Bathymetry and water column correction
at Rangiroa and Tikehau atolls, French Polynesia

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


Tikehau bathymetry
Rangiroa bathymetry

3454*1590, 30 m pixel size, UTM zone 6     

scene LC80530702013233LGN00,  downloaded from USGS
August 21rst 2013

Work done september 2013 

This image is a mess.
Waters inside the lagon become distinctly less clear:in 2013,  4SM can't cope
The data

The data

Seven bands are used: Purple, Blue, Green, PAN, Red, NIR and SWIR1



GREEN band

Panchromatic band, sum-aggregated to 30 m,



Glint regression based on SWIR1 band


Glint regression based on NIR band

Deglinted TCC

Note: PAN not usable
that the PAN band exhibits very poor correlation
  • this means that the PAN band may not be deglinted to satisfaction, and therefore shall not be usable for shallow water work
  • unlike at Caicos


Optical calibration
Water type OIB of Jerlov
Spectral reflectance of the brightest bottoms (LsM):
0.207 0.252 0.294 0.314 0.329 0.463 0.343
on the scale 0-1, as calibrated using the _MTL.txt textfile 
This is distinctly darker than at Caicos Bank

Calibration diagram
for bands Blue, Green, Red and NIR

Calibration diagram
for bands Purple, GreenRed and NIR
Spectral operational 2K
  • This calibration yields the following operational 2K:
2Kblue  =0.106 m-1
2Kgreen=0.242 m-1
2Kred    =0.807 m-1
2Knir   =0.450 m-1 a customary value for NIR
  • Quite possibly, seatruth should reveal that these values are realistic, i.e. that retrieved depths shall be correctly estimated.
  • Final_Z = CoefZ*Z  - Tide_to_chart_datum
Operational wavelengths
  • These diagrams demonstrate that a very good fit of the BPL mode has been achieved among all visible bands
  • This was obtained by setting
    • WLpurple at 450 nm
    • WLgreen   at 577 nm
    • WLred       at 655 nm
This is much more straightforward and acceptable than what was adopted at Caicos


Water column correction: retrieved depth along Profile Red
Performance of the Green band reaches ~30 m over bright bottoms
in this OIB +0.6 water type of Jerlov

Retrieved depth  shows Profile Red

Retrieved depth  shows Profile Green

Retrieved depth along Profile Red
also shows water column corrected Blue band

Plot of   Z3 vs Z5 along Profile Green
  • Z5 uses Purple, Blue, Green vs Red
  • Z3 uses Purple, Blue           vs Green
Deglinting and Smart-Smoothing applied
  • This plot is used to fine-tune several critical model parameters, like
    • WL: wavelengths
    • Lsw: deep water radiances
    • LsM: brightest shallow bottom
    • Lm: threshold value
  • until a satisfactory fit is obtained

Plot of Z3 and Z5  along Profile Green
  • Z5 uses Purple, Blue, Green vs Red
  • Z3 uses Purple, Blue            vs Green
This plot also shows
the watercolumn-corrected reflectances (scaled 0-250)
in the Purple, Blue and Green bands

Deglinting and Smart-Smoothing applied


Command Line
nice -20  4SM -Process    -Origin/USGS                                       
-SCL/02243/02397/03003/02892/02939/03207/02742     @-Prepare/Scale                       
-Z/MSL0.00d/cSL1.5/N_2/nDR_53_zDTM/mask_3              -LL10                       
-AutoCAL/print_2_3/mapBPL/MakeNewMask/getGlint/GlintM58/offset5/slope1.10/Clouds @-DNshp

nice -20  4SM  -Process  -Origin/USGS                       
-KK2_3_0.44/Knir15.70/Bm400_BG520_GR590_RN700/mask_4    OIB+0.6   
-B/tclNe/cNorm2.50/LBref200_100/Bot_0_250_254_253/cLM1 .5   
-extract/v/rawBDH/FullBDH/NIRband7/NIRmax5/mapBPL/mSOIL21/mBPL3/mask_3 Eshp    
-Model/v/runWV2/mask_3        @-Tp/2/4/text -LL1       
@ProfileAB/ZrvwB/profile_red/dTM/chAB_2 1_2_3_5          

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