Ls<Lm in the green band needs an assumption on the bottom brightness. -
This gives interesting results which exhibit the deeper features in earnest, but are very deconnected from the rest of the DTM wherever the assumed brightness does not apply...... -
If wanted, I just have to enable some features of the 4SM commandline, in order to allow the blue band to yield results when it finds itself on his own: this is the "one band case" -
First is the -M... argument -
With -M/000001/00... specified -
4SM shall use specified LBref value to operate the one-band case -
-B/tclNe5.00/LBref50_20/Bmin0/cLM1.00 -
instead of -B/tclNe5.00/LBref200_100/Bmin0/cLM1.00 -
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In addition, where water properties or deglinting are lousy, a pixel can yield a very lousy -usually very dark bottom and unacceptably shallow depth- -
this is controlled by the Bmin variable in the -B/tclNe5.00/LBref200_100/Bmin0/cLM1.00 -
Bmin0 all pixels are accepted, whatever the results... -
Bmin20 pixels that retrurn B<20 are deemed deep water or recomputed using the one band case -
either the current pixel is mapped "deep water" if its computed bottom brightness is less than specified Bmin: this is how I forced deep waters in some channels closest to the coastline, by using Bmin20 for example -
or the one-band case is used if -M/000001/00... is specified: this is how I can force depth results to appear where only the blue band exhibits significant bottom contrast -
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Whether this can satisfy some select end user, I leave it to your appreciation. -
But it is a risky game, as the computed depths can be very odd even though they actually exhibit realistic depth variations and mainy of them are very real. -
see the series of ETM_2000-11-01... illustrations |
| Deglinting "Also the deglinted image seems to lose more detail than I would expect due to correction of surface waves. "
- ==>Hardly any surface waves glint affects in those RasHatibah images
- ==>BUT YES, adjacency effect, and variations of atmospheric thickness, and some very small clouds (yes).
- ==>They are all returning skydome light to the sensor, and are efficiently removed by so-called "deglinting"
- ==>Deglinting transfers noise from the NIR band to other bands, adding to their own noise. This requires quite some smart smoothing
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Processed in isolation?
"Is there any possibility of pixels being affected by other local pixels during the deglinting process.
Or are all the pixels processed in isolation?" - The only step where processing of current pixel accounts for surrounding pixels is smoothing, although smart-smoothing is designed to reduce loss of details and to preserve sharp changes of bottom contrast.
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