Bathymetry and water column correction
at SanLorenzoChannel, Baja california
Image courtesy of the U.S. Geological Survey
7671*7841 30 m pixel size, UTM zone 12
Using the Panchromatic band for water column correction
to derive water depth and spectral bottom signature:

Landsat 8 OLIP bandset used for this work
Purple=1Blue=2Green=3PAN=4Red=5NIR=6 and SWIR1=7


scene LC80340432016301LGN00, Octber 27th 2016
DATE_ACQUIRED = 2016-10-27
    SCENE_CENTER_TIME = "17:48:12.6812300Z"

Work done november 2016

GSD 15 m Rstudio_sharpened data
are scaled into a weird range

No sweat though: 4SM is a "ratio" method

Ground truth

October 27th 2016    vs   Sonar Depths
RMSE=2.11 m


Sonar Two Days seatruth depths raster

not corrected for tide

15 m GSD
see depth legend

October 27th  2016   vs   DTM

DTM from U. of La Paz, Mexico
resampled to 15 m GSD
see depth legend

Depth residuals ZDTM - Z4SM
DTM - October 27th  2016
see legend 

Data and Deglinting

TOA TCC: raw image
logarithmic enhancement


BOA TCC deglinted image
logarithmic enhancement

Glint regressions using SWIR1

R2 values are fairly high
15 m pansharpening does not increase noise
R_sharpened data include a very large offset

Waters feel "bloomy"

Optical calibration
for the whole image


16U data are scaled to allow for comfortable screen display

Calibration diagram
for the whole image
for bands Blue, Green, Red and NIR


Calibration diagram
for the whole image
for bands Blue, PAN, Red, NIR
  • 0-15m: KBLUE/KGREEN=0.545
    • Jerlov water type OIB+0.5
    • clear waters
  • 15-30m: becoming clearer
Calibration ignores
the "Green" waters
  • which are likely to be less clear
  • which are likely to cause artifacts:
    • depth underestimation
    • dark bottoms

Ready for modeling
A complex situation produces weird results
Combined depths shall be needed

BOA CC WCC normalized
CoefNorm=5.0 (usually 2.5)
BGR color composite:
  • Blue=Coastal band
  • Green=Green band
  • Red=Blue band

Retrieved depth
see legend

Profile Black

Profile Black

Location of Profile Black
  • WEST sections A and B
  • EAST sections C and D

Bottom typing

SAM classified image
see legend for image SAM

Average bottom brightness
NOTE the very dark bottom artifact

see legend for image B
How weird that the scaling of the data
by the R pan-sharpening routine
does not preclude SAM mapping!

Well: that's what they mean by
a "ratio" method!

Applying ZDTM

Applying ZDTM
see legend for image SAM
As I have an estimate of water depth through the existing (and crude) DTM,
I can use it in the inversion of the RTE.
This means that there is no Soil Line assumption any more.

To me, this result is astounding, as it means that
  • FIRST, produce a combined depth image using all scenes available over the study site
    • very detailed at a 15 m GSD and free of weird artifacts
    • without any smoothing thanks to R_pan-sharpening
  • THEN use this detailed combined depth image as a DTM as above,
    • and get a very detailed time series of SAM result like this one above
    • for each of the scenes available
    • at a 15 m GSD without any smoothing
    • free of artifacts caused by bad depths
    • but still suffering from horizontal variations of water optical properties

Download 60 MB
from my GoogleDrive

Contains the following
Channel Descriptor    file="slcOLI_20161027_15mresults.pix";
 1 U8 SAM bottom typing-----------------------------
 2 U8 image B average bottom brightness (0-200)-----
 3 U8 image Z in decimeters-------------------------
 4 U8 WCC reflectance (0-250) at 440.0 nm-----------
 5 U8 WCC reflectance (0-250) at 480.0 nm-----------

 6 U8 WCC reflectance (0-250) at 560.0 nm-----------
 7 U8 WCC reflectance (0-250) at 590.0 nm-----------
 8 U8 WCC reflectance (0-250) at 655.0 nm-----------
 9 U8 WCCnormalized (0-250) at 440.0 nm>B-----------
10 U8 WCCnormalized (0-250) at 560.0 nm>G-----------
11 U8 WCCnormalized (0-250) at 480.0 nm>R-----------
12 S16 Z4SM in centimeters--------------------------
13 S16 ZDTM in centimeters--------------------------
14 S16 ZDTM-Z4SM in centimeters---------------------
I also added Rasterscript.R : 30 minutes on my machine!

ProfileFabio 1

In the profiles below:
  • RED profile is ZDTM: the Combined Depth DTM
  • BLACK profile is Z4SM: retrieved depth
In the profiles below:
  • applied Z4SM: the retrieved depth is used to compute water column corrected spectral bottom signature
  • applied ZDTM: the Combined Depth is used to compute water column corrected spectral bottom signature
applied Z4SM
applied ZDTM


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