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


Sonar Two Days seatruth depths raster
not corrected for tide

15 m GSD
see depth legend

scene LC80340432013308LGN00, November 04th 2013
DATE_ACQUIRED = 2013-11-04
    SCENE_CENTER_TIME = 17:49:36.3644549Z

Work done november 2016

GSD 15 m Rsudio_sharpened
data are scaled into a weird range
No sweat though: 4SM is a "ratio" method

Ground truth

November 4th 2013    vs   Sonar Depths
RMSE=1.28 m


Sonar Two Days seatruth depths raster
not corrected for tide

15 m GSD
see depth legend

November04th 2013   vs   DTM
DTM resampled to 15 m GSD

DTM - November04th 2013
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


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
  • 0-30m: KBLUE/KGREEN=0.60
    • Jerlov water type OIB+0.8

Ready for modeling
red pollution

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

Location of Profile Black
  • WEST sections A and B: more complex
    • turbid waters play trick from km3 to km5 on section A, coming up from South
  • EAST sections C and D: very nice results

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

TCC_BOA_WCC normalized

The PANsharpening artefact
Note the dubious rosy trenches, one pixel wide and several meters deep

Retrieved depth
Rosy trenches are artefacts


SWIR1 pansharpened
This is an artifact of the PAN sharpening applied to a band that does not have any water penetration:
  • structural bottom features of the PAN band are added to the SWIR band
    • which does not have any water penetration
  • then the SWIR band is used for deglinting
    • this transfers any SWIR noise into deglinted bands

SWIR1 raw

Download 52 MB
from my GoogleDrive

Contains the following
Channel Descriptor    file="slcOLI_20131104_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---------------------

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